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  <xsd:element name="CommitmentsAndContingenciesLineItems" id="mrkr_CommitmentsAndContingenciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="BasisOfPresentationAbstract" id="mrkr_BasisOfPresentationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="ClassOfWarrantOrRightExerciseAxis" id="mrkr_ClassOfWarrantOrRightExerciseAxis" type="xbrli:stringItemType" substitutionGroup="xbrldt:dimensionItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="ClassOfWarrantOrRightExerciseDomain" id="mrkr_ClassOfWarrantOrRightExerciseDomain" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="ClinicalTrialAgreementWithBaylorCollegeOfMedicineMember" id="mrkr_ClinicalTrialAgreementWithBaylorCollegeOfMedicineMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="LiquidityFinancialConditionAndGoingConcernAbstract" id="mrkr_LiquidityFinancialConditionAndGoingConcernAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="LiquidityFinancialConditionAndGoingConcernTextBlock" id="mrkr_LiquidityFinancialConditionAndGoingConcernTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="EquityIncentivePlan2020Member" id="mrkr_EquityIncentivePlan2020Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="CommonStockSharesCommissionRateCalculationOnGrossSalesPricePerSharePercent" id="mrkr_CommonStockSharesCommissionRateCalculationOnGrossSalesPricePerSharePercent" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="FundsReceivedFromCpritGrant" id="mrkr_FundsReceivedFromCpritGrant" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="FundsReceivedFromGrant" id="mrkr_FundsReceivedFromGrant" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="ReceiptOfProductDevelopmentResearchAward" id="mrkr_ReceiptOfProductDevelopmentResearchAward" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element name="WilsonWolfManufacturingCorporationMember" id="mrkr_WilsonWolfManufacturingCorporationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="RevenueFromGrantRelatedToCprit" id="mrkr_RevenueFromGrantRelatedToCprit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element name="GrantIncomeTable" id="mrkr_GrantIncomeTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="GrantIncomeLineItems" id="mrkr_GrantIncomeLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="GrantReceived" id="mrkr_GrantReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element name="FinancialConditionGoingConcernAndManagementPlansTable" id="mrkr_FinancialConditionGoingConcernAndManagementPlansTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="FinancialConditionGoingConcernAndManagementPlansLineItems" id="mrkr_FinancialConditionGoingConcernAndManagementPlansLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="NetLossPerShareTableTextBlock" id="mrkr_NetLossPerShareTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="OrphanProductsGrantProgram" id="mrkr_OrphanProductsGrantProgram" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="CellReadyAgreementMember" id="mrkr_CellReadyAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="CpritGrantMember" id="mrkr_CpritGrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="FdaGrantMember" id="mrkr_FdaGrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="IndaptaMember" id="mrkr_IndaptaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="CellReadyMember" id="mrkr_CellReadyMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="NationalInstitutesOfHealthSmallBusinessInnovationResearchMember" id="mrkr_NationalInstitutesOfHealthSmallBusinessInnovationResearchMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="AccountsPayableAndAccruedLiabilitiesIncludingRelatedPartyPayableCurrent" id="mrkr_AccountsPayableAndAccruedLiabilitiesIncludingRelatedPartyPayableCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="credit" />
  <xsd:element name="TaxFeesPayable" id="mrkr_TaxFeesPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="credit" />
  <xsd:element name="CashAtFinancialInstitutions" id="mrkr_CashAtFinancialInstitutions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="debit" />
  <xsd:element name="RecentlyIssuedAccountingStandardsNotYetAdoptedPolicyTextBlock" id="mrkr_RecentlyIssuedAccountingStandardsNotYetAdoptedPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="InvoicesReceivedForServicesAndManufacturingCosts" id="mrkr_InvoicesReceivedForServicesAndManufacturingCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <xsd:element name="GrantAssistanceTerm" id="mrkr_GrantAssistanceTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="NationalInstitutesOfHealthNationalCancerInstituteGrantMember" id="mrkr_NationalInstitutesOfHealthNationalCancerInstituteGrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="NationalInstitutesOfHealthSmallBusinessInnovationResearchForLymphomaGrantMember" id="mrkr_NationalInstitutesOfHealthSmallBusinessInnovationResearchForLymphomaGrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="CancerPreventionAndResearchInstituteOfTexasGrantAgreementMember" id="mrkr_CancerPreventionAndResearchInstituteOfTexasGrantAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="GrantAgreementPaymentsRequiredPercentageOfNetSalesToGrantsReceived" id="mrkr_GrantAgreementPaymentsRequiredPercentageOfNetSalesToGrantsReceived" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="GrantAgreementRevenueSharingPercentageRemainderOfRevenueTerm" id="mrkr_GrantAgreementRevenueSharingPercentageRemainderOfRevenueTerm" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="BaylorCollegeOfMedicineLicenseAgreementMember" id="mrkr_BaylorCollegeOfMedicineLicenseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="SaleOfStockValueOfSharesIssuedInTransaction" id="mrkr_SaleOfStockValueOfSharesIssuedInTransaction" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="LicenseAgreementMaximumMilestonePaymentsAgreedToBePaid" id="mrkr_LicenseAgreementMaximumMilestonePaymentsAgreedToBePaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="LicenseAgreementLiquidityIncentivePaymentPercentage" id="mrkr_LicenseAgreementLiquidityIncentivePaymentPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="MasterServicesAgreementTerm" id="mrkr_MasterServicesAgreementTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="PreFundedWarrantMember" id="mrkr_PreFundedWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="PrivatePlacementWarrantMember" id="mrkr_PrivatePlacementWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="NationalInstitutesOfHealthSmallBusinessInnovationResearchForPancreaticCancerMember" id="mrkr_NationalInstitutesOfHealthSmallBusinessInnovationResearchForPancreaticCancerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="AdditionalCpritGrantMember" id="mrkr_AdditionalCpritGrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="ClassOfWarrantOrRightExercised" id="mrkr_ClassOfWarrantOrRightExercised" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="AtMarketOfferingMember" id="mrkr_AtMarketOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="GainLossOnEarlyTerminationOfVendorAgreement" id="mrkr_GainLossOnEarlyTerminationOfVendorAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="StockIssuedDuringPeriodValueWarrantsExercised" id="mrkr_StockIssuedDuringPeriodValueWarrantsExercised" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="StockIssuedDuringPeriodSharesWarrantsExercised" id="mrkr_StockIssuedDuringPeriodSharesWarrantsExercised" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="ProceedsFromWarrantsAndStockOptionsExercised" id="mrkr_ProceedsFromWarrantsAndStockOptionsExercised" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <xsd:element name="CancerPreventionAndResearchInstituteOfTexasAcuteMyeloidLeukemiaMember" id="mrkr_CancerPreventionAndResearchInstituteOfTexasAcuteMyeloidLeukemiaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="CancerPreventionAndResearchInstituteOfTexasMetastaticPancreaticCancerMember" id="mrkr_CancerPreventionAndResearchInstituteOfTexasMetastaticPancreaticCancerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="EquityIncentiveAward2025Member" id="mrkr_EquityIncentiveAward2025Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="BaylorCollegeOfMedicineMember" id="mrkr_BaylorCollegeOfMedicineMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="PrepaidExpenseAndDepositsCurrent" id="mrkr_PrepaidExpenseAndDepositsCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="debit" />
  <xsd:element name="IncreaseDecreaseInPrepaidExpenseAndDeposits" id="mrkr_IncreaseDecreaseInPrepaidExpenseAndDeposits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
</xsd:schema>
