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  <xsd:element name="StockBasedCompensationExpensesTableTextBlock" id="mrkr_StockBasedCompensationExpensesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="AccountsPayableAndAccruedLiabilitiesTable" id="mrkr_AccountsPayableAndAccruedLiabilitiesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="AccountsPayableAndAccruedLiabilitiesLineItems" id="mrkr_AccountsPayableAndAccruedLiabilitiesLineItems" 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="IssuanceOfCommonStockValueAsCommitmentFeeForFutureFinancing" id="mrkr_IssuanceOfCommonStockValueAsCommitmentFeeForFutureFinancing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element name="IssuanceOfCommonStockSharesAsCommitmentFeeForFutureFinancing" id="mrkr_IssuanceOfCommonStockSharesAsCommitmentFeeForFutureFinancing" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="NonCashIssuanceOfCommonStockAsCommitmentFeeForFutureFinancing" id="mrkr_NonCashIssuanceOfCommonStockAsCommitmentFeeForFutureFinancing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:balance="debit" 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="ControlledEquityOfferingSalesAgreementMember" id="mrkr_ControlledEquityOfferingSalesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="CantorFitzgeraldCo.AndRbcCapitalMarketsLlcMember" id="mrkr_CantorFitzgeraldCo.AndRbcCapitalMarketsLlcMember" 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="BindingServicesAgreementMember" id="mrkr_BindingServicesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="StockBasedCompensationTable" id="mrkr_StockBasedCompensationTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="StockBasedCompensationLineItems" id="mrkr_StockBasedCompensationLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" 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="CancerPreventionAndResearchInstituteOfTexasMember" id="mrkr_CancerPreventionAndResearchInstituteOfTexasMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="OrganizationConsolidationAndPresentationOfFinancialStatementsTable" id="mrkr_OrganizationConsolidationAndPresentationOfFinancialStatementsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="OrganizationConsolidationAndPresentationOfFinancialStatementsLineItems" id="mrkr_OrganizationConsolidationAndPresentationOfFinancialStatementsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="LincolnParkMember" id="mrkr_LincolnParkMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="AtmAgreementMember" id="mrkr_AtmAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" 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="CommitmentFee" id="mrkr_CommitmentFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element name="RevenueFromOrphanProductsGrantProgram" id="mrkr_RevenueFromOrphanProductsGrantProgram" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" 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="StockPurchaseAgreementMember" id="mrkr_StockPurchaseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="StockPurchaseAgreementTimeToTimeTermToPurchaseShares" id="mrkr_StockPurchaseAgreementTimeToTimeTermToPurchaseShares" type="xbrli:durationItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="StockIssuedDuringPeriodSharesFractionalSharesAdjustmentDueToReverseSplit" id="mrkr_StockIssuedDuringPeriodSharesFractionalSharesAdjustmentDueToReverseSplit" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="CellReadyAgreementMember" id="mrkr_CellReadyAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="OffersEmploymentToNumberOfEmployees" id="mrkr_OffersEmploymentToNumberOfEmployees" type="xbrli:integerItemType" substitutionGroup="xbrli:item" abstract="false" 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="DiscontinuedOperationIncomeLossFromDiscontinuedOperationAbstract" id="mrkr_DiscontinuedOperationIncomeLossFromDiscontinuedOperationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="RelatedPartyServiceMember" id="mrkr_RelatedPartyServiceMember" 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="AdditionalRevenueRecognized" id="mrkr_AdditionalRevenueRecognized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="StockCompensationInContinuingOperations" id="mrkr_StockCompensationInContinuingOperations" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <xsd:element name="StockCompensationInDiscontinuedOperations" id="mrkr_StockCompensationInDiscontinuedOperations" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <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="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="OtherTaxesPayableCurrent" id="mrkr_OtherTaxesPayableCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="credit" />
  <xsd:element name="InvoicesReceivedForServicesAndManufacturingCosts" id="mrkr_InvoicesReceivedForServicesAndManufacturingCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
</xsd:schema>
