Altered Macrophage Differentiation and Immune Dysfunction in Tumor Development

Review series

TheJournalofClinicalInvestigation http://www.jci.org Volume117 Number5 May2007 1155

Altered macrophage differentiation and immune dysfunction in tumor development

Antonio Sica1 and Vincenzo Bronte2

1Istituto Clinico Humanitas, Instituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Rozzano, Italy. 2Istituto Oncologico Veneto, IRCCS, Padua, Italy.

Tumorsrequireaconstantinfluxofmyelomonocyticcellstosupporttheangiogenesisandstromaremodelingneededfortheirgrowth.Thisismediatedbytumor-derivedfactors,whichcausesustainedmyelopoiesisandtheaccumulationandfunctionaldifferentiationofmyelomonocyticcells,mostofwhicharemacrophages,atthetumorsite.Animportantsideeffectoftheaccumulationandfunctionaldifferentiationofthesecellsisthattheycaninducelymphocytedysfunction.Acompleteunderstandingofthecomplexinterplaybetweenneoplasticandmyelomono-cyticcellsmightoffernoveltargetsfortherapeuticinterventionaimedatdeprivingtumorcellsofimportantgrowthsupportandenhancingtheantitumorimmuneresponse.

Althoughclinicaltrialsevaluatingtheeffectivenessofnovelcancervaccinesindicatethatincancerpatientstheycaninducerobustimmuneresponsesagainsttumorantigens,theclinicalbenefitsofthesevaccineshavebeenlimited(1,2).Thereasonsbehindtheselimitedclinicalresponsesarenotknownbutmightberelated,inpart,totheimmunosuppressiveeffectsoftumors.Immunedysregulationandsuppressionincancerpatientsisacompositeeventinwhichtumor-derivedfactorsconditionnotonlyperiph-eral immuneniches, inwhichdysfunctionandevendeathoftumor-specificTcellscanoccur,butalsothebonemarrowandotherhematopoieticorgans(suchasthemousespleen),leadingtoabnormalmyelopoiesisandtheaccumulationofimmunosuppres-sivemyelomonocyticcellsatthetumorsite(3,4).Dysregulationand/orsuppressionoftumor-specificTcellfunction(s)isthere-forelikelytooccurat2separatesites:locally,atthetumor-hostinterface,wherecancercellsdirectlyconditionthetumorstroma;andsystemically,whereanexpandedpoolofimmatureandimmu-nosuppressivemyeloidcellsarefreetocirculateandmediatesup-pressioninthebloodandlymphoidorgans.ThisReviewattemptstoanalyzethemainmyeloidcellpopulationsthatrestrainantitu-morimmuneresponses.

Immunosuppression and cancer: history and nomenclatureAlthoughapopulationofnotverywelldefinedcellscallednatural suppressorswasassociatedintheearly1980swithimmunesuppres-sionandtumordevelopment(5),thefirstdescriptionindicatingthatincreasednumbersofmyeloidcellsintumor-bearinghostsmightalterantitumorimmunereactivitywasprovidedbyHansSchreibersgroup(6,7).Inonekeyexperiment,theadministra-tionofaGr-1specificantibodythatrecognizesbothLy6CandLy6Gtoimmunocompetentmicereducedthegrowthofavari-antofaUVlightinducedtumorabletoprogressmoreaggres-sivelythanitsparentaltumorcellline(6).Thisvariantwasknown

toattractmoreleukocytesthantheparentalcellline,apropertyattributedtothereleaseofanoncharacterizedchemotacticfactor,anditsgrowthinvivowasknowntoberestrainedmainlybyCD8+Tcells.Interestingly,eliminationofGr-1+cellsinathymicnudemice(whichlackmostTcells)alsoslowedthegrowthofthisaggressivevariant,suggestingthatGr-1+leukocytesintumor-bearinghostsmightalsopromotetumorgrowthanddevelopment(7).TheeffectofinvivotreatmentwiththisGr-1specificantibodywasoriginallyattributedtotheeliminationofgranulocytes(whichareknowntoexpresshighlevelsofLy6GbutlowlevelsofLy6C),butsuccessivereportsfromseveralgroupsindicatedthattheGr-1specificanti-bodycouldbindandeliminateothercellsintheblood.Gr-1+cellsintumor-bearinghostswere,infact,mostlyCD11b+andcom-prisedbothpolymorphonuclearandmononuclearcells,includingcellsatdifferentstagesofmaturationalongthemyelomonocyticdifferentiationpathway, thereby revealingaprofoundaltera-tioninmyelopoiesisduringtumorprogression(4,8)(Figure1).Myelopoiesis,infact,isnotonlyincreasedinthebonemarrowandspleenoftumor-bearingmicebutisalsoaltered,sincethemyelo-monocyticcellscannotproperlydifferentiateintoprofessionalAPCs,suchasDCs(reviewedinref.9).

Heterogeneity of myeloid-derived suppressor cellsTheheterogeneityoftheCD11b+Gr-1+cellshasgeneratedsomeconfusion,inparticularbecauseofthenomenclatureusedpre-viouslytodefinethem(i.e.,immaturemyeloidcellsormyeloidsuppressorcells).Recently,apanelofleadinginvestigatorsinthefieldagreedtousethecommontermmyeloid-derived suppressor cells (MDSCs)(10).TheMDSCdefinitioninvolvesasynthesisofthefunctionalandphenotypicpropertiesofthecells.MDSCscanbedefinedasapopulationofmyelomonocyticcellsnormallylack-ingthemarkersofmaturemyeloidcellsandcommonlyexpressingbothGr-1andCD11binmice,withahighpotentialtosuppressimmuneresponsesinvitroandinvivo.TheexactnatureoftheMDSCpopulationdependsonvariousfactorsdescribedbelow,themostimportantofwhichisprobablythetumortype.Eventhoughnumerousfindingssuggestthatthemonocytic,

ratherthanthegranulocytic,fractionofmouseCD11b+Gr-1+cellsisresponsiblefortheimmunedysfunctionsinducedbythiscellpopulation,bothinvitroandinvivo,inantigen-specificCD8+Tcells (1113), theuseof thetermmyeloid is justifiedbytheincompleteunderstandingoftherelationshipbetweenthetwo

Nonstandardabbreviationsused:ARG1,arginase1;CCL2,CCchemokineligand2;CD3,chainoftheCD3componentoftheTCRcomplex;CXCL12,CXCchemokineligand12;CXCR4,CXCchemokinereceptor4;HIF-1,hypoxia-induciblefactor1;IL-4R,IL-4receptor-chain;MDSC,myeloid-derivedsuppressorcell;SHIP,Srchomology2domaincontaininginositol-5-phosphatase;TAM,tumor-associatedmacrophage.

Conflictofinterest:Theauthorshavedeclaredthatnoconflictofinterestexists.

Citationforthisarticle:J. Clin. Invest.117:11551166(2007).doi:10.1172/JCI31422.

Downloaded from http://www.jci.org on April 25, 2015. http://dx.doi.org/10.1172/JCI31422

review series

1156 TheJournalofClinicalInvestigation http://www.jci.org Volume117 Number5 May2007

mainprogenyoftheenhancedmyelopoiesisobservedintumor-bearinghosts(i.e.,granulocytesandmonocytes;Figure1).BothMDSCsandtumor-associatedmacrophages(TAMs)haveaphe-notypesimilartothatofalternativelyactivatedmacrophages(alsoknownasM2macrophages)inthemouse,asdiscussedbelow,andtumor-conditionedgranulocytesmighthavearoleininfluenc-ingthisactivationprocess.Itmustbepointedout,infact,thatinmice,threedifferentneutrophilsubsetshavebeenisolatedthatcanconditionmonocyte/macrophagedifferentiationtowardtheclassicoralternativeactivationpathwaybyreleasingdifferentcytokinesandchemokines(14).Furthermore,humangranulocytesubpopulationsinpatientswithrenalcellcancerhavebeenshowntofunctionasMDSCs(15,16).CD11b+Gr-1+cellsarenormallypresentinthebonemarrowof

healthymiceandaccumulateinthespleenandbloodoftumor-bearingmice(1720).CD11b+Gr-1+cellspresentinsteady-stateconditionsarenotabletoinducesuppressionofantigen-stimulatedTcells,atleastnottothesameextentasthecellsthataccumulateintumor-bearingmice,andrecentdatasupportthepossibility

thatexogenouslyprovidedIL-13mightconferonthemsuppres-siveactivity(21,22).BerzofskyandcolleagueshaveshownthatasubsetofNKTcellsrecognizingtumor-derivedglycolipidspresent-edbytheMHC-likemoleculeCD1releasesIL-13.ThisIL-13canthenactivateCD11b+GR-1+cellstosuppresstumor-specificCTLsthroughaSTAT6pathwayinitiatedbytheIL-4receptor-chain(IL-4R),whichiscommontothereceptorsforIL-4andIL-13(21,22).Thiscircuitisactivatedveryearlyaftertumorimplantationinmice,beforeanyincreaseinthenumberofCD11b+Gr-1+cellsisdetected.Inseveralexperimentalmodels,however,systemicaccu-mulationofCD11b+Gr-1+cells,probablyresultingfrombothdif-ferentiationofprecursorsandrecruitmenttoparticularanatomi-calsites,precedesandisimportantformediatingsuppressionofTcells,notonlyincancerbutalsoduringinfections(Table1).

MDSC suppression of T cell functionThebiologyandpropertiesofMDSCsintumor-bearinghostshavebeenextensivelydescribedinrecentreviews(4,8,23)andaresum-marizedhereinProperties of MDSCs.Themechanismsunderlying

Figure 1Current view of TAM and MDSC differentiation. HSCs give rise to common myeloid precursors (CMPs), which subsequently originate at least three subsets of cells circulating in tumor-bearing hosts that can be identified by specific markers: monocytes (CD11b+Gr-1+F4/80+), granulocytes (CD11b+Gr-1highF4/80IL-4R), and MDSCs (CD11b+Gr-1medF4/80low/IL-4R+). Circulating monocytes are recruited by tumors and differentiate into TAMs, acquiring protumoral functions. During tumor progression, MDSCs accumulating in blood and in lymphoid organs such as the spleen may also be recruited to the tumor microenvironment, where they become F4/80+. This latter pathway of MDSC-TAM phenotype transition (dashed arrow) was recently proposed (13, 27). Finally, it has been hypothesized that immature forms of granulocytes might differentiate into MDSCs or condition their function and/or further differentiation (red arrows), as suggested by some studies (14).


review series


theinhibitoryactivityofMDSCsareprobablyvarious,rangingfromthoserequiringdirectcell-cellcontacttoothersindirectlymediatedbymodificationofthemicroenvironment.MDSCsfresh-lyisolatedfromthespleensoftumor-bearingmicewereoriginallyshowntosuppressthefunctionalactivityofCD8+Tcells,butnotCD4+Tcells,byinterferingwiththeirabilitytosecreteIFN-whenstimulatedwithspecificantigens(19,24).ThiseffectwasthoughttoberelatedtothefactthatMDSCsexpressedMHCclassIbutnotMHCclassIIandwasmediatedbycell-cellcontactandtheproductionofROSsuchashydrogenperoxide(H2O2),triggeredbyMDSCexpressionoftheenzymearginase1(ARG1)(19).TheroleofH2O2asamediatorofTcelldysfunctionseemstocorrelate,atleastinsomestudies,withdecreasedexpressionofthechainoftheCD3componentoftheTCRcomplex(CD3)(25).OtherstudieshaveshownthatcirculatingMDSCshavetobeactivatedbyantigen-experiencedTcellstoexecutetheirsuppressiveprogramandthattheycansuppress,inanMHC-independentfashion,bothantigen-activatedCD4+andCD8+Tcells(11,13,20).Moreover,asubsetofMDSCs(expressingCD11b,Gr-1,CD115,andF4/80)isolatedfromthebonemarrowandspleensoftumor-bearingmicecaninducethedevelopmentofFOXP3+CD4+(FOXP3,fork-headboxp3)TregsinvivobyapathwayrequiringIFN-andIL-10(26).Interestingly,productionofNOwasnotrequiredforMDSC

inductionofTregswhereasNO,releasedbyNOS,hasbeenshowntobeextensivelyinvolvedintheTcelldysfunctioninducedbyMDSCs(Table1),suggestingthatthedifferentbiologicalactivitiesofMDSCsmightbeseparatedatthemolecularlevelandperhapstargetedbydistincttherapeuticapproaches.Someissuesmustbeconsideredwhenanalyzingthepartially

conflictingresultsonthemechanismofMDSC-dependentsup-pressionofTcells.TheinvitroassaysevaluatingtheinhibitorypropertiesofMDSCsarenotstandardized,soindifferentstudiestheymightdifferbothinthetypeofstimuliandsourceofTcells.WhenTcellsarestimulatedinvitrointhepresenceofsupraphysi-ologicnumbersofMDSCs,themechanismsgoverningsuppres-sionmightdifferfromthoseactivatedininvitroassayswheretheratioofMDSCstoTcellsisthesameasfoundinthelymphoidorgansofmice,whereMDSCsarerecruitedinpathologicalsitu-ations.Incontrasttotheinvitroassays,theabilityofMDSCstoinducetumor-specificCD8+Tcellstobecomenonfunctionalinvivohasbeenrepeatedlyconfirmed,althoughmanystudiesarebasedontheuseofeithersmallmoleculesaffectingMDSCinhibi-torypathwaysorantibodiesdepletingGr-1+cells(11,22,2729).Itmustbeemphasizedthattheinterpretationofinvivoexperi-mentswithinhibitorsiscomplicatedbythepossibilitythatthesemoleculesaffectcellsotherthanMDSCs.

Table 1Myeloid celldependent suppression of T cells in mice

Pathology Suppressorcells Phenotype Mousestrain MechanismofTcellinhibition References isolatedfrom:

Cancer

Colon carcinomas Spleen and tumor CD11b+Gr-1+ BALB/c ARG and NO dependent (11, 17, (CT26 and C26) 44, 115)Melanoma (B16) Spleen CD11b+Gr-1+ C57BL/6 NOS dependent (45)Lymphoma (EL-4) Tumor CD11b+Gr-1+F4/80+ C57BL/6 ARG and NO dependent (13)Colon adenocarcinoma Tumor F4/80+ C57BL/6 NO and cell-associated form (116) (MCA-38) of TNF-Mammary carcinoma (4T1) Spleen CD11b+Gr-1+CD11c+ BALB/c ARG dependent (20)Lewis lung carcinoma Tumor CD11b+Gr-1F4/80CD80+ C57BL/6 ARG dependent (47)Lewis lung carcinoma Tumor CD31+ C57BL/6 NO and TGF- dependent (117)T cell lymphoma (BW-Sp3) Spleen CD11b+Gr-1intLy6GCD115int AKR ARG and NO independent; (12, 118) partially dependent on PPARFibrosarcoma (C3) Spleen CD11b+Gr-1+ C57BL/6 ARG and H2O2 (19)Transformed fibroblasts Spleen CD11b+Gr-1+ BALB/c NKT cells, IL-13, STAT6, TGF-; (21, 22) (1512RM) NOS independent; ARG not tested

Infection

Candida albicans Blood, spleen CD11b+Gr-1+CD80+ BALB/c IFN-/NO and CD80 (119) polymorphonuclear cellsTrypanosoma cruzi Spleen CD11b+Gr-1+ C57BL/6 and Sv129 IFN-/NOS (120)Schistosoma mansoni Spleen CD11b+Gr-1+CD16+ BALB/c and B10.D2 Unidentified soluble factor (121) (not IL-4, IL-10, or TGF-)Taenia crassiceps Peritoneum CD11b+Gr-1+ BALB/c 12/15-Lipoxygenase, NO and ARG (122)Porphyromonas Spleen, BM but CD11b+Gr-1+ BALB/c IFN- (52) gingivalis not lymph nodesSchistosome Peritoneum CD11b+Gr-1+F4/80+ BALB/c and C57BL/6 IFN-/NO; partly IL-10 dependent (123) oligosaccharide (Lacto-N-neotetraose)Cruzipain antigen Spleen CD11b+Gr-1+ BALB/c Not investigated; ARG and NOS (124) from T. cruzi (extramedullary activity increased in macrophages hematopoiesis)


review series


General properties of MDSCs and their relationship with M2 macrophagesThesuppressiveprogramofMDSCscanbetriggeredbytheirinter-actionwithantigen-activatedCD8+Tcellsbothinvitroandinvivo,throughanIFN-andcell-contactdependentstepthatmightrequiretheexpressionofCD80andCD11bonthesurfaceoftheMDSCs(11,19,30).Interestingly,simpleinvitrocultureofMDSCsalonecanactivatethisprogram.Thereasonbehindthecommonfindingthatcells isolatedeitherwithGr-1specificorCD11b-specificantibodiesandculturedinvitro(withorwithoutGM-CSF)becomemacrophage-likecells(i.e.,theygainaCD11b+Gr-1

F4/80+CD80+MHCclassII/lowphenotype)withenhancedimmuno-suppressiveactivity(1113)hasnotbeenfullyinvestigated.TheinhibitorypropertiesofMDSCsareprobablymediatedby

theexpressionofinducibleformsofNOS(i.e.,NOS2)andARG(i.e.,ARG1).BothNOS2andARG1areinvolvedinthemetabolismoftheaminoacidl-Arg(Figure2).NOS2,aheme-containingenzymethatcatalyzesthesynthesisofNOandcitrullinefroml-Arg,isexpressedbyvariouscellsoftheimmunesystem,anditsactiva-tionisconsideredahallmarkofclassicallyactivatedmacrophages(alsoknownasM1macrophages),amacrophagesubsetthatpro-ducesproinflammatorycytokinesandactsastheeffectorcellinthekillingofinvadingpathogens(3133).InM1macrophages,expressionofthegeneencodingNOS2dependsontheactiva-tionoftranscriptionfactors,suchasNF-B,JAK3,andSTAT1aswellasJNK(34),anditcanbetranscriptionallyupregulatedbyproinflammatorycytokines(e.g.,IFNs,IL-1,IL-2,andTNF-),bac-terialLPS,andhypoxia(35,36).Bycontrast,ARG1(alsoknownasliver-typeARGbecauseitisfoundpredominantlyinhepatocytes)isamanganesemetalloenzymethatcatalyzesthehydrolysisofl-Argtol-ornithineandurea(Figure2).However,ARG1isalsoinducedincellsoftheinnateimmunesystembyseveralcytokines

includingTGF-(37),themacrophage-stimulatingprotein(MSP)actingonthereceptorRON(38),GM-CSF(39),andeitherIL-4orIL-13,bothofwhichactivateaSTAT6signalingpathway(40).IncontrasttoNOS2,whoseactivationisconsideredahallmarkofM1macrophages,ARG1activationhasbeenregardedasoneofthemostspecificmarkersofM2macrophages,whichactasimpor-tantmediatorsofallergicresponses,controlparasiticinfections,mediatewoundrepairandfibrosis,andhavebeenfoundintheleukocyteinfiltratesofvarioushumanandmousetumors,wheretheyhavebeensuspectedofpromotingtumorigenesis(31,32),asfurtherdiscussedbelow.DespitethisdistinctexpressionofNOS2andARG1inM1andM2macrophages,respectively,MDSCshavebeenshowntoexpressNOS2and/orARG1,andrecentstudiesindicatethatMDSCshavecharacteristicsofbothM1andM2macrophages.Indeed,werecentlydescribedintumor-bearingmiceapopulationofcirculatingCD11b+Gr-1+inflammatorymonocytesexpressingIL-4RandabletoreleasebothIL-13andIFN-(11),characteristicsthatarecompatiblewithafunctionintermediatebetweenthoseofM1andM2macrophages.TosuppressCD8+Tcells,thesecirculatinginflammatorymonocyteshadtobeacti-vatedbyIFN-producedbyantigen-stimulatedTcells,releasetheirownIFN-andIL-13,andberesponsivetoIL-13byexpress-ingafunctionalIL-13receptor,includingtheIL-4Rsubunit(11).IL-4RisthereforeausefulmarkerfordiscriminatingbetweenpopulationsofimmunosuppressiveMDSCs(IL-4R+)andnon-suppressivegranulocytes(IL-4R),bothofwhichareincreasedinthebloodandspleensoftumor-bearingmice(Figure1).Coopera-tionbetweenIL-13andIFN-ledtosustainedactivationofbothARG1andNOS2inMDSCpopulations,causingdysfunctionalTcellresponses(11).Importantly,CD11b+TAMsalsorequirethesamecombinationofcytokines(IL-13andIFN-)tomediatesup-pressionofCD8+Tcells(11).TheseresultssuggestthatMDSCs

Properties of MDSCs

CoexpressionofthemyeloidcellmarkersCD11bandGr-1mustbeassociatedwiththefunctionalabilitytoinhibitTcellactivation.

Normallyfoundinthebonemarrow(inthespleenofnormalmicetheynormallyaccountforlessthan5%ofnucleatedcells),MDSCscanbeincreasedinnumbersinspleenandbloodunderpathologicalconditions.AnincreaseinMDSCnumbersinlymphnodeshasbeenreportedbysomestudiesunderpathologicalsituations(27,105).

MDSCspresentatthetumorsiteandafractionofcellspresentinthespleenofmicebearingtumorsareCD11b+F4/80+Gr-1;thesecellscanariseinvivoandinvitrofromCD11b+Gr-1+precursorsandretaintheirsuppressiveproperties(12,13,17,28).

Invitroeffects:MDSCsinhibitTcellactivation(CD8+TcellsmorethanCD4+Tcells)inducedbyeitherantigensorpolyclonalstimulithroughanMHC-independentmechanismrequiringcell-cellcontact.

EventhoughdirectantigenpresentationtotheTcellsbyMDSCsisnotrequiredforinvitrosuppression,MDSCscantakeupandcross-presenttumor-associatedantigensinthecontextofMHCclassImoleculesinvivo(27).Inthiscase,selectiveimpairmentoftumor-specificimmunityhasbeenshown,indicatingthatMHC-dependentresponsesmightberelevantinvivo.

HumanMDSCequivalentsarenotentirelyknown,butgranulocytesubpopulationsmightbeinvolvedinmediatingsomehumanMDSCinhibitoryactivities(15,16).

VEGF,GM-CSF,IL-3,M-CSF,andIL-6havebeenshowntobeinvolvedinthealterationofnormalmyelopoiesisandrecruitmentofMDSCstoperipheralorgansunderpathologicalsituations.Cytokinesmightberelevantforenhancedmyelopoiesis,mobiliza-tionofMDSCs,andconditioningthematurationofthesecells(4,9).


review series


andTAMsrespondwithanM2macrophageorientedprogramtoclassicsignalsdrivingmacrophageactivation(dependentonTh1cytokines)andreconcileconflictingdataattributingaprevalenceofeitherIFN-,NOS2,andSTAT1orIL-4/IL-13,ARG,andSTAT6axesinthesuppressionoftheimmuneresponseintumor-bearinghosts(Table1,Figure2;alsodiscussedfurtherbelow).Manyquestions,however,stillawaitanswers.It isnotclear,

forexample,whetheralltheMDSCprecursorsinapopulationrespondsimilarly(andsynchronously)toTcellmediatedacti-vationorwhetherMDSCpopulationsareheterogeneous,withsomecellsprogrammedtoactivateanM1phenotypeandotherstoactivateanM2phenotype.Alternatively,someplasticitymightexist,i.e.,MDSCsmightbeabletooscillatebetweenM1andM2phenotypes,dependinguponthestimulationtheyreceive.More-over,withrespecttothestatusofpolarization,somedifferenceshavebeen reportedbetweenmiceandhumans.For example,ARG1isexpressedinmouse,butnothuman,M2macrophages(41).Inhumans,ARG1isconstitutivelyexpressedbygranulocytes

(42),andARG1-expressinggranulocyteshavebeenreportedtoinducebothdecreasedCD3expressionandattenuatedactivationinTcellsfromrenalcellcarcinomapatients(15).Thesediscrepanciesbetweenhumansandmicemightreflectour incompleteunderstandingof thehighlydynamicprocessofmyeloiddifferentia-tionincancer,andonlytheidentificationofthemoleculesreleasedbytumorsandthetranscrip-tionfactorsactivatedinhematopoieticprecur-sorscanaddresstheseissues.WearecurrentlyevaluatingthepossibilityofgeneratingMDSCsfrombonemarrowprecursorsusingdefinedinvitroculturesystemsinanattempttoaddresssomeoftheseissues.

l-Arg metabolism as the mechanism of MDSC immunosuppressionIncreasedl-Argmetabolism,eitherinmyeloidcellsinfiltratingthetumorstromaorintumor

cells,canimpairantigenresponsivenessofTcells,bothatthetumor-hostinterfaceandsystemically(23,29,43).Immuneregulationbyl-Argmetabolismisnotantigen-specific,buttobesusceptibletotheinhibitoryactivityoftheARG-andNOS-dependentl-Argmetabo-lismpathways,aTcellmustbeactivatedthroughitsTCR.Activa-tionthroughtheTCRpromotesTcellcycling,andmanyoftheinhibitoryeffectsofl-Argmetabolizingenzymesrequireactivelyproliferatingcells.NOS2andARG1canfunctionseparatelyorsynergisticallytoalterTcellfunction;activationofeitherenzymealoneinanAPCinhibitsitsabilitytoinduceTcellproliferationbyinterferingwithintracellularTcellsignaltransductionpath-wayswhereasinductionofbothenzymesgenerateshighlyreactiveoxygenandnitrogenspecies,suchasH2O2andperoxynitrites,thatmightinducesignalingdefectsinproximalimmunecellsandforceantigen-activatedTcellstoundergoapoptosis(Figure2andref.23).Therelativelevelsofexpressionofthe2enzymesseemtoberelatedtothestimulusdrivingMDSCaccumulation(Table1).Inthecaseoftumor-inducedMDSCs,themainfactorsdetermining

Figure 2Inhibitory effects of MDSC l-Arg metabolism on antigen-activated T cells. l-Arg enters MDSCs through a cationic amino acid transporter (CAT-2B) and is mainly metabolized by the inducible forms of NOS and ARG (i.e., NOS2 and ARG1, respec-tively) although the contribution of other isoforms cannot be ruled out. Depending on the balance between these enzymes, depletion of extracellular l-Arg concentration, NO release, and enhanced production of reactive oxygen and nitrogen species (for example, O2 and H2O2, and ONOO, respec-tively) can ensue. T cells that are activated in the MDSC-conditioned environment stop proliferating and eventually die by apoptosis through pathways involving activation of general control nondere-pressible 2 (GCN2) and soluble guanylate cyclase (sGC); tyrosine nitration and S-cysteine nitrosylation of various proteins; loss of CD3; and interference with the IL-2R signaling pathway (reviewed in ref. 23). cEBP-, CCAAT enhancerbinding protein ; MSP, macrophage-stimulating protein.


review series


whichl-Argmetabolizingenzymeisexpressedatthehighestlevelareasfollows:tumorhistology,anatomicalsitefromwhichtheMDSCsareisolated(spleen,blood,ortumor),geneticbackgroundofmouse(whichprobablydictatestheTh1vs.Th2orientationoftheimmuneresponse),andtypeofstimulatorysignaldeliveredtotheactivatingTcells(Table1andrefs.4446).Interestingly,asdiscussedabove,activationofARG1canlead

tolossofcellsurfaceexpressionofCD3inantigen-activatedTcellsbyconsumptionofl-Argandactivationof theaminoaciddeficiencysensorgeneralcontrolnonderepressible2(GCN2)(47,48),asensorthatisalsotriggeredbyanotheraminoacidmetabolizingenzymecausingimmunesuppression,indoleamine2,3-dioxygenase (49,50).The lossofCD3 seemstobemoreimportantforinhibitionofCD4+TcellfunctionthanofCD8+Tcellfunction(51).Indeed,splenicMDSCswereshowntoinducetheCD3chaindownregulationinantigen-stimulatedCD4+butnotCD8+Tcells(51).Moreover,CD3lossmightnotberelat-edexclusivelytotumorMDSCs,sinceMDSCsexpandedduringchronic inflammation inducedby infectionwithPorphyromo-nas gingivaliscanalsoinduceitsdownregulation(52).IthasbeenproposedthatthefunctionalroleofMDSCsistolimitchronicstimulationoftheimmuneresponseandpreventunmitigatedTcellactivation,whichcanbedangerous(53).DownregulationofCD3expressionandtheunresponsivenessofTcellsthatensuescontributetotheinflammatoryresponsebeingattenuated;i.e.,thereleaseofproinflammatorycytokinesandothermediatorsthatmightbedetrimentaltothebodywhenproducedinexcessorforaprolongedperiodisattenuated.LossofCD3Tcellsisnottheonlymechanismbywhichheight-

enedl-ArgmetabolismmediatesTcellsuppression.Forexample,CD8+tumor-infiltratinglymphocytes(TILs)presentinindividualswithprostatecancerareinhibitedbyapathwaydependentontheintratumoralactivationofARG2andNOS2(expressedbythecan-cercells),buttheseTILsdonotshowalteredexpressionofCD3

orotherprofounddefectsintheTCRsignalingpathway(54).WethereforethinkthatitisprobablethatCD3downregulationisalateeventintumorprogression,associatedwithadeeperaltera-tioninhostmyelopoiesis.

Origin and molecular basis of TAM functionsTAMsarethesecondwell-describedpopulationofmyeloidcellsthathavebeenshowntoexertanegativeeffectonantitumorimmuneresponses.TherelationshipbetweenTAMsandMDSCsisnotcompletelydefined,butdatadiscussedbelowsuggestTAMsmight,inpart,bederivedfromorrelatedtoMDSCs(Figure1andProperties of TAMs).Fordecades,solidtumorshavebeenknowntobestrongly

infiltratedbyinflammatoryleukocytes,andaccumulatingevi-dencehasclearlydemonstrated,invariousmouseandhumanmalignancies,includingcolon,breast,lung,andprostatecan-cer(32,5557),astrictcorrelationbetweenincreasednumbersand/ordensityofmacrophagesandpoorprognosis.Basedonthis,boththerecruitmentandactivationofTAMsareregardedaspivotaltotumorprogression,andTAMsareputativetargetsfortherapeuticintervention.AsoriginallydescribedbyAlbertoMantovaniandcolleaguesin

theearly1980s(57),circulatingmonocytes(Figure1)arerecruit-edtothetumor,wheretheydifferentiateintoTAMs,byatumor-derivedchemotacticfactor,originallyidentifiedasCCchemokineligand2(CCL2;alsoknownasMCP-1)(32).Followingthisobser-vation,otherchemokinesabletorecruitmonocytesweredetect-edinneoplastictissuesasproductsofeitherthetumorcellsorhoststromalelements(55).Inadditiontorecruitingmonocytes,thesemoleculesplayanimportantroleintumorprogressionbydirectlystimulatingneoplasticgrowth,promotinginflamma-tion,andinducingangiogenesis(58).Evidencesupportingapiv-otalroleforchemokines,inadditiontoCCL2,intherecruitmentofmonocytestoneoplastictissuesincludesadirectcorrelation

Properties of TAMs

TAMsarederivedfromcirculatingmonocytesthatarerecruitedtotumorsbychemotacticfactorssuchasCCL2,VEGF,andM-CSF(32,106).

TAMspreferentiallylocalizeinhypoxicareasoftumors(64,107).

M2macrophagepolarization:TAMsexpresshighlevelsofM2macrophagemarkers(IL-10,TGF-,ARG1,andthemannoserecep-tor)andlowlevelsofmediatorsofM1macrophagemediatedinflammation(IL-12,TNF-,andIL-6)(32,75,81).

TAMsexhibitdefectiveNF-BactivityandfunctionalIRF-3/STAT1pathwayactivityinresponsetoTLR4ligands(75).

TAMsexhibitthefollowingprotumoralfunctions: (a)Inductionofangiogenesisthroughexpressionoftissuefactors,VEGF,CCL2,FGF2,CXCL8,CXCL1,andCXCL2 (32,85,108,109)

(b)Productionofgrowthfactors(e.g.,PDGF,EGF,andVEGF)(85,110,111) (c)InductionofmatrixremodelingthroughtheproductionofTGF-,CCL2,andMMPssuchasMMP9(32,112) (d)Immunesuppression,throughtheproductionofimmunosuppressivecytokines(e.g.,IL-10andTGF-)(32,75,76) andtherecruitmentofTregsthroughthesecretionofCCL22(113)

(e)SkewingofadaptiveimmunitytoaTh2-typeimmuneresponsethroughtheproductionofCCL17(32),CCL18(114), andCCL22(113).

IncreasednumbersofTAMscorrelatewithvesseldensityandpoorprognosis(56).


review series


betweenchemokineproductionandmonocyteinfiltrationinmouseandhumantumors(32).Moleculesotherthanchemokinescanalsopromotemono-

cyterecruitment.Inparticular,tumor-derivedcytokinessuchasVEGFandM-CSFpromotemonocyterecruitmentaswellasmacrophagesurvivalandproliferation,andtheirexpressioncor-relateswithtumorgrowth(59).Someofthesefactors,expressedinthetumormicroenvironment,alsoinhibitthedifferentiationofmonocytesintoDCsbyactivatingSTAT3-dependentsignaling(9),therebyimpairingtheinductionofDC-inducedantigen-spe-cificimmuneresponses(60).SeverallinesofevidencesuggestthatsomecirculatingMDSCs

reachthetumorsiteandbecomepartofthetumorstroma,indi-catingthat,inadditiontoperipheralmonocytes,CD11b+Gr-1+MDSCsmightalsobeprecursorsofF4/80+TAMs.Indeed,ithasbeenshownthatGr-1+cellsisolatedfromthespleensoftumor-bearingmicecanreachthetumorandbecomeF4/80+TAMschar-acterizedbyincreasedSTAT1phosphorylationandconstitutiveexpressionofARG1andNOS2(13,27)(Figure1).Intumor-bear-inghosts,increasedbioavailabilityofVEGFandreleaseofsolubleKITligandinthebonemarrowarepromotedthroughthehighexpressionofMMP9bysplenicCD11b+Gr+cells,whichindirectlypromotetumorvascularizationandregulatethemobilizationofmoreCD11b+Gr+cells.TheseCD11b+Gr-1+cellswerealsofoundtodirectlyincorporateintothetumorendothelium(61),wheretheycontributetotumorgrowthandvascularizationbyproduc-ingMMP9anddifferentiatingintoendothelialcells.Moreover,theconceptofashareddifferentiationpathwaybetweencirculatingMDSCsandTAMs(Figure1)isreinforcedbythecommonmolec-ularpathways(activatedbyIFN-andIL-13)necessaryfortheirimmunosuppressiveactivity,aspreviouslydescribed(11).TAMspreferentiallylocalizetopoorlyvascularizedregionsof

tumors(62,63).Thisenvironmentpromotesthemetabolicadap-tationofTAMstohypoxiathroughtheactivationofhypoxia-induciblefactor1(HIF-1)andHIF-2(63).WerecentlyhaveshownthatHIF-1activatedinTAMsbyhypoxiainfluencestheposi-tioningandfunctionoftumorcells,stromalcells,andTAMsbyselectivelyupregulatingtheirexpressionofCXCchemokinerecep-tor4(CXCR4)(64).Moreover,HIF-1activationcanhavearoleintheinductionoftheCXCR4ligand,CXCchemokineligand12(CXCL12)(65),achemokineinvolvedincancermetastasis(66).Together,thesedatasuggestthatoxygenavailabilityhasaroleinguidingthemicroanatomicallocalizationandfunctionofTAMs.Moreover,hypoxiacanalsohaveimportantconsequencesonl-ArgmetabolisminTAMsandtherebyonthesuppressionofadaptiveimmunity,sinceitcaninduceNOS2andARGexpression(inthiscasewithacertainvariabilityintermsofARG1andARG2)invari-ouscelltypes(6769).InadditiontoHIF-1,analysisofthemolecularbasisofthe

TAMphenotypehasidentifiedNF-BasthemasterregulatorofTAMtranscriptionalprograms,andsomeevidencesuggeststhatmodulationofNF-Bactivityinthesecellsisanimportantmecha-nismbywhichtheirprotumoralfunctionscanbecontrolled(32).Although in inf lammatory leukocytes, in particular

macrophages,NF-Bisanessentialtranscriptionfactorguid-ingtheinflammatoryresponse,thisfactorisalsorecognizedasamajoreffectorofcancercellproliferationandsurvival(70).Incan-cer,NF-Binducesmoreaggressivetumorphenotypesbypromot-ingcellstogrowindependentlyofgrowthsignals;byincreasingtheirinsensitivitytogrowthinhibition;byincreasingtheirresis-

tancetoapoptoticsignals;byimmortalizingthecells;byenhanc-ingangiogenesis;andbyenhancingtissueinvasionandmetastasis(71).TheconstitutiveNF-Bactivationoftenobservedintumorcellsmightbepromotedbyeithersignalsfromthemicroenviron-ment,includingcytokines,hypoxia,andROS,orbygeneticaltera-tions(71).Inparticular,proinflammatorycytokines(e.g.,IL-1andTNF-)expressedbydifferentsubsetsoftumor-infiltratingleuko-cytes(72)canactivateNF-Bincancercellsandcontributetotheirproliferationandsurvival(71).Strikingly,theproliferativeroleofTNF-wasrecentlyconfirmedinprimaryandinvitroestablishedhumanrenalcarcinomacells(73).Thepeculiarabilityoftumorstopromoteleukocyterecruitmentlargelyreliesontheirconstitutiveexpressionofthegenesthatencodeinflammatorychemokines,whoseexpressioniscontrolledbyNF-B(74).Thesedataunder-pinthecentralroleofNF-BinthefunctionalcrosstalkbetweentumorsandtheimmunesystemandsuggestacausalrelationshipbetweenNF-Bmediatedinflammationandtumorigenesis(70).DifferencesareemergingabouttheeffectsofNF-Bincancer

cellsandTAMs.Incontrastwithcancercells,infact,TAMsfromadvancedtumorsshowdefectiveNF-Bactivationinresponsetodifferentproinflammatorysignals(55,75,76).ThisdefectiveNF-BactivationinTAMscorrelateswithimpairedexpressionofNF-Bdependentinflammatoryfunctions(e.g.,theexpressionofcytotoxicmediatorssuchasTNF-,IL-1,andIL-12)(32).Theseobservationsareinapparentcontrastwithaprotumorfunctionofinflammatoryreactionsobservedinmodelsofspontaneousorchemicallyinducedcarcinogenesis(77,78).Althoughintheselattermodels,NF-Binhibitionresultedintumorgrowthdelay(77,78),intumorsatamoreadvancedstageofprogression,atherapeuticeffectwasachievedthroughthereactivationofNF-Bdependentinflammationinthemyeloidcellcompartment(75,79,80).Thisdiscrepancymightreflectadynamicchangeinthetumormicro-environmentduringthetransitionfromearlyneoplasticeventstoadvancedtumorstages,whichwouldresultinprogressivemodula-tionoftheNF-BactivityexpressedbyinfiltratinginflammatorycellsandprogressiveconversionoftheTAMsfromanM1toanM2macrophagephenotype.Importantly,restorationofNF-Bactiv-ityinTAMsfromadvancedtumorsresultsinincreasedexpressionofinflammatorycytokines(e.g.,TNF-)andisassociatedwithadelayintumorgrowth(75).Sofar,NF-Bpathwayshavebeencharacterized,inpart,inTAMs,andsimilarstudiesshouldberep-licatedinMDSCs.

TAMs mediate an M2 macrophageoriented persistent inflammationCharacterizationofthetranscriptomeofTAMsisolatedfromamousefibrosarcomaconfirmedthatthesecellsmainlyhaveanM2macrophagephenotypebutalsoexpressIFN-inducibleche-mokines(acharacteristicofM1macrophages) (81).Asimilarmixtureofgeneprofiles(mostlyanM2profilewithM1traits)wasalsorecentlyfoundinmouseMDSCs(11).ThemainlyM2macrophagelikephenotypeofTAMsisassociatedwiththemhav-ingprotumoralfunction.Evidenceforthiscomesfromanumberofstudies.First,pharmacologicalskewingofTAMpolarizationfromanM2macrophagelikephenotypetoafullM1macro-phagephenotypesustainsantitumorimmunity(79,82).Indeed,acombinationofCpGoligodeoxynucleotidesandanIL-10recep-torspecificantibodyswitchedTAMsfromanM2toanM1mac-rophagelikephenotypeandtriggeredaninnateresponsethatwasabletodebulklargetumorswithin16hours(82).Second,


review series


recentresultssuggestthatSRChomology2domaincontaininginositol-5-phosphatase(SHIP)functionsinvivotorepressskew-ingtoanM2macrophagelikephenotype.PeritonealandalveolarmacrophagesisolatedfromShip/miceconstitutivelyexpresshighlevelsofARG1andshowimpairedLPS-inducedNOproduction.Consistentwiththis,transplantedtumorsgrowmorerapidlyinShip/micethaninwild-typemice(83,84).Third,aDNAvac-cineagainsttheM2macrophageassociatedmoleculelegumain,whichishighlyexpressedbyTAMs,inducedarobustCD8+Tcell

responseagainstTAMs,reducingtheirdensityintumortissuesandleadingtothesuppressionofangiogenesis,tumorgrowth,andmetastasis(85).Finally,wehaverecentlydemonstratedthatTAMsarecharacterizedbynuclearlocalizationoftheinhibitoryp50NF-Bhomodimer,aphenotypeassociatedwithtumorprogres-sionandalackofM1macrophagelikefunction(75).Interest-ingly, theM2macrophageinducingsignalsPGE2, IL-10,andTGF-wereshowntopromoteincreasednuclearlocalizationofthep50NF-Bhomodimer(75).Moreover,micelackingexpres-

Figure 3Molecular pathways of macrophage polarization and their role in tumor progression. The major pathways of macrophage polarization and cur-rent evidence linking their activation with either tumor progression (+) or regression () are outlined. The overall view suggests that M2 macro-phagepolarizing signals (such as IL-10, IL-4, and IL-13) are mainly associated with tumor progression. Contrasting evidence associates M1 macrophagepolarizing pathways (such as IFN- and TLR ligation) with either tumor progression or regression. The crosstalk between the M1 and M2 macrophagepolarizing pathways, which results in reciprocal modulation, are also indicated. As shown, IL-10mediated induction of the p50 NF-B homodimer interferes with NF-B activation and M1 macrophageinduced inflammation. The balance between activation of M1 macrophageassociated STAT1 and M2 macrophageassociated STAT3 and STAT6 finely regulates macrophage polarization and activity. A predominance of NF-B and STAT1 activation results in M1 macrophage polarization, which promotes cytotoxic and inflammatory functions. In contrast, a predominance of STAT3 and STAT6 activation results in M2 macrophage polarization, which is associated with immune suppression and tumor progression. As discussed in the text, IL-23 might also contribute to the polarization decision as it activates different STATs, includ-ing STAT1 and STAT3, in TAMs, but direct evidence is missing. CC, colorectal carcinoma; HCC, hepatocarcinoma; Fibr, fibrosarcoma; Mel, melanoma; BC, breast carcinoma; SCC, squamous cell carcinoma; Bl. Carc, bladder carcinoma.


review series


sionofp50alsolackexpressionoftheM2macrophagepolarizingcytokinesIL-4,IL-5,andIL-13(86),andintumor-bearingmicelackingexpressionofp50,TAMsexpresscytokinescharacteristicofM1macrophages,andsplenocytesproduceTh1cytokines,bothofwhichareassociatedwithadelayintumorgrowth(75).AllthesefindingstogethersuggestthatM2macrophagelike

inflammationfuelscancerprogressionandleadtothesugges-tionthatNF-BinhibitioninTAMsisassociatedwithM2macro-phagelikeinflammatoryfunctions.Itisprobablethat,althoughfullactivationofNF-Binmacrophagesresidentinpreneoplas-ticsitesmightexacerbatelocalM1macrophagelikeinflamma-tionandfavortumorigenesis(77,78,87),tumorgrowthresultsinprogressiveinhibitionofNF-Bininfiltratingleukocytes,asobservedinbothmyeloid(75,88)andlymphoid(89)cellsfromindividualswithtumors,andintheprogressiveskewingtoM2macrophagelikeinflammation.Ifso,thetherapeuticefficacyofstrategiestargetingNF-Bforthetreatmentofcancersmightbedeterminedbyboththetumorstageandpolarizationstatusoftheinfiltratingleukocytes.

STATs in TAM and MDSC functionAcentralroleinthepolarizationofmyeloidcellfunctionsaswellasintumorprogressionandthealteredimmuneresponsetocan-cerisemergingforselectedmembersoftheSTATfamilyoftran-scriptionfactors.Inparticular,STAT1,STAT3,andSTAT6havebeenshowntohaveamajorroleintransmittingpolarizingsig-nalstothenucleus(90)andtohavedistinctrolesinmacrophagepolarization(Figure3).STAT1isactivatedinresponsetoM1mac-rophagepolarizingsignals(e.g.,IFN-andLPS)whereasSTAT3andSTAT6areselectivelyactivatedbyM2macrophagepolarizingcytokines(e.g.,IL-10,IL-4,andIL-13)(91).ActivationofspecificSTATs,centralinducersofmacrophagepolarizationprograms,isexpectedtoparalleleithertheantitumoralorprotumoralroleofM1andM2macrophagemediatedinflammation,respectively.OriginalevidenceindicatesthatSTAT1activationisessential

forimmunesurveillanceagainsttumors(92).Inparticular,micedeficientforeithertheIFN-receptor(signalingthroughwhichactivatesSTAT1;ref.93)orSTAT1displayedenhancedresistancetotheinductionoftumorsbymethylcholanthrene(94).Overtheyears,theSTAT1-mediatedantitumoraleffecthasbeenconfirmedinpreclinicaltumormodels(95,96).However,recentreportsargueagainstthissimpleviewandsuggestthattheIFN-/STAT1pathwaymighthaveaprotumoralrole,atleastincertaintumors.Forexam-ple,STAT1wasrecentlydescribedasresponsibleforTAM-mediatedsuppressiveactivityandtumorprogression,anditwasshownthatTAMsisolatedfromSTAT1-deficientmicefailedtosuppressTcellresponses(13).Inaddition,inamousesquamouscellcarcinoma,STAT1deficiencyenhancedIL-12mediatedtumorregressionbyaTcelldependentmechanism(97).InagreementwiththeroleofSTAT1asthecentralmediatorofthebiologicalactivitiesofIFN-,administrationofneutralizingantibodiesspecificforIFN-inhib-itedtumorgrowthinIL-12treatedStat1+/+mice(97).Morerecent-ly,ithasalsobeenshownthatactivationoftheCD8+Tcellsuppres-siveactivityoftumor-inducedMDSCsrequirestheactionofIFN-,thoughincombinationwithIL-13(11).Inlinewiththispicture,micelackingSOCS1,whicharecharacterizedbyhyperactivationofSTAT1,displayspontaneousdevelopmentofcolorectalcarcino-mas(98),supportingtheideathatpersistentactivationofSTAT1-dependentsignalingmightbeassociatedwithtumorprogression.Interestingly,molecularanalysisofthetranscriptomeofTAMs

showedthatthesecellsexpresshighlevelsofIFN-induciblechemo-kinesandSTAT1activity(81).Together,theseresultssuggestthat,alongwithapredominantexpressionofM2macrophagepolarizedfunctionsinTAMsandMDSCs,theparallelactivationofSTAT1inthesecellsmightenhanceimmunedysfunctions,furtherfavoringtumorprogression.ThiscontrastingevidenceontheinfluenceofSTAT1mightbeexplainedbydifferencesamongthetumormodelsinvestigated,thestateoftumorprogression,andthenumberandtypeofinfiltratingleukocytes.STAT3andSTAT6activationareassociatedwithM2macrophage

polarization(32,91).IthasbeenshownthatSTAT3isconstitu-tivelyactivatedintumorcells(99)andindiversetumor-infiltrat-ingimmunecells,includingTAMs(80),leadingtoinhibitionofproinflammatorycytokineandchemokineproductionandtothereleaseoffactorsthatsuppressDCmaturation.AblatingSTAT3inhematopoieticcellstriggersanintrinsicimmunesurveillancesystemthatinhibitstumorgrowthandmetastasisandisassociatedwithenhancedfunctionalactivityofDCs,Tcells,NKcells,andneutro-phils(80).STAT3/JAK2activationinmyeloidcellsbytumor-derivedfactorscanleadtotheaccumulationofCD11b+Gr-1+MDSCs,pre-ventingtheirdifferentiationintomatureDCs,whereasinterferingwithSTAT3signalingreversestheseinhibitoryeffects(100,101).TAMsfromStat6/tumor-bearingmicedisplayanM1macrophagephenotype,withlowlevelsofexpressionofARG1andhighlevelsofexpressionofNOS2,whichpromotestumorcelldeaththroughthecytotoxicactivityofthehighlevelsofNOthatareproduced.Asaresult,thesemicerejectedspontaneousmammarycarcinomasinanimmunesystemdependentmanner(20,102).Therefore,althoughcurrentliteraturestronglysuggestsacrucialroleforpolar-izedinflammationincancerprogression,additionalstudiesshouldclarifywhetheraccumulatingandcontrastingevidencemightbeascribedtospecificmicroenvironmentalconditionsorrelatedtotumortypeand/orstageofdisease.TherecentobservationthatthecytokineIL-23,amemberof

the IL-12cytokine family, isexpressed inhumanandmousetumorshasunveiledanotherpotentialplayerinTAM-depen-dentimmunosuppression.Inmousetumormodels,expressionofthemRNAencodingtheIL-23p19subunitwasincreasedinCD11b+andCD11c+cells(probablyTAMsandDCs)presentintumorstroma.SimilarlytoIL-12,IL-23promotes inflamma-toryresponses,buttheneteffectofthecytokineisdeleteriousforantitumorimmunity.IL-23,infact,promotesupregulationofMMP9andincreasestumorangiogenesisbutreducesCD8+Tcellinfiltration(103).Importantly,geneticdeletionstudiesandantibody-mediatedneutralizationofIL-23havedemonstratedadirectnegativeeffectofthecytokineontumorimmunesurveil-lance(103).Furthermore,IL-23stimulationcanactivateSTAT1,STAT3,STAT4,andSTAT5andleadtoenhancedproductionofIL-6(104);itthereforemighthaveanimportantroleininfluenc-ingtheTAMtranscriptomeandfunction.

For the future: therapeutic perspectivesMDSCsandTAMsprobablyrepresentacontinuumofauniquemyeloidcelldifferentiationprograminducedbytumor-derivedfactorstosupportanincessant influxofcellsthataidtumorinvasionofnearbytissues,stromaremodeling,andcellprolifera-tionandthatinhibittheinnateandadaptiveantitumorimmuneresponse.Targetingthisdynamicprocessmightofferinterestingperspectivesfornewtherapiesforthetreatmentofcancer(4,79).Inapplyingnovelapproachestorelievingtheimmunosuppression


review series


inducedbyMDSCsandTAMs,oneaspectmustbeconsidered:therelativecontributionofMDSCsandTAMstotheoverallimpair-mentofantitumorTcellresponseshasnotbeenclearlyestimated.ItisprobablethatinhibitionofCD8+TcellantitumorimmunitybyMDSCsandTAMsintumor-bearinghostsmightoccurindif-ferentplaces,primarilythetumorsiteandthedraininglymphnodesbutalsodistantsitesoftheimmunesystem.MDSCsandTAMsmightalsoaffectdifferentlythesubsetsofcirculatingCD8+Tcellsinrelationtothespreadofmalignanttumorsindifferentpatients.WethinkthatcombiningprotocolsthatinterferewithMDSC-and/orTAM-mediatedimmunesuppressionwitheithercancervaccination(activeimmunotherapy)ortheadoptivetrans-ferofexvivoexpandedtumor-infiltratingTcells(passiveimmu-notherapy)mightprovidetherapeuticbenefitforthetreatment

ofcancer.However,thebenefitofsuchcombinationapproachesislikelytodifferineverypatientaccordingtothestateofimpair-mentoftheantitumorimmuneresponse.

AcknowledgmentsWethankAlbertoMantovaniforhiscriticalreadingandconstantsuggestions.ThisworkhasbeensupportedbygrantsfromtheItal-ianMinistryofHealth,theItalianFoundationforMultipleSclero-sis(FISM),theItalianAssociationforCancerResearch(AIRC),andtheEuropeanCommunity.

Addresscorrespondenceto:VincenzoBronte,IstitutoOncologicoVeneto,ViaGattamelata64,35128Padua,Italy.Phone:39-049-8215897;Fax:39-049-8072854;E-mail:[email protected].

1.Mocellin,S.,etal.2004.PartI:Vaccinesforsolidtumours.Lancet Oncol.5:681689.

2.Rosenberg,S.A.,Yang,J.C.,andRestifo,N.P.2004.Cancerimmunotherapy:movingbeyondcurrentvaccines.Nat. Med.10:909915.

3.Rabinovich,G.A.,Gabrilovich,D., and Soto-mayor,E.M.2007.Immunosuppressivestrate-giesthataremediatedbytumorcells.Annu. Rev. Immunol.25:267296.

4.Serafini, P., Borrello, I., and Bronte, V. 2006.Myeloidsuppressorcellsincancer:recruitment,phenotype, properties, and mechanisms ofimmunesuppression.Semin. Cancer Biol.16:5365.

5.Maier,T.,Holda,J.H.,andClaman,H.N.1989.Natu-ralsuppressorcells.Prog. Clin. Biol. Res.288:235244.

6.Seung,L.P.,Rowley,D.A.,Dubey,P.,andSchreiber,H.1995.SynergybetweenT-cellimmunityandinhi-bitionofparacrinestimulationcausestumorrejec-tion.Proc. Natl. Acad. Sci. U. S. A.92:62546258.

7.Pekarek,L.A.,Starr,B.A.,Toledano,A.Y.,andSch-reiber,H.1995.Inhibitionoftumorgrowthbyelim-inationofgranulocytes.J. Exp. Med.181:435440.

8.Kusmartsev,S.,andGabrilovich,D.I.2006.Roleofimmaturemyeloidcellsinmechanismsofimmuneevasion in cancer.Cancer Immunol. Immunother.55:237245.

9.Gabrilovich,D.2004.Mechanismsandfunctionalsignificance of tumour-induced dendritic-celldefects.Nat. Rev. Immunol.4:941952.

10.Gabrilovich,D.I.,etal.2007.Theterminologyissueformyeloid-derivedsuppressorcells.Cancer Res.67:425;authorreply426.

11.Gallina,G.,etal.2006.TumorsinduceasubsetofinflammatorymonocyteswithimmunosuppressiveactivityonCD8Tcells.J. Clin. Invest.116:27772790.doi:10.1172/JCI28828.

12.VanGinderachter, J.A., etal.2006.Peroxisomeproliferator-activatedreceptorgamma(PPARga-mma)ligandsreverseCTLsuppressionbyalterna-tivelyactivated(M2)macrophagesincancer.Blood.108:525535.

13.Kusmartsev,S.,andGabrilovich,D.I.2005.STAT1signalingregulatestumor-associatedmacrophage-mediatedTcelldeletion.J. Immunol.174:48804891.

14.Tsuda,Y.,etal.2004.Threedifferentneutrophilsubsetsexhibitedinmicewithdifferentsuscepti-bilitiestoinfectionbymethicillin-resistantStaphy-lococcusaureus.Immunity.21:215226.

15.Zea,A.H.,etal.2005.Arginase-producingmyeloidsuppressorcellsinrenalcellcarcinomapatients:a mechanism of tumor evasion. Cancer Res.65:30443048.

16.Schmielau,J.,andFinn,O.J.2001.Activatedgranu-locytesandgranulocyte-derivedhydrogenperoxidearetheunderlyingmechanismofsuppressionoft-cellfunctioninadvancedcancerpatients.Cancer Res.61:47564760.

17.Bronte,V.,etal.1999.Unopposedproductionofgranulocyte-macrophagecolony-stimulatingfac-

torbytumorsinhibitsCD8+Tcellresponsesbydysregulatingantigen-presentingcellmaturation.J. Immunol.162:57285737.

18.Melani,C.,Chiodoni,C.,Forni,G.,andColombo,M.P.2003.Myeloidcellexpansionelicitedbytheprogressionofspontaneousmammarycarcinomasinc-erbB-2transgenicBALB/cmicesuppressesimmunereactivity.Blood.102:21382145.

19.Kusmartsev, S., Nefedova, Y., Yoder, D., andGabrilovich,D.I.2004.Antigen-specificinhibitionofCD8+Tcellresponsebyimmaturemyeloidcellsincancerismediatedbyreactiveoxygenspecies.J. Immunol.172:989999.

20.Sinha,P.,Clements,V.K.,andOstrand-Rosenberg,S.2005.Reductionofmyeloid-derivedsuppressorcellsandinductionofM1macrophagesfacilitatethe rejectionof establishedmetastaticdisease.J. Immunol.174:636645.

21.Terabe,M.,etal.2000.NKTcell-mediatedrepres-sionoftumorimmunosurveillancebyIL-13andtheIL-4R-STAT6pathway.Nat. Immunol.1:515520.

22.Terabe,M.,etal.2003.Transforminggrowthfac-tor-{beta}productionandmyeloid cells are aneffectormechanismthroughwhichCD1d-restrict-edTcellsblockcytotoxicTlymphocyte-mediatedtumorimmunosurveillance:abrogationpreventstumorrecurrence.J. Exp. Med.198:17411752.

23.Bronte,V., andZanovello,P. 2005.RegulationofimmuneresponsesbyL-argininemetabolism[review].Nat. Rev. Immunol.5:641654.

24.Gabrilovich,D.I.,Velders,M.P.,Sotomayor,E.M.,andKast,W.M.2001.Mechanismofimmunedys-functionincancermediatedbyimmaturegr-1(+)myeloidcells.J. Immunol.166:53985406.

25.Otsuji,M.,etal.1996.Oxidativestressbytumor-derivedmacrophagessuppressestheexpressionofCD3zetachainofT-cellreceptorcomplexandanti-gen-specificT-cellresponses.Proc. Natl. Acad. Sci. U. S. A.93:1311913124.

26.Huang,B., et al. 2006.Gr-1+CD115+ immaturemyeloidsuppressorcellsmediatethedevelopmentoftumor-inducedTregulatorycellsandT-cellanergyintumor-bearinghost.Cancer Res.66:11231131.

27.Kusmartsev, S., Nagaraj, S., and Gabrilovich,D.I.2005.Tumor-associatedCD8+Tcell toler-anceinducedbybonemarrow-derivedimmaturemyeloidcells.J. Immunol.175:45834592.

28.Bronte,V.,etal.1998.ApoptoticdeathofCD8+Tlymphocytesafterimmunization:inductionofasuppressivepopulationofMac-1+/Gr-1+cells.J. Immunol.161:53135320.

29.Serafini,P.,etal.2006.Phosphodiesterase-5inhibi-tionaugmentsendogenousantitumorimmunitybyreducingmyeloid-derivedsuppressorcellfunc-tion.J. Exp. Med.203:26912702.

30.Yang,R.,etal.2006.CD80inimmunesuppres-sionbymouseovariancarcinoma-associatedGr-1+CD11b+myeloidcells.Cancer Res.66:68076815.

31.Gordon, S. 2003. Alternative activation of

macrophages.Nat. Rev. Immunol.3:2335. 32.Mantovani,A.,etal.2002.Macrophagepolariza-

tion:tumor-associatedmacrophagesasaparadigmforpolarizedM2mononuclearphagocytes.Trends Immunol.23:549555.

33.Mantovani,A.,etal.2004.Thechemokinesystemindiverse formsofmacrophageactivationandpolarization.Trends Immunol.25:677686.

34.Ganster,R.W.,Taylor,B.S.,Shao,L.,andGeller,D.A.2001.Complexregulationofhumaninduc-iblenitricoxidesynthasegenetranscriptionbyStat1andNF-kappaB.Proc. Natl. Acad. Sci. U. S. A.98:86388643.

35.Kleinert,H.,Schwarz,P.M.,andForstermann,U.2003.Regulationoftheexpressionofinduciblenitricoxidesynthase.Biol. Chem.384:13431364.

36.Melillo,G.,etal.1995.Ahypoxia-responsiveele-mentmediatesanovelpathwayofactivationoftheinduciblenitricoxidesynthasepromoter.J. Exp. Med.182:16831693.

37.Boutard,V.,etal.1995.Transforminggrowthfactor-betastimulatesarginaseactivityinmacrophages.Implications for the regulationofmacrophagecytotoxicity.J. Immunol.155:20772084.

38.Morrison,A.C.,andCorrell,P.H.2002.Activationofthestemcell-derivedtyrosinekinase/RONrecep-tor tyrosinekinasebymacrophage-stimulatingproteinresultsintheinductionofarginaseactiv-ityinmurineperitonealmacrophages.J. Immunol.168:853860.

39.Jost,M.M.,etal.2003.DivergenteffectsofGM-CSFandTGFbeta1onbonemarrow-derivedmac-rophagearginase-1activity,MCP-1expression,andmatrixmetalloproteinase-12:apotentialroledur-ingarteriogenesis.FASEB J.17:22812283.

40.Munder,M., Eichmann, K., andModolell,M.1998. Alternative metabolic states in murinemacrophages reflectedby thenitricoxide syn-thase/arginasebalance:competitiveregulationbyCD4+TcellscorrelateswithTh1/Th2phenotype.J. Immunol.160:53475354.

41.Raes,G.,etal.2005.Arginase-1andYm1aremark-ersformurine,butnothuman,alternativelyacti-vatedmyeloidcells.J. Immunol.174:6561;authorreply65616562.

42.Munder,M., et al. 2006.SuppressionofT cellfunctionsbyhumangranulocytearginase.Blood.108:16271634.

43.Rodriguez,P.C.,andOchoa,A.C.2006.Tcelldys-functionincancer:roleofmyeloidcellsandtumorcellsregulatingaminoacidavailabilityandoxida-tivestress.Semin. Cancer Biol.16:6672.

44.Bronte,V.,etal.2003.IL-4-inducedarginase1sup-pressesalloreactiveTcellsintumor-bearingmice.J. Immunol.170:270278.

45.Mazzoni,A.,etal.2002.Myeloidsuppressorlinesinhibit T cell responses by anNO-dependentmechanism.J. Immunol.168:689695.

46.Apolloni,E.,etal.2000.Immortalizedmyeloidsup-


review series


pressorcellstriggerapoptosisinantigen-activatedTlymphocytes.J. Immunol.165:67236730.

47.Rodriguez,P.C., etal.2004.Arginase Iproduc-tioninthetumormicroenvironmentbymaturemyeloidcellsinhibitsT-cellreceptorexpressionandantigen-specificT-cellresponses.Cancer Res.64:58395849.

48.Rodriguez,P.C.,Quiceno,D.G.,andOchoa,A.C.2006.L-ArginineavailabilityregulatesTlympho-cytecellcycleprogression.Blood.109:15681573.

49.Fallarino,F.,etal.2006.Thecombinedeffectsoftryptophan starvationand tryptophancatabo-litesdown-regulateTcellreceptorzeta-chainandinducearegulatoryphenotype innaiveTcells.J. Immunol.176:67526761.

50.Munn,D.H.,etal.2005.GCN2kinaseinTcellsmediatesproliferativearrestandanergyinductioninresponsetoindoleamine2,3-dioxygenase.Immu-nity.22:633642.

51.Sinha,P.,Clements,V.K.,andOstrand-Rosenberg,S.2005.Interleukin-13-regulatedM2macrophagesincombinationwithmyeloidsuppressorcellsblockimmunesurveillanceagainstmetastasis.Cancer Res.65:1174311751.

52.Ezernitchi,A.V.,etal.2006.TCRzetadown-regula-tionunderchronicinflammationismediatedbymyeloidsuppressorcellsdifferentiallydistributedbetween various lymphatic organs. J. Immunol.177:47634772.

53.Baniyash,M.2004.TCRzeta-chaindownregula-tion:curtailinganexcessiveinflammatoryimmuneresponse.Nat. Rev. Immunol.4:675687.

54.Bronte,V.,etal.2005.Boostingantitumorrespons-esofTlymphocytesinfiltratinghumanprostatecancers.J. Exp. Med.201:12571268.

55.Sica,A.,Schioppa,T.,Mantovani,A.,andAllavena,P.2006.Tumour-associatedmacrophagesareadis-tinctM2polarisedpopulationpromotingtumourprogression:potentialtargetsofanti-cancerthera-py.Eur. J. Cancer.42:717727.

56.Bingle,L.,Brown,N.J.,andLewis,C.E.2002.Theroleoftumour-associatedmacrophagesintumourprogression:implicationsfornewanticancerthera-pies.J. Pathol.196:254265.

57.Mantovani,A.,etal.1992.Theoriginandfunctionoftumor-associatedmacrophages.Immunol. Today.13:265270.

58.Balkwill,F.2003.Chemokinebiologyincancer.Semin. Immunol.15:4955.

59.Pollard,J.W.2004.Tumour-educatedmacrophagespromotetumourprogressionandmetastasis.Nat. Rev. Cancer.4:7178.

60.Mellman,I.,andSteinman,R.M.2001.Dendriticcells:specializedandregulatedantigenprocessingmachines.Cell.106:255258.

61.Yang,L.,etal.2004.ExpansionofmyeloidimmunesuppressorGr+CD11b+cellsintumor-bearinghostdirectlypromotestumorangiogenesis.Cancer Cell.6:409421.

62.Lewis,C.E.,andPollard,J.W.2006.Distinctroleofmacrophagesindifferenttumormicroenviron-ments.Cancer Res.66:605612.

63.Leek,R.D.,etal.2002.Relationofhypoxia-induc-ible factor-2alpha (HIF-2alpha) expression intumor-infiltrativemacrophagestotumorangio-genesisandtheoxidativethymidinephosphory-lasepathwayinhumanbreastcancer.Cancer Res.62:13261329.

64.Schioppa,T.,etal.2003.Regulationoftheche-mokinereceptorCXCR4byhypoxia.J. Exp. Med.198:13911402.

65.Ceradini,D.J.,etal.2004.ProgenitorcelltraffickingisregulatedbyhypoxicgradientsthroughHIF-1inductionofSDF-1.Nat. Med.10:858864.

66.Muller,A.,etal.2001.Involvementofchemokinereceptors in breast cancer metastasis. Nature.410:5056.

67.Albina,J.E.,etal.2005.Macrophagearginaseregu-

lationbyCCAAT/enhancer-bindingproteinbeta.Shock.23:168172.

68.Morris,S.M.,Jr.2002.Regulationofenzymesoftheureacycleandargininemetabolism.Annu. Rev. Nutr.22:87105.

69.Semenza,G.L.2003.TargetingHIF-1forcancertherapy.Nat. Rev. Cancer.3:721732.

70.Karin,M., andGreten, F.R. 2005.NF-kappaB:linking inflammationand immunity to cancerdevelopmentandprogression.Nat. Rev. Immunol.5:749759.

71.Karin,M.,andLin,A.2002.NF-kappaBatthecross-roadsoflifeanddeath.Nat. Immunol.3:221227.

72.Balkwill,F.,Charles,K.A.,andMantovani,A.2005.Smolderingandpolarizedinflammationintheini-tiationandpromotionofmalignantdisease.Cancer Cell.7:211217.

73.Falkensammer,C.,etal.2006.IL-4 inhibitstheTNF-alphainducedproliferationofrenalcellcar-cinoma(RCC)andcooperateswithTNF-alphatoinduceapoptoticandcytokineresponsesbyRCC:implications forantitumor immuneresponses.Cancer Immunol. Immunother.55:12281237.

74.Richmond,A.2002.Nf-kappaB,chemokinegenetranscriptionandtumourgrowth.Nat. Rev. Immu-nol.2:664674.

75.Saccani,A.,etal.2006.p50nuclearfactor-{kappa}Boverexpressionintumor-associatedmacrophagesinhibitsM1inflammatoryresponsesandantitu-morresistance.Cancer Res.66:1143211440.

76.Sica,A.,etal.2000.AutocrineproductionofIL-10mediatesdefectiveIL-12productionandNF-kappaBactivation in tumor-associatedmacrophages.J. Immunol.164:762767.

77.Greten,F.R.,andKarin,M.2004.TheIKK/NF-kap-paBactivationpathway-atargetforpreventionandtreatmentofcancer.Cancer Lett.206:193199.

78.Pikarsky,E.,etal.2004.NF-kappaBfunctionsasatumourpromoterininflammation-associatedcancer.Nature.431:461466.

79.Colombo,M.P.,andMantovani,A.2005.Targetingmyelomonocyticcellstorevertinflammation-depen-dentcancerpromotion.Cancer Res.65:91139116.

80.Kortylewski,M.,etal.2005.InhibitingStat3signal-inginthehematopoieticsystemelicitsmulticompo-nentantitumorimmunity.Nat. Med.11:13141321.

81.Biswas,S.K.,etal.2006.Adistinctanduniquetran-scriptionalprogramexpressedbytumor-associatedmacrophages(defectiveNF-kappaBandenhancedIRF-3/STAT1activation).Blood.107:21122122.

82.Guiducci,C.,etal.2005.Redirectinginvivoelicitedtumorinfiltratingmacrophagesanddendriticcellstowardstumorrejection.Cancer Res.65:34373446.

83.Rauh,M.J.,etal.2005.SHIPrepressesthegenera-tionofalternativelyactivatedmacrophages.Immu-nity.23:361374.

84.Mantovani,A.,Sica,A.,andLocati,M.2005.Mac-rophage polarization comes of age. Immunity.23:344346.

85.Luo,Y.,etal.2006.Targetingtumor-associatedmacrophagesasanovel strategyagainstbreastcancer.J. Clin. Invest.116:21322141.doi:10.1172/JCI27648.

86.Das,J.,etal.2001.AcriticalroleforNF-kappaBinGATA3expressionandTH2differentiationinaller-gicairwayinflammation.Nat. Immunol.2:4550.

87.Moore,R.J.,etal.1999.Micedeficientintumornecrosisfactor-alphaareresistanttoskincarcino-genesis.Nat. Med.5:828831.

88.Sica,A.,etal.2000.Defectiveexpressionofthemonocytechemotacticprotein-1receptorCCR2inmacrophagesassociatedwithhumanovariancarci-noma.J. Immunol.164:733738.

89.Ghosh,P.,etal.1994.AlterationsinNFkappaB/RelfamilyproteinsinsplenicT-cellsfromtumor-bearingmiceandreversalfollowingtherapy.Cancer Res.54:29692972.

90.Yoshimura,A.2006.Signaltransductionofinflam-

matorycytokinesandtumordevelopment.Cancer Sci.97:439447.

91.OShea,J.J.,Pesu,M.,Borie,D.C.,andChangelian,P.S.2004.Anewmodalityforimmunosuppression:targetingtheJAK/STATpathway.Nat. Rev. Drug Discov.3:555564.

92.Dunn,G.P.,Koebel,C.M.,andSchreiber,R.D.2006.Interferons,immunityandcancerimmunoediting.Nat. Rev. Immunol.6:836848.

93.Bach,E.A.,Aguet,M.,andSchreiber,R.D.1997.TheIFNgammareceptor:aparadigmforcytokinerecep-torsignaling.Annu. Rev. Immunol.15:563591.

94.Kaplan,D.H.,etal.1998.Demonstrationofaninterferongamma-dependenttumorsurveillancesysteminimmunocompetentmice.Proc. Natl. Acad. Sci. U. S. A.95:75567561.

95.Lesinski,G.B.,etal.2003.TheantitumoreffectsofIFN-alphaareabrogatedinaSTAT1-deficientmouse.J. Clin. Invest.112:170180.doi:10.1172/JCI200316603.

96.Zhou,Y.,Wang,S.,Gobl,A.,andOberg,K.2001.InterferonalphainductionofStat1andStat2andtheirprognosticsignificanceincarcinoidtumors.Oncology.60:330338.

97.Torrero,M.N.,etal.2006.Stat1deficiencyinthehost enhances interleukin-12-mediated tumorregression.Cancer Res.66:44614467.

98.Hanada,T.,etal.2006.IFNgamma-dependent,spon-taneousdevelopmentofcolorectalcarcinomasinSOCS1-deficientmice.J. Exp. Med.203:13911397.

99.Wang,T.,etal.2004.RegulationoftheinnateandadaptiveimmuneresponsesbyStat-3signalingintumorcells.Nat. Med.10:4854.

100.Nefedova,Y.,etal.2004.HyperactivationofSTAT3isinvolvedinabnormaldifferentiationofdendriticcellsincancer.J. Immunol.172:464474.

101.Nefedova,Y.,etal.2005.Activationofdendriticcells via inhibition of Jak2/STAT3 signaling.J. Immunol.175:43384346.

102.Ostrand-Rosenberg,S.,etal.2002.ResistancetometastaticdiseaseinSTAT6-deficientmicerequireshemopoieticandnonhemopoieticcellsandisIFN-gammadependent.J. Immunol.169:57965804.

103.Langowski,J.L.,etal.2006.IL-23promotestumourincidenceandgrowth.Nature.442:461465.

104.Watford,W.T.,etal.2004.SignalingbyIL-12andIL-23andtheimmunoregulatoryrolesofSTAT4.Immunol. Rev.202:139156.

105.Serafini,P.,etal.2004.High-dosegranulocyte-macrophagecolony-stimulatingfactor-producingvaccinesimpairtheimmuneresponsethroughtherecruitmentofmyeloidsuppressorcells.Cancer Res.64:63376343.

106.Condeelis,J.,andPollard,J.W.2006.Macrophages:obligatepartnersfortumorcellmigration,inva-sion,andmetastasis.Cell.124:263266.

107.Talks,K.L.,etal.2000.Theexpressionanddistribu-tionofthehypoxia-induciblefactorsHIF-1alphaandHIF-2alphainnormalhumantissues,cancers,andtumor-associatedmacrophages.Am. J. Pathol.157:411421.

108.Bolat,F.,etal.2006.Microvesseldensity,VEGFexpression,andtumor-associatedmacrophagesinbreasttumors:correlationswithprognosticparam-eters.J. Exp. Clin. Cancer Res.25:365372.

109.Ueno,T.,etal.2000.Significanceofmacrophagechemoattractantprotein-1inmacrophagerecruit-ment,angiogenesis,andsurvivalinhumanbreastcancer.Clin. Cancer Res.6:32823289.

110.Kataki,A.,etal.2002.Tumorinfiltratinglympho-cytesandmacrophageshaveapotentialdualroleinlungcancerbysupportingbothhost-defenseandtumorprogression.J. Lab. Clin. Med.140:320328.

111.OSullivan,C.,Lewis,C.E.,Harris,A.L.,andMcGee,J.O.1993.Secretionofepidermalgrowthfactorbymacrophagesassociatedwithbreastcarcinoma.Lancet.342:148149.

112.vanKempen,L.C.,andCoussens,L.M.2002.MMP9


review series


potentiatespulmonarymetastasisformation.Can-cer Cell.2:251252.

113.Curiel,T.J.,etal.2004.Specificrecruitmentofregu-latoryTcellsinovariancarcinomafostersimmuneprivilegeandpredictsreducedsurvival.Nat. Med.10:942949.

114.Schutyser,E.,etal.2002.Identificationofbiologi-callyactivechemokineisoformsfromasciticfluidandelevatedlevelsofCCL18/pulmonaryandacti-vation-regulatedchemokineinovariancarcinoma.J. Biol. Chem.277:2458424593.

115.Bronte,V.,etal.2000.IdentificationofaCD11b+/Gr-1+/CD31+myeloidprogenitorcapableofactivatingorsuppressingCD8+Tcells.Blood.96:38383846.

116.Saio,M.,Radoja,S.,Marino,M.,andFrey,A.B.2001. Tumor-infiltratingmacrophages induceapoptosisinactivatedCD8(+)Tcellsbyamecha-nismrequiringcellcontactandmediatedbyboththecell-associatedformofTNFandnitricoxide.

J. Immunol.167:55835593.117.Young,M.R., et al.1996.SuppressionofTcell

proliferationbytumor-inducedgranulocyte-mac-rophageprogenitorcellsproducingtransforminggrowthfactor-betaandnitricoxide.J. Immunol.156:19161922.

118.Liu,Y.,etal.2003.Nitricoxide-independentCTLsuppressionduringtumorprogression:associa-tionwitharginase-producing(M2)myeloidcells.J. Immunol.170:50645074.

119.Mencacci,A.,etal.2002.CD80+Gr-1+myeloidcellsinhibitdevelopmentofantifungalTh1immunityinmicewithcandidiasis.J. Immunol.169:31803190.

120.Goni, O., Alcaide, P., and Fresno, M. 2002.Immunosuppression during acute Trypano-soma cruzi infection: involvement of Ly6G(Gr1(+))CD11b(+)immaturemyeloidsuppressorcells.Int. Immunol.14:11251134.

121.Marshall,M.A., et al. 2001.Mice infectedwith

Schistosomamansonidevelopanovelnon-T-lym-phocyte suppressor populationwhich inhibitsvirus-specificCTLinductionviaasolublefactor.Microbes Infect.3:10511061.

122.Brys,L.,etal.2005.Reactiveoxygenspeciesand12/15-lipoxygenasecontributetotheantiprolif-erativecapacityofalternativelyactivatedmyeloidcellselicitedduringhelminthinfection.J. Immunol.174:60956104.

123.Terrazas,L.I.,etal.2001.Theschistosomeoligo-saccharide lacto-N-neotetraose expandsGr1(+)cells that secrete anti-inflammatory cytokinesandinhibitproliferationofnaiveCD4(+)cells:apotentialmechanismforimmunepolarizationinhelminthinfections.J. Immunol.167:52945303.

124.Giordanengo,L.,etal.2002.Cruzipain,amajorTrypanosomacruziantigen,conditionsthehostimmuneresponseinfavorofparasite.Eur. J. Immu-nol.32:10031011.


Date post:	09-Nov-2015
Category:	Documents
Upload:	cristiangutierrezvera
View:	223 times
Download:	1 times

Altered Macrophage Differentiation and Immune Dysfunction in Tumor Development

Documents