<?xml version="1.0" encoding="us-ascii"?>
<!--Generated by Broadridge PROfile 23.3.2.5148 Broadridge-->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:t1="http://xbrl.org/2005/xbrldt">
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#PvpAdjustmentsOnly" />
  <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/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: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:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#ecd_AllAdjToCompMember" xlink:label="AllAdjToCompMember" xlink:title="AllAdjToCompMember" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_ExclusionOfStockAwardsAndOptionAwardsMember" xlink:label="ExclusionOfStockAwardsAndOptionAwardsMember" xlink:title="ExclusionOfStockAwardsAndOptionAwardsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ExclusionOfStockAwardsAndOptionAwardsMember" xlink:title="definition: AllAdjToCompMember to ExclusionOfStockAwardsAndOptionAwardsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_TotalInclusionOfEquityValuesMember" xlink:label="TotalInclusionOfEquityValuesMember" xlink:title="TotalInclusionOfEquityValuesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="TotalInclusionOfEquityValuesMember" xlink:title="definition: AllAdjToCompMember to TotalInclusionOfEquityValuesMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_YearEndFairValueOfEquityAwardsGrantedDuringYearThatRemainedUnvestedAsOfLastDayOfYearMember" xlink:label="YearEndFairValueOfEquityAwardsGrantedDuringYearThatRemainedUnvestedAsOfLastDayOfYearMember" xlink:title="YearEndFairValueOfEquityAwardsGrantedDuringYearThatRemainedUnvestedAsOfLastDayOfYearMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TotalInclusionOfEquityValuesMember" xlink:to="YearEndFairValueOfEquityAwardsGrantedDuringYearThatRemainedUnvestedAsOfLastDayOfYearMember" xlink:title="definition: TotalInclusionOfEquityValuesMember to YearEndFairValueOfEquityAwardsGrantedDuringYearThatRemainedUnvestedAsOfLastDayOfYearMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_ChangeInFairValueFromLastDayOfPriorYearToLastDayOfYearOfUnvestedEquityAwardsMember" xlink:label="ChangeInFairValueFromLastDayOfPriorYearToLastDayOfYearOfUnvestedEquityAwardsMember" xlink:title="ChangeInFairValueFromLastDayOfPriorYearToLastDayOfYearOfUnvestedEquityAwardsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TotalInclusionOfEquityValuesMember" xlink:to="ChangeInFairValueFromLastDayOfPriorYearToLastDayOfYearOfUnvestedEquityAwardsMember" xlink:title="definition: TotalInclusionOfEquityValuesMember to ChangeInFairValueFromLastDayOfPriorYearToLastDayOfYearOfUnvestedEquityAwardsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_VestingDateFairValueOfEquityAwardsGrantedDuringYearThatVestedDuringYearMember" xlink:label="VestingDateFairValueOfEquityAwardsGrantedDuringYearThatVestedDuringYearMember" xlink:title="VestingDateFairValueOfEquityAwardsGrantedDuringYearThatVestedDuringYearMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TotalInclusionOfEquityValuesMember" xlink:to="VestingDateFairValueOfEquityAwardsGrantedDuringYearThatVestedDuringYearMember" xlink:title="definition: TotalInclusionOfEquityValuesMember to VestingDateFairValueOfEquityAwardsGrantedDuringYearThatVestedDuringYearMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_ChangeInFairValueFromLastDayOfPriorYearToVestingDateOfUnvestedEquityAwardsThatVestedDuringYearMember" xlink:label="ChangeInFairValueFromLastDayOfPriorYearToVestingDateOfUnvestedEquityAwardsThatVestedDuringYearMember" xlink:title="ChangeInFairValueFromLastDayOfPriorYearToVestingDateOfUnvestedEquityAwardsThatVestedDuringYearMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TotalInclusionOfEquityValuesMember" xlink:to="ChangeInFairValueFromLastDayOfPriorYearToVestingDateOfUnvestedEquityAwardsThatVestedDuringYearMember" xlink:title="definition: TotalInclusionOfEquityValuesMember to ChangeInFairValueFromLastDayOfPriorYearToVestingDateOfUnvestedEquityAwardsThatVestedDuringYearMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="nktr-20230608.xsd#nktr_FairValueAtLastDayOfPriorYearOfEquityAwardsForfeitedDuringYearMember" xlink:label="FairValueAtLastDayOfPriorYearOfEquityAwardsForfeitedDuringYearMember" xlink:title="FairValueAtLastDayOfPriorYearOfEquityAwardsForfeitedDuringYearMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TotalInclusionOfEquityValuesMember" xlink:to="FairValueAtLastDayOfPriorYearOfEquityAwardsForfeitedDuringYearMember" xlink:title="definition: TotalInclusionOfEquityValuesMember to FairValueAtLastDayOfPriorYearOfEquityAwardsForfeitedDuringYearMember" order="5.0" />
  </link:definitionLink>
</link:linkbase>
