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Mechanisms of Ad5-Induced Immune Dysfunction
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Citation Alayo, Quazim A. 2016. Mechanisms of Ad5-Induced ImmuneDysfunction. Master's thesis, Harvard Medical School.
Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:33789913
Terms of Use This article was downloaded from Harvard University’s DASHrepository, and is made available under the terms and conditionsapplicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA
MechanismsofAd5-InducedImmuneDysfunction
QuazimA.AlayoMBBS
AThesisSubmittedtotheFacultyof
TheHarvardMedicalSchool
inPartialFulfillmentoftheRequirements
fortheDegreeofMasterofMedicalSciencesinImmunology
HarvardUniversity
Boston,Massachusetts.
May,2016
ii
ThesisAdvisor:Dr.DanH.BarouchMDPhD QuazimA.Alayo
MechanismsofAd5-InducedImmuneDysfunction
Abstract
ThefailureofanAdenovirus5(Ad5)-basedhumanimmunodeficiencyvirustype1(HIV-1)
vaccineintheSTEPtrialwarrantedadetailedevaluationoftheimmunologicalpropertiesof
Ad5.PreviousstudieshaverevealedthatimmunizationwithAd5inducesapartiallyexhaustedT
cellresponsebutthemechanismofAd5-inducedimmunedysfunctionisunknown.Using
classicalanimalmodels,ithasbeenshownthatalteringantigendose,andmodulatingthePD-
1/PD-L1signalingpathway,ormodulatingregulatoryTcells(Tregs)caninfluencethequalityof
memoryCD8Tcell.Therefore,weinterrogatedwhetherthesefactorsplaysimilarrolesinAd5-
induceddysfunction.Here,weshowthatreducingAd5vaccinedoseinduceshighlyfunctional
memoryCD8Tcellresponses,characterizedbylowerPD-1expression,highercytokineco-
expression,andanimprovedrecallexpansionfollowingaheterologousboost.Interestingly,we
showthatthedysfunctionalrecallofAd5-primedTcellsfollowinghigh-doseimmunizationmay
partlybemediatedbyaPD-1-dependentCD8Tcellintrinsicphenomenon,asblockadeofPD-L1
leadstoasubstantialimprovementinanamnesticTcellexpansion.Furthermore,weprovide
preliminarydatasuggestingthatTregmaynotplayacrucialroleinthedevelopmentofAd5-
induceddysfunction.Overall,ourdatacontributetotheunderstandingofthemechanismof
Ad5-inducedimmunedysfunction,andmayberelevantforimprovingvaccinationmodalities
forHIVandotherchronicviralinfection.
iii
TaleofContents
1. Chapter1:Background....................................................................................................1
1.1 Introduction.........................................................................................................................1
1.2 AdenovirusBiology..............................................................................................................3
1.3 AdenovirusasaVaccineVector............................................................................................5
1.4 HumanAdenovirus5VaccineVector....................................................................................6
1.5 Ad5-inducedImmuneDysfunction.......................................................................................8
1.6 FactorsInfluencingAd5-inducedImmuneDysfunction.........................................................9
1.6.1 VectorDose..........................................................................................................................10
1.6.2 ImmunoinhibitoryReceptors................................................................................................11
1.6.3 ConventionalandRegulatoryCD4Tcells.............................................................................13
1.6.4 AntigenPresentingCells,Co-stimulatoryandCo-inhibitoryMolecules...............................14
1.7 Summary...........................................................................................................................14
1.8 Figures...............................................................................................................................16
1.8.1 FigureA:PotentialfactorsinfluencingAd5-inducedimmunedysfunction..........................16
2. Chapter2:DataandMethods........................................................................................18
2.1 Introduction.......................................................................................................................18
2.1.1 Hypothesis............................................................................................................................18
2.1.2 Specificresearchquestions:.................................................................................................18
2.2 MaterialsandMethods......................................................................................................19
2.2.1 Miceandimmunizations......................................................................................................19
2.2.2 Isolationoflymphocytes.......................................................................................................19
2.2.3 Tetramerbindingassayandflowcytometry........................................................................20
iv
2.2.4 Intracellularcytokinestaining(ICS)assays...........................................................................21
2.2.5 Monoclonalantibodiestreatments......................................................................................21
2.2.6 InvitroTregsuppressionassay.............................................................................................22
2.2.7 Statisticalanalysis.................................................................................................................22
2.3 Results...............................................................................................................................23
2.3.1 Thekinetics,phenotypeandfunctionalityofvaccine-inducedCD8Tcellsfollowing
vaccinationwithdifferentdosesofAd5............................................................................................23
2.3.2 ImprovedanamnesticCD8TcellresponsesaftervaccinationwithlowdoseAd5vector...25
2.3.3 Excessiveup-regulationofPD-1onAd5-inducedmemoryCD8Tcellsimpairstheirrecall
response............................................................................................................................................27
2.3.4 SimilarTregsfrequencyandsuppressivefunctioninAd5-andAd26-immunizedmice.......29
2.4 Figures...............................................................................................................................31
2.4.1 Figure1:Kineticsofvaccine-elicitedCD8Tcellfollowingvaccinationwithdifferentdosesof
Ad5…………..........................................................................................................................................31
2.4.2 Figure2:Phenotypeandpolyfunctionalityofvaccine-inducedCD8Tcellfollowing
vaccinationwithdifferentdosesofAd5............................................................................................32
2.4.3 Figure3:LoweringtheprimingdoseofAd5vectorpartiallyimprovesthephenotypeand
therecallresponsesafterAd35boosting..........................................................................................33
2.4.4 Figure4:PrimingwithlowdoseAd5inaAd5-Ad35heterologousprime-boostregimen
producemorepolyfunctionalCD8Tcells..........................................................................................34
2.4.5 Figure5:Excessiveup-regulationofPD-1onAd5-inducedmemoryCD8Tcellsimpairstheir
recallresponse...................................................................................................................................35
v
2.4.6 Figure6:PD-L1blockadepriortoprimingdoesnotaffectthekinetics,memoryconversion
oranamnesticresponseofAd5-inducedCD8Tcells.........................................................................36
2.4.7 Figure7:SimilarTregfrequenciesandsuppressivefunctionsinAd5-andAd26-immunized
mice………………………………………………………………………………………………………………………………………………37
3. Chapter3:Discussionandperspectives..........................................................................38
3.1 Limitations.........................................................................................................................44
3.2 Futuredirections................................................................................................................44
4. Bibliography..................................................................................................................47
vi
Figures Pages
1.8.1FigureA:PotentialfactorsinfluencingAd5-inducedimmunedysfunction 16
2.4.1 Figure1:Kineticsofvaccine-inducedCD8Tcellfollowing vaccinationwithdifferentdosesofAd5. 31
2.4.2 Figure2:Phenotypeandpolyfunctionalityofvaccine-induced CD8TcellfollowingvaccinationwithdifferingdosesofAd5. 32
2.4.3 Figure3:LoweringtheprimingdoseofAd5vectorpartiallyimprovesthephenotypeandtherecallresponsesafterAd35boosting. 33
2.4.4 Figure4:PrimingwithlowdoseAd5inaheterologousprime-boostregimen(Ad5/Ad35)producemorepolyfunctionalCD8Tcells. 34
2.4.5 Figure5:Excessiveup-regulationofPD-1onAd5-inducedmemoryCD8Tcellsimpairstheirrecallresponse. 35
2.4.6 Figure6:PD-1blockadepriortoprimingdoesnotaffectthekinetics,memoryconversionoranamnesticresponseofAd5-inducedCD8Tcells. 36
2.4.7 Figure7:SimilarTregfrequencyandsuppressivefunctioninAd5-andAd26immunizedmice. 37
vii
Tables Pages
TableA:SpectrumofexhaustedCD8Tstates 17
viii
Acknowledgement
Firstly,IwouldliketoexpressmyprofoundgratitudetoDrDanBarouchforacceptingmein
hislab,hisunwaveringsupport,andguidancethroughoutthedurationofmyresearch.
IwouldalsoliketoappreciateDrPabloPenaloza,forteachingmealltheprotocolsand
providingaday-to-dayguidanceasIcrawledupthelearningcurve.Pablo,thankyouforthose
insightfulcommentsandtheencouragingwords,especiallyduringthechallengingmoments.I
wishyouallthebestasyoumovetoNorthwesterntostartyournewlab.Also,aspecialthank
youtoDr.AlexanderBadamchi-Zadehforhelpingwiththeintramuscularinjections,reviewing
mythesis,andprovidingveryusefulcomments.Iwouldalsoliketoexpressmygratitudeto
ErynBlassforassistingwithsomeofmyexperiments,teachingmeagreatdealoflabetiquettes
andhelpingtoreviewmythesis.Mysincerethanksalsogoestoallotherpost-docs,graduate
studentsandothermembersoftheBarouchlabfortheirwarmthwelcomeandeagernessto
help.Inparticular,IamgratefultoJade(andhernewbornbaby),Ben,Lily,andEricafor
assistingwithmiceorderingandinjections.Jess,CrystalandLauren,thankyoufor
accommodatingmeinyourbay.
Myheartfeltgratitudetomyfamilymembersandfriendsfortheirsupportandprayers.I
wouldalsoliketothankthePRESSIDscholarshipboardforsponsoringme.Aboveall,myutmost
gratitudegoestotheAlmightyAllaahSWTforaidingmeandgrantingmesuccess.�
ix
ThisworkwasconductedwithsupportfromStudentsintheMasterofMedicalSciencesin
ImmunologyprogramofHarvardMedicalSchool.Thecontentissolelytheresponsibilityofthe
authoranddoesnotnecessarilyrepresenttheofficialviewsofHarvardUniversityandits
affiliatedacademichealthcarecenters.
1
1. Chapter1:Background
1.1 Introduction
Vaccinesareoneofthemostimportantpublichealthtoolsinthefightagainstinfectious
diseases.Thegoalofvaccinesistogeneratelong-livedimmunologicalprotection,withmemory
immuneresponsethatcanpreventnaturalinfectionorsignificantlylessenthediseaseburden1.
Mostofthecurrentlylicensedvaccineshaveprimarilyconferredthisimmunologicalprotection
viatheinductionofhigh-affinityneutralizingantibodies.However,developinghighlyeffective
vaccinesagainstintracellularpathogenssuchashumanimmunodeficiencyvirus-1(HIV-1),
Mycobacteriumtuberculosis,Plasmodiumfalciparum,hepatitisCvirus(HCV)willalsorequire
thegenerationofpotentmemoryCD8Tcells2,3,4,5,6.Inordertoelicitapotentcellularimmune
response,thevaccineantigenmustbeprocessedendogenouslywithinantigenpresentingcells
andpresentedinthecontextofclassImajorhistocompatibilitycomplex(MHC-I)moleculesto
CD8Tcells.Untilrecently,achievingthisgoalhasbeenhamperedbyalackofvaccineplatforms
capableofsuch,whichhasledtothedevelopmentofnovelplatformsincludingDNAvaccines
andviralvectors.
DNAvaccinesaregeneticallyengineeredplasmidscontainingtheDNAsequenceofthe
antigenofinterestthatcanbedelivereddirectlyintotheappropriatetissue7.DNAvaccinesare
safeandcapableofelicitingprotectivecellularandhumoralimmuneresponsesinsmallanimal
models8,9.However,theirapplicationislimitedbytheirlowimmunogenicityinhumanand
otherprimates9.ThesuboptimalimmunogenicityofDNAvaccinesinprimatesmaypartlybe
2
duetobindingoftheDNAtoserumamyloidPcomponent(SAP),anegativeregulatorofthe
innateimmuneresponse10.ThelimitedefficacyDNAvaccinesledtothedevelopmentofmore
immunogenicviralvectorvaccines.
IncontrasttoDNAvaccines,viralvectorshavebeenshowntobehighlyimmunogenic,both
inpreclinicalandclinicalstudies11.Theyaretypicallyattenuatedvirusesthataregenetically
modifiedtocarryanantigentowhichanimmuneresponseisbeingsoughtintothebody.They
alsoelicitverypotentinnateimmuneresponsesthroughthebindingofspecificToll-like
receptors(TLRs)leadingtothegenerationofacytokinemilieuwhichmodulatetheadaptive
immuneresponse12.Theadaptiveimmuneresponseinducedbythesevectorsdiffer
quantitativelyandqualitativelybasedonthedistinctbiologicalpropertiesofthevector.Over
thelastcoupleofyears,awiderangeofvirusfamilieshavebeendevelopedandtestedas
vaccinevectorsforeitherhumanorveterinaryuse11,13,14,15.Amongthesewidearrayofviruses
whichincludecanarypoxvirus16,flavivirus17,lentivirus18,modifiedvacciniavirusAnkara19and
sendaivirus20,adenovirus21hasbeenthemostwidelystudiedreplication-defectivevaccine
vectors.Ofalltheadenovirusserotypesisolatedsofar,adenovirus5(Ad5)isthebest
characterized22.
However,followingthefailureofanAd5-basedHIVvaccineinclinicaltrials,adetailed
evaluationoftheimmunologicalpropertiesrevealedthatitelicitedadysfunctionalimmune
response23.Ithasbeensuggestedthatthisdysfunctionalresponse,coupledwiththeprevalent
pre-existingAd5-vectorimmunitymayhavecontributedtothefailureoftheAd5-based
vaccine.However,thepossiblebiologicalorimmunologicalparametersresponsibleforthe
3
immunedysfunctionisnotfullyunderstood.Althoughthereareongoingpre-clinicaland
clinicalstudiesevaluatingtheimmunogenicityandprotectiveefficacyofotherserotypesof
adenoviruses12,understandingthebiologicalandimmunologicalpropertiesofAd5thatmay
havecontributedtothedysfunctionalTcellresponsewillhelpintheselectionofnovelvaccine
vectors,someofwhicharephylogeneticallyrelatedtoAd5.
1.2 AdenovirusBiology
Adenovirusesareafamilyofairbornevirusesthatinfectvirtuallyallmajorclassesof
vertebratescausingmildtoseverediseasesoftheairwaysandgastrointestinaltracts24.
Currently,morethan60distinctadenovirusserotypesofhumanoriginhavebeenidentified25.
Thesevirusesaresubdividedintosevendifferentserotypes(subgroupsAthroughG)basedon
theneutralizingantibodiesprofilesandthiscorrespondstothedivergenceofnucleotide
sequenceofthecapsidproteingenes25.
AdenovirusesaredoublestrandedDNAviruseswithanon-envelopedicosahedralshell,70-
100nmindiameter,enclosingabout~26-43kilobaseslonglineargenomicmaterial26.The
genomeismadeupofearlyandlategenes,classifiedbasedonthetimeofexpressionin
relationtoDNAreplication.Theearlygenes(E1a,E1b,E2a,E2b,E3,andE4)expressproteins
beforeDNAreplicationandtheyareinvolvedinactivatingandmodulatingtranscription,the
cell-cycle,cellsignaling,DNArepairandimmuneevasion27,28,29.Thelategenes(L1–L5)which
areexpressedfollowingDNAreplication,codemostlyforstructuralprotein30.E1,E2,andE4
geneproductsregulatetranscriptionoflategeneswhileE3geneproductssubvertthehost
4
immuneresponsebyaffectingtheintracellulartraffickingmachinery,preventingantigen
presentationandmodulatingcytokinepathways31.Geneticmanipulationoftheseearlygenesis
oftenemployedinordertoadaptadenovirusforuseasvectors
Structurally,theadenoviruscapsidisicosahedral,witheachicosahedroncontaining12
copiesofhexontrimersandapentamericpentonslocatedatthe12vertices32.Projectingfrom
thepentonbasesaretrimericfiberswhicharemadeupofadistalknobdomain,ashaft,andan
N-terminaltail32.Thedistalknobdomainofthefibersselectivelybindswithhighaffinityto
cellularreceptors,leadingtocellulartransduction.Entryreceptorsidentifiedsofarinclude
coxsackievirusBandadenovirusreceptor(CAR),CD46,sialicacids,desmoglein2,and
CD80/8633,34,35,36,37,38.ThemostcharacterizedincludethecoxsackievirusBandadenovirus
receptor(CAR),whichisexpressedmainlyonepithelialandendothelialcellsinhuman,non-
humanprimatesandmice34;andCD46,aregulatoryproteininthecomplementsystemthatis
expressedonmostcellsinhumans,yetrestrictedtothetestisandsperminmice39.
AdenovirusesbelongingtoserotypesA,C,D,E,andFusesCARforcellularattachmentwhile
CD46isusedbytheadenovirusesinserotypesBandD40.Inadditiontothedifferencein
receptorusage,adenovirusesalsodifferintheirintracellulartraffickingcharacteristicsand
associationwiththenuclearenvelope,withsomeexitingtheendosomalspacerapidlyfollowing
endocytosisandtranslocatingimmediatelytothenucleus(subgroupC)whileotherstrafficto
thelateendosomeandthereforeexhibitaslowerassociationwiththenucleus(subgroupsB
andD)41,42,43,44.Thedifferencesincellularreceptorandintracellulartraffickinginfluence
cellulartropism,particularlytheimmunecellsubsetsthesevirusesinteractwith,thepattern
5
recognitionreceptors(PRRs)theyactivate,thespecifictissuesiteswherethetransgeneare
expressed,andthereforethecharacteristicsofinnateandadaptiveimmuneresponseactivated
bytheseviruses.Appreciationofhowthesepropertiesinfluencetheimmuneresponseis
particularlyimportantwhenadenovirusesareusedasvaccinevectors.
1.3 AdenovirusasaVaccineVector
Followingtheirdiscoveryoversixdecadesago45,adenoviruseshaveevolvedtobean
importantbiologicaltoolutilizedasmodelsystemprovidingsignificantinsightsintocomplex
cellularprocessessuchasDNAreplicationandtranscription,DNArepairresponses,oncogenesis
andalternateRNAsplicing46,47.Additionally,theirabilitytoreadilyinfecthumanandother
mammaliancellshavemadethemapopularchoiceforgenedelivery48.Theirapplicationin
genetherapywashoweverhinderedbytherobustimmuneresponsetheyinduceleadingtoa
shorteneddurationoftransgeneexpression49.Interestingly,thisstrongimmunogenicityhas
beenexploitedbyvaccinologistswiththedevelopmentofmanyadenoviralvaccinevectors.
Adenoviruseshavesomeuniquefeaturesthatmakethemparticularlysuitableforuseas
vaccinevectors12,22.First,theyhaveaverybroadcellulartropismwiththeabilitytoinfectand
expressitstransgeneinawidevarietyofrapidlydividingandnon-dividingcells.Secondly,they
arestableandcanbereadilygrownandpurifiedinlargequantities.Thirdly,theycause
relativelymilddiseaseinhumanandcomparedtolentiviralvectors,theydonotintegrateinto
thehostcellgenome,reducingtheriskofmalignanttransformation.Fourthly,theirgenomeis
wellcharacterizedandcanbeeasilymanipulatedtorenderthemreplication-defective.Thisis
typicallyachievedbydeletingtheearlygeneE1,whichisrequiredforadenovirusreplication.In
6
addition,E3,anotherearlygeneimportantforhost-vectorimmuneinteraction,isoften
deleted.AlthoughnotessentialinE1-deletedadenovirus,deletionofE3orE3/E4regionsoffers
thebenefitofincreasingthetransgeneinsertioncapacitytoupto7.5kbptocarrymedium-sized
proteintransgenes50,51.Furthermore,vectorizedadenovirusesarethermostableandhavebeen
demonstratedinbothpreclinicalandclinicalstudiestobesafeforbothsystemicandmucosal
surfaceapplication22.Finally,andmostimportantly,replicationincompetentadenovirusesare
highlyimmunogenic,inducingrobustantibodyandcell-mediatedimmunitytotheinserted
transgeneswiththeabilitytoelicitbothsystemicandmucosalimmuneresponsefollowing
parenteraldelivery52,53,54.
1.4 HumanAdenovirus5VaccineVector
Ad5isthemoststudiedoftheadenovirusvectors.ItisaserotypeCvirusandtransduces
cellseitherthroughtheuseofthecoxsackie-adenovirusreceptor(CAR)34orinaCAR-
independentpathway55.Asastandalonevaccinevector,itisarguablythemostimmunogenic
humanadenovirusserotype.BallayA.etalwasthefirsttoreportthatrecombinant
replication–competentAd5carryinghepatitisBsurfaceelicitsantibodyresponseagainstthe
transgeneinrabbits51.Notlongafterwards,theabilityofE1-deletedreplication-incompetent
Ad5vectorsexpressingrabiesvirusglycopeptide(GP)toinduceprotectivetitersofneutralizing
antibodiesandrabies-virusspecificCD8andCD4Tcellswasdemonstrated56.Followingthis
importantfinding,replication-incompetentAd5hasbeentestedinseveralotherpreclinicaland
clinicalstudiesandshowntoelicitbothneutralizingantibodiesandcellularimmuneresponses
7
againstpathogenssuchasdenguevirus,ebolavirus,hepatitisCvirus,Epstein-Barrvirus,
Streptococcuspneumonia,Mycobacteriatuberculosis,Plasmodiumfalciparum,HIVamong
others57,58,59,60,61,62,63.
IntheHIVfield,Ad5expressingsimianimmunodeficiencyvirus(SIV)Gagpeptideconferred
aprotectiveimmuneresponsefollowingchallengeofrhesusmonkeyswithpathogenicSIV/HIV
chimeraSHIV89.6P10,butfailedtoprotectagainstamorestringent,neutralization-resistant
strainSIVmac23964,65.Subsequently,twolargePhaseIIbclinicaltrials(STEPinNorthAmerica
andPhambilitrialsinSouthAfrica)werecommenced66,67.Inthesestudies,theMerckAd5-Gag-
Pol-Nefvaccinewasadministeredthreetimestovolunteersthathadeithernoneormoderate-
to-hightitersofneutralizingantibodiesagainstAd5withtheaimofelicitingHIV-specificT-cell
responsescapableofprovidingcompleteorpartialprotectionfromHIV-1infectionora
decreaseinviralloadsetpointspost-infection.Bothstudieswerestoppedandunblinded
beforecompletionofenrollmentfollowinganinterimanalysisoftheSTEPtrialthatshoweda
lackofefficacy67.Evenmorealarmingwasasubsequentanalysisthatrevealedatrendtoward
higherHIV-1acquisitioninvaccinerecipientscomparedtoplacebocontrols,particularlyina
subgroupofuncircumcisedmenwithhighbaselineAd5seropositivity67.Althoughnot
completelyproven,aprobableexplanationforthisunexpectedfindingisthatthevaccineledto
anincreaseinthenumberofHIV-1targetcells,resultingfromtheactivationofAd5-specific
CD4Tcellsatmucosalsurfaces68,69.Furthermore,asecondAd5-basedPhaseIIbHIVvaccine
clinicaltrial(HVTN505)didnotshowprotectiveefficacyagainstHIV-1infectioninhuman70.Itis
8
importanttonotehowever,thattheAd5usedinthisstudywasdifferentindesignfromthe
MerckAd5vector,andwasusedasaboostingvectorfollowingaDNAvaccineprime.
ThefailureoftheAd5vectorintheseclinicaltrialsledtoarenewedinterestintwoareasof
Advectorresearch.Firstisthedevelopmentandevaluationofrareradenovirusserotypesof
humanorigin50,71,aswellasserotypesderivedfromotherspeciessuchaschimpanzees72,73,74
andrhesusmonkeys75,andstructurallymodifiedAd5vectorexpressingheterologous
adenovirushexons76inordertocircumventtheproblemofpre-existingAd5vectorimmunity.
TheotherareaofintenseresearchistheanalysisofthebiologicpropertiesofAdvector-
inducedimmuneresponses23,77,78,79,80,81,82.Thesedetailedanalyseshaveshedmorelighton
theinherentpropertiesofAd5-inducedTcellresponses,highlightinghowtheseresponses
substantiallydifferfromthoseelicitedbyalternativeserotypeAdvectorsuchasadenovirus26
(Ad26)oradenovirus35(Ad35).
1.5 Ad5-inducedImmuneDysfunction
Themostsurprisingfindingfromthecomprehensiveevaluationofthephenotypeand
qualityofAdvector-inducedimmuneresponsewasthatAd5,comparedtootherserotype
adenoviruses,inducesapartiallyimpairedimmuneresponse.Thisobservationwasfirst
reportedbyYangetalwhentheyanalyzedthephenotypicprofileoftheimmuneresponses
elicitedbyanAd5vaccineinmice83.TheyobservedthatAd5-elicitedCD8Tcellsexhibita
protractedeffectorphenotypewithadelayedcontractionphase,aphenomenontheyargued
maybeduetotheprolongedantigenpresentationseenfollowingAd5immunization83.Inline
9
withthisobservation,othershaveshownthat,comparedtoalternativeserotypeAdvectors,
Ad5inducesapartiallydysfunctionalTcellresponseinmice.Ad5-inducedmemoryTcellswere
foundtoexpresslowlevelsofIL-7alphachainreceptorCD127,lymphoidhomingreceptor
CD62L,antiapoptoticmoleculeBcl-2,aswellashighlevelsofinhibitoryreceptorsPD-1andTim
323,81,82,84.AlthoughAd5immunizationinducesahighmagnitudeprimaryTcellresponse,
theseTcellsarelesspolyfunctionalwithreducedcapabilitytosecreteIFN-γ,TNF-α,andIL-2,
comparedtoalternativeserotypeadenovirus23,82.Furthermore,circulatingandtissueresident
antigen-specificmemoryCD8TcellsinducedbyAd5proliferatelessrobustlyfollowinga
secondaryexposure(boosting)toantigens81.Similarfindingshavealsobeenobservedinnon-
humanprimates79.ItisimportanttonotethatalthoughrecombinantE1-deletedAd5vector
doesnotreplicate,itinducesamemoryCD8Tcellpopulationthattosomeextent–exceptfor
itsfunctionality–isreminiscentofanexhaustedTcellresponseseeninmodelsofchronic
infectionorcancercharacterizedbypersistentantigenicstimulation85,andassuchsuggests
thatAd5-inducedCD8Tcellsmaybe“partiallyexhausted”(TableA).
1.6 FactorsInfluencingAd5-inducedImmuneDysfunction
InordertounderstandwhyAd5-inducedmemoryCD8Tcellsexhibitsuchdysfunctionalor
“partiallyexhausted”phenotypes,itisIttmportanttoconsiderthevirologicaland
immunologicalcuesthatinfluencethedevelopmentandmaintenanceofexhaustedCD8Tcells
intheclassicalimmuneexhaustionmodelofchronicinfection,andassesswhetherthese
factorsplaysimilarrolesinmediatingAd5-inducedimmunedysfunction,andmoreimportantly,
10
ifmodulationoftheseparameterswillleadtoanimprovementinthephenotypeandqualityof
Ad5-inducedmemoryCD8Tcells.Extrapolatingfromthisclassicalmodelandrelyingonour
currentunderstandingofthebiologyofAd5,possiblefactorsthatmayfavorthedevelopment
ofAd5-inducedimmunedysfunctioninclude1)vectordose,2)immuno-inhibitoryreceptors,3)
CD4Tcells-conventionalandregulatoryTcellsand4)antigenpresentingcellsandexpression
ofco-stimulatoryand/orco-inhibitorymolecules.(Figure.A).
1.6.1 VectorDose
Theamountanddurationofantigenexposureimpactantigen-specificCD8Tcellsboth
intermsofquantityandquality.Inanacuteinfectionmodel,antigendoseaffectsthenumber
ofnaïveCD8Tcellsrecruitedforactivationandtheirdifferentiationintoeffectorandmemory
CD8Tcells86.Whileinchronicinfections,suchasthechronicmodeloflymphocytic
choriomeningitisvirus(LCMV)infectioninmice,differentiationofprimedCD8Tcellsintoeither
anexhaustedormemoryphenotypeisdependentontheamountanddurationofantigen
exposure87,88.Likewise,inAdvectorvaccineresearch,thedoseofAdvectorimpactsthequality
oftransgene-specificCD8Tcelldifferentiationandfunctionality78.HighdoseAd5immunization
hasbeenshowntoinducetransgenespecificCD8TcellsbearingfeaturesofadysfunctionalT
cellpopulation:reducedfunctionalCD8TcellsasevidencedbylowerpercellexpressionofIFN-
γ,lowerfractionofcellscoproducingTNF-αorIL-2andIFN-γ;impairedmemoryconversion
withlowerexpressionofCD127andhighexpressionofKLRG-1;andanabsenceofacontraction
phase78,89.Conversely,reducingthedoseofAd5significantlyimprovessomeofthese
11
impairments78.However,theeffectofloweringtheprimingdoseofAd5onrecallexpansion
followingantigenre-exposurehasnotbeeninvestigatedtodate.Inaddition,itisalsonot
knownwhetherloweringthedosewillleadtoareducedexpressionofimmunoinhibitory
receptors,suggestingareducedimmuneexhaustion.
1.6.2 ImmunoinhibitoryReceptors
ImmunoinhibitoryreceptorssuchasPD-1(ProgrammedCellDeath1),Tim-3(T-cell
immunoglobulinandmucin-domaincontaining-3),and2B4(CD244)areinducedonTcells
immediatelyfollowingactivation,andatthisstage,theyserveassafeguardstocurtailexcessive
immuneresponse23,85.However,thesustainedup-regulationofimmunoinhibitoryreceptors
hasbeenrecognizedasaprominentfeatureofexhaustedCD8Tcells,wheretheyplaya
significantroleinnegativelyregulatingTcellfunction90.Themostwidelystudiedofthese
receptorsisPD-1,amemberoftheCD28superfamily,whichisinduciblyexpressedonTcells,B
cells,naturalkillerT(NKT)cells,andsomemyeloidcells91.Likeothermembersofthefamily,
PD-1transducessignalsonlyinthecontextofTcellreceptor(TCR)crosslinkingfollowingaTCR-
antigen-MHCengagement.PD-1hastwoligands:PD-L1andPD-L2.PD-L1,alsoknownasB7-H1,
hasabroadtissuedistributionandisexpressedonBcells,DCs,macrophages,BM-derivedmast
cells,andTcellsandperipheralepithelialandendothelialcellsuponstimulationby
proinflammatorycytokines,suchasinterferonsandtumornecrosisfactor92,93,94.PD-L2orB7-
DCismorerestrictivelyexpressedondendriticcellsandmacrophages93.Uponinteractionwith
itsligands,PD-1sendssignalsthatlimitproliferation,interferewithcytotoxicactivityandIFN-γ
12
productionthroughtheup-regulationofthetranscriptionfactorBATFinCD8Tcells95,96.The
suppressivefunctionofPD-1isalsoachievedviathereductioninthedurationofDC:Tcell
contact,andthedirectdephosphorylationofproximalTCRsignalingthroughtherecruitmentof
SHP1andSHP2phosphatasesbytheimmunoreceptortyrosine-basedswitch(ITSM)motifon
theintracellularcytoplasmictailofthePD-1receptor97,98,99.Otherimmunoinhibitoryreceptors
thatareup-regulatedonexhaustedTcellsincludeCTLA4,Tim-3,LAG-2,CD160and2B4and
thesereceptorshavebeenshowntoacteitherindependentlyorinsynergywithoneanother
and/orwithPD-1toinfluencethedegreeofTcellexhaustion85.PartialrestorationofTcell
functioncanbeachievedbyblockingthesignalingpathwaysofthesereceptors(knownas
immunecheckpointblockade)100.
Asmentionedearlier,Ad5vectorelicitedgreaterpercentagesoftransgene-specificCD8
Tcellsco-expressingbothPD-1andTim-3orsingly-positiveforeitherPD-1orTim-323
(Penaloza-MacMaster,P.etal.unpublisheddata).Indeed,PD-1andTim-3expressiononAd5-
inducedTcellsisassociatedwithlessfunctionality(Penaloza-MacMaster,P.etal,unpublished
data)similartofindingsinthechronicmodelofLCMVinfectioninmice85orHIVinfectionin
humans101.Additionally,thehigherco-expressionofPD-1andTim-3correlateswithreduced
levelsofmemorymarkersonCD8Tcells,possiblyexplainingthepooranamnesticpotential
seenwithAd5immunization.Similarly,increasedPD-1expressionwasalsoobservedon
“helpless”memoryCD8TcellscomparedtomemoryCD8TcellsprimedinthepresenceofCD4
Tcells102.Interestingly,PD-1blockadeduringantigenre-exposureenhancedexpansionofthese
‘helpless’memoryCD8Tcells102,indicatingthatPD-1maylimitmemoryCD8Tcellexpansion.
13
Furthermore,PD-1blockadehasbeenshowntorestorepulmonaryCD8Teffectorfunctions
(degranulationandcytokineproduction)andenhancedviralclearanceinamodelofrespiratory
virusreinfection103.Itisnotknownwhetherasimilarimprovedrecallexpansionandrestoration
ofpolyfunctionalitywillbeseenfollowingcheckpointblockadeinthecontextofAd5
immunization.
1.6.3 ConventionalandRegulatoryCD4Tcells
ItiswellestablishedthatconventionalCD4TcellhelpisrequiredformemoryCD8Tcell
differentiationfollowingnaturalinfection104,105orvaccination106.IthasbeenreportedthatAd5
inducesadysfunctionalCD4TcellresponsecharacterizedbyhighPD-1expressionandIL-10
expression80,whileanalternativeserotypeadenovirus,Ad26,whichinducesamorefavorable
CD8Tcellresponsewithbetterphenotypicandqualitativeprofileefficientlyelicitsfunctional
CD4Tresponse79.TheimpairedCD4TcellhelpassociatedwithAd5maythereforebe
responsibleforAd5-inducedCD8Tcelldysfunction.Ontheotherhand,regulatoryCD4Tcells
(Tregs),whoseprimaryroleistocontrolanddampenimmuneresponse,havebeenshownto
helpinmaintainingCD8Tcellexhaustion,andtheablationofTregsinmicechronicallyinfected
withLCMVledtoasignificantrescueandexpansionofexhaustedLCMV-specificCD8Tcells107.
SinceAd5-inducedimmunedysfunctionexhibitssomeexhaustedTcellphenotype,itisnot
impossiblethatregulatoryTcellsmayplayaroleindrivingthisexhaustion.Thisishoweveryet
tobedetermined.
14
1.6.4 AntigenPresentingCells,Co-stimulatoryandCo-inhibitoryMolecules
Adenoviralvectorsdifferentiallyinteractwithantigenpresentingcells(APCs)suchas
dendriticcells(DCs)55duetotheirdistinctinvivobiologicalproperties108,109.Ithasbeenshown
thatAdvectorsformimmunecomplexeswithspecificneutralizingantibodieswhichaffect
transductionefficiencyandmaturationofdendriticcellsinaFcRandToll-likereceptor9(TLR9)
interaction68.ComparativeevaluationofthepotencyofimmunecomplexesformedbyAd5and
alternativeserotypeadenovirusvectorssuchasAd26andAd36showedthatimmune
complexesofAd5werestrongerinducersofDCmaturation(asmeasuredbytheup-regulation
ofco-stimulatorymoleculesandproductionofproinflammatorycytokines)comparedtoAd26
andAd35immunecomplexes68.ItishowevernotknownifthestrongerDCinductioncombined
withthemoreprotractedpersistenceofAd5influencestheimpairedimmuneresponseseenin
Ad5.Theroleofco-stimulatory(e.g.B7-1)andco-inhibitorymolecules(e.g.PD-L1)expressed
onantigenpresentingcellsfollowingAdvectortransductionandhowtheymaycontributeto
theimpairedimmuneresponseisnotfullyunderstood.
1.7 Summary
Vaccine-mediatedprotectionagainstintracellularinfectionssuchasHIV-1,malariaand
tuberculosiswillmostlikelyrequirethegenerationofpotenthumoralandcellularimmune
responses.UntilitsfailureintheHIV-1vaccinetrial(STEPtrial),Ad5wasoneofthemost
promisingvectorsusedforelicitingsuchresponses.Evidenceisaccumulatingthattheimmune
responseelicitedbyAd5-basedvaccinevectorsexhibitsadysfunctionalphenotype,andthat
15
thisdysfunctionmayhavecontributedtoitsfailure.Assessingtheimmunologicalandbiological
cuesthataffectasimilarlyimpairedTcellresponseinthechronicviralinfection(LCMV)model
mayhelpuselucidatethemechanismofAd5-inducedimmunedysfunction.
16
1.8 Figures
1.8.1 FigureA:PotentialfactorsinfluencingAd5-inducedimmunedysfunction
Aschematicrepresentationofthepossiblefactorsinfluencingthedevelopmentand
maintenanceofAd5-inducedimmunedysfunction
Ad5-inducedimmune
dysfunction
Virologicalfactors:VectordoseRouteofAdministrationCellulartropism
CD8Tcellintrinsic:ImmunoinhibitoryreceptorsEpigeneticmodifiers
CD8Tcellextrinsic:ImpairedCD4 helpRegulatoryTcellsAPCs+co-stimulatoryandco-inhibitorymoleculesCytokinemilieu
17
TableA:SpectrumofexhaustedCD8Tstates
FullyFunctionalMemoryCD8Tcells(e.g.AcuteLCMVinfection,Ad26-InducedmemoryCD8Tcells)
Ad5-inducedmemoryCD8Tcells
PartiallyexhaustedCD8Tcells(e.g.EarlychronicLCMVinfection)
SeverelyExhaustedCD8Tcell(e.g.LateChronicLCMVinfection)
Antigenload -- ?-/+ ++ ++++CD4help +++ ?++ ++ ---
IL-2 ++ - - -TNF-α +++ ++/- +/- -IFN-y +++ ++ ++ -
Cytotoxicity +++ ++ + -InhibitoryReceptors + ++ ++ +++
ProliferativePotential +++ + + -
Apoptosis - - +/- ++++
Classicalimmuneexhaustioninchronicinfectionsandcancersischaracterizedbyastep-wiseand
progressivelossofeffectorcapabilities,thesustainedupregulationofinhibitoryreceptors,and
the loss of self-renewal capabilities. Ad5-elicited CD8 T cells lie in a spectrum between fully
functionalmemoryCD8Tcellsgeneratedfollowingtheclearanceofanacuteinfection(e.g.Acute
LCMVinfectionoralternativeserotypeadenoviral(e.g.Ad26)immunization)andfullyexhausted
CD8TcellsfromchronicLCMVinfection.Theroleofvectorload/persistenceandCD4Tcellhelp
inmodulatingAd5-inducedimmuneexhaustionhasnotyetbeenfullydetermined.(Adaptedand
modifiedfromKahanSMetal.Virology.201385)
18
2. Chapter2:DataandMethods
2.1 Introduction
Replication-incompetenthumanadenovirusserotype5(Ad5)vectorelicitspotentand
protectiveCD8+Tcellresponsesinpreclinicalstudies.However,adetailedevaluationofthe
immunologicalpropertiesofAd5inmouseandnon-humanprimateshasrevealedthatAd5
elicitsapartiallyexhaustedTcellresponse,characterizedbylowfrequencyofpolyfunctionalT
cells,highexpressionofimmunoinhibitoryreceptors,dysfunctionalcytokinesecretion,andan
impairedmemoryrecall.Recently,ithasbeenshownthatfactorssuchasvectorprimingdose
orantigenload,expressionofimmunoinhibitoryreceptors,andregulatoryTcellsmaymodulate
thephenotype,qualityandanamnesticpotentialofmemoryTcells.Inthisstudy,we
investigatedthepossibleroleofvectordose,PD-1signalingpathway,andregulatoryTcellsin
modulatingAd5-inducedcellularimmuneresponse.
2.1.1 Hypothesis
Vectordose,PD-1signalingandregulatoryTcellsmodulateAd5-inducedcellular
immuneresponse.
2.1.2 Specificresearchquestions:
1. IsitpossibletoovercometheimpairedanamnesticimmuneresponseassociatedwithAd5
byalteringtheprimingdose?
2. WhatistheeffectofimmunoinhibitoryreceptorblockadeontherecallofAd5-induced
memoryCD8Tcells?
3. IstherearoleforregulatoryTcellsinmodulatingtheAd5-elicitedimmunedysfunction?
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2.2 MaterialsandMethods
2.2.1 Miceandimmunizations
Sixto8-week-oldfemaleC57BL/6mice(fromJacksonLaboratories)wereusedforall
immunizationexperiments.Replication-incompetent,E1/E3-deletedAd5,Ad26andAd35
vectorsexpressingSIVmac239Gagwerepreparedaspreviouslydescribed71,110,whilemodified
vacciniaAnkara(MVA)expressingSIVGag-Pol-EnvwaspreparedbytheNationalInstitutesof
Health(NIH).Micewereimmunizedintramuscularlyinbothhindlegmuscles(quadriceps)with
escalatingdoses(107,108,109or1010viralparticles(vp))ofAd5orAd26vectorspermouse.
Micewereboosted60dayspostprimeintramuscularlywithMVAatadoseof≤107plaque-
formingunits(PFU)orAd35-SIVmac239Gag(109vp).Intramuscular(i.m)injectionswere
administeredin100μlphosphate-bufferedsaline(PBS)solution(50μlperquadricep).Animals
werehousedattheBethIsraelDeaconessMedicalCentre(BIDMC)animalfacilityandall
experimentswereperformedaccordingtoapprovedIACUCprotocol.
2.2.2 Isolationoflymphocytes
Single-cellsuspensionsofbloodandtissuesweregeneratedaspreviouslydescribed71,
111.Briefly,mousebloodwascollectedinRPMI1640containing40U/mlheparin.PBMCswere
isolatedfromwholebloodusingFicoll-Hypaquedensitycentrifugationat1900rpmfor20min.
Liver,lymphnodeandspleenwerehomogenizedtosinglecellsuspensionbyforcingtissue
chunkthrougha100µmsterilecellstrainerusingthebarrelofa5-ccsyringe.Redbloodcells
werelysedusingammoniumchloride(ACK)LysingBuffer(ThermoFischer).Resultingcell
20
suspensionwaspelleted,re-suspendedinRPMIcontaining10%fetalcalfserumand
penicillin/streptomycin.Cellswerecountedthereafter.Homogenizedlivertissuewasappliedto
a44/67%Percollgradientandcentrifugedat2,000rpmfor10minat20oC.Theinterface
containingtheintrahepaticlymphocytepopulationwasharvestedandwashed,andthe
resultinglymphocytessuspensionwasre-suspendedinRPMIcontaining10%fetalcalfserum
andpenicillin/streptomycin,andcounted.
2.2.3 Tetramerbindingassayandflowcytometry
MHCclassItetramerstainingwasperformedonsinglecellsuspensionusinganH-2Db
tetramerfoldedaroundtheimmunodominantSIVGagAL11epitope(AAVKNWMTQTL)as
describedpreviously112.BiotinylatedclassImonomerswereobtainedfromtheNational
InstitutesofHealthTetramerCoreFacility(EmoryUniversity,GA)andtetramerisedin-house.
BackgroundstainingofCD8Tcellsfromnaïveanimalswas≤0.1%.Surfacestainingwas
performedwithanti-CD8a(53-6.7),-CD44(IM7),-CD127(A7R34),-CD62L(MEL-14),-KLRG1
(2F1)and-PD-1(RMP1-30).Transcriptionfactorstainingwasperformedbyfirstpermeabilizing
thecellswiththeFoxP3Fixation/PermeabilizationKit(eBioscience)andsubsequentlystaining
withanti-T-bet(4B10),–Eomes(Dan11mag)and–FoxP3(150D/E4).AllAntibodieswere
purchasedfromBDBiosciences,eBioscience,orBioLegend.Live/DeadFixableNear-IRstaining
kitwasobtainedfromLifeTechnologies.Afterstaining,cellswerewashedinPBScontaining2%
fetalbovineserum(FBS)andfixedusingcytofix/cytopermbuffer(BDBioscience).Sampleswere
acquiredonanLSRIIflowcytometer(BDBiosciences),anddatawereanalyzedusingFlowJo
21
version9.7.7(TreeStar).
2.2.4 Intracellularcytokinestaining(ICS)assays
CytokineexpressionofGag-specificcellularimmuneresponsesinimmunizedmicewas
assessedbymultiparameterintracellularcytokinestaining(ICS)assaysaspreviously
described110,withsomemodifications.Briefly,lymphocytesisolatedfromtheblood(~5x105),
spleen(106)ortheliver(106)wereincubatedfor5hoursat37°Cwith0.2μg/mlofSIVGag
peptidepool(togetherwithbrefeldinA(GolgiPlug)andmonensin(GolgiStop).Afterincubation,
cellswerestainedwithanti-CD8(53-6.7),-CD44PacificBlue(IM7),-CD4(RM4-5)andLive/Dead
FixableNear-IRstainingkit.Afterwards,cellswerefixedandpermeabilizedwith
Cytofix/Cytopermpriortointracellularstainingwithanti-IFN-γ(XMG1.2),anti-TNF(MP6-XT22),
andanti-IL-2(JES6-5H4).AllICSreagentswerepurchasedfromBDBiosciences.
2.2.5 Monoclonalantibodiestreatments
PD-L1blockadewasachievedviainjectionof200microgram10F.9G2(BioXCell)atthe
timeofprimingorboostingimmunization.Theregimenconsistedoffivedosesevery3daysas
previouslydescribed100,withthefirstdosegivenadaypriortoimmmunization.Allantibodies
(ab)weredilutedinDPBSandadministeredintraperitoneally(i.p).RatIgG2b(BioXCell)was
usedascontrol.MemoryCD8Tcellrecallresponseswereassessedinbloodonday7,andin
bloodandtissuesonday15postboost.
22
2.2.6 InvitroTregsuppressionassay
InvitroTregsuppressionassaywasperformedaspreviouslydescribed113,withsome
modifications.Briefly,CD4Tcellswereenrichedbynegativemagneticselectionfromthe
spleenofadenoviralvector-immunizedFoxp3gfpmice(pooledfrom2spleenspergroup)using
anEasySep™MouseCD4TCellIsolationKit(StemcellTechnologies).AfterenrichmentofCD4T
cells,FoxP3+GFP+CD4TcellsweresortedusingaFACSAriaIIcellsorter(BDBioscience).Naive
CD8TcellswereisolatedfromthespleenofC57BL/6mice,labeledwithCellTraceViolet(CTV)
dye(5μM;LifeTechnologies)for10minatroomtemperatureinPBSandwashedwith
completemediabeforeculture.Forthesuppressionassay,2.5x104CTV-labelledCD8Tcells
wereco-culturedwithDynabeads®MouseT-ActivatorCD3/CD28beads(ThermoFischer
Scientific)ataratioof4to5(beads:CD8Tcells),andvaryingnumbers(0,1.5x103,3x103,6x103,
1.25x104,2.5x104)ofsortedFoxP3+GFP+CD4Tcellsperwellina96-wellflatbottomplate.After
72hofincubationat37oC,cellswereharvested,stainedwithanti-CD8a(53-6.7),-CD44(IM7),
and-CD4(RM4-5),-CD25(3C7)andLive/DeadFixableNear-IRstainingkit(RMP1-30).CD8T
cellswereanalyzedforCTVdilutionbyflowcytometry.
2.2.7 Statisticalanalysis
StatisticalanalysiswasperformedonGraphPadPrismversion6.0husingtwo-tailed
nonparametricMann-WhitneyUtest.
23
2.3 Results
2.3.1 Thekinetics,phenotypeandfunctionalityofvaccine-inducedCD8Tcellsfollowing
vaccinationwithdifferentdosesofAd5
Weinitiatedstudiesbyassessingthemagnitude,phenotypeandqualityoftransgene-
specificCD8TcellselicitedbydifferentdosesofAd5vector.Weimmunized6-8weekold
C57BL/6miceintramuscularly(i.m)withescalatingdosesofAd5(108,109and1010vp)
expressingtheGagantigenfromSIVstrainmac239.Gag-specificCD8Tcellresponsesin
peripheralbloodwereassessedlongitudinallyusinganMHCclassItetramerloadedwiththe
immunodominantepitopeAL11112.Micevaccinatedwith1010vpofAd26expressingthesame
antigenalsowereincludedascontrol(Fig.1A).Consistentwithpreviousreports78,81,alldoses
ofAd5elicitedsimilarpeakCD8Tcellresponsesatday15post-prime,butthelowdoseAd5
prime(108vp)wasassociatedwithmorepronouncedCD8Tcellcontractioncomparedtohigh
doseAd5prime(1010)(p<0.001)(Fig.1B-1C).
Next,weexaminedthephenotypeofDb-AL11+CD8Tcellsfollowingvaccinationwith
differentdosesofAd5.IthaspreviouslybeenshownthatAd5,comparedtoalternateserotype
AdvectorssuchasAd26andAd35,leadstoanup-regulationoftheimmunoinhibitoryreceptor,
PD-1onvaccine-elicitedCD8Tcells23,81.WethereforesoughttoassesswhetherPD-1up-
regulationonAd5-elicitedCD8Tcellsisdose-dependent.Wenoticedthatantigen-specificCD8
TcellsinmiceprimedwithlowdoseAd5expressedsignificantlylowerPD-1relativetohigh
doseAd5-primedmiceatthepeakoftheprimaryresponse(day15postimmunization(p.i))
24
(p<0.0001;Fig.2A)andatmemorytime-point(day60p.i)(p=0.0059;Fig.2B),suggestingthat
PD-1expressiononAd5-elicitedCD8Tcellsisdose-dependent.
Wefurtherassessedthecellsurfaceexpressionofkillercelllectin-likereceptorG1
(KLRG1)andIL-7receptoralpha-chain(CD127),twomarkersoftenusedtodelineateterminal
(KLRG1+CD127-)andmemoryprecursor(KLRG1-CD127+)effectorCD8Tcellsinmice114,115.We
foundthat,onday60postimmunization,theproportionofKLRG1+CD127–memoryprecursor
effectorcells(MPECs)inbloodwasreducedinthelowdoseAd5-immunizedgroupcompared
withthehighdosegroup(Ad5108vp,18%MPECs;Ad51010vp,10%MPECs;p<0.05),while
therewasacorrespondinghigherproportionofKLRG1+CD127–shortlivedeffectorcells(SLECs)
inmiceimmunizedwithhighdoseAd5relativetolowdoseAd5-immunizedmice(Ad5108vp,
45%MPECs;Ad51010vp,50%MPECs;p<0.05)(Fig.2C).Thissuggeststhatthereisa
preferentialdifferentiationofvaccine-inducedeffectorCD8Tcellstowardsthememory
precursorlineagefollowinglowdoseAd5immunizationcomparedwithhighdoseAd5
immunization.
PolyfunctionalTcellsareTcellswhichsecretemultiplecytokinesconcurrently.They
havebeenshowntoplayanessentialroleinthecontrolofHIVinfection,andcorrelatewith
protectioninsomevaccinemodels2,116,117,118.Therefore,weassessedtheabilityofvaccine-
elicitedmemoryCD8Tcellstosecretemultiplecytokinesfollowingex-vivoantigenre-
stimulationwithanoverlappingSIVGagpeptidepool.WeobservedthatlowdoseAd5induces
ahigherfrequencyofGag-specificCD8Tcellsco-expressingtwo(IFN-γandTNF-α)orthree
(IFN-γ,TNF-αandIL-2)cytokines,whilehighdoseAd5leadstotheinductionofmoreCD8T
25
cellsexpressingonlyIFN-γrelativetolowdoseAd5(P=0.0029(forAd5108vpversusAd51010
vp;IFN-γ,TNF-αandIL-2co-producers);P<0.0001(forAd5108vpversusAd51010vp;IFN-γand
TNF-αco-producers);P<0.0001(forAd5108vpversusAd51010vp;IFN-γonly)(Fig.2D).Forall
parametersexamined,thephenotypeandqualityofCD8TcellsinducedbylowdoseAd5
closelyresemblesthoseofAd26-inducedCD8Tcells(Fig.1B-1C;Fig.2A-2D).Altogether,these
findingsbuildonpreviousreportsbyshowingthatlowdoseAd5vectorisassimilarly
immunogenicashighdoseAd5andyetelicitsamorefunctionaltransgene-specificCD8Tcell
populationcharacterizedbylowerPD-1expression,enhancedmemoryconversionand
improvedfunctionality.
2.3.2 ImprovedanamnesticCD8TcellresponsesaftervaccinationwithlowdoseAd5vector
Ithaspreviouslybeenshownthat,comparedwithalternativeadenovirusserotype,Ad5-
inducedCD8Tcellsexhibitreducedanamnesticexpansionfollowingaheterologousvector
boost23,81orasecondaryantigenchallenge119.Wethereforesoughttoassesstherecall
expansionofthephenotypicallyfavorableCD8TcellinducedbylowdoseAd5comparedwith
CD8TcellsinducedbyhighdoseAd5.MicevaccinatedwithescalatingdosesofAd5orafixed
doseofAd26vectorsexpressingSIVGagwereboostedwithAd35vectorexpressingthesame
SIVGagtransgene(Fig.2A).Intriguingly,weobservedarobustrecallexpansionoflow-doseAd5
primedCD8TcellscomparedwithhighdoseAd5primebyday7post-boost(difference
betweenpreandpost-boostforlowdoseAd5was5.37-fold;forhighdoseAd5,1.92-fold;a2.8-
folddifference,p=0.0012)(Fig.3B-3D).Similarly,onday14and30postboost,therewasa
26
trendtowardsahighernumberofGag-specificCD8Tcellsinthegroupprimedwithlowdose
Ad5comparedwithhighdoseAd5-primedmice,althoughthiswasnotsignificant(datanot
shown)
Onday7postboost,weanalyzedthephenotypeofantigen-specificCD8Tcellsinblood.
WeobservedahigherexpressionofKi-67,amarkerofproliferativepotential,onGag-specific
CD8TcellsfromlowdoseAd5-primedmicecomparedwithhighdoseAd5-primed(Fig.2E)(p=
0.029),correlatingwiththeimprovedrecallexpansionseeninthelowdosegroup.Additionally,
granzymeBexpressiononGag-specificCD8TcellsinlowdoseAd5-vaccinatedmicewasgreater
thanthoseofhighdoseAd5-vaccinatedmicefollowingboost,suggestingimprovedcytotoxic
potential(Fig.2F)(p=0.029).Furthermore,antigen-specificCD8Tcellsinmiceprimedwithlow
doseAd5expressedsignificantlylowerPD-1relativetohighdoseAd5-primedmicefollowing
boost(Fig.3G)(p<0.0005).Nosignificantdifferenceswereobservedamongdosegroupsinthe
expressionofotherphenotypicmarkerssuchasCD127,KLRG-1orthelymphoidhoming
receptorCD62L(datanotshown).
Todeterminethefunctionalityofvaccine-elicitedCD8Tcellsfollowingheterologous
boost,weisolatedsplenocytesonday30postboostandanalyzedtheirabilitytoexpressIFN-γ,
TNF-αandIL-2concurrentlyafterre-stimulationwithGagpeptide.Weshowedthatthenumber
ofindividualvaccineelicitedCD8Tcellsco-expressingthreecytokineswassignificantlygreater
inlowdoseAd5-primedmicecomparedwithhighdoseAd5-primedmice(Fig.4A-4C).Inline
withthisfinding,wealsoobservedthatthefrequencyofGag-specificCD8Tcellsco-producing
IFN-γandTNF-αinmiceprimedwithlowdoseAd5was2.4%comparedwith0.8%inlowdose
27
Ad5-primedmice,a3folddifference(P=0.031),whilethefrequencyofGag-specificCD8Tcells
co-producingIFN-γandIL-2was4foldhigherinlowdoseAd5-primedmicethaninhighdose
Ad5primedmice(%ofCD8Tcellsco-producingIFN-γandIL-2:mean(lowdoseAd5)=0.3%,
mean(lowdoseAd5)=0.07%;P=0.0079).Representativeflowcytometryplotsofcytokineco-
expressiononGag-specificCD8Tcellsareshown(Fig.4D).Furthermore,wefoundthatthe
proportionofcellsco-expressingallthreecytokines(IFN-γ,TNF-αandIL-2)wassignificantly
higherinthelowdosegroupcomparedwiththehighdose(P=0.008)(Fig.4E).However,there
wasnodifferenceinthepercellexpressionofthesecytokines(datanotshown).Similar
findingswereseenfollowinganMVAboost(datanotshown).Takentogether,thesedata
suggestthatloweringthedoseofAd5atprimewillimproveanamnesticrecallofvaccine-
inducedmemoryCD8Tcells,theircytotoxicpotential,andfunctionality,withoutcompromising
themagnitudeofitsprimaryresponse.
2.3.3 Excessiveup-regulationofPD-1onAd5-inducedmemoryCD8Tcellsimpairstheir
recallresponse
HigherPD-1expressiononmemoryCD8Tcellshaspreviouslybeenshowntocorrelate
withimpairedmemoryrecallinsomemodelsofimmuneexhaustion102.Wethereforereasoned
thatthehigherPD-1expressiononhighdoseAd5-inducedmemoryCD8Tcellsmaybe
responsibleforthebluntingofrecallresponse.Datafrompre-clinicalandclinicalstudieshave
shownthatPD-1blockadecanbeachievedbyinvivoadministrationofeitheranti–PD-1oranti–
PD-1ligand(aPD-L1)100,120,121,122,123,124.ToassessthefunctionalsignificanceofPD-1expression
28
onAd5inducedmemoryCD8Tcells,weinhibitedthePD-L1:PD-1pathwaybyadministering
anti-PD-L1blockingantibody(aPD-L1)atthetimeofboostingwithaheterologousvector,Ad35
(Fig.5A).MicevaccinatedwithAd26wereusedascontrolsinceCD8Tcellselicitedbythis
vectorarenotassociatedwithhighPD-1expression23.Treatmentwithanti-PD-L1significantly
enhancedtherecallresponseofAd5-inducedmemoryCD8Tcellsfollowingboost,ascompared
withcontrols(3.8foldexpansioninPD-L1blockadegroup,comparedwith1.6foldexpansionin
isotypecontrolgroup,P=0.0317)(Fig.5B-5C).SimilartreatmentofAd26-inducedmemoryCD8
Tcellsdoesnotaltermemoryrecall.Thissuggeststhattheimprovementinrecallresponse
observedfollowinganti-PD-L1treatmentcanonlyoccurinthecontextofhighPD-1expression.
Wealsodidnotobserveanydifferentialup-regulationofPD-L1expressiononTcellsorDCs
followingAd5vaccinationcomparedtoAd26immunization(datanotshown),suggestingthat
theeffectisaCD8Tcellintrinsicphenomenon.Therewerenodifferencesinexpressionprofiles
ofphenotypicmarkerssuchasCD62L,CD127,orKLRG-1ontheexpandedGag-specificmemory
CD8Tbetweenbothtreatmentgroups(datanotshown).Onday14postboost,weisolated
splenocytesandassessedthefunctionalityofGagspecificCD8Tcellsasdescribedearlier.Inthe
Ad5-immunizedgroup,wefoundahigherfrequencyofIFN-γ-producingGag-specificCD8Tcells
(P=0.04)andTNF-αproducingGag-specificCD8Tcells(P=0.03)followinganti-PD-L1-treatment
comparedtountreated(Fig.5Dand5E).TherewasnosignificantdifferenceinfrequencyofIL-
2-producingGag-specificCD8Tcellsbetweenbothgroups(Fig.5F).However,therewasatrend
towardsamorepolyfunctionalantigen-specificCD8Tcellsinthetreatmentgroupcompared
withthoseuntreated(Fig.5G).
29
TodeterminetheeffectofblockingPD-1signalingpathwayontheprimaryimmune
responsesofAd5vectorandassessifthisearlyblockadewillleadtoasimilarimprovementin
memoryrecallasseenwhenthePD-1pathwaywasblockedatalatertime-point,we
administeredanti-PD-L1treatmentatthetimeofAd5prime(Fig.6A).Micewerefollowed
longitudinallytoassesstetramerkineticsinblood,andboostedwithAd35onday60post
immunizationtoassessmemoryrecall.WeobservedthatPD-1blockadedoesnotalterthe
kineticsofprimaryresponseinbothAd5-orAd26-primedmice.Inaddition,therewasno
differenceinexpressionlevelofsurfacemarkerslikeCD62L,CD127andKLRG-1(datanot
shown),andcytokineco-expressionongag-specificCD8Tcellswassimilarinbothtreatedand
controlgroup(Fig.6C).Inaddition,PD-L1blockadeatprimedoesnotleadtoasignificant
enhancementofmemoryrecallfollowingaheterologousAd35boost(Fig.6Eand6F).Taken
together,thesedatasuggestthattheestablishmentofan“immunedysfunction”state
characterizedbyup-regulationofPD-1isrequiredforPD-1blockadetohaveasignificanteffect
onrecallresponse
2.3.4 SimilarTregsfrequencyandsuppressivefunctioninAd5-andAd26-immunizedmice
RegulatoryTcellshavebeenshowntomodulateCD8Tcellactivation,proliferation,
differentiationandmemoryrecall125.IncreasedfrequencyandsuppressivefunctionofFoxP3+
CD4TcellshavebeenreportedinLCMVclone13infection,amousemodelofchronicinfection,
inwhichPD-1isup-regulated107,126.AsapreludetodeterminingwhetherTregsmayplayarole
intheimpairedmemoryrecallassociatedwithAd5-elicitedCD8Tcells,wesoughttodetermine
30
whetherTregsfollowingAd5immunizationaredifferentiallyactivatedcomparedtoalternative
serotypeAdvectorimmunizedmice.WevaccinatedFoxP3gfpmicewithAd5expressingSIVGag
orAd26expressingSIVGagandassessedthefrequencyofFoxP3+CD4Tcellsatthepeakof
infection(day15p.i)(Fig.7A).TregsisolatedfromnaïvemiceorLCMVclone13infectedmice
servedascontrols.Asexpected,thefrequencyofTregswassignificantlyhigherinLCMVclone
13infectedmicecomparedtonaïveorAd-immunizedmice.However,thenumberand
frequencyofFoxP3+CD4TcellsinthespleenandbloodofAd5immunized,Ad26immunized
andnaïvemicewassimilar.RepresentativeflowcytometryplotsareshowninFig.7A.Toassess
whetherthereisadifferenceinthesuppressivecapacityofTregsinducedbythesevectors,we
isolatedsplenocytesfromAd5orAd26vaccinatedmice,enrichedforCD4Tcellsfollowedby
FACSsortingforGFP+Tregs.Weco-cultureisolatedTregswithCellTraceViolet(CTV)-labeled
naiveCD8Tcells(targetcells)isolatedfromnaïvemice,inthepresenceofantiCD3/antiCD28
beads,andassessedCD8Tcellproliferation72hoursfollowingincubation.Interestingly,we
observedthatatpeakprimaryresponse(day15postimmunization),TregsfromAd5
immunizedandAd26immunizedmiceweresimilarlysuppressiveofCD8proliferation,with
bothbeinglesssuppressivecomparedwithnaïve,andTregsfromClone13infectedmicebeing
themostsuppressiveamongstallgroups(Fig.7B-7C).Althoughmorerigorousinvestigations
arerequired,theseresultssuggestthatregulatoryTcellsmaynotplayanimportantroleinthe
impairedimmunerecallseenwithAd5,furthersupportingthehypothesisthattheimpaired
immuneresponseseenfollowingAd5immunizationisprobablyaCD8Tcellintrinsic
phenomenon.
31
2.4 Figures
2.4.1 Figure1:Kineticsofvaccine-elicitedCD8Tcellfollowingvaccinationwithdifferent
dosesofAd5
(A)Experimentaloutline.(B)RepresentativeflowcytometryplotsshowingthepercentagesofGag-specificCD8TcellsinbloodfollowingimmunizationwithAd5-SIVGag(108,109,and1010)vporAd26-SIVGag(1010vp)(C)NumberofGag-specificCD8Tcellsinblood.Dataarerepresentativeofatleastthreeindependentexperiments,withn=4-5micepergroupperexperiment.Errorbarsrepresentstandarderrorsofthemeans(SEM).;***,P<0.001;ns;notsignificant.
32
2.4.2 Figure2:Phenotypeandpolyfunctionalityofvaccine-inducedCD8Tcell
followingvaccinationwithdifferentdosesofAd5.
(AandB)MFIofPD-1onGag-specificCD8Tcellsinbloodat(A)peaktimepoint(Day15p.i)andat(B)memorytimepoint(Day60p.i)followingimmunizationwithindicateddosesofAd5andAd26.(C)Proportion(%)ofGag-specificCD8TcellsthatexpressvariouscombinationsofCD127/KLRG1atday60followingAd5orAd26vaccination.(D)Proportion(%)oftotalGag-specificCD8Tcellsinbloodco-expressing3(IFN-γ,TNF-αandIL-2)cytokines,2(IFN-γandTNF-α)cytokinesor1(IFN-γ)cytokineatday60 followingAd5orAd26 vaccination.Data are representativeof at least three independentexperiments,withn=4-5micepergroupperexperiment.Errorbarsrepresentstandarderrorsofthemeans(SEM).*,P<0.05;**,P<0.01;***,P<0.001;****,P<0.001
Ad5 (108vp)
Ad5 (109vp)
Ad5 (1010vp)
Ad26 (1010vp)
0
100
200
300
400
500
PD-1
(MFI
)
****
*******
Day 15 Post-primeA
Ad5 (108vp)
Ad5 (109vp)
Ad5 (1010vp)
Ad26 (1010vp)
0
25
50
75
100
125
PD-1
(MFI
)
**
***
Day 60 Post-primeB
Ad5 108vp
45
186
31
Ad5 109vp
47
15
33
5
Ad5 1010vp
50
104
36
Ad26 1010vp
35
28
13
24
CD127- KLRG1+ (SLEC)CD127+ KLRG1- (MPEC)CD127+ KLRG1+CD127- KLRG1-
C
| |
+
| +
+
+ +
+
0
5
1020
40
60
80
100
% o
f G
ag-s
peci
fic C
D8+
T c
ells
pr
oduc
ing
indi
cate
d cy
toki
nes
IFN-γTNF-αIL-2
Ad5 (108vp)Ad5 (109vp)Ad5 (1010vp)Ad26 (1010vp)
**
****
****
**
**
ns
****
**
***
D
33
2.4.3 Figure3:LoweringtheprimingdoseofAd5vectorpartiallyimprovesthe
phenotypeandtherecallresponsesafterAd35boosting.
(A)Experimentaloutline.(B)RepresentativeFACSplotsshowingthepercentagesofGag-specificCD8TcellsinbloodpreandpostAd35boost.(C)NumberofGag-specificCD8Tcellsinblood.(D)Summaryshowingthefold-increaseofGag-specificCD8TcellsinbloodafterAd35boost.(E)MFIofKi-67onGag-specificCD8TcellsinbloodonDay7postAd35Boost.(F)MFIofGranzymeBonGag-specificCD8TcellsinbloodonDay7postAd35Boost.(G)MFIofPD-1onGag-specificCD8TcellsinbloodonDay7postboost.Dataarerepresentativeoftwoindependentexperiments,withn=4-5micepergroupperexperiment.Errorbarsrepresentstandarderrorsofthemeans(SEM).*,P<0.05;**,P<0.01;ns,notsignificant;vp,viralparticle.
34
2.4.4 Figure4:PrimingwithlowdoseAd5inaAd5-Ad35heterologousprime-boost
regimenproducemorepolyfunctionalCD8Tcells.
(A-C)NumberofsplenicGag-specificCD8Tcellsexpressing(A)IFN-γ,(B)TNF-α,and(C)IL-2onday30 followingAd35boost (D) RepresentativeFACSplots showing thepercentagesofGag-specificCD8Tcells inspleenco-expressing IFN-γandTNF-α,or IFN-γand IL-2 followingAd35boost.(E)Proportion(%)oftotalGag-specificCD8Tcellsinspleenco-expressing3(IFN-γ,TNF-αandIL-2)cytokines,2(IFN-γandTNF-α)cytokinesor1(IFN-γ)cytokineatday30followingAd35boost.Dataarerepresentativeoftwoindependentexperiments,withn=4-5micepergroupperexperiment.Errorbarsrepresentstandarderrorsofthemeans(SEM).*,P<0.05;**,P<0.01;ns,notsignificant;vp,viralparticle.
| |
+
| +
+
+ +
+
1
2
3
4
20
40
60
80
100
% o
f G
ag-s
peci
fic C
D8+
T c
ells
pr
oduc
ing
indi
cate
d cy
toki
nes
IFN-γ
TNF-αIL-2
**
Ad5 1 x 108 vp
Ad5 1 x 109 vp
ns
Ad5 1 x 1010 vp
Ad26 1 x 1010 vp
*
6.32 0.124
0.11193.4
5.33 0.0674
0.059994.5
7.86 0.219
0.060891.9
16.7 0.487
0.068382.7
4.41 2.04
0.14493.4
4.58 0.824
0.19194.4
6.45 1.63
0.11391.8
13.4 3.79
0.32782.5
TNF-! IL-2
IFN-γ
Ad5108vp
Ad5109vp
Ad51010
vp
Ad261010
vp
D
E
35
2.4.5 Figure5:Excessiveup-regulationofPD-1onAd5-inducedmemoryCD8Tcells
impairstheirrecallresponse.
(A)Experimentaloutline.(B)NumberofGag-specificCD8TcellsinbloodfollowingAd35boost+/-aPD-L1orIgGtreatment.(C)Summaryshowingthefold-increaseofGag-specificCD8TcellsinbloodafterAd35boost+/-aPD-L1orIgGtreatment.(D-F)PercentageofsplenicGag-specificCD8Tcellsexpressing(D)IFN-γ,(E)TNF-α,and(F)IL-2onday14followingAd35boost+/-aPD-L1orIgGtreatment.(G)Proportion(%)oftotalGag-specificCD8Tcellsinspleenco-expressing3(IFN-γ,TNF-αandIL-2)cytokines,2(IFN-γandTNF-α)cytokinesor1(IFN-γ)cytokineatday30following Ad35 boost in Ad5-primed mice. Data are representative of two independentexperiments,withn=4-5micepergroupperexperiment.Errorbarsrepresentstandarderrorsofthemeans(SEM).*,P<0.05;**,P<0.01;ns,notsignificant;vp,viralparticle.
36
2.4.6 Figure6:PD-L1blockadepriortoprimingdoesnotaffectthekinetics,memory
conversionoranamnesticresponseofAd5-inducedCD8Tcells
(A)Experimentaloutline.(B)NumberofGag-specificCD8TcellsinbloodfollowingAd5orAd26immunization +/- aPD-L1 or IgG treatment. (C) Representative FACS plots showing thepercentagesofGag-specificCD8Tcells inspleen(D60post immunization)co-expressingIFN-γand TNF-α, or IFN-γ and IL-2 following Ad5 or Ad26 immunization +/- aPD-L1 or control IgGtreatment.(D)NumberofGag-specificCD8TcellsinbloodfollowingAd35boost(E)Summaryshowing the fold-increase of Gag-specific CD8 T cells in blood after Ad35 boost. Data arerepresentative of two independent experiments,with n=4-5mice per groupper experiment.Errorbarsrepresentstandarderrorsofthemeans(SEM).ns,notsignificant;vp,viralparticle.
TNF-! IL-2
IFN-γ
37
2.4.7 Figure7:SimilarTregfrequenciesandsuppressivefunctionsinAd5-andAd26-
immunizedmice.
(A)Experimentaloutline.(B)RepresentativeFACSplotsshowingthepercentagesoffoxP3+CD4Tcellsinspleenonday15followingvaccinationwithAd51010vpandAd261010vp.ControlarenaïvemiceandLCMVclone13infectedmice.(C)SuppressionofCD8TcellproliferationbyTregsisolatedatday15followingvaccinationwithAd51010vpandAd261010vp.Numbersrepresentpercentageofproliferatingcells.(D)SummaryshowingpercentageproliferationofCD8Tcellsatday15followingvaccinationwithAd51010vpandAd261010vpDataarerepresentativeoftwoindependentexperiments,withn=4-5micepergroup.Suppressionassaywasdoneintriplicates.Errorbarsrepresentstandarderrorsofthemeans(SEM).;**,P<0.01;ns,notsignificant;vp,viralparticle.
38
3. Chapter3:Discussionandperspectives
TheinductionofhighmagnitudeCD8Tcellresponseshasbeenshowntocorrelatewith
vaccine-mediatedprotectionagainstebola,malariaandSIV3,4,127.Althoughasingle
administrationofanAdvectorcanelicitdetectableCD8Tcellresponses,heterologousprime-
boostregimensaretypicalusedtogeneratehighermagnituderesponsesinconventional
vaccinationregimes.Asastandalonevaccine,Ad5elicitshighmagnitudeCD8Tcellresponse
thatconfersomeprotectioninpreclinicalstudies78.However,followingaheterologousboost,
theseprimaryCD8Tcellsexhibitanimpairedproliferativecapacity,whichsubsequently
impactsprotectiveefficacy23.FurtherevaluationhasrevealedthattheprimaryCD8Tcells
inducedbyAd5vaccinationdisplayapartiallyexhaustedphenotypicprofilecharacterizedby
highexpressionofimmunoinhibitoryreceptors,poorpolyfunctionality,andanimpaired
memoryconversion,comparablewithchronicLCMVinfectioninmice23,83.Inthisstudy,we
evaluatedthemechanismunderlyingAd5-inducedimpairedimmuneresponsesbyassessing
theeffectofreducingvectordose,blockingPD-1signalingpathway,andevaluatingtreg–
mediatedsuppressionfollowingAd5immunization.
First,wecorroboratedearlierfindingsthatthereductionofvectordosesignificantly
improvesthephenotypicandqualitativeprofilesoftransgene-specificCD8Tcellswithout
affectingthemagnitudeoftheprimaryimmuneresponse.Wethenextendedthisobservation
byshowingthatvectordosereductionandPD-1signalingblockaderesultinanimprovementin
Ad5-inducedimmunedysfunctionasevidencedbytheimprovedmemoryrecallfollowing
boost.Finally,weshowedthat,comparedtoalternativeserotypeadenovirus,Ad5
39
immunizationdoesnotdifferentiallyaffectthemagnitudeorsuppressivefunctionofTregs.
Takentogether,thesedataprovidesomemechanisticunderstandingofAd5-inducedimmune
dysfunction.
Inbroadterms,thefactorsinfluencingimmuneresponseelicitedbyAdvectorsmaybe
categorizedintovirologicalandimmunologicalfactors(FigureA).Possiblevirologicalfactors
includetheserotypeoftheAdvector,itscellularreceptorspecificity,intracellulartrafficking
routeemployedbythevector,thevectordoseorrouteofadministration.Intermsof
immunologicalfactorsinfluencingAd5-inducedimmunedysfunction,thesemayeitherbeCD8T
cellintrinsicorCD8Tcellextrinsic.Likelyintrinsicfactorsareimmunoinhibitoryreceptors
expressedonCD8Tcells,transcriptionfactors(e.g.T-betandEomes)orepigeneticfactors,
suchasDNAexpressionregulatoryenzymes(e.g.histonedeacetylases(HDAC)),similartowhat
hasbeenobservedinchronicLCMVinfection128,129.ExtrinsicCD8Tcellfactorsincludethe
innateimmunesystem,suchasinnatecytokineandchemokineprofilesorthesubsetof
dendriticcellstransduced.Otherextrinsicfactorsincludetheinductionofco-stimulatoryorco-
inhibitorymoleculese.g.PD-L1ontransducedantigenpresentingcells,ortheeffectofother
cellsoftheadaptiveimmunesystemsuchasconventionalCD4TcellsorregulatoryTcells.All
thesefactorsareknowntoplayimportantrolesinthedevelopmentandmaintenanceofTcell
exhaustioninclassicalmodelsofimmuneexhaustion.
Itisknownthatthedoseanddurationofantigenicstimulationprofoundlyaffectthe
phenotype,differentiation,functionality,andproliferativecapacityofeffectorTcells
produced130,131,132,133.ThetypicalprimaryCD8Tcellresponsefollowinganexposuretoa
40
rapidly-clearedantigenasseeninacuteinfectionorvaccinationcanbedividedintothree
phases:(1)anexpansionphase,characterizedbyactivationandrapidexpansionofantigen-
specificnaïvecellsintoeffectorTcells,thatmediateantigenclearance;followedby(2)a
contractionphase,inwhichapproximately90-95%oftheeffectorCD8T-cellpopulation
undergoapoptoticcelldeath,leavingasmallsubsetofcellthatgothroughthe(3)memory
differentiationandmaintenancephase,inwhichstable,polyfunctionalmemoryCD8Tcellsare
maintainedviahomeostaticproliferation134.Incontrast,persistentantigenstimulationasseen
inchronicinfectioninmiceusuallyleadstoamuchdelayedCD8Tcellcontractionphasedueto
antigenpersistence135.IthasbeenshownthatAd5immunizationleadstoaprotractedCD8T
cellexpansionphase,withlittleornoimmunecontraction23,81,83,84,136.Inourstudy,we
showedthatreducingthedoseofAd5leadstoamorepronouncedCD8Tcellcontraction,
similartowhatisobservedfollowingimmunizationwithalternativeserotypeAdvectors23,81,
MVA136,orfollowinganacuteLCMVinfection137.Ithasalsobeenshownthatthedurationand
persistenceofantigenicstimulationisdependentontheAdvectortypeandvectordosage138.
Although,ourstudydidnotdirectlyassessthepersistenceofantigenstimulationfollowing
administrationofdifferentdosesofAd5vector,wehypothesizethattheimprovedcontraction
weobservedislikelyduetoareductioninamountanddurationofantigenexpressionfollowing
lowdoseAd5immunization.
UsingtheLCMVmiceinfectionmodel,Joshietal.showedthateffectorCD8Tcellscanbe
differentiatedintoSLEC(CD127-KLRG1+)andMPEC(CD127+KLRG1-)populationsbasedon
expressionofbothCD127andKLRG1onCD8+Tcells114.SLECs,whichareshortlived,
41
predominateinsituationsofantigenpersistencebutundergosignificantapoptosisfollowing
antigenclearance,whileMPECsdevelopedintolong-lived,self-renewingmemoryCD8Tcells.In
addition,comparedtoSLECs,MPECsaremore“functionallymature”withanincreasedcapacity
toproliferateandproduceIL-2inadditiontoIFNγandTNF-α,i.e.greaterpolyfunctionality.We
observedthatalowdoseAd5immunizationleadstoahigherproportionofCD8Tcells
differentiatingintotherelativelymorestableMPECswithimprovedpolyfunctionality(IFN-
γ+TNF-α+IL-2+).Thisimprovedmemorydifferentiationprobablyresultedintheenhancedrecall
expansionweobservedfollowingheterologousboostingwithAd35(Fig,2C-D)orMVA(data
notshown).WealsoshowedthatthereisalowerpercellPD-1expressionfollowinglowdose
Ad5immunizationcomparedtohighdoseAd5.Sincethedurationofantigenicstimulationis
alsoknowntoaffecttheexpressionofthesemarkers139,140,141,142,wespeculatethattheoverall
improvementseenwithlowerdoseofAd5isaresultofreducedantigenpersistence.
TherouteofadministrationofAd5vectorimmunizationmayalsoinfluencetheimmune
responseelicited,suchthatintravenousadministrationleadstoamoredysfunctionalimmune
responsecomparedtoothermodesofadministration.Intravenousinjectionofadenovirus5
leadstoarapidaccumulationoftheviruswithintheliverduetoitshepatictropism143.High
viralloadintheliverleadstoTcellexhaustionanddepletionofantigen-specificcytotoxicT
lymphocytes144,145.Therefore,anotherplausibleexplanationforAd5-immunedysfunctionis
thathighdoseAd5immunizationresultsinasignificantlyhighernumberofviralparticles
migratingtotheliver,wheretheycancontributetothedevelopmentofdysfunctionalTcells.
Thispossibilityneedstobefurtherexplored.
42
ExhaustedTcellsseenduringchronicinfectionssuchasHIV,malaria,HCV,andHBVin
humans,orchronicLCMVinfectioninmiceareknowntoup-regulateimmunoinhibitory
receptorssuchasPD-1.ThePD-1/PD-L1signalingpathwayisinvolvedinnormalimmune
responses,andseveralregulatoryprocessesrangingfromtolerancetoTcellexhaustion.The
significantreductioninPD-1expressionfollowinglowdoseAd5immunization,coupledwiththe
improvedrecallresponsesuggeststhatthehigherPD-1expressionmaybemediatingthe
impairedrecallresponseassociatedwithhigh-doseAd5.Indeed,Fuseetel.showedthat
“helpless“CD8Tcells(withoutCD4Tcellshelp)highlyexpressPD-1andexhibitimproverecall
responsefollowingPD-1blockade102.Similarly,weobservedthatblockingPD-1signalingviaan
invivoPD-L1blockadeledtoanimprovedmemoryrecallfollowingsecondaryantigen
encounter.Interestingly,thisobservationwasseenonlywhentheblockadewasdoneatthe
timeofboosting,withnoeffectseenwithPD-L1blockadeatthetimeofprimingwithAd5.The
failureofPD-L1blockadeatprimecouldbeduetotheneedforan“exhausted”state
(upregulationofPD-1)tobeestablishedbeforetheeffectofblockingPD-L1:PD-1interaction
canbeseen.PD-L1isexpressedonTcells,Bcells,DCs,andisup-regulatedfollowingIFN-γ
treatment.However,therewasnodifferentialup-regulationofPD-L1ontransducedDCinthe
draininglymphnodefollowingAd5immunizationcomparedtoAd26immunization(Penaloza-
MacMaster,P,etal,unpublisheddata).OurdatathereforesuggestthattheintrinsicPD-1
signalingmaybepartlymediatingAd-5inducedimmunedysfunction.
Tregsplayamajorroleinmaintainingperipheraltolerance,inadditiontocontrolling
immuneresponsetoinfections.TheirroleinmaintainingTcellsinanexhaustedstatewas
43
demonstratedbythestrikingrescueofexhaustedTcellsfollowingTregsablation.Inacancer
vaccinemodel,vaccinationwithalphavirusvectorexpressinghumanpapillomavirus(HPV)type
16peptidesdidnotresultinchangesinthenumberand/oractivityofTregs,andthedepletion
ofTregsdidnotimprovetheefficacyofthisvaccineagainsttumours146.However,alphavirus
vectorelicitedimmuneresponsesarenotknowntoexhibitimmuneexhaustion.WithCD8T
cellsinducedbyAd5exhibitingapartialexhaustedphenotypeandthesignificantroleTregs
playinmaintainingexhaustedTcells,itispossiblethatregulatoryTcellsmaybecontributingto
theimpairedTcellsresponseseenfollowingAd5immunization.Ourstudydidnotfindany
differenceinthemagnitudeandsuppressivefunctionofTregsfollowingAd5orAd26
immunization.WechoseAd26ascontrolbecauseitdoesnotelicitadysfunctionalimmune
responselikeAd523.AlthoughfurtherstudiesareneededtocompletelyexcludearoleforTregs,
ourdataprovideahintthattheregulatoryTcellmaynotplayasignificantroleinmodulating
Ad5-inducedimmunedysfunction.
Insummary,ourdatasuggestthatantigenicstimulationandtheimmunoinhibitory
receptorPD-1playsasignificantroleinmodulatingAd5-inducedimmunedysfunction.The
absenceofaneffectofAd5immunizationonTregsandtheexpressionofPD-L1onantigen
presentingcellsalsosuggestthattheimmunedysfunctionseenwithAd5isprimarilyaCD8
intrinsicphenomenon.Althoughpre-existingvectorimmunitymayimpedetheuseofAd5in
futureclinicalvaccinetrials,particularlyinregionsofhighseroprevalence,themechanistic
implicationofthedatashownherewillbeusefulinselectingandtestingothersimilarviral
vectorsforfuturevaccinedevelopment.
44
3.1 Limitations
Theimmunogenicitydatapresentedinthisstudywereacquiredbyassessingimmune
responseslongitudinallyinblood,withveryfewevaluationoftheresponsesintissues.Itis
possiblethattheimmuneresponseinbloodmayslightlydifferfromthoseoftissues-both
lymphoidandnonlymphoidtissues.Thedecisiontofocusonbloodwasduetotheneedto
evaluatememoryrecall.Theassessmentoftissueimmuneresponsepriorofboostwillrequire
sacrificingtheanimalwhichwillprecludeaninternallycontrolledevaluationofthemagnitude
ofimmuneexpansion.Inaddition,theexperimentsreportedherewereallcarriedoutinmice.
Whethersimilarfindingswillbeseeninnon-humanprimatesandhumansisyettobe
determined.
3.2 Futuredirections
TheimprovedimmuneresponseseenfollowingimmunizationwithlowerdoseAd5maybe
duetoanacceleratedantigenclearance.Futureexperimentsmayutilizeinvivoimagingstudies,
transgenetranscriptPCRandmeasurementofinvivoproliferationofadoptivelytransfer
antigen-specificTcellstocomparethedurationoftransgeneexpressionfollowinglowdoseand
highdoseAd5immunization,andcomparingAd5tootherserotypeadenovirussuchasAd26.In
ourstudy,themagnitudeoftransgene-specificmemoryCD8Tcellswassignificantlyhigherin
highdoseAd5-primedmicecomparedtolowdoseAd5-primedmicepriortoheterologous
boostbecauseoftheprofoundimmunecontractionseenwithlowdoseAd5immunization.
Futureadoptivetransferexperimentswillnormalizeforthenumberofantigenspecificmemory
cellstransferredintocongenicallydistinctmicebeforeheterologousboost.Futureexperiments
45
willalsohelptodetermineifAd5-induceddysfunctionistrulyaCD8Tcellintrinsic
phenomenonorwhetheritisduetodifferencesintheimmuneenvironment.Inaddition,an
assessmentoftheamountofvectorreachingtheliverfollowingintramuscularimmunization
withhighdoseAd5,andthedegreeofhepatotoxicity,ifany,willhelptodetermineifliver
sequestrationofAd5vectorcontributestotheimpairedresponse.
WeshowherethatPD-L1blockadeleadstoanimprovementinimmunerecallfollowing
heterologousboosteventhoughPD-L1expressionisnotdifferentiallyup-regulatedonantigen
presentingcellsfollowingAd5comparedtoAd26immunization.Itisthereforeimportantto
determineiftreatmentwithPD-1blockingantibodywillleadtoasimilarimprovementin
immuneexpansion.Inaddition,futurestudiesshouldalsoassessifacombinationofdose
reductionandPD-1signalingblockadewillleadtoasynergisticimprovementinimmunerecall.
TheeffectoflowdoseAd5immunizationontheexpressionofotherimmmunoinhibitory
moleculessuchasTim-3andCTLA-4,andwhetherblockadeofthesereceptorswillsimilarly
leadtoimmunerescueshouldalsobedetermined.
OurpreliminaryfindingsalsosuggestthatTregsmaynotplayacriticalroleinmodulating
Ad5-inducedimmunedysfunction.Futureexperimentshoulddeterminetheeffectof
immunizationonTregmagnitudeandfunctionatlater(memory)timepoints.Itisalso
importanttodeterminemoreconclusivelytheroleofTregsbyassessingtheeffectofTreg
depletionusingtheFoxP3DTRmousemodel.Finally,andmostimportantly,futureresearch
shouldassesstheprotectiveefficacyoftheimprovedimmuneresponseobservedfollowinglow
doseAd5immunizationandPD-1signalingblockadeastheultimategoalofvaccinesisto
46
protectagainstpathogensorsignificantlylessendiseaseburden.
47
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