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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2021-11-09T15:20:04.9248753+00:00 -->
<!-- Version            : 5.0.1.702 -->
<!-- Package ID         : 174ae26fd4774129b6eeaf008e8957be -->
<!-- Copyright (c) 2021 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="nktx_StockIssuedDuringPeriodValueVestingOfSharesOfCommonStockSubjectToRepurchase" name="StockIssuedDuringPeriodValueVestingOfSharesOfCommonStockSubjectToRepurchase" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_StockIssuedDuringPeriodSharesVestingOfSharesOfCommonStockSubjectToRepurchase" name="StockIssuedDuringPeriodSharesVestingOfSharesOfCommonStockSubjectToRepurchase" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_TemporaryEquityReclassificationOfPreferredStockPurchaseRightLiabilityToEquityUponIssuanceOfConvertiblePreferredStock" name="TemporaryEquityReclassificationOfPreferredStockPurchaseRightLiabilityToEquityUponIssuanceOfConvertiblePreferredStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues" name="TemporaryEquityStockIssuedDuringPeriodSharesNewIssues" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_IncreaseDecreaseInAccountsPayableAndAccruedAndOtherLiabilities" name="IncreaseDecreaseInAccountsPayableAndAccruedAndOtherLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_ProceedsFromIssuanceOfConvertiblePreferredStockNetOfIssuanceCosts" name="ProceedsFromIssuanceOfConvertiblePreferredStockNetOfIssuanceCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
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  <xsd:element id="nktx_CollaborationAgreementAbstract" name="CollaborationAgreementAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_UnusualOrInfrequentItemsDisclosurePolicyTextBlock" name="UnusualOrInfrequentItemsDisclosurePolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_ScheduleOfPrepaidExpensesAndOtherCurrentAssetsTableTextBlock" name="ScheduleOfPrepaidExpensesAndOtherCurrentAssetsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_AtMarketProgramMember" name="AtMarketProgramMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_CashCashEquivalentsRestrictedCashAndShortTermInvestments" name="CashCashEquivalentsRestrictedCashAndShortTermInvestments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_ProceedsFromSaleOfOffering" name="ProceedsFromSaleOfOffering" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_AccountingPoliciesLineItems" name="AccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_AccountingPoliciesTable" name="AccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_WeightedAverageNumberOfSharesUnvestedCommonStockIssuedUponEarlyExerciseOfCommonStockOptions" name="WeightedAverageNumberOfSharesUnvestedCommonStockIssuedUponEarlyExerciseOfCommonStockOptions" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
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  <xsd:element id="nktx_UnvestedCommonStockUponEarlyExerciseOfCommonStockOptionsMember" name="UnvestedCommonStockUponEarlyExerciseOfCommonStockOptionsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_Impairments" name="Impairments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_ResearchEquipmentMember" name="ResearchEquipmentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_ComputersAndSoftwareMember" name="ComputersAndSoftwareMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_AccruedResearchAndDevelopmentCostsCurrent" name="AccruedResearchAndDevelopmentCostsCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_AccruedPropertyAndEquipmentLiabilitiesCurrent" name="AccruedPropertyAndEquipmentLiabilitiesCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_CurrentCorporateOfficesAndLaboratorySpaceMember" name="CurrentCorporateOfficesAndLaboratorySpaceMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="nktx_ThirdAmendmentMember" name="ThirdAmendmentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="nktx_ExpectedBaseRentOverLeaseTerm" name="ExpectedBaseRentOverLeaseTerm" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_MonthlyBaseRent" name="MonthlyBaseRent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_MaximumMonthlyBaseRentAfterIncreaseOnAnnualBasis" name="MaximumMonthlyBaseRentAfterIncreaseOnAnnualBasis" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_TenantImprovementsYetToReceiveFromLessor" name="TenantImprovementsYetToReceiveFromLessor" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_CashReceivedForTenantImprovementAllowancesToBeRepaid" name="CashReceivedForTenantImprovementAllowancesToBeRepaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_AgreementWithFinancialInstitutionMember" name="AgreementWithFinancialInstitutionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_LetterOfCreditNoticePeriodByFinancialInstitutionBeforeAnnualExpirationDate" name="LetterOfCreditNoticePeriodByFinancialInstitutionBeforeAnnualExpirationDate" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_NumberOfNonExclusiveRightsToGeneEditingTargets" name="NumberOfNonExclusiveRightsToGeneEditingTargets" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_ResearchCollaborationAgreementMember" name="ResearchCollaborationAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_NKCellProductsMember" name="NKCellProductsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_DevelopmentAndRegulatoryApprovalMilestonesMember" name="DevelopmentAndRegulatoryApprovalMilestonesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_PotentialFuturePaymentsBasedOnAchievementOfMilestones" name="PotentialFuturePaymentsBasedOnAchievementOfMilestones" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_AmountsOwedUnderAgreement" name="AmountsOwedUnderAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_PaymentsMadeUnderCollaborativeArrangement" name="PaymentsMadeUnderCollaborativeArrangement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="nktx_ReceivableUnderResearchCostSharingProvision" name="ReceivableUnderResearchCostSharingProvision" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="nktx_IncreaseInShareLimitAsPercentageOfOutstandingSharesOfCommonStockOnLastTradingDayInPriorYear" name="IncreaseInShareLimitAsPercentageOfOutstandingSharesOfCommonStockOnLastTradingDayInPriorYear" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="nktx_TwoThousandTwentyPerformanceIncentivePlanMember" name="TwoThousandTwentyPerformanceIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="nktx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
