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<link:definition>1019 - Disclosure - RELATED PARTY TRANSACTIONS</link:definition>
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<link:definition>1021 - Disclosure - NET LOSS PER SHARE APPLICABLE TO COMMON SHAREHOLDER (Tables)</link:definition>
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<link:definition>1022 - Disclosure - PROPERTY AND EQUIPMENT (Tables)</link:definition>
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<link:definition>1023 - Disclosure - LEASES (Tables)</link:definition>
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<link:definition>1024 - Disclosure - ACCOUNTS PAYABLE AND ACCRUED LIABILITIES (Tables)</link:definition>
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<link:definition>1025 - Disclosure - WARRANT LIABILITY AND FAIR VALUE MEASUREMENTS (Tables)</link:definition>
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<link:definition>1026 - Disclosure - STOCKHOLDERS' EQUITY (Tables)</link:definition>
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<link:definition>1027 - Disclosure - STOCK-BASED COMPENSATION (Tables)</link:definition>
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<link:definition>1028 - Disclosure - LIQUIDITY AND FINANCIAL CONDITION - Additional Information (Detail)</link:definition>
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<link:definition>1029 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES- Additional Information (Detail)</link:definition>
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<link:definition>1038 - Disclosure - WARRANT LIABILITY AND FAIR VALUE MEASUREMENTS - Conversion Option - Valuation Methodology (Detail)</link:definition>
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<link:definition>1039 - Disclosure - WARRANT LIABILITY AND FAIR VALUE MEASUREMENTS - Conversion Option - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail)</link:definition>
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<link:definition>1040 - Disclosure - WARRANT LIABILITY AND FAIR VALUE MEASUREMENTS - Conversion Option - Schedule of Changes in Level 3 Liabilities Reflected in Accrued Expenses Measured at Fair Value (Detail)</link:definition>
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<link:definition>1042 - Disclosure - STOCKHOLDERS' EQUITY - Additional Information (Detail)</link:definition>
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<link:definition>1043 - Disclosure - STOCK-BASED COMPENSATION (Details)</link:definition>
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<link:definition>1044 - Disclosure - STOCK-BASED COMPENSATION - Additional Information (Detail)</link:definition>
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<link:definition>1045 - Disclosure - COMMITMENTS - Additional Information (Detail)</link:definition>
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<link:definition>1046 - Disclosure - RELATED PARTY TRANSACTIONS - Additional Information (Detail)</link:definition>
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<import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" />
<import namespace="http://fasb.org/us-types/2018-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2018/elts/us-types-2018-01-31.xsd" />
<import namespace="http://fasb.org/srt/2018-01-31" schemaLocation="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd" />
<element name="DocumentAndEntityInformationAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_DocumentAndEntityInformationAbstract" substitutionGroup="xbrli:item" />
<element name="ExerciseOfWarrantsAmount" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ExerciseOfWarrantsAmount" substitutionGroup="xbrli:item" xbrli:balance="credit" />
<element name="ExerciseOfWarrantsShare" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ExerciseOfWarrantsShare" substitutionGroup="xbrli:item" />
<element name="AmortizationOfOperatingLeaseRightOfUseAssets" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_AmortizationOfOperatingLeaseRightOfUseAssets" substitutionGroup="xbrli:item" xbrli:balance="debit" />
<element name="IncreasedecreaseInOperatingLeaseLiability" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_IncreasedecreaseInOperatingLeaseLiability" substitutionGroup="xbrli:item" xbrli:balance="debit" />
<element name="LiquidityAndFinancialConditionTextblock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_LiquidityAndFinancialConditionTextblock" substitutionGroup="xbrli:item" />
<element name="DerivativesAndFairValueAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_DerivativesAndFairValueAbstract" substitutionGroup="xbrli:item" />
<element name="RelatedPartyDisclosureAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_RelatedPartyDisclosureAbstract" substitutionGroup="xbrli:item" />
<element name="NetLossPerShareTableTextBlockTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_NetLossPerShareTableTextBlockTableTextBlock" substitutionGroup="xbrli:item" />
<element name="ScheduleOfLeaseCostAndOtherInformationRelatedToOperatingLeasesTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ScheduleOfLeaseCostAndOtherInformationRelatedToOperatingLeasesTableTextBlock" substitutionGroup="xbrli:item" />
<element name="ValuationMethodology" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ValuationMethodology" substitutionGroup="xbrli:item" />
<element name="FinancialAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_FinancialAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisTableTextBlock" substitutionGroup="xbrli:item" />
<element name="MeasuredAtFairValue" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_MeasuredAtFairValue" substitutionGroup="xbrli:item" />
<element name="StockholdersEquityTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_StockholdersEquityTable" substitutionGroup="xbrldt:hypercubeItem" />
<element name="StockholdersEquityLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_StockholdersEquityLineItems" substitutionGroup="xbrli:item" />
<element name="SharePurchaseWarrantsTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_SharePurchaseWarrantsTableTextBlock" substitutionGroup="xbrli:item" />
<element name="StockBasedCompensationExpensesTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_StockBasedCompensationExpensesTableTextBlock" substitutionGroup="xbrli:item" />
<element name="LiquidityAndFinancialConditionabstractAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_LiquidityAndFinancialConditionabstractAbstract" substitutionGroup="xbrli:item" />
<element name="NotestofinancialstatementsAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_NotestofinancialstatementsAbstract" substitutionGroup="xbrli:item" />
<element name="CommonStockWarrantsEquityTreatment" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_CommonStockWarrantsEquityTreatment" substitutionGroup="xbrli:item" />
<element name="CommonStockWarrantsLiabilityTreatmentMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_CommonStockWarrantsLiabilityTreatmentMember" substitutionGroup="xbrli:item" />
<element name="OperatingLeaseExpenseAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_OperatingLeaseExpenseAbstract" substitutionGroup="xbrli:item" />
<element name="OtherLeaseInformationAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_OtherLeaseInformationAbstract" substitutionGroup="xbrli:item" />
<element name="AccountsPayableAndAccruedLiabilitiesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_AccountsPayableAndAccruedLiabilitiesTable" substitutionGroup="xbrldt:hypercubeItem" />
<element name="AccountsPayableAndAccruedLiabilitiesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_AccountsPayableAndAccruedLiabilitiesLineItems" substitutionGroup="xbrli:item" />
<element name="AccruedTechnologyLicenseFees" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="mrkr_AccruedTechnologyLicenseFees" substitutionGroup="xbrli:item" xbrli:balance="credit" />
<element name="AccruedInvestorRelationsFeesCurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="mrkr_AccruedInvestorRelationsFeesCurrent" substitutionGroup="xbrli:item" xbrli:balance="credit" />
<element name="FairValuesAssumptionsAndMethodologyForAssetsAndLiabilitiesAbstractAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_FairValuesAssumptionsAndMethodologyForAssetsAndLiabilitiesAbstractAbstract" substitutionGroup="xbrli:item" />
<element name="SharePurchaseWarrantsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_SharePurchaseWarrantsMember" substitutionGroup="xbrli:item" />
<element name="FairValuesAssumptionsExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="mrkr_FairValuesAssumptionsExercisePrice" substitutionGroup="xbrli:item" />
<element name="FairValuesAssumptionsExpectedTerm" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_FairValuesAssumptionsExpectedTerm" substitutionGroup="xbrli:item" />
<element name="FairValuesAssumptionsExpectedVolatilityRate" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_FairValuesAssumptionsExpectedVolatilityRate" substitutionGroup="xbrli:item" />
<element name="FairValuesAssumptionsRiskFreeInterestRate" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_FairValuesAssumptionsRiskFreeInterestRate" substitutionGroup="xbrli:item" />
<element name="FairValuesAssumptionsExpectedDividendRate" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_FairValuesAssumptionsExpectedDividendRate" substitutionGroup="xbrli:item" />
<element name="NumberOfWarrantExercisedForCash" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_NumberOfWarrantExercisedForCash" substitutionGroup="xbrli:item" />
<element name="NumberOfWarrantExpiredOrCancelled" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_NumberOfWarrantExpiredOrCancelled" substitutionGroup="xbrli:item" />
<element name="ClassOfWarrantOrRightsOutstandingWeightedAverageExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="mrkr_ClassOfWarrantOrRightsOutstandingWeightedAverageExercisePrice" substitutionGroup="xbrli:item" />
<element name="ClassOfWarrantOrRightsOutstandingExercisedWeightedAverageExercisedForCash" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ClassOfWarrantOrRightsOutstandingExercisedWeightedAverageExercisedForCash" substitutionGroup="xbrli:item" />
<element name="ClassOfWarrantOrRightsOutstandingExpiredOrCancelledWeightedAverageExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ClassOfWarrantOrRightsOutstandingExpiredOrCancelledWeightedAverageExercisePrice" substitutionGroup="xbrli:item" />
<element name="ClassOfWarrantOrRightsOutstandingWeightedAverageRemainingContractualLife" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ClassOfWarrantOrRightsOutstandingWeightedAverageRemainingContractualLife" substitutionGroup="xbrli:item" />
<element name="ClassOfWarrantOrRightOutstandingIntrinsicValue" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="mrkr_ClassOfWarrantOrRightOutstandingIntrinsicValue" substitutionGroup="xbrli:item" xbrli:balance="debit" />
<element name="CommonStockCapitalSharesReservedForFutureIssuanceTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_CommonStockCapitalSharesReservedForFutureIssuanceTable" substitutionGroup="xbrldt:hypercubeItem" />
<element name="ConsultingAgreementsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_ConsultingAgreementsMember" substitutionGroup="xbrli:item" />
<element name="ExerciseOfStockWarrantsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_ExerciseOfStockWarrantsMember" substitutionGroup="xbrli:item" />
<element name="CommonStockCapitalSharesReservedForFutureIssuanceLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_CommonStockCapitalSharesReservedForFutureIssuanceLineItems" substitutionGroup="xbrli:item" />
<element name="ArrangementsAxis" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_ArrangementsAxis" substitutionGroup="xbrldt:dimensionItem" />
<element name="ArrangementsDomain" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_ArrangementsDomain" substitutionGroup="xbrli:item" />
<element name="PeterHoangMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_PeterHoangMember" substitutionGroup="xbrli:item" />
<element name="CommitmentsAndContingenciesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_CommitmentsAndContingenciesTable" substitutionGroup="xbrldt:hypercubeItem" />
<element name="MythiliKoneruMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_MythiliKoneruMember" substitutionGroup="xbrli:item" />
<element name="CommitmentsAndContingenciesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_CommitmentsAndContingenciesLineItems" substitutionGroup="xbrli:item" />
<element name="AnnualBaseSalary" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_AnnualBaseSalary" substitutionGroup="xbrli:item" xbrli:balance="debit" />
<element name="ConsultingFees" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" nillable="true" id="mrkr_ConsultingFees" substitutionGroup="xbrli:item" xbrli:balance="debit" />
<element name="PaymentForSponsoredResearchFees" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" nillable="true" id="mrkr_PaymentForSponsoredResearchFees" substitutionGroup="xbrli:item" xbrli:balance="credit" />
<element name="ChiefDevelopmentOfficerMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_ChiefDevelopmentOfficerMember" substitutionGroup="xbrli:item" />
<element name="ConsultingArrangementsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="mrkr_ConsultingArrangementsMember" substitutionGroup="xbrli:item" />
</schema>
