<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019eae6b-39eb-7f57-89c4-76272dd5c6f7,g:50cb3308-1f8b-4dfb-858f-f455a15c8818-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://immuneering.com/role/COVERPAGE" xlink:type="simple" xlink:href="imrx-20260630.xsd#COVERPAGE"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/COVERPAGE" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019eae6b-3ab0-721c-9e86-88f8bb50fc16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_us-gaap_StatementTable_019eae6b-3ab0-721c-9e86-88f8bb50fc16" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-7a31-a264-64531fc5d645" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eae6b-3ab0-721c-9e86-88f8bb50fc16" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-7a31-a264-64531fc5d645" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7a31-a264-64531fc5d645_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-7a31-a264-64531fc5d645" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7a31-a264-64531fc5d645_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7934-845b-9b41b81cdd18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-7a31-a264-64531fc5d645" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7934-845b-9b41b81cdd18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3ab0-76e5-9f00-3f6d582f1825" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7934-845b-9b41b81cdd18" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3ab0-76e5-9f00-3f6d582f1825" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019eae6b-3ab0-79a4-a511-291c39ad48e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7934-845b-9b41b81cdd18" xlink:to="loc_us-gaap_CommonClassBMember_019eae6b-3ab0-79a4-a511-291c39ad48e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019eae6b-3ab0-72ba-8425-718c5d0ce436" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_DocumentType_019eae6b-3ab0-72ba-8425-718c5d0ce436" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019eae6b-3ab0-71a1-8a7c-dfea10e450c3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_DocumentQuarterlyReport_019eae6b-3ab0-71a1-8a7c-dfea10e450c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019eae6b-3ab0-7cb3-a963-8c85c913175b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_DocumentPeriodEndDate_019eae6b-3ab0-7cb3-a963-8c85c913175b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019eae6b-3ab0-7420-b07d-fc3a49047e0f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_DocumentTransitionReport_019eae6b-3ab0-7420-b07d-fc3a49047e0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019eae6b-3ab0-78a8-b43c-7335b36d7cfe" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityFileNumber_019eae6b-3ab0-78a8-b43c-7335b36d7cfe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019eae6b-3ab0-77b9-aecf-3066e320d367" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityRegistrantName_019eae6b-3ab0-77b9-aecf-3066e320d367" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019eae6b-3ab0-7e88-985d-081c51cc2d9a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019eae6b-3ab0-7e88-985d-081c51cc2d9a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019eae6b-3ab0-731f-a113-1b1852d9cc57" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityTaxIdentificationNumber_019eae6b-3ab0-731f-a113-1b1852d9cc57" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019eae6b-3ab0-7d68-8407-2b2f89c4acd9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityAddressAddressLine1_019eae6b-3ab0-7d68-8407-2b2f89c4acd9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019eae6b-3ab0-7a23-b865-66345b96d67f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityAddressAddressLine2_019eae6b-3ab0-7a23-b865-66345b96d67f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019eae6b-3ab0-773b-b80b-cdc3e9d371be" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityAddressCityOrTown_019eae6b-3ab0-773b-b80b-cdc3e9d371be" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019eae6b-3ab0-773a-8554-2bd983af67c3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityAddressStateOrProvince_019eae6b-3ab0-773a-8554-2bd983af67c3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019eae6b-3ab0-74b6-ba15-4f0bfd851ce5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityAddressPostalZipCode_019eae6b-3ab0-74b6-ba15-4f0bfd851ce5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019eae6b-3ab0-784d-88f2-029c4c647259" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_CityAreaCode_019eae6b-3ab0-784d-88f2-029c4c647259" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019eae6b-3ab0-7967-bcb7-8fa8821c0f64" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_LocalPhoneNumber_019eae6b-3ab0-7967-bcb7-8fa8821c0f64" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019eae6b-3ab0-7af5-8106-787a89bfc0ad" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_Security12bTitle_019eae6b-3ab0-7af5-8106-787a89bfc0ad" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019eae6b-3ab0-77fa-90db-dcae9a842cc8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_TradingSymbol_019eae6b-3ab0-77fa-90db-dcae9a842cc8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019eae6b-3ab0-7b84-ac66-2805015b649c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_SecurityExchangeName_019eae6b-3ab0-7b84-ac66-2805015b649c" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019eae6b-3ab0-74d1-bc32-5b40da81054e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityCurrentReportingStatus_019eae6b-3ab0-74d1-bc32-5b40da81054e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019eae6b-3ab0-7b52-82ea-c0003d5d1028" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityInteractiveDataCurrent_019eae6b-3ab0-7b52-82ea-c0003d5d1028" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019eae6b-3ab0-7828-9afb-2130bf4004fb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityFilerCategory_019eae6b-3ab0-7828-9afb-2130bf4004fb" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019eae6b-3ab0-7471-9dcc-8666d5d428e0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntitySmallBusiness_019eae6b-3ab0-7471-9dcc-8666d5d428e0" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019eae6b-3ab0-7d42-8af4-5ebd90cdcfa7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityEmergingGrowthCompany_019eae6b-3ab0-7d42-8af4-5ebd90cdcfa7" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_019eae6b-3ab0-7002-b8c2-4953f2be532b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityExTransitionPeriod_019eae6b-3ab0-7002-b8c2-4953f2be532b" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019eae6b-3ab0-700c-9a2b-fca5b30ae5d7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityShellCompany_019eae6b-3ab0-700c-9a2b-fca5b30ae5d7" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019eae6b-3ab0-748e-8154-77003aad648b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019eae6b-3ab0-748e-8154-77003aad648b" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019eae6b-3ab0-7aa2-b8e7-ad1856bc550b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_EntityCentralIndexKey_019eae6b-3ab0-7aa2-b8e7-ad1856bc550b" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019eae6b-3ab0-708b-a34b-614c332404b5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_CurrentFiscalYearEndDate_019eae6b-3ab0-708b-a34b-614c332404b5" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019eae6b-3ab0-71de-a9ae-28f5946b20e0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_DocumentFiscalYearFocus_019eae6b-3ab0-71de-a9ae-28f5946b20e0" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019eae6b-3ab0-7921-9a52-a99053e4fae0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019eae6b-3ab0-7921-9a52-a99053e4fae0" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019eae6b-3ab0-7bc4-8d67-45bd962e5808" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-7a11-84d0-33572c67a01e" xlink:to="loc_dei_AmendmentFlag_019eae6b-3ab0-7bc4-8d67-45bd962e5808" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="imrx-20260630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019eae6b-3ab0-76e7-b6ea-be6c03cd9f98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019eae6b-3ab0-7653-a86d-e1f52ef137d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-76e7-b6ea-be6c03cd9f98" xlink:to="loc_us-gaap_StatementTable_019eae6b-3ab0-7653-a86d-e1f52ef137d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-731b-8d88-da85b38c3bf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eae6b-3ab0-7653-a86d-e1f52ef137d5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-731b-8d88-da85b38c3bf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-731b-8d88-da85b38c3bf7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-731b-8d88-da85b38c3bf7" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-731b-8d88-da85b38c3bf7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7ba9-83a5-a7e3aac92e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3ab0-731b-8d88-da85b38c3bf7" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7ba9-83a5-a7e3aac92e9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3ab0-7a78-a9bb-b376f34dbdfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7ba9-83a5-a7e3aac92e9c" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3ab0-7a78-a9bb-b376f34dbdfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019eae6b-3ab0-760e-bc03-26ada8da2b11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3ab0-7ba9-83a5-a7e3aac92e9c" xlink:to="loc_us-gaap_CommonClassBMember_019eae6b-3ab0-760e-bc03-26ada8da2b11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-76e7-b6ea-be6c03cd9f98" xlink:to="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019eae6b-3ab0-71d2-bcae-664d073ed9f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019eae6b-3ab0-71d2-bcae-664d073ed9f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019eae6b-3ab0-73f6-a05b-f4bf5c41f7d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019eae6b-3ab0-71d2-bcae-664d073ed9f2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019eae6b-3ab0-73f6-a05b-f4bf5c41f7d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019eae6b-3ab0-7057-a829-07e3e91a9ad1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019eae6b-3ab0-71d2-bcae-664d073ed9f2" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019eae6b-3ab0-7057-a829-07e3e91a9ad1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019eae6b-3ab0-7f32-a590-c8c36a96a320" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019eae6b-3ab0-71d2-bcae-664d073ed9f2" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019eae6b-3ab0-7f32-a590-c8c36a96a320" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019eae6b-3ab0-7de6-90f8-98bfa0f1bc5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019eae6b-3ab0-71d2-bcae-664d073ed9f2" xlink:to="loc_us-gaap_AssetsCurrent_019eae6b-3ab0-7de6-90f8-98bfa0f1bc5a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent_019eae6b-3ab0-791f-8bce-9e82321cc1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent_019eae6b-3ab0-791f-8bce-9e82321cc1cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019eae6b-3ab0-7763-a8d0-93d2b30ceb58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019eae6b-3ab0-7763-a8d0-93d2b30ceb58" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019eae6b-3ab0-71d6-9a4b-8c1255cb34a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_Goodwill_019eae6b-3ab0-71d6-9a4b-8c1255cb34a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019eae6b-3ab0-77ba-9598-9bb76889c3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019eae6b-3ab0-77ba-9598-9bb76889c3e5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019eae6b-3ab0-7842-a8c7-d8d8ce1d1d95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019eae6b-3ab0-7842-a8c7-d8d8ce1d1d95" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019eae6b-3ab0-79dc-9d18-b926b8043971" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019eae6b-3ab0-79dc-9d18-b926b8043971" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019eae6b-3ab0-796b-8652-ce7126e28501" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019eae6b-3ab0-770c-81c7-9d788228c35d" xlink:to="loc_us-gaap_Assets_019eae6b-3ab0-796b-8652-ce7126e28501" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3ab0-76e7-b6ea-be6c03cd9f98" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019eae6b-3ab0-7344-8f44-82e9839a57b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:to="loc_us-gaap_AccountsPayableCurrent_019eae6b-3ab0-7344-8f44-82e9839a57b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_019eae6b-3ab0-784a-98ec-a27680072dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_019eae6b-3ab0-784a-98ec-a27680072dc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019eae6b-3ab0-766d-a9ab-5c204898f04e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019eae6b-3ab0-766d-a9ab-5c204898f04e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_019eae6b-3ab0-7240-bac2-8c1c8e8dfa3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_019eae6b-3ab0-7240-bac2-8c1c8e8dfa3a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019eae6b-3ab0-7fa1-9d88-8dddf652503a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019eae6b-3ab0-7273-828e-1ac1c8e83fd7" xlink:to="loc_us-gaap_LiabilitiesCurrent_019eae6b-3ab0-7fa1-9d88-8dddf652503a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_019eae6b-3ab0-7eb6-99d9-1ac99b69a258" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_019eae6b-3ab0-7eb6-99d9-1ac99b69a258" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019eae6b-3ab0-7bb4-b363-9bc991b5ccb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019eae6b-3ab0-7eb6-99d9-1ac99b69a258" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019eae6b-3ab0-7bb4-b363-9bc991b5ccb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019eae6b-3ab0-743c-acf8-e11cd07280c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:to="loc_us-gaap_Liabilities_019eae6b-3ab0-743c-acf8-e11cd07280c3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019eae6b-3ab0-7dbe-ba2c-6e4664209677" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019eae6b-3ab0-7dbe-ba2c-6e4664209677" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019eae6b-3ab0-7ae0-83d5-17dd728c29f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:to="loc_us-gaap_PreferredStockValue_019eae6b-3ab0-7ae0-83d5-17dd728c29f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019eae6b-3ab0-7acc-8d0a-eb8719c7ed25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:to="loc_us-gaap_CommonStockValue_019eae6b-3ab0-7acc-8d0a-eb8719c7ed25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019eae6b-3ab0-78a9-be76-68200b56e65a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019eae6b-3ab0-78a9-be76-68200b56e65a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019eae6b-3ab0-77db-a297-6a893e6e0387" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019eae6b-3ab0-77db-a297-6a893e6e0387" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019eae6b-3ab0-711b-82aa-419a8c707850" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019eae6b-3ab0-711b-82aa-419a8c707850" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eae6b-3ab0-7583-b962-c294d3985723" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019eae6b-3ab0-771d-a424-08ac4c1f4b31" xlink:to="loc_us-gaap_StockholdersEquity_019eae6b-3ab0-7583-b962-c294d3985723" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019eae6b-3ab0-78f1-9925-502ca317880f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019eae6b-3ab0-7e41-8b60-ee1dd0919c54" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019eae6b-3ab0-78f1-9925-502ca317880f" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="imrx-20260630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019eae6b-3b62-7906-8df2-323edaefcf84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_StatementTable_019eae6b-3b62-7906-8df2-323edaefcf84" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-7432-be60-48c15988c249" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eae6b-3b62-7906-8df2-323edaefcf84" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-7432-be60-48c15988c249" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7432-be60-48c15988c249_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-7432-be60-48c15988c249" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7432-be60-48c15988c249_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7400-b222-80531597975b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-7432-be60-48c15988c249" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7400-b222-80531597975b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b62-7b1c-a695-19ac2df53e79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7400-b222-80531597975b" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b62-7b1c-a695-19ac2df53e79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019eae6b-3b62-789d-aebe-17e2f50f40d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7400-b222-80531597975b" xlink:to="loc_us-gaap_CommonClassBMember_019eae6b-3b62-789d-aebe-17e2f50f40d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019eae6b-3b62-7f15-bd53-a5d71df78a4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019eae6b-3b62-7f15-bd53-a5d71df78a4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019eae6b-3b62-7c4b-a8b6-2b757e5734e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019eae6b-3b62-7c4b-a8b6-2b757e5734e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019eae6b-3b62-752c-8d35-8b81cb91c72e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019eae6b-3b62-752c-8d35-8b81cb91c72e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019eae6b-3b62-75bb-b79d-7a01e1c82c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019eae6b-3b62-75bb-b79d-7a01e1c82c1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b62-74bf-b057-f7a082b7110f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b62-74bf-b057-f7a082b7110f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019eae6b-3b62-78ca-9250-6f9b409a450a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019eae6b-3b62-78ca-9250-6f9b409a450a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019eae6b-3b62-7b94-8c2f-c9bf9817e2e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_CommonStockSharesIssued_019eae6b-3b62-7b94-8c2f-c9bf9817e2e9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b62-7979-afaa-9b3c5e006582" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7cb7-9a3f-3001eb1f360c" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b62-7979-afaa-9b3c5e006582" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="imrx-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019eae6b-3b62-7202-926d-11b1963dab90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019eae6b-3b62-7c62-84eb-81a4e65e8202" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7202-926d-11b1963dab90" xlink:to="loc_us-gaap_StatementTable_019eae6b-3b62-7c62-84eb-81a4e65e8202" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019eae6b-3b62-70cb-a987-89d4d29e2e39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eae6b-3b62-7c62-84eb-81a4e65e8202" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019eae6b-3b62-70cb-a987-89d4d29e2e39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-70cb-a987-89d4d29e2e39_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019eae6b-3b62-70cb-a987-89d4d29e2e39" xlink:to="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-70cb-a987-89d4d29e2e39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-7fbd-8cbd-13cd59bf0ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019eae6b-3b62-70cb-a987-89d4d29e2e39" xlink:to="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-7fbd-8cbd-13cd59bf0ba8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019eae6b-3b62-73b4-94e6-b8f967b095eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-7fbd-8cbd-13cd59bf0ba8" xlink:to="loc_us-gaap_CommonStockMember_019eae6b-3b62-73b4-94e6-b8f967b095eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019eae6b-3b62-7833-8f1d-cf5f17ecf4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-7fbd-8cbd-13cd59bf0ba8" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019eae6b-3b62-7833-8f1d-cf5f17ecf4ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019eae6b-3b62-7681-914e-028dcb175c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-7fbd-8cbd-13cd59bf0ba8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019eae6b-3b62-7681-914e-028dcb175c4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019eae6b-3b62-7460-ac07-a0dedf451912" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eae6b-3b62-7fbd-8cbd-13cd59bf0ba8" xlink:to="loc_us-gaap_RetainedEarningsMember_019eae6b-3b62-7460-ac07-a0dedf451912" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-76cf-9f89-a00247a396d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eae6b-3b62-7c62-84eb-81a4e65e8202" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-76cf-9f89-a00247a396d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-76cf-9f89-a00247a396d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-76cf-9f89-a00247a396d5" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-76cf-9f89-a00247a396d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7354-9d04-f52c59d396d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-76cf-9f89-a00247a396d5" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7354-9d04-f52c59d396d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b62-7caa-b9e8-8f95950a5913" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7354-9d04-f52c59d396d4" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b62-7caa-b9e8-8f95950a5913" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019eae6b-3b62-7b6b-8d74-54488fc22750" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7354-9d04-f52c59d396d4" xlink:to="loc_us-gaap_CommonClassBMember_019eae6b-3b62-7b6b-8d74-54488fc22750" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7202-926d-11b1963dab90" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b62-75dc-bff2-21f9564cb829" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b62-75dc-bff2-21f9564cb829" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eae6b-3b62-74be-84fd-a785e0dd529d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockholdersEquity_019eae6b-3b62-74be-84fd-a785e0dd529d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019eae6b-3b62-7ec6-ab8c-5e8f34708ac6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019eae6b-3b62-7ec6-ab8c-5e8f34708ac6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019eae6b-3b62-7a80-9674-2b06e666b395" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019eae6b-3b62-7a80-9674-2b06e666b395" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f24c6-550c-76f1-b362-5bd24f7d316d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f24c6-550c-76f1-b362-5bd24f7d316d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f24c6-550c-7836-a662-e2c6b40cc8f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f24c6-550c-7836-a662-e2c6b40cc8f7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019eae6b-3b62-7d30-918d-c3e08ea63c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019eae6b-3b62-7d30-918d-c3e08ea63c8b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019eae6b-3b62-7312-bc47-3e15cfa6bc97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019eae6b-3b62-7312-bc47-3e15cfa6bc97" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019eae6b-3b62-706a-9408-e05e6ad653d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019eae6b-3b62-706a-9408-e05e6ad653d8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eae6b-3b62-7add-ab18-caecce417058" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_NetIncomeLoss_019eae6b-3b62-7add-ab18-caecce417058" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019eae6b-3b62-7c25-ac35-04dc9832c9eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eae6b-3b62-7f21-bc8b-3799dc829292" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019eae6b-3b62-7c25-ac35-04dc9832c9eb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b62-7c61-b4c7-7abd1c4bb921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eae6b-3b62-7123-a4c4-bb577e213432" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="simple" xlink:href="imrx-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019eae6b-3b62-7985-8e58-ab24643f4880" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:to="loc_us-gaap_StatementTable_019eae6b-3b62-7985-8e58-ab24643f4880" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-71e7-a7ee-bf37ccca9094" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eae6b-3b62-7985-8e58-ab24643f4880" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-71e7-a7ee-bf37ccca9094" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-71e7-a7ee-bf37ccca9094_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-71e7-a7ee-bf37ccca9094" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-71e7-a7ee-bf37ccca9094_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-79d7-985c-392d742167a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-71e7-a7ee-bf37ccca9094" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-79d7-985c-392d742167a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AtMarketOfferingMember_019eae6b-3b62-7a69-b13b-3831a3ab36e1" xlink:href="imrx-20260630.xsd#imrx_AtMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-79d7-985c-392d742167a8" xlink:to="loc_imrx_AtMarketOfferingMember_019eae6b-3b62-7a69-b13b-3831a3ab36e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-74e5-a483-08797290f4d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-74e5-a483-08797290f4d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eae6b-3b62-7bef-a095-52f0ca1013ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-74e5-a483-08797290f4d2" xlink:to="loc_us-gaap_NetIncomeLoss_019eae6b-3b62-7bef-a095-52f0ca1013ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-74e5-a483-08797290f4d2" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019eae6b-3b62-7ebd-925f-5931cc07c6ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019eae6b-3b62-7ebd-925f-5931cc07c6ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_019eae6b-3b62-7598-94f0-9d7eee1ec3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_019eae6b-3b62-7598-94f0-9d7eee1ec3bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019eae6b-3b62-7ca8-bf05-c1db24fca23d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019eae6b-3b62-7ca8-bf05-c1db24fca23d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019eae6b-3b62-7e32-87eb-170093484909" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:to="loc_us-gaap_ShareBasedCompensation_019eae6b-3b62-7e32-87eb-170093484909" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_019eae6b-3b62-73ef-b777-c7186746d671" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:to="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_019eae6b-3b62-73ef-b777-c7186746d671" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019eae6b-3b62-7c28-8038-037e578a341c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-7070-812e-a2060013fc0e" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019eae6b-3b62-7c28-8038-037e578a341c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_019eae6b-3b62-719c-8372-1f5f3ddc81b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019eae6b-3b62-7c28-8038-037e578a341c" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_019eae6b-3b62-719c-8372-1f5f3ddc81b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019eae6b-3b62-7adb-9ec7-b599d1744956" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_019eae6b-3b62-719c-8372-1f5f3ddc81b6" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019eae6b-3b62-7adb-9ec7-b599d1744956" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_019eae6b-3b62-78fe-8a30-cdc2d79c2f4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_019eae6b-3b62-719c-8372-1f5f3ddc81b6" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_019eae6b-3b62-78fe-8a30-cdc2d79c2f4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_019eae6b-3b62-7e11-94c6-f74c9a569516" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019eae6b-3b62-7c28-8038-037e578a341c" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_019eae6b-3b62-7e11-94c6-f74c9a569516" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019eae6b-3b62-77be-9b4b-afc6248e9248" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_019eae6b-3b62-7e11-94c6-f74c9a569516" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019eae6b-3b62-77be-9b4b-afc6248e9248" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_019eae6b-3b62-71f7-876c-cfe48637df2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_019eae6b-3b62-7e11-94c6-f74c9a569516" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_019eae6b-3b62-71f7-876c-cfe48637df2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_019eae6b-3b62-7d03-bcd3-73fd24cce75a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_019eae6b-3b62-7e11-94c6-f74c9a569516" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_019eae6b-3b62-7d03-bcd3-73fd24cce75a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_019eae6b-3b62-7f43-adb3-e68d999b9e93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_019eae6b-3b62-7e11-94c6-f74c9a569516" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_019eae6b-3b62-7f43-adb3-e68d999b9e93" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eae6b-3b62-70c9-b10f-cf2a7f95db83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019eae6b-3b62-74e5-a483-08797290f4d2" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eae6b-3b62-70c9-b10f-cf2a7f95db83" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019eae6b-3b62-73c4-a9d2-09ba7021fdca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019eae6b-3b62-73c4-a9d2-09ba7021fdca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019eae6b-3b62-73ac-9ed4-de47077bf3dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019eae6b-3b62-73c4-a9d2-09ba7021fdca" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019eae6b-3b62-73ac-9ed4-de47077bf3dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireMarketableSecurities_019eae6b-3b62-7e1a-b5fd-b38445dfdae2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019eae6b-3b62-73c4-a9d2-09ba7021fdca" xlink:to="loc_us-gaap_PaymentsToAcquireMarketableSecurities_019eae6b-3b62-7e1a-b5fd-b38445dfdae2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities_019eae6b-3b62-7e9b-8837-09982164d7fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019eae6b-3b62-73c4-a9d2-09ba7021fdca" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities_019eae6b-3b62-7e9b-8837-09982164d7fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eae6b-3b62-7a26-b6df-4f8e7eafbe21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019eae6b-3b62-73c4-a9d2-09ba7021fdca" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eae6b-3b62-7a26-b6df-4f8e7eafbe21" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_019eae6b-3b62-7f36-8848-6fec6350e779" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_019eae6b-3b62-7f36-8848-6fec6350e779" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockPlans_019eae6b-3b62-7d8b-a365-e2a7401f6ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromStockPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:to="loc_us-gaap_ProceedsFromStockPlans_019eae6b-3b62-7d8b-a365-e2a7401f6ebf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019eae6b-3b62-7d04-93a3-bf7527907d29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019eae6b-3b62-7d04-93a3-bf7527907d29" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_019f8105-30a4-7761-aae8-a58d0b316b0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_019f8105-30a4-7761-aae8-a58d0b316b0c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eae6b-3b62-7f70-b4f8-4606eda2ff57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019eae6b-3b62-77a2-8a0b-ded26300e534" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eae6b-3b62-7f70-b4f8-4606eda2ff57" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019eae6b-3b62-7ef6-a16d-8a717766c68e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019eae6b-3b62-7ef6-a16d-8a717766c68e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019eae6b-3b62-7595-b6b8-a4aef99e1406" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eae6b-3b62-7285-bf8c-f97523761638" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019eae6b-3b62-7595-b6b8-a4aef99e1406" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019eae6b-3b62-7206-9dca-83cd043e9ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/OrganizationandNatureofBusinessDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#OrganizationandNatureofBusinessDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/OrganizationandNatureofBusinessDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable_019eae6b-3b62-7853-996a-ef6e88491926" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable_019eae6b-3b62-7853-996a-ef6e88491926" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-747d-9be4-775712be7347" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable_019eae6b-3b62-7853-996a-ef6e88491926" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-747d-9be4-775712be7347" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-747d-9be4-775712be7347_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-747d-9be4-775712be7347" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-747d-9be4-775712be7347_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7a08-952d-f0de1a52176f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b62-747d-9be4-775712be7347" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7a08-952d-f0de1a52176f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b62-7774-908f-2c4cb3d5fbf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b62-7a08-952d-f0de1a52176f" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b62-7774-908f-2c4cb3d5fbf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-7d8e-b196-9b884e45e13d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable_019eae6b-3b62-7853-996a-ef6e88491926" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-7d8e-b196-9b884e45e13d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-7d8e-b196-9b884e45e13d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-7d8e-b196-9b884e45e13d" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-7d8e-b196-9b884e45e13d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b62-7d8e-b196-9b884e45e13d" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_A2022ATMProgramMember_019eae6b-3b62-7850-bcfb-fdb523b40e7f" xlink:href="imrx-20260630.xsd#imrx_A2022ATMProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:to="loc_imrx_A2022ATMProgramMember_019eae6b-3b62-7850-bcfb-fdb523b40e7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_019eae6b-3b62-7c79-b500-4a1b4a4e0281" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:to="loc_us-gaap_OverAllotmentOptionMember_019eae6b-3b62-7c79-b500-4a1b4a4e0281" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_A2025ATMProgramMember_019eae6b-3b62-79d9-9bfd-b064c1cfef3c" xlink:href="imrx-20260630.xsd#imrx_A2025ATMProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:to="loc_imrx_A2025ATMProgramMember_019eae6b-3b62-79d9-9bfd-b064c1cfef3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AtMarketOfferingMember_019eae6b-3b62-7ede-bcfd-37c2437c7cfc" xlink:href="imrx-20260630.xsd#imrx_AtMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:to="loc_imrx_AtMarketOfferingMember_019eae6b-3b62-7ede-bcfd-37c2437c7cfc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_019eae6b-3b62-772b-90f3-d6e450f7c611" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b62-73f5-ac6b-ada94089e553" xlink:to="loc_us-gaap_PrivatePlacementMember_019eae6b-3b62-772b-90f3-d6e450f7c611" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b62-7b0d-8c57-477698a76f16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable_019eae6b-3b62-7853-996a-ef6e88491926" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b62-7b0d-8c57-477698a76f16" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b62-7b0d-8c57-477698a76f16_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b62-7b0d-8c57-477698a76f16" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b62-7b0d-8c57-477698a76f16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b62-7314-9a65-c3a59dde2438" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b62-7b0d-8c57-477698a76f16" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b62-7314-9a65-c3a59dde2438" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_PreFundedWarrantsMember_019eae6b-3b62-77cd-935c-cec709c6e7ad" xlink:href="imrx-20260630.xsd#imrx_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b62-7314-9a65-c3a59dde2438" xlink:to="loc_imrx_PreFundedWarrantsMember_019eae6b-3b62-77cd-935c-cec709c6e7ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_PurchaseWarrantsMember_019eae6b-3b62-7bb6-ac1a-88bff7ff8322" xlink:href="imrx-20260630.xsd#imrx_PurchaseWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b62-7314-9a65-c3a59dde2438" xlink:to="loc_imrx_PurchaseWarrantsMember_019eae6b-3b62-7bb6-ac1a-88bff7ff8322" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019eae6b-3b62-75a8-80c4-d189ee4098f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable_019eae6b-3b62-7853-996a-ef6e88491926" xlink:to="loc_srt_CounterpartyNameAxis_019eae6b-3b62-75a8-80c4-d189ee4098f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b62-75a8-80c4-d189ee4098f0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019eae6b-3b62-75a8-80c4-d189ee4098f0" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b62-75a8-80c4-d189ee4098f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b62-7d6a-a29e-83f5523068f6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019eae6b-3b62-75a8-80c4-d189ee4098f0" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b62-7d6a-a29e-83f5523068f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AventisInc.Member_019eae6b-3b62-7420-a079-9a2f05b7b047" xlink:href="imrx-20260630.xsd#imrx_AventisInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b62-7d6a-a29e-83f5523068f6" xlink:to="loc_imrx_AventisInc.Member_019eae6b-3b62-7420-a079-9a2f05b7b047" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockMaximumPotentialConsiderationReceivableOnTransaction_019eae6b-3b62-76b1-b316-e3c08320d8c7" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockMaximumPotentialConsiderationReceivableOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_SaleOfStockMaximumPotentialConsiderationReceivableOnTransaction_019eae6b-3b62-76b1-b316-e3c08320d8c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019eae6b-3b62-743a-9271-90a044b47ec0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019eae6b-3b62-743a-9271-90a044b47ec0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019eae6b-3b62-7abc-8f89-c83a548ecf44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019eae6b-3b62-7abc-8f89-c83a548ecf44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019eae6b-3b62-75df-828e-e31661b2757d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019eae6b-3b62-75df-828e-e31661b2757d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockEquityIssuanceCosts_019eae6b-3b62-7dba-bad1-d5edd7c07985" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockEquityIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_SaleOfStockEquityIssuanceCosts_019eae6b-3b62-7dba-bad1-d5edd7c07985" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b62-709b-80d3-e528a3093012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b62-709b-80d3-e528a3093012" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SalesOfStockValueIncreaseDecreaseInMaximumOffering_019eae6b-3b62-7820-8920-e806c5e472a6" xlink:href="imrx-20260630.xsd#imrx_SalesOfStockValueIncreaseDecreaseInMaximumOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_SalesOfStockValueIncreaseDecreaseInMaximumOffering_019eae6b-3b62-7820-8920-e806c5e472a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockMaximumNumberOfSharesIssuableInTransaction_019eae6b-3b62-7a4b-9d6c-a805a2527278" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockMaximumNumberOfSharesIssuableInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_SaleOfStockMaximumNumberOfSharesIssuableInTransaction_019eae6b-3b62-7a4b-9d6c-a805a2527278" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019eae6b-3b62-7952-8e6d-cbdea702db4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019eae6b-3b62-7952-8e6d-cbdea702db4c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019eae6b-3b62-7349-8573-39016419fccd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019eae6b-3b62-7349-8573-39016419fccd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019eae6b-3b62-771c-89b3-6d4f3bbca5f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019eae6b-3b62-771c-89b3-6d4f3bbca5f5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_ShareUnfundedExercisePrice_019eae6b-3b62-7b99-afed-e2760144d974" xlink:href="imrx-20260630.xsd#imrx_ShareUnfundedExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_ShareUnfundedExercisePrice_019eae6b-3b62-7b99-afed-e2760144d974" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SalesOfStockSharesWithheldInLieuOfCashPayments_019eae6b-3b62-7b56-8006-264f5bdd1fc6" xlink:href="imrx-20260630.xsd#imrx_SalesOfStockSharesWithheldInLieuOfCashPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_SalesOfStockSharesWithheldInLieuOfCashPayments_019eae6b-3b62-7b56-8006-264f5bdd1fc6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019eae6b-3b62-78a7-b318-6d379a67507b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019eae6b-3b62-78a7-b318-6d379a67507b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockAggregateConsiderationReceivedOnTransaction_019eae6b-3b62-798b-b70e-aecd7d3f33d4" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockAggregateConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_imrx_SaleOfStockAggregateConsiderationReceivedOnTransaction_019eae6b-3b62-798b-b70e-aecd7d3f33d4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_019eae6b-3b62-718c-aeb5-fc5c6ff31cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_019eae6b-3b62-718c-aeb5-fc5c6ff31cc1" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019eae6b-3b62-7695-b66c-62ded2a059fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems_019eae6b-3b62-7d3d-848b-b7d1ee49804f" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019eae6b-3b62-7695-b66c-62ded2a059fc" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/SummaryofSignificantAccountingPoliciesDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#SummaryofSignificantAccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/SummaryofSignificantAccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b62-720f-921c-734fa92dbfc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b62-75cf-ae12-ca7ffdbeb433" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b62-720f-921c-734fa92dbfc5" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b62-75cf-ae12-ca7ffdbeb433" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019eae6b-3b62-7029-be5c-d87959ff16f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b62-75cf-ae12-ca7ffdbeb433" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019eae6b-3b62-7029-be5c-d87959ff16f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019eae6b-3b62-7029-be5c-d87959ff16f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019eae6b-3b62-7029-be5c-d87959ff16f7" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019eae6b-3b62-7029-be5c-d87959ff16f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019eae6b-3b62-748b-94bf-027205715f82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019eae6b-3b62-7029-be5c-d87959ff16f7" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019eae6b-3b62-748b-94bf-027205715f82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_EquityDistributionAgreementMember_019eae6b-3b62-753a-8aff-781fbf1057ea" xlink:href="imrx-20260630.xsd#imrx_EquityDistributionAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019eae6b-3b62-748b-94bf-027205715f82" xlink:to="loc_imrx_EquityDistributionAgreementMember_019eae6b-3b62-753a-8aff-781fbf1057ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019eae6b-3b62-790f-9714-3bbe58453673" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b62-75cf-ae12-ca7ffdbeb433" xlink:to="loc_dei_LegalEntityAxis_019eae6b-3b62-790f-9714-3bbe58453673" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019eae6b-3b62-790f-9714-3bbe58453673_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019eae6b-3b62-790f-9714-3bbe58453673" xlink:to="loc_dei_EntityDomain_019eae6b-3b62-790f-9714-3bbe58453673_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019eae6b-3b62-75f4-8545-d6d02e1296aa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019eae6b-3b62-790f-9714-3bbe58453673" xlink:to="loc_dei_EntityDomain_019eae6b-3b62-75f4-8545-d6d02e1296aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SandlerAndCoMember_019eae6b-3b62-7b76-ab5d-622ce2987824" xlink:href="imrx-20260630.xsd#imrx_SandlerAndCoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019eae6b-3b62-75f4-8545-d6d02e1296aa" xlink:to="loc_imrx_SandlerAndCoMember_019eae6b-3b62-7b76-ab5d-622ce2987824" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019eae6b-3b62-722d-a6f3-14fae26e2e9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b62-720f-921c-734fa92dbfc5" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019eae6b-3b62-722d-a6f3-14fae26e2e9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredOfferingCosts_019eae6b-3b62-7a6c-970a-9a6d43151fd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredOfferingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b62-720f-921c-734fa92dbfc5" xlink:to="loc_us-gaap_DeferredOfferingCosts_019eae6b-3b62-7a6c-970a-9a6d43151fd2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/MarketableSecuritiesScheduleofMarketableSecuritiesDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#MarketableSecuritiesScheduleofMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/MarketableSecuritiesScheduleofMarketableSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7238-8399-7d71cef735c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7238-8399-7d71cef735c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019eae6b-3b62-7349-97c9-b5890d5cda9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019eae6b-3b62-7349-97c9-b5890d5cda9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019eae6b-3b62-7ec9-8e49-5fca63454092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019eae6b-3b62-7ec9-8e49-5fca63454092" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019eae6b-3b62-7d2f-8930-ed7e2186773a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_DebtSecuritiesMember_019eae6b-3b62-7d2f-8930-ed7e2186773a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019eae6b-3b62-7ac3-b619-006c4b7cf7cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_CommercialPaperMember_019eae6b-3b62-7ac3-b619-006c4b7cf7cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019eae6b-3b62-769a-8a1f-1c8b6a4dd481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019eae6b-3b62-769a-8a1f-1c8b6a4dd481" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eae6b-3b62-7bed-a464-a61607527439" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eae6b-3b62-7bed-a464-a61607527439" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eae6b-3b62-7cdd-9dfb-9ed6a9e6f696" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eae6b-3b62-7cdd-9dfb-9ed6a9e6f696" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eae6b-3b62-739a-b1d9-8a0a445d17ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eae6b-3b62-739a-b1d9-8a0a445d17ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019eae6b-3b62-7d1d-9776-41e6dfe394c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019eae6b-3b62-7d1d-9776-41e6dfe394c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent_019eae6b-3b62-7494-8930-1079a454f392" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent_019eae6b-3b62-7494-8930-1079a454f392" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019eae6b-3b62-7cec-b738-bcd4e91c1bdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019eae6b-3b62-7cec-b738-bcd4e91c1bdf" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/MarketableSecuritiesScheduleofMarketableSecuritiesDetails_1" xlink:type="simple" xlink:href="imrx-20260630.xsd#MarketableSecuritiesScheduleofMarketableSecuritiesDetails_1"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/MarketableSecuritiesScheduleofMarketableSecuritiesDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_019eae6b-3b62-7326-bef4-f41551377096" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7238-8399-7d71cef735c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7238-8399-7d71cef735c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b62-7238-8399-7d71cef735c0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019eae6b-3b62-7349-97c9-b5890d5cda9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019eae6b-3b62-7349-97c9-b5890d5cda9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019eae6b-3b62-7ec9-8e49-5fca63454092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019eae6b-3b62-7ec9-8e49-5fca63454092" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019eae6b-3b62-7d2f-8930-ed7e2186773a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_DebtSecuritiesMember_019eae6b-3b62-7d2f-8930-ed7e2186773a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019eae6b-3b62-7ac3-b619-006c4b7cf7cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b62-7d2a-a0d2-ebae1ca8fd1c" xlink:to="loc_us-gaap_CommercialPaperMember_019eae6b-3b62-7ac3-b619-006c4b7cf7cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eae6b-3b62-7bed-a464-a61607527439" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eae6b-3b62-7bed-a464-a61607527439" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eae6b-3b62-7cdd-9dfb-9ed6a9e6f696" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eae6b-3b62-7cdd-9dfb-9ed6a9e6f696" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eae6b-3b62-739a-b1d9-8a0a445d17ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eae6b-3b62-739a-b1d9-8a0a445d17ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019eae6b-3b62-7d1d-9776-41e6dfe394c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestCurrent_019eae6b-3b62-7d1d-9776-41e6dfe394c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent_019eae6b-3b62-7494-8930-1079a454f392" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestNoncurrent_019eae6b-3b62-7494-8930-1079a454f392" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019eae6b-3b62-7cec-b738-bcd4e91c1bdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019eae6b-3b62-728e-adab-5b43e5eac8e9" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019eae6b-3b62-7cec-b738-bcd4e91c1bdf" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/FairValueMeasurementsScheduleofCashEquivalentsandMarketableSecuritiesDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#FairValueMeasurementsScheduleofCashEquivalentsandMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/FairValueMeasurementsScheduleofCashEquivalentsandMarketableSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eae6b-3b63-7b7d-aff5-b49fb3a278ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eae6b-3b63-734a-a4f8-1474150d893a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eae6b-3b63-7b7d-aff5-b49fb3a278ae" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eae6b-3b63-734a-a4f8-1474150d893a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eae6b-3b63-76b6-8fdf-64b8f9b7f0ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eae6b-3b63-734a-a4f8-1474150d893a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eae6b-3b63-76b6-8fdf-64b8f9b7f0ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b6-8fdf-64b8f9b7f0ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eae6b-3b63-76b6-8fdf-64b8f9b7f0ae" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b6-8fdf-64b8f9b7f0ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b7-9208-aee7359f6463" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eae6b-3b63-76b6-8fdf-64b8f9b7f0ae" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b7-9208-aee7359f6463" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019eae6b-3b63-7a2a-bb2b-4f0a15c5ef19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b7-9208-aee7359f6463" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019eae6b-3b63-7a2a-bb2b-4f0a15c5ef19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019eae6b-3b63-7ef9-870e-e1efad940bf8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b7-9208-aee7359f6463" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019eae6b-3b63-7ef9-870e-e1efad940bf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019eae6b-3b63-774b-a6a8-d70c9c680784" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eae6b-3b63-76b7-9208-aee7359f6463" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019eae6b-3b63-774b-a6a8-d70c9c680784" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b63-7430-b9f2-12f62b7ddbd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eae6b-3b63-734a-a4f8-1474150d893a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b63-7430-b9f2-12f62b7ddbd7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7430-b9f2-12f62b7ddbd7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b63-7430-b9f2-12f62b7ddbd7" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7430-b9f2-12f62b7ddbd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eae6b-3b63-7430-b9f2-12f62b7ddbd7" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019eae6b-3b63-79e0-8b68-65ad7c42dce8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019eae6b-3b63-79e0-8b68-65ad7c42dce8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019eae6b-3b63-75cd-b371-8359e35ba012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019eae6b-3b63-75cd-b371-8359e35ba012" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019eae6b-3b63-782b-b891-6b5314f908ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019eae6b-3b63-782b-b891-6b5314f908ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019eae6b-3b63-709b-9aad-8aa6c4eedc31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:to="loc_us-gaap_DebtSecuritiesMember_019eae6b-3b63-709b-9aad-8aa6c4eedc31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019eae6b-3b63-7b7c-b94f-e51582cf31cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eae6b-3b63-7c4e-90b5-178e82050659" xlink:to="loc_us-gaap_CommercialPaperMember_019eae6b-3b63-7b7c-b94f-e51582cf31cc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019eae6b-3b63-7fc9-9b0a-e3f328fa867c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eae6b-3b63-7b7d-aff5-b49fb3a278ae" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019eae6b-3b63-7fc9-9b0a-e3f328fa867c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019eae6b-3b63-7b29-9b1c-370fc5c768bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019eae6b-3b63-7fc9-9b0a-e3f328fa867c" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019eae6b-3b63-7b29-9b1c-370fc5c768bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019eae6b-3b63-712a-8378-5fa9626bcc95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019eae6b-3b63-7fc9-9b0a-e3f328fa867c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019eae6b-3b63-712a-8378-5fa9626bcc95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019eae6b-3b63-7fde-9a6c-440fd55c570b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019eae6b-3b63-7fc9-9b0a-e3f328fa867c" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019eae6b-3b63-7fde-9a6c-440fd55c570b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/PropertyandEquipmentnetScheduleofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#PropertyandEquipmentnetScheduleofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/PropertyandEquipmentnetScheduleofPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eae6b-3b63-7277-b608-20d5460d323b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eae6b-3b63-72c1-946d-63f27711c2fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eae6b-3b63-7277-b608-20d5460d323b" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eae6b-3b63-72c1-946d-63f27711c2fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-7f91-9062-78d72d9106d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eae6b-3b63-72c1-946d-63f27711c2fc" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-7f91-9062-78d72d9106d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7f91-9062-78d72d9106d0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-7f91-9062-78d72d9106d0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7f91-9062-78d72d9106d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-7f91-9062-78d72d9106d0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_019eae6b-3b63-7fff-a321-66add4f4eeba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:to="loc_us-gaap_ComputerEquipmentMember_019eae6b-3b63-7fff-a321-66add4f4eeba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019eae6b-3b63-7704-9063-ee6da062a9e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019eae6b-3b63-7704-9063-ee6da062a9e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_LabEquipmentMember_019eae6b-3b63-7236-95d0-3aaff147013a" xlink:href="imrx-20260630.xsd#imrx_LabEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:to="loc_imrx_LabEquipmentMember_019eae6b-3b63-7236-95d0-3aaff147013a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019eae6b-3b63-74ae-bc1f-25b8279c0012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019eae6b-3b63-74ae-bc1f-25b8279c0012" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019eae6b-3b63-7396-bce8-8d64b93b6a30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-7999-a09d-9e4722601a9a" xlink:to="loc_us-gaap_ConstructionInProgressMember_019eae6b-3b63-7396-bce8-8d64b93b6a30" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019eae6b-3b63-7821-b3a4-67d5189f1b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eae6b-3b63-7277-b608-20d5460d323b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019eae6b-3b63-7821-b3a4-67d5189f1b8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019eae6b-3b63-7546-9fe2-bd6efca41cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eae6b-3b63-7277-b608-20d5460d323b" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019eae6b-3b63-7546-9fe2-bd6efca41cb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019eae6b-3b63-79b5-9b6e-543000f031c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eae6b-3b63-7277-b608-20d5460d323b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019eae6b-3b63-79b5-9b6e-543000f031c1" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CommonStockClassACommonStockDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#CommonStockClassACommonStockDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CommonStockClassACommonStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-76f7-aa42-1dbc552f3f37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-76f7-aa42-1dbc552f3f37" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-739b-8217-8e6dbea8bae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-76f7-aa42-1dbc552f3f37" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-739b-8217-8e6dbea8bae0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-8217-8e6dbea8bae0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-739b-8217-8e6dbea8bae0" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-8217-8e6dbea8bae0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7a0d-a8a4-cc8321d97736" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-739b-8217-8e6dbea8bae0" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7a0d-a8a4-cc8321d97736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7e3c-8e76-9c4697edf8d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7a0d-a8a4-cc8321d97736" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7e3c-8e76-9c4697edf8d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019eae6b-3b63-771d-8e51-a4a7f813cdd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019eae6b-3b63-771d-8e51-a4a7f813cdd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b63-7b42-8dd5-941d27d3e2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b63-7b42-8dd5-941d27d3e2e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b63-7880-976a-4f0c845b5824" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b63-7880-976a-4f0c845b5824" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019eae6b-3b63-7e8b-bdc5-d5b5ccfc9041" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:to="loc_us-gaap_CommonStockSharesIssued_019eae6b-3b63-7e8b-bdc5-d5b5ccfc9041" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_NumberOfVotesEachShare_019eae6b-3b63-71e9-95bf-9e4a8ca2dfe2" xlink:href="imrx-20260630.xsd#imrx_NumberOfVotesEachShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-75a1-a78b-80791b952bac" xlink:to="loc_imrx_NumberOfVotesEachShare_019eae6b-3b63-71e9-95bf-9e4a8ca2dfe2" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CommonStockClassBCommonStockDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#CommonStockClassBCommonStockDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CommonStockClassBCommonStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-7223-b439-f52506fb9007" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-7223-b439-f52506fb9007" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7621-8247-3a6a1beb9379" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-7223-b439-f52506fb9007" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7621-8247-3a6a1beb9379" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7621-8247-3a6a1beb9379_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7621-8247-3a6a1beb9379" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7621-8247-3a6a1beb9379_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-78a9-b4a5-b4b1cf58916e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7621-8247-3a6a1beb9379" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-78a9-b4a5-b4b1cf58916e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019eae6b-3b63-786e-9aa9-e13273711b7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-78a9-b4a5-b4b1cf58916e" xlink:to="loc_us-gaap_CommonClassBMember_019eae6b-3b63-786e-9aa9-e13273711b7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019eae6b-3b63-720e-b05f-a2e9fda85886" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019eae6b-3b63-720e-b05f-a2e9fda85886" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b63-7f44-a8a7-05701f9ff8fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b63-7f44-a8a7-05701f9ff8fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019eae6b-3b63-7294-ba7f-e265b946abc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:to="loc_us-gaap_CommonStockSharesIssued_019eae6b-3b63-7294-ba7f-e265b946abc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b63-77e0-b1b8-4068baa29455" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019eae6b-3b63-77e0-b1b8-4068baa29455" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_NumberOfVotesEachShare_019eae6b-3b63-7c2d-bc50-be24687fc3bf" xlink:href="imrx-20260630.xsd#imrx_NumberOfVotesEachShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7a91-a2f0-26a209fd9cb2" xlink:to="loc_imrx_NumberOfVotesEachShare_019eae6b-3b63-7c2d-bc50-be24687fc3bf" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CommonStockEquityOfferingsDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#CommonStockEquityOfferingsDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CommonStockEquityOfferingsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eae6b-3b63-7424-beda-c3f712482bf0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:to="loc_srt_RangeAxis_019eae6b-3b63-7424-beda-c3f712482bf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-7424-beda-c3f712482bf0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-7424-beda-c3f712482bf0" xlink:to="loc_srt_RangeMember_019eae6b-3b63-7424-beda-c3f712482bf0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-7520-8b5f-14c3b73d4762" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-7424-beda-c3f712482bf0" xlink:to="loc_srt_RangeMember_019eae6b-3b63-7520-8b5f-14c3b73d4762" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eae6b-3b63-736f-a903-fbdae1ad748c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eae6b-3b63-7520-8b5f-14c3b73d4762" xlink:to="loc_srt_MaximumMember_019eae6b-3b63-736f-a903-fbdae1ad748c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7c96-bce2-bf43504aab94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7c96-bce2-bf43504aab94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7c96-bce2-bf43504aab94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7c96-bce2-bf43504aab94" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7c96-bce2-bf43504aab94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-758f-92c3-71722718a254" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7c96-bce2-bf43504aab94" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-758f-92c3-71722718a254" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7eca-a1e4-6560f0f1e91f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-758f-92c3-71722718a254" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7eca-a1e4-6560f0f1e91f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b63-7b94-aa91-d3149706fbbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b63-7b94-aa91-d3149706fbbb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7b94-aa91-d3149706fbbb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b63-7b94-aa91-d3149706fbbb" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7b94-aa91-d3149706fbbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eae6b-3b63-7b94-aa91-d3149706fbbb" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AtMarketOfferingMember_019eae6b-3b63-7a80-8d07-940097646417" xlink:href="imrx-20260630.xsd#imrx_AtMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:to="loc_imrx_AtMarketOfferingMember_019eae6b-3b63-7a80-8d07-940097646417" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_A2022ATMProgramMember_019eae6b-3b63-7880-b3ad-6f8a04a90d14" xlink:href="imrx-20260630.xsd#imrx_A2022ATMProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:to="loc_imrx_A2022ATMProgramMember_019eae6b-3b63-7880-b3ad-6f8a04a90d14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_A2025ATMProgramMember_019eae6b-3b63-76e1-a2e3-eca2e1dc03f9" xlink:href="imrx-20260630.xsd#imrx_A2025ATMProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:to="loc_imrx_A2025ATMProgramMember_019eae6b-3b63-76e1-a2e3-eca2e1dc03f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_019eae6b-3b63-7173-baa0-ebf8b5476f54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:to="loc_us-gaap_PrivatePlacementMember_019eae6b-3b63-7173-baa0-ebf8b5476f54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_PurchaseWarrantsMember_019eae6b-3b63-7c0c-8996-e8fdcc89cd69" xlink:href="imrx-20260630.xsd#imrx_PurchaseWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:to="loc_imrx_PurchaseWarrantsMember_019eae6b-3b63-7c0c-8996-e8fdcc89cd69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_019eae6b-3b63-7662-a6ac-473605cd06a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eae6b-3b63-7bc8-9aec-503f416dc29c" xlink:to="loc_us-gaap_OverAllotmentOptionMember_019eae6b-3b63-7662-a6ac-473605cd06a1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b63-738d-8624-6253040571c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b63-738d-8624-6253040571c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b63-738d-8624-6253040571c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b63-738d-8624-6253040571c2" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b63-738d-8624-6253040571c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b63-7a99-a727-cce94959d9e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019eae6b-3b63-738d-8624-6253040571c2" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b63-7a99-a727-cce94959d9e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_PreFundedWarrantsMember_019eae6b-3b63-74ef-8464-a3e94f698bfe" xlink:href="imrx-20260630.xsd#imrx_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b63-7a99-a727-cce94959d9e0" xlink:to="loc_imrx_PreFundedWarrantsMember_019eae6b-3b63-74ef-8464-a3e94f698bfe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_PurchaseWarrantsMember_019eae6b-3b63-7c49-a46b-422170b5a278" xlink:href="imrx-20260630.xsd#imrx_PurchaseWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019eae6b-3b63-7a99-a727-cce94959d9e0" xlink:to="loc_imrx_PurchaseWarrantsMember_019eae6b-3b63-7c49-a46b-422170b5a278" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019eae6b-3b63-7fc1-917b-295cadc5f8ef" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019eae6b-3b63-78ae-97ae-ce82c77ac473" xlink:to="loc_srt_CounterpartyNameAxis_019eae6b-3b63-7fc1-917b-295cadc5f8ef" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b63-7fc1-917b-295cadc5f8ef_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019eae6b-3b63-7fc1-917b-295cadc5f8ef" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b63-7fc1-917b-295cadc5f8ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b63-722f-8e8d-516f0d5501a4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019eae6b-3b63-7fc1-917b-295cadc5f8ef" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b63-722f-8e8d-516f0d5501a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AventisInc.Member_019eae6b-3b63-705f-b64a-dc5e670dee86" xlink:href="imrx-20260630.xsd#imrx_AventisInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019eae6b-3b63-722f-8e8d-516f0d5501a4" xlink:to="loc_imrx_AventisInc.Member_019eae6b-3b63-705f-b64a-dc5e670dee86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_EquityOfferingCombinedAggregateAmount_019eae6b-3b63-7ec7-9b0a-2ffc3f868cc2" xlink:href="imrx-20260630.xsd#imrx_EquityOfferingCombinedAggregateAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_EquityOfferingCombinedAggregateAmount_019eae6b-3b63-7ec7-9b0a-2ffc3f868cc2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_EquityOfferingCombinedAggregateDateOfEffectivePeriod_019eae6b-3b63-7be5-bec6-6b25128b908d" xlink:href="imrx-20260630.xsd#imrx_EquityOfferingCombinedAggregateDateOfEffectivePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_EquityOfferingCombinedAggregateDateOfEffectivePeriod_019eae6b-3b63-7be5-bec6-6b25128b908d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b63-7440-89ad-b7477a2facb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019eae6b-3b63-7440-89ad-b7477a2facb0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockMaximumPotentialConsiderationReceivableOnTransaction_019eae6b-3b63-7b36-83f5-7cbfe52cfea8" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockMaximumPotentialConsiderationReceivableOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SaleOfStockMaximumPotentialConsiderationReceivableOnTransaction_019eae6b-3b63-7b36-83f5-7cbfe52cfea8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SalesOfStockCommissionRate_019eae6b-3b63-7a46-b03e-feeecd2d7f30" xlink:href="imrx-20260630.xsd#imrx_SalesOfStockCommissionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SalesOfStockCommissionRate_019eae6b-3b63-7a46-b03e-feeecd2d7f30" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019eae6b-3b63-739c-a654-51e1ae1d14f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_019eae6b-3b63-739c-a654-51e1ae1d14f4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_019eae6b-3b63-77c1-962b-eb4f841d8c73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_019eae6b-3b63-77c1-962b-eb4f841d8c73" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019eae6b-3b63-7b40-97dc-a7bdb2b382ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_019eae6b-3b63-7b40-97dc-a7bdb2b382ea" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockEquityIssuanceCosts_019eae6b-3b63-739a-bdda-ce8d3522741a" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockEquityIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SaleOfStockEquityIssuanceCosts_019eae6b-3b63-739a-bdda-ce8d3522741a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredOfferingCosts_019eae6b-3b63-74e4-a374-4e245d23d094" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredOfferingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_DeferredOfferingCosts_019eae6b-3b63-74e4-a374-4e245d23d094" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SalesOfStockValueIncreaseDecreaseInMaximumOffering_019eae6b-3b63-7600-b876-8d8d9c641904" xlink:href="imrx-20260630.xsd#imrx_SalesOfStockValueIncreaseDecreaseInMaximumOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SalesOfStockValueIncreaseDecreaseInMaximumOffering_019eae6b-3b63-7600-b876-8d8d9c641904" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_CommonStockAuthorizedAggregateGrossSalesProceedsRemaining_019eae6b-3b63-73ac-afc0-d664a38e174e" xlink:href="imrx-20260630.xsd#imrx_CommonStockAuthorizedAggregateGrossSalesProceedsRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_CommonStockAuthorizedAggregateGrossSalesProceedsRemaining_019eae6b-3b63-73ac-afc0-d664a38e174e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockMaximumNumberOfSharesIssuableInTransaction_019eae6b-3b63-7b5d-87e9-d5c5f74ba322" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockMaximumNumberOfSharesIssuableInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SaleOfStockMaximumNumberOfSharesIssuableInTransaction_019eae6b-3b63-7b5d-87e9-d5c5f74ba322" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019eae6b-3b63-75d3-9237-d5d6b943a77a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019eae6b-3b63-75d3-9237-d5d6b943a77a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019eae6b-3b63-7069-ae7f-a08f4d5fda2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019eae6b-3b63-7069-ae7f-a08f4d5fda2e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019eae6b-3b63-7358-819c-6045c041313a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019eae6b-3b63-7358-819c-6045c041313a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_ShareUnfundedExercisePrice_019eae6b-3b63-751c-8409-7fb629589b8e" xlink:href="imrx-20260630.xsd#imrx_ShareUnfundedExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_ShareUnfundedExercisePrice_019eae6b-3b63-751c-8409-7fb629589b8e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SalesOfStockSharesWithheldInLieuOfCashPayments_019eae6b-3b63-7953-8cfc-71455b26fa8b" xlink:href="imrx-20260630.xsd#imrx_SalesOfStockSharesWithheldInLieuOfCashPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SalesOfStockSharesWithheldInLieuOfCashPayments_019eae6b-3b63-7953-8cfc-71455b26fa8b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019eae6b-3b63-7e3f-b685-b15351207651" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019eae6b-3b63-7e3f-b685-b15351207651" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_ClassOfWarrantOrRightIssued_019eae6b-3b63-7296-b05d-585eb5da813c" xlink:href="imrx-20260630.xsd#imrx_ClassOfWarrantOrRightIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_ClassOfWarrantOrRightIssued_019eae6b-3b63-7296-b05d-585eb5da813c" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_SaleOfStockAggregateConsiderationReceivedOnTransaction_019eae6b-3b63-7e7e-94ef-fd814801cb37" xlink:href="imrx-20260630.xsd#imrx_SaleOfStockAggregateConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_imrx_SaleOfStockAggregateConsiderationReceivedOnTransaction_019eae6b-3b63-7e7e-94ef-fd814801cb37" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_019eae6b-3b63-7000-bd4c-ac43893b76c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019eae6b-3b63-7acd-a23c-4f88f85d308f" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_019eae6b-3b63-7000-bd4c-ac43893b76c3" xlink:type="arc" order="21"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/NetLossPerShareAttributabletoCommonStockholdersScheduleofAntidilutiveEffectDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#NetLossPerShareAttributabletoCommonStockholdersScheduleofAntidilutiveEffectDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/NetLossPerShareAttributabletoCommonStockholdersScheduleofAntidilutiveEffectDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019eae6b-3b63-7922-960e-77b7669c87d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019eae6b-3b63-7ba0-843e-0ec4586f5734" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019eae6b-3b63-7922-960e-77b7669c87d7" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019eae6b-3b63-7ba0-843e-0ec4586f5734" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eae6b-3b63-7d8d-b37a-ec59a597d39b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019eae6b-3b63-7ba0-843e-0ec4586f5734" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eae6b-3b63-7d8d-b37a-ec59a597d39b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eae6b-3b63-7d8d-b37a-ec59a597d39b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eae6b-3b63-7d8d-b37a-ec59a597d39b" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eae6b-3b63-7d8d-b37a-ec59a597d39b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eae6b-3b63-7754-b997-5dc664976b08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eae6b-3b63-7d8d-b37a-ec59a597d39b" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eae6b-3b63-7754-b997-5dc664976b08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019eae6b-3b63-7a52-a0af-a513126748c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eae6b-3b63-7754-b997-5dc664976b08" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019eae6b-3b63-7a52-a0af-a513126748c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019eae6b-3b63-7836-9650-a5442c999a3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eae6b-3b63-7754-b997-5dc664976b08" xlink:to="loc_us-gaap_WarrantMember_019eae6b-3b63-7836-9650-a5442c999a3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019eae6b-3b63-77a2-83b8-5c18d02a0e0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019eae6b-3b63-7922-960e-77b7669c87d7" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019eae6b-3b63-77a2-83b8-5c18d02a0e0d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7d79-ae81-3b39d29b2e53_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:to="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7d79-ae81-3b39d29b2e53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:to="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_StockIncentivePlan2015Member_019eae6b-3b63-7473-99fc-d6eef7b9c40d" xlink:href="imrx-20260630.xsd#imrx_StockIncentivePlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_StockIncentivePlan2015Member_019eae6b-3b63-7473-99fc-d6eef7b9c40d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_TwoThousandTwentyOneIncentiveAwardPlanMember_019eae6b-3b63-735f-a020-92825fc0a4ae" xlink:href="imrx-20260630.xsd#imrx_TwoThousandTwentyOneIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_TwoThousandTwentyOneIncentiveAwardPlanMember_019eae6b-3b63-735f-a020-92825fc0a4ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_TwoThousandTwentyOneEmployeeStockPurchasePlanMember_019eae6b-3b63-7ec0-84da-b102f1bda775" xlink:href="imrx-20260630.xsd#imrx_TwoThousandTwentyOneEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_TwoThousandTwentyOneEmployeeStockPurchasePlanMember_019eae6b-3b63-7ec0-84da-b102f1bda775" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_InducementAwardPlanMember_019eae6b-3b63-7c06-8542-ffbfafb69e24" xlink:href="imrx-20260630.xsd#imrx_InducementAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_InducementAwardPlanMember_019eae6b-3b63-7c06-8542-ffbfafb69e24" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-7a07-9932-2bb34bde8cd0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:to="loc_srt_RangeMember_019eae6b-3b63-7a07-9932-2bb34bde8cd0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-7d74-9340-a097c7539353" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:to="loc_srt_RangeMember_019eae6b-3b63-7d74-9340-a097c7539353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eae6b-3b63-7f02-b5eb-ca5552f2f7c3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eae6b-3b63-7d74-9340-a097c7539353" xlink:to="loc_srt_MaximumMember_019eae6b-3b63-7f02-b5eb-ca5552f2f7c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7237-b293-421eb372f0be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7237-b293-421eb372f0be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-ae6f-72ede17ec142" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-ae6f-72ede17ec142" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7a40-87bc-236a81b6b376" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-ae6f-72ede17ec142" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7a40-87bc-236a81b6b376" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-790b-b919-fe24ad6df3c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-790b-b919-fe24ad6df3c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_VestedRepricedOptionMember_019eae6b-3b63-783d-9072-4536b642e66c" xlink:href="imrx-20260630.xsd#imrx_VestedRepricedOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:to="loc_imrx_VestedRepricedOptionMember_019eae6b-3b63-783d-9072-4536b642e66c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_UnvestedRepricedOptionMember_019eae6b-3b63-7501-b802-16c1bb7c53c0" xlink:href="imrx-20260630.xsd#imrx_UnvestedRepricedOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:to="loc_imrx_UnvestedRepricedOptionMember_019eae6b-3b63-7501-b802-16c1bb7c53c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019eae6b-3b63-7c0b-805e-2d441430edb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019eae6b-3b63-7c0b-805e-2d441430edb6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019eae6b-3b63-7d0a-8d0e-6767716e6daf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019eae6b-3b63-7d0a-8d0e-6767716e6daf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019eae6b-3b63-7823-943c-6ba239be7db2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019eae6b-3b63-7823-943c-6ba239be7db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AggregateNumberOfSharesOutstanding_019eae6b-3b63-7ff0-a321-9471a0f93d95" xlink:href="imrx-20260630.xsd#imrx_AggregateNumberOfSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_imrx_AggregateNumberOfSharesOutstanding_019eae6b-3b63-7ff0-a321-9471a0f93d95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019eae6b-3b63-7030-b95d-5aecb154952e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019eae6b-3b63-7030-b95d-5aecb154952e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019eae6b-3b63-7df3-b7e9-832f884c05a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019eae6b-3b63-7df3-b7e9-832f884c05a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019eae6b-3b63-795b-ab06-88aeba973f7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019eae6b-3b63-795b-ab06-88aeba973f7c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7ff2-8654-5252af65c0b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7ff2-8654-5252af65c0b9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019eae6b-3b63-7d3d-9bc4-cb06244ddb21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019eae6b-3b63-7d3d-9bc4-cb06244ddb21" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019eae6b-3b63-753c-8160-247e899ef1af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019eae6b-3b63-753c-8160-247e899ef1af" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019eae6b-3b63-7229-b6f1-ae8accf556e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019eae6b-3b63-7229-b6f1-ae8accf556e7" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/StockBasedCompensationNarrativeDetails_1" xlink:type="simple" xlink:href="imrx-20260630.xsd#StockBasedCompensationNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/StockBasedCompensationNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7d79-ae81-3b39d29b2e53_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:to="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7d79-ae81-3b39d29b2e53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019eae6b-3b63-7d79-ae81-3b39d29b2e53" xlink:to="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_StockIncentivePlan2015Member_019eae6b-3b63-7473-99fc-d6eef7b9c40d" xlink:href="imrx-20260630.xsd#imrx_StockIncentivePlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_StockIncentivePlan2015Member_019eae6b-3b63-7473-99fc-d6eef7b9c40d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_TwoThousandTwentyOneIncentiveAwardPlanMember_019eae6b-3b63-735f-a020-92825fc0a4ae" xlink:href="imrx-20260630.xsd#imrx_TwoThousandTwentyOneIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_TwoThousandTwentyOneIncentiveAwardPlanMember_019eae6b-3b63-735f-a020-92825fc0a4ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_TwoThousandTwentyOneEmployeeStockPurchasePlanMember_019eae6b-3b63-7ec0-84da-b102f1bda775" xlink:href="imrx-20260630.xsd#imrx_TwoThousandTwentyOneEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_TwoThousandTwentyOneEmployeeStockPurchasePlanMember_019eae6b-3b63-7ec0-84da-b102f1bda775" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_InducementAwardPlanMember_019eae6b-3b63-7c06-8542-ffbfafb69e24" xlink:href="imrx-20260630.xsd#imrx_InducementAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eae6b-3b63-7276-a101-997bd3bdaa44" xlink:to="loc_imrx_InducementAwardPlanMember_019eae6b-3b63-7c06-8542-ffbfafb69e24" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-7a07-9932-2bb34bde8cd0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:to="loc_srt_RangeMember_019eae6b-3b63-7a07-9932-2bb34bde8cd0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-7d74-9340-a097c7539353" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-7a07-9932-2bb34bde8cd0" xlink:to="loc_srt_RangeMember_019eae6b-3b63-7d74-9340-a097c7539353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eae6b-3b63-7f02-b5eb-ca5552f2f7c3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eae6b-3b63-7d74-9340-a097c7539353" xlink:to="loc_srt_MaximumMember_019eae6b-3b63-7f02-b5eb-ca5552f2f7c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7237-b293-421eb372f0be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-7237-b293-421eb372f0be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-ae6f-72ede17ec142" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019eae6b-3b63-7237-b293-421eb372f0be" xlink:to="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-ae6f-72ede17ec142" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7a40-87bc-236a81b6b376" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019eae6b-3b63-739b-ae6f-72ede17ec142" xlink:to="loc_us-gaap_CommonClassAMember_019eae6b-3b63-7a40-87bc-236a81b6b376" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-756e-99f1-984fc8b2406d" xlink:to="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-790b-b919-fe24ad6df3c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-790b-b919-fe24ad6df3c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019eae6b-3b63-790b-b919-fe24ad6df3c8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_VestedRepricedOptionMember_019eae6b-3b63-783d-9072-4536b642e66c" xlink:href="imrx-20260630.xsd#imrx_VestedRepricedOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:to="loc_imrx_VestedRepricedOptionMember_019eae6b-3b63-783d-9072-4536b642e66c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_UnvestedRepricedOptionMember_019eae6b-3b63-7501-b802-16c1bb7c53c0" xlink:href="imrx-20260630.xsd#imrx_UnvestedRepricedOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eae6b-3b63-771d-a428-4f70c7cd9d64" xlink:to="loc_imrx_UnvestedRepricedOptionMember_019eae6b-3b63-7501-b802-16c1bb7c53c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019eae6b-3b63-7d0a-8d0e-6767716e6daf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019eae6b-3b63-7d0a-8d0e-6767716e6daf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019eae6b-3b63-7823-943c-6ba239be7db2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019eae6b-3b63-7823-943c-6ba239be7db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AggregateNumberOfSharesOutstanding_019eae6b-3b63-7ff0-a321-9471a0f93d95" xlink:href="imrx-20260630.xsd#imrx_AggregateNumberOfSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_imrx_AggregateNumberOfSharesOutstanding_019eae6b-3b63-7ff0-a321-9471a0f93d95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019eae6b-3b63-7030-b95d-5aecb154952e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019eae6b-3b63-7030-b95d-5aecb154952e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019eae6b-3b63-7df3-b7e9-832f884c05a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019eae6b-3b63-7df3-b7e9-832f884c05a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019eae6b-3b63-795b-ab06-88aeba973f7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019eae6b-3b63-795b-ab06-88aeba973f7c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7ff2-8654-5252af65c0b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7ff2-8654-5252af65c0b9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019eae6b-3b63-7d3d-9bc4-cb06244ddb21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019eae6b-3b63-7d3d-9bc4-cb06244ddb21" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019eae6b-3b63-753c-8160-247e899ef1af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019eae6b-3b63-753c-8160-247e899ef1af" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019eae6b-3b63-7229-b6f1-ae8accf556e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7e3e-9082-a37cfe41d988" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019eae6b-3b63-7229-b6f1-ae8accf556e7" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/StockBasedCompensationScheduleofAssumptionsinitsApplicationoftheBlackScholesOptionPricingModelforGrantsDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#StockBasedCompensationScheduleofAssumptionsinitsApplicationoftheBlackScholesOptionPricingModelforGrantsDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/StockBasedCompensationScheduleofAssumptionsinitsApplicationoftheBlackScholesOptionPricingModelforGrantsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-77ed-9821-aafe7665fa68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-77ed-9821-aafe7665fa68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eae6b-3b63-73e9-a023-e36422c4d2fb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-77ed-9821-aafe7665fa68" xlink:to="loc_srt_RangeAxis_019eae6b-3b63-73e9-a023-e36422c4d2fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-73e9-a023-e36422c4d2fb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-73e9-a023-e36422c4d2fb" xlink:to="loc_srt_RangeMember_019eae6b-3b63-73e9-a023-e36422c4d2fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eae6b-3b63-73c0-b54e-22ee27bfbf92" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eae6b-3b63-73e9-a023-e36422c4d2fb" xlink:to="loc_srt_RangeMember_019eae6b-3b63-73c0-b54e-22ee27bfbf92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019eae6b-3b63-7996-ad85-47802d425933" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eae6b-3b63-73c0-b54e-22ee27bfbf92" xlink:to="loc_srt_MinimumMember_019eae6b-3b63-7996-ad85-47802d425933" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eae6b-3b63-7cc1-94ce-8bc9810f92c3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eae6b-3b63-73c0-b54e-22ee27bfbf92" xlink:to="loc_srt_MaximumMember_019eae6b-3b63-7cc1-94ce-8bc9810f92c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_019eae6b-3b63-7d24-be16-94d8231bc796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_019eae6b-3b63-7d24-be16-94d8231bc796" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_019eae6b-3b63-7614-837a-4c84a2840ec6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_019eae6b-3b63-7614-837a-4c84a2840ec6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019eae6b-3b63-7c5c-9b1d-f38c5823727b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019eae6b-3b63-7c5c-9b1d-f38c5823727b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019eae6b-3b63-7755-9bf8-d1c159e47c78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019eae6b-3b63-7755-9bf8-d1c159e47c78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019eae6b-3b63-7bd1-9e80-a6736d58f72e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019eae6b-3b63-7bd1-9e80-a6736d58f72e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019eae6b-3b63-7665-a27b-8f34b215524c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-73e0-b098-b32b5fdb0f9d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019eae6b-3b63-7665-a27b-8f34b215524c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/StockBasedCompensationScheduleofRecognizedSharebasedCompensationExpenseRecognizedDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#StockBasedCompensationScheduleofRecognizedSharebasedCompensationExpenseRecognizedDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/StockBasedCompensationScheduleofRecognizedSharebasedCompensationExpenseRecognizedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7ced-8c2a-ec6c6de55e90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-7f51-a592-a475444ec4ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7ced-8c2a-ec6c6de55e90" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-7f51-a592-a475444ec4ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019eae6b-3b63-7b32-b952-a441a6d6ab2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-7f51-a592-a475444ec4ad" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019eae6b-3b63-7b32-b952-a441a6d6ab2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7346-b8d5-faf363ab3b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7ced-8c2a-ec6c6de55e90" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7346-b8d5-faf363ab3b7c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/StockBasedCompensationScheduleofRecognizedSharebasedCompensationExpenseRecognizedDetails_1" xlink:type="simple" xlink:href="imrx-20260630.xsd#StockBasedCompensationScheduleofRecognizedSharebasedCompensationExpenseRecognizedDetails_1"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/StockBasedCompensationScheduleofRecognizedSharebasedCompensationExpenseRecognizedDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7ced-8c2a-ec6c6de55e90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-7f51-a592-a475444ec4ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7ced-8c2a-ec6c6de55e90" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eae6b-3b63-7f51-a592-a475444ec4ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7346-b8d5-faf363ab3b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eae6b-3b63-7ced-8c2a-ec6c6de55e90" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7346-b8d5-faf363ab3b7c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019eae6b-3b63-7c8e-8b42-0d38f3e6e25a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019eae6b-3b63-7c8e-8b42-0d38f3e6e25a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermAxis_019eae6b-3b63-74e5-ba2e-12d6bfeddfdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019eae6b-3b63-7c8e-8b42-0d38f3e6e25a" xlink:to="loc_us-gaap_LeaseContractualTermAxis_019eae6b-3b63-74e5-ba2e-12d6bfeddfdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_019eae6b-3b63-74e5-ba2e-12d6bfeddfdf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LeaseContractualTermAxis_019eae6b-3b63-74e5-ba2e-12d6bfeddfdf" xlink:to="loc_us-gaap_LeaseContractualTermDomain_019eae6b-3b63-74e5-ba2e-12d6bfeddfdf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_019eae6b-3b63-79f3-847e-309f17f0495f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LeaseContractualTermAxis_019eae6b-3b63-74e5-ba2e-12d6bfeddfdf" xlink:to="loc_us-gaap_LeaseContractualTermDomain_019eae6b-3b63-79f3-847e-309f17f0495f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_LeaseTerminationOnApril302032Member_019eae6b-3b63-77d1-98ee-f9f9e06878bf" xlink:href="imrx-20260630.xsd#imrx_LeaseTerminationOnApril302032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_019eae6b-3b63-79f3-847e-309f17f0495f" xlink:to="loc_imrx_LeaseTerminationOnApril302032Member_019eae6b-3b63-77d1-98ee-f9f9e06878bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_OfficeSpaceInCambridgeMassachusettsAndNewYorkNewYorkMember_019eae6b-3b63-749e-957f-4f038d3330a7" xlink:href="imrx-20260630.xsd#imrx_OfficeSpaceInCambridgeMassachusettsAndNewYorkNewYorkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_019eae6b-3b63-79f3-847e-309f17f0495f" xlink:to="loc_imrx_OfficeSpaceInCambridgeMassachusettsAndNewYorkNewYorkMember_019eae6b-3b63-749e-957f-4f038d3330a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-790d-a531-258899690526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019eae6b-3b63-7c8e-8b42-0d38f3e6e25a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-790d-a531-258899690526" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-790d-a531-258899690526_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-790d-a531-258899690526" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-790d-a531-258899690526_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-74b8-8fd3-01a417122925" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eae6b-3b63-790d-a531-258899690526" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-74b8-8fd3-01a417122925" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_OfficeSpaceInCambridgeMassachusettsNewYorkMember_019eae6b-3b63-7c72-8a5b-55d4730f39d3" xlink:href="imrx-20260630.xsd#imrx_OfficeSpaceInCambridgeMassachusettsNewYorkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eae6b-3b63-74b8-8fd3-01a417122925" xlink:to="loc_imrx_OfficeSpaceInCambridgeMassachusettsNewYorkMember_019eae6b-3b63-7c72-8a5b-55d4730f39d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_019eae6b-3b63-7cb6-b09b-fa8bd586d342" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AreaOfRealEstateProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:to="loc_us-gaap_AreaOfRealEstateProperty_019eae6b-3b63-7cb6-b09b-fa8bd586d342" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019eae6b-3b63-7267-81b0-f3d5c138a807" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019eae6b-3b63-7267-81b0-f3d5c138a807" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseTermOfContract_019eae6b-3b63-7dee-9891-fbd7253778a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:to="loc_us-gaap_LessorOperatingLeaseTermOfContract_019eae6b-3b63-7dee-9891-fbd7253778a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_019eae6b-3b63-7688-a575-ec74986cee40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_019eae6b-3b63-7688-a575-ec74986cee40" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_NoticePeriodForContractTermination_019eae6b-3b63-73fc-82f1-01aed520d145" xlink:href="imrx-20260630.xsd#imrx_NoticePeriodForContractTermination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019eae6b-3b63-71f4-b27e-a4354c23db79" xlink:to="loc_imrx_NoticePeriodForContractTermination_019eae6b-3b63-73fc-82f1-01aed520d145" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://immuneering.com/role/SegmentsScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="imrx-20260630.xsd#SegmentsScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://immuneering.com/role/SegmentsScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019eae6b-3b63-79c4-813d-a2f264bb06ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019eae6b-3b63-79c4-813d-a2f264bb06ce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019eae6b-3b63-7ff3-b4ec-3aa298e3c6d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019eae6b-3b63-79c4-813d-a2f264bb06ce" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019eae6b-3b63-7ff3-b4ec-3aa298e3c6d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019eae6b-3b63-7ff3-b4ec-3aa298e3c6d6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019eae6b-3b63-7ff3-b4ec-3aa298e3c6d6" xlink:to="loc_us-gaap_SegmentDomain_019eae6b-3b63-7ff3-b4ec-3aa298e3c6d6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019eae6b-3b63-72af-927f-079e245c969b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019eae6b-3b63-7ff3-b4ec-3aa298e3c6d6" xlink:to="loc_us-gaap_SegmentDomain_019eae6b-3b63-72af-927f-079e245c969b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_ReportableSegmentMember_019eae6b-3b63-7f10-af42-e136c0fcc294" xlink:href="imrx-20260630.xsd#imrx_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019eae6b-3b63-72af-927f-079e245c969b" xlink:to="loc_imrx_ReportableSegmentMember_019eae6b-3b63-7f10-af42-e136c0fcc294" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019eae6b-3b63-76a0-8307-83e69bb1ec16" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019eae6b-3b63-79c4-813d-a2f264bb06ce" xlink:to="loc_srt_ProductOrServiceAxis_019eae6b-3b63-76a0-8307-83e69bb1ec16" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-76a0-8307-83e69bb1ec16_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019eae6b-3b63-76a0-8307-83e69bb1ec16" xlink:to="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-76a0-8307-83e69bb1ec16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-7f9e-ad78-7e6041946ddf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019eae6b-3b63-76a0-8307-83e69bb1ec16" xlink:to="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-7f9e-ad78-7e6041946ddf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_AtebimetinibIMM1104Member_019eae6b-3b63-7c0b-879b-071e2287b5f4" xlink:href="imrx-20260630.xsd#imrx_AtebimetinibIMM1104Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-7f9e-ad78-7e6041946ddf" xlink:to="loc_imrx_AtebimetinibIMM1104Member_019eae6b-3b63-7c0b-879b-071e2287b5f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_EnvometinibIMM6415Member_019eae6b-3b63-7699-be04-fd021c4c6088" xlink:href="imrx-20260630.xsd#imrx_EnvometinibIMM6415Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-7f9e-ad78-7e6041946ddf" xlink:to="loc_imrx_EnvometinibIMM6415Member_019eae6b-3b63-7699-be04-fd021c4c6088" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_OtherProgramsMember_019eae6b-3b63-7ebd-8c13-9ec1311fdf74" xlink:href="imrx-20260630.xsd#imrx_OtherProgramsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eae6b-3b63-7f9e-ad78-7e6041946ddf" xlink:to="loc_imrx_OtherProgramsMember_019eae6b-3b63-7ebd-8c13-9ec1311fdf74" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_ProgramExpenses_019eae6b-3b63-76f3-88f8-96ee811182cc" xlink:href="imrx-20260630.xsd#imrx_ProgramExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_imrx_ProgramExpenses_019eae6b-3b63-76f3-88f8-96ee811182cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_imrx_NonProgramExpenses_019eae6b-3b63-76cd-a044-83ac08a3ddf1" xlink:href="imrx-20260630.xsd#imrx_NonProgramExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_imrx_NonProgramExpenses_019eae6b-3b63-76cd-a044-83ac08a3ddf1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019eae6b-3b63-7d78-970c-8cb6438d07bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019eae6b-3b63-7d78-970c-8cb6438d07bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7a43-897d-1f2f5a9957f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eae6b-3b63-7a43-897d-1f2f5a9957f7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019eae6b-3b63-7c1a-ad92-d00ee7c15c95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019eae6b-3b63-7c1a-ad92-d00ee7c15c95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019eae6b-3b63-75e8-9658-87bdf07c5a2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019eae6b-3b63-75e8-9658-87bdf07c5a2e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eae6b-3b63-7bfa-a9d4-e8d33614fb7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019eae6b-3b63-70d1-9357-fd739f621b74" xlink:to="loc_us-gaap_NetIncomeLoss_019eae6b-3b63-7bfa-a9d4-e8d33614fb7a" xlink:type="arc" order="6"/>
  </link:definitionLink>
</link:linkbase>
