ImmunologyofbacterialpolysaccharideantigensAndrejWeintraubKarolinskaIn - PDF document

ImmunologyofbacterialpolysaccharideantigensAndrejWeintraubKarolinskaInstitute,DepartmentofLaboratoryMedicine,DiisionofClinicalBacteriology,HuddingeUniersityHospital,S-14186Stockholm,ed13June2003;accepted13July2003Carbohydratesintheformofcapsularpolysaccharidesand/orlipopolysaccharidesarethemajorcomponentsonthesurfaceofbacteria.Thesemoleculesareimportantirulencefactorsinmanybacteriaisolatedfrominfectedpersons.Immunityagainstthesecomponentsconfersprotectionagainstthedisease.Howeer,deaccinesbasedonpolysaccharidesisdifficultandseproblemshaetobesoled.Firstofall,mostofthebacterialpolysaccharidesareT-lymphocyteindependentantigens.Anti-polysaccharideimmuneresponseischaracterisedbylackofT-lymphocytememory,isotyperestrictionanddelayedontogeny.Childrenbelow2yearsofageandelderlyrespondpoorlytopolysaccharideantigens.Secondly,thewidestructuralheterogeneityamongthepolysaccharideswithinandbetweenspeciesisalsoaproblem.Thirdly,somebacterialpolysaccharidesarepoorimmunogensinhumansduetotheirstructuralsimilaritieswithglycolipidsandglycoproteinspresentinman.TheT-lymphocyteindependentnatureofapolysaccharidemaybeoercomebyconjugatingthenatieordepolymerisedpolysaccharidetoaproteincarrier.SuchneoglycoconjugateshaebeenproentobeefficientininducingT-lymphocytedependentimmunityandtoprotectbothinfantsaswellaselderlyfromdisease.AnotherapproachtocircumenttheT-lymphocyteindependentpropertyofpolysaccharidesistoselectpeptidesmimickingtheimmunodominantstructures.Seeralexamplesofsuchpeptideshaebeen2003ElseierLtd.Allrightsreserved.Bacterialpolysaccharides;Immunology;Presentandfuture1.Introduction....................................................................2.Clinicallyimportantbacteriaandtheirpolysaccharides............................................2.1.Diersityofbacterialsurfacecarbohydrates...............................................2.2.PolysaccharidesasTlymphocyteindependentantigens.........................................2.3.Encapsulatedbacteria,diseaseand...............................................Haemophilusinfluenzaetypeb(Hib)..............................................2.3.2.Hibcapsularpolysaccharide...............................................Streptococcuspneumoniae....................................................Streptococcuspneumoniaecapsulartypes............................................Neisseriameningitides.......................................................3.Neoglycoconjugate...........................................................Haemophilusinfluenzaeb(Hib)neoglycoconjugateaccine......................................3.2.Meningococcalneoglycoconjugates....................................................3.2.1.MeningitidisserogroupB.....................................................3.3.Otherneoglycoconjugates.........................................................4.Alternatiaccinestrategies...........................................................4.1.Polysaccharidepeptidemimics......................................................4.2.DNA...............................................................5.Concludingremarks...............................................................References........................................................................ *Tel.:46-8-585-87831;fax:E-mailaddress:(A.Weintraub).CarbohydrateResearch338(2003)2539 0008-6215/03/$-seefrontmatter2003ElseierLtd.Allrightsreserved.doi:10.1016/j.carres.2003.07.008 1.IntroductionThesurfaceofmanybacterialspeciesiscoeredbypolysaccharides.Thesecanbeintheformofcapsules,glycoproteinsorglycolipids.InGram-negatiebacteria,thelipopolysaccharide(LPS)alsoreferredtoasendo-toxin,coersca.40%ofthebacterialsurface.Thecapsularpolysaccharides(CPS)aremadeupofeithermonosaccharidesmakingahomopolymerlikelinkedsialicacidinN.meningitidisEscherichiacoliK1,orfromrepeatingunitsnormallyconsistingoftwotosixsugarresidues.TheCPSmaybepresentinbothGram-negatiebacteriasuchasN.meningitidismophilusinfluenzaeE.coliSalmonellatyphiandinGram-positiesuchasStreptococciStaphylococciInmostcasesthebacterialCPSsareacidic.TheglycolipidLPSisonlypresentinGram-negatiebacteriaandispartoftheoutermembrane.Itisbuiltofalipidpartandapolysaccharidepart.ThepolysaccharidecanbediidedinacoreoligosaccharideproximaltothelipidpartandanO-polysaccharide.TheO-polysaccharideis,liketheCPS,eitherahomopolymer(VibriocholeraeBrucellaabortusB.melitensis)ormadeupfromrepeatingunitswhichmaybedi-tohexasaccharides.Itiswellestablishedthatanimmuneresponseagainstthesurfacepolysaccharidesconfersprotectionagainstthedisease.TheimmunologicalpropertiesofbacterialCPSsbecamethetargetofseeralinestigatorsinthe1920sand1930s.Inthemid-1940sitwaseidentthat:(i)CPSelicitedtype-specificprotectieimmunere-sponses;(ii)infantsandyoungchildrendidnotrespondwithtype-specificantibodies;(iii)type-specificantibodiesconferredprotection;tionwithpolysaccharidesreducedthecarrierrateofbacteriaofthesametypesasintheand(neoglycoconjugatesusingoligosaccharidescoalentlylinkedtoacarrierprotein,could,inrabbits,inducehightitredantibodyresponseswhichwere,boostableandprotectieagainstchallengeinfection.er,theintroductionofantibioticsputaneffectiestopforseeraldecadestothedeaccinesbasedoneitherCPSsorneoglycoconjugates.Inthe1970s,itwasrealizedthattreatmentwithantibiotics,althoughlargelysuccessful,wasnottheultimatesolutiontohandleinfections.AdancesinimmunologywithdelineationofBandTlymphocyteresponses,andtheroleofTlymphocytesfortheimmunologicalmemoryfunctions,aswellasthestruc-turalelucidationofthesurfacepolysaccharidemadepossiblethedeelopmentofnew,polysaccharide-basedaccines.Today,seaccinesbasedoneitherpurifiedCPSsoronneoglycoconjugatesareaailable.Inspiteoftheincreasedknowledgeinimmunology,thereareseeralproblemsthatremaintobesoli)Carbohydrateantigensexhibitalargedegreeofantigenicariation.Thisiseidentfromstructuraldifferencesinthesurfacepolysaccharideswithinthesamespeciesandisthebasisofserogroupingorserotypingsystems.Forexample,todateoer10differentserogroupsofN.meningitidisandoer90differentserotypesofStreptococcuspneumoniaebasedontheCPSshaebeenidentified.ThenumberofLPSO-antigensforseeralspeciesisexceedingwelloer100.Inaddition,anti-polysac-charideantibodiesareusually,serotype/serogroup-ii)Homologybetweencarbohydratestructurespresentonbacterialsurfaceandthoseofhostcellmem-braneshaebeenreported.Forexample,themeningitidisserogroupBCPSaswellastheE.coliK1antigenareantigenicallysimilartostructuresexpressedonhumanfoetalneuronalcellsandconsequently,poorimmunogensinhumans.There-fore,theuseofN.meningitidisserogroupBCPSinaccinehasthepotentialriskofinducingauto-antibodies.Themimicryofhostassociatedcarbo-hydratestructuresbybacterialpolysaccharidescouldbeapotentialirulenceandeasionfactoriii)Polysaccharideantigensaremostlypoorimmuno-gensduetotheirT-lymphocyteindependent(TI)nature.Often,anti-polysaccharideimmuneresponseischaracterisedbylackofT-lymphocytememory,isotyperestrictionanddelayedontogeny.Childrenbelow2yearsofageandelderlyrespondpoorlytopolysaccharideantigens.Thepurposeofthisreiewistoshedsomelightontheantagesanddisadantagesoftheuseofbacterialpolysaccharidesinaccinesandonrecentlydescribedalternatiewaystoinduceimmunityagainstpolysac-charidestructures.2.Clinicallyimportantbacteriaandtheirpolysaccharides2.1.DiversityofbacterialsurfacecarbohydratesAlistofsomeexamplesofclinicallyimportantbacterialspeciesandtheapproximatenumbersofnowknownserogroupsand/orserotypesisshowninTable1.Theserogrouping/serotypingisbasedonthereactiityofspecificantibodies,oftengeneratedinanimals,usingreferencestrainsofparticularspecies,withthemicro-organism.Thespecificantibodiesareusuallydirectedagainstthesurfacepolysaccharideantigens,eithertheCPSoragainstthepolysaccharidepartoftheLPS.Thereactiityoftheantibodiesreflectsthestructuraldisityofthepolysaccharides.AsseeninTable1,sespeciesarehighlyheterogeneousintermsofthenumbersofCPSand/orLPSstructures.Serotypingofmicro-A.Weintraub/CarbohydrateResearch338(2003)2539 organismsisofgreatimportancemainlyfromtheepidemiologicalpointofiew.Inepidemicsorlocaloutbreaksofacertaindisease,itisimportanttomonitorthespreadofthecausingagentandserotyping,ifpossible,isthesimplesttool.Inaddition,certaindiseasescausedbysomebacterialspeciesmaybelimitedtoafewserotypesorserogroups.Thereareseexamplesofthisphenomenon,Vibriocholeraebeingone.Althoughmorethan200serotypesofV.choleraearenowrecognised,untiladecadeago,onlyV.choleraeserotypeO1wasisolatedfrompatientswiththecholeradisease.In1992,anewserotypecausingepidemiccholeraemergedandwasdesignatedV.choleraeThemajordifferencesbetweentheV.choleraeO1andO139arethestructuresofthecellwallassociatedpolysaccharides.AnotherexampleisthespeciesE.coli.Thisspecies,atpresentcomprisesmorethan70CPSantigensi.e.,K-antigensandmorethan170O-antigens.E.colicausedifferenttypesofdiseaselikeurinarytractinfections,diarrhoea,septicaemiaandmeningitis.ThediarrhoeagenicE.colistrainscanbefurtherdiidedintodifferentcategories,basedonthetypeofillnessitcauses.ThisisduetothefactthatthedifferentE.colistrainsproducedifferentirulencefactorsintheformoftoxins,colonizationfactorsorothers.Manyoftheseirulencefactorsareencodedbyplasmids,yettheyareassociatedwithcertainserotypes.Forexample,theenterohaemor-E.colistrainsarerestrictedtoO26,O55,O111ab,O113,O117andO157serogroups,whileamongtheenterotoxigenicE.colimorethan13differentser-ogroupsareprealent.ThespeciesS.pneumoniaeisdiidedintomorethan90serotypesbasedontheCPSstructure.Howeer,thepresent23-accinecoersmorethan90%oftheS.pneumoniaeserotypesisolatedfrominfections.2.2.PolysaccharidesasTlymphocyteindependentantigensImmunologically,anantigencanbeclassifiedeitherasTlymphocytedependent(TD)orTlymphocyteindepen-dent(TI).ProteinsandpeptidesareusuallyTDantigenssincetheyrequirestimulationfromhelperTlympho-cytesinordertoelicitanimmuneresponse.TheTDantigenispresentedtoTlymphocytesbytheMajorHistocompatibilityComplex(MHC)moleculespresentonmacrophages,Blymphocytesordendriticcells.TDantigensinduceanimmuneresponsethatislonglastingduetoformationofmemoryBandTlymphocytes.TheantibodiesagainstTDantigensareofhighaffinityandofmultipleisotypes(IgA,IgM,IgG,IgG,IgG).Theaffinityofanantibodyisathermodynamicparameterthatquantifiesthestrengthoftheassociationbetweentheantibodyandtheantigenanddependsonthestructuralcomplementarityofthebindingsiteontheantibodyandthebindingsiteontheantigen.IncontrasttoTDantigens,theTIantigensdonoterisetoimmunologicalmemoryneitherdotheyrequireTlymphocytestoinduceanimmuneresponse.Memoryresponsesarecharacterizedbytheproductionofhigh-aidityantibody,i.e.,antibodiesstronglybind-ingtotheantigen.AmajorityofcarbohydratesarecategorizedasTIantigensinnature.TheTIantigensarefurtherdiidedintoTItype1andTItype2basedontheirinteractionwithBlympho-cytes.TItype1antigensaredefinedasantigenscapableofinducingproliferationanddifferentiationofbothnaõeandmatureBlymphocytes.TheseantigensateBlymphocytesandmayinduceimmunere-sponsesinneonates,adultsandinmicewithanX-linkedBlymphocytedefect(1419CommonexamplesoftheTItype1antigensarethebacterialLPS.ersely,TItype2antigensareofhighmolecularmassrepetitiepolysaccharidestructuresthatexhibitnointrinsicBlymphocytestimulatingactiTheseantigensarealsocharacterizedbytheirpoorindegradabilityandinabilitytostimulateMHCclassIIrestrictedTlymphocytehelp.TItype2antigenswillateonlymatureBlymphocytesandmostlikelyactbycross-linkingthecellsurfaceimmunoglobulin(Ig)ofspecific,matureBlymphocytes.Thisresultsintheproductionofantigen-specificantibodies.Howeer,theTI-type2antigensarenotsuitableasaccinesforchildrenbelow2yearsofageandforadultsaboe65yearsofagesincethesepopulationsdonotrespond. Table1Numberofserogroups/serotypesinsomeclinicallyimportantbacterialspeciesSpeciesCapsular1(Viantigen)40majorserogroupsEscherichiacoliVibriocholerae1(O139)N.meningitidis10(immunotypes)6(aGroupBA.Weintraub/CarbohydrateResearch338(2003)2539 CPSfromS.pneumoniae,N.meningitidisandinfluenzaearesomeexamplesofTItype2antigens.2.3.Encapsulatedbacteria,diseaseandvaccine2.3.1.Haemophilusinßuenzaetypeb(Hib).HaemophilusinßuenzaeisaGram-negatiemicroorganismthatisoftenfoundintheoropharynxofman.ThemajorityofH.inßuenzaestrainsarenon-encapsulated,generallycallednon-typableH.inßuenzaeNTHi.Howesomestrainsmaybeencapsulated.SixstructurallydifferentCPStypes,atof,haebeenrecognizedwithtypebbeingthemostcommontypeisolatedfrominfections.H.inßuenzaetypeb,Hib,causesmeningitis,epiglottitis,septicaemiaandpneumonia.Beforetheailabilityofaaccine,mostHibinfectionsoccurredinchildren,below5yearsofage.Inthisagegroup,theincidenceofineHibinfectionrangedfrom30to100casesper100,000inEuropeandtheUSA.AdultsrarelygetineHibinfectionsunlessthereisapredisposingunderlyingdisease.Anannualinci-denceof0.22per100,000hasbeenreported.ThepeakincidenceofHibdiseaseinthepre-accineerawasinchildrenbetween5and12monthsofage,coincidingwiththedisappearanceofmaternalantibodiesandpriortoappearanceofanti-capsularantibodies.Alargescaledouble-blindstudyinFinland30yearsagoofsome100,000childrenbetween3monthsand5yearsofageshowedthat(i)childrenaboe18monthswereprotectedwithanefficacy90%,(ii)childrenbetween12and18monthshadlittleprotection,and(iii)noprotectionwasseenintheagegroupof312months.24262.3.2.Hibcapsularpolysaccharidevaccine.Theprotec-eroleofantibodiestotheHibCPSwasknownalreadyin1933.TheFinnishstudywithpuriÞedHibCPSasaccinedemonstratedtherelationshipofbacter-icidalantitypebspeciÞcantibodiesandprotectionagainstthedisease.AdultsregularlyhaeantibodiestotheHibCPS.TheaccinationswithpuriÞedHibCPSresultedinlowleelsofspeciÞcantibodies.Itis,er,importanttonotethattheseantibodycon-centrationsaretheresultofimmunizationwiththeTI-type2antigenlackingtheabilitytoinduceimmunolo-gicalmemoryresponse.Ithasrecentlybeenshownthatantibodyaiditywasrelatielylowfollowingprimaryimmunization,andsigniÞcantlyhigherfollowingboost-Mostoftheincreaseinaiditywasobseredforafewmonthsaftertheprimaryimmunization.2.3.3.StreptococcuspneumoniaeStreptococcuspneumo-isstillamajorcauseofmorbidityandmortalityinadultsandchildrendespitetheaailabilityofeffectiantimicrobialtherapy,althoughresistanceagainstseeralofthecommonantimicrobialagentsisanemergingproblemworldwide.TheirulenceiscausedbytheCPS,andtherearenow90differentcapsulartypesdescribed.Theclearanceoftheinfectingbacteriadependsonthepresenceoftype-speciÞcantibodiesagainsttheCPS.Duetointeractionoftheantibodieswithcomplement,thebacteriaareopsonisedandphagocytised.Pneumococciareresponsibleforaarietyofinfec-tionsrangingfrommildmucosalinfectionslikeotitismedia,toseriousbronchopneumoniaandpotentiallylifethreateningmeningitis.PneumococcicolonizetherespiratorymucosaofbothhealthyandsickindiHealthyadultsandchildrenmaycarrypneumococci,er,thecarrierrateishigherinchildrenespeciallythoseattendingdaycarecentres,andstillhigherinthosewithrespiratoryinfectionscomparedwithhealthychildren.Theillnessisaresultofthespreadofthepneumococcitotissuesfromtheoropharynx.Epidemiologicalstudiesinthe1980shaefoundanannualincidenceofpneumococcalbacteraemiatobebetween9and18casesper100,000personsofallages.Inchildren,therateariedfrom105to234casesper100,000indiIthasbeenestimatedthatintheUSAthereisonanannualbasis3000casesofmeningitis,50,000ofbacteraemia,500,000ofpneumonia,and7,000,000casesofacuteotitismedia.3132Approximately40,000deathscausedbypneumococcioccureachyearintheUSA.Inelopingcountriesithasbeenestimatedthatacutelowerrespiratoryinfectionscausedbypneumococciaccountformorethan4milliondeathsannually,mostoftheminchildrenbeingbelow5yearsofage.2.3.4.Streptococcuspneumoniaecapsulartypes.immunogenicityandimmunochemistryofpneumococ-calCPSshasbeenreiewedrecently.OfthecapsulartypesidentiÞed,onlyafewarecommoncausesofpneumococcaldisease.Theseenmostcommonlyisolatedserotypescoerupto85%ofallpneumococcalstrainscausingineinfectionsinchildren.Someoftheaailablepneumococcalpolysaccharideaccinesarecomposedof23ofthemostcommonpneumococcalserotypes.Theyrepresent8590%oftheserotypesthatcauseineinfectionsinadultsinindustrializedcountries.Asmentionedbefore,childrendorespondpoorlytoCPSsuptotheageof2years,andtheleastimmunogenicpneumococcalserotypes(6B,14,19F,23F)uptotheageof53536Inaddition,thepneumococcalpolysaccharidesareTItype2antigensandfailtoinduceamemoryfunction.2.3.5.NeisseriameningitidesMeningitiscausedbymeningitidisisaseriousdiseasewithhighmortality.TheirulencefactorinmeningitiscausedbymeningitidesisaCPS.N.meningitidisisanexclusihumanpathogen,andtransmissionisaccomplishedbydropletsfromcolonizedupperrespiratorymucosalA.Weintraub/CarbohydrateResearch338(2003)2539 membranes.Therearemorethan10serogroupsbasedonthestructureoftheCPS,howe90%ofcasesofmeningitisarecausedbystrainsbelongingtoserotypesA,B,C,W135andY.AllÞeserotypescancauseepidemics.Howeer,thegroupAstrainsarethecausatieagentinrepeatingepidemicsinsub-SaharanInEuropeandLatinAmericaserogroupBismostprealent,causingmorethan50%ofthecases,whereasserogroupCismostprealentinNorthAmerica.Meningococcalmeningitisisspreadallertheworldandaffectsallagegroups.Thereforethereisaneedtoaccinatethewholepopulation.Alreadyin1913,FlexnershowedthatserumcontainingspeciÞcanti-CPSantibodies,whenusedtherapeutically,decreasedthefatalityrateofmeningococcalmeningi-3.NeoglycoconjugatevaccinesHaemophilusinßuenzaeb(Hib)neoglycoconjugatevaccineIntheearly1990s,differentHibconjugateaccineswereintroducedandresultedinadramaticreductionofmeningitisinchildreninFinland,theUKandtheThereportedefficacyforinfantsbelow1yearwas99%,for12yearoldinfants,97%andfor2yearoldchildrenitwas94%.AnotherbenefitoftheHibconjugateaccineswasareductionofcarriageofthatprobablyledtolowertransmissionratestochildrenwholackedprotectieantibodies.3.2.MeningococcalneoglycoconjugatesPurifiedCPSsfromserogroupsA,C,W135andYaremarketedaccineproducts,andasTItype2antigenselicitantibodyresponseswithnomemoryfunction,withthepossibleexceptionofserogroupApolysaccharidewhichinducesanantibodyresponsealsoininfants.TheserogroupCpolysaccharideisnotimmunogenicinchildrenbelow2yearsofage,anddeelopmentofantibodytitersisslow.NeoglycoconjugatesarebeingelopedusingthesameprinciplesasforHib.ThetypeAandCneoglycoconjugateaccinesaresafeandwelltoleratedininfantsandyoungchildren.Athree-doseregimeforprimaryimmunisationresultedinspecificanti-Aandanti-Cpolysaccharideantibodytiters.accinatedchildrenhadeleatedtitresofbacterici-dalantibodies.Sofar,alldataindicatethatmeningo-coccalneoglycoconjugateaccineswillhaeasgreatachancetobesuccessfulastheHib.Mostlikely,meningococcalACandmeningococcalAYneoglycoconjugateswillbesoonaailableonthemarket.3.2.1.MeningitidisserogroupB.ThemeningococcalserogroupBpolysaccharide,ahomopolymerof8)-linkedsialicacidresidues,ispoorlyimmunogenicinThedeelopmentofaneffectiaccineagainstN.meningitidisserogroupBiscomplicatedbytheinabilityofthispolysaccharidetoinduceasigniÞcantantibodyresponse,enwhenconjugatedtoacarrierprotein,ThepoorimmunogenicityoftheserogroupBpolysaccharideisduetoimmunologictoleranceinducedbyfoetalexposuretocross-reactipolysialylatedglycoproteinsexpressedinaarietyofhosttissues,suchasneuronalcelladhesionmole-cules.3.3.OtherneoglycoconjugatesThesuccessoftheHibconjugatesresultedinafocusedinterestonconertingotherCPSantigensfromTItoTDantigens.GroupBstreptococci(GBS)arethemajorcauseofmeningitisandsepsisinneonates.Atleastsixcapsulartypeshaebeenassociatedwithhumandisease,andtype-specificantibodiesareresponsibleforprotec-iaopsonisationofthebacteriaandinteractionwiththecomplementcascade.Immunogenicneoglyco-conjugateshaebeendeelopedabletoinduceprotec-eantibodiesinanimals.SimilarattemptshabeenmadetodeelopimmunogenicandsafeagainsttheVipolysaccharideofS.typhiandCPSandLPSofE.coliS.sonnei,andS.flexneri4.Alternativevaccinestrategies4.1.PolysaccharidepeptidemimicsAnotheraccinestrategyisthedeelopmentofpeptidesthatmimicpolysaccharideantigens.Thesepeptidescanbeidentifiedusinganti-idiotypicantibodiesorphagedisplaylibraries,andcanmimictheimmunologicalfunctionofpolysaccharides.Theexactmechanismsresponsibleforthismimicryareyetunknown.Peptidemimicscommonlycontainalargenumberofhydrophobicaminoacidresidues,oftenwitharomaticsidechains.Basedonthesesimila-rities,itishypothesisedthataromaticaromaticandhydrophobicinteractionsarecriticalforcesthatmod-ulatebindingandthatthebasisofcross-reactiisstructuralmimicry.Thishasbeenchallengedbyotherswhoshoweddataindicatingthatthemechanismofpeptidebindingdiffersfromthatofcarbohydratebinding.Thespecificinteractionsinedinmolecu-larmimicryarecomplex,howeer,thisconceptmaybeofuseindeelopingnoaccinestrategiesagainstpolysaccharideantigens.TheprimaryadantageofusingpeptidesasantigensratherthancarbohydratesistheirpotentialtostimulateA.Weintraub/CarbohydrateResearch338(2003)2539 TDimmunity.Peptidescanbeprocessedbyantigenpresentingcells(APC)andpresentedtoTlymphocytesbyMHCmolecules.Sincepeptidesaresimplermole-cules,theyalsohaethepotentialtofocustheimmuneresponseonprotectieepitopes.Howeer,seproblemsassociatedwithpeptideantigensneedtobeed.ThemajorissueistheirpoorchemicalstabilityandsubsequentlowerantigenicityinSmallerpeptidesareoftendegradedrapidlyandconsequentlyareweakimmunogens.Differentdelierysystems,likeliposomes,immunestimulatingcomplexes(ISCOMs),proteosomesandbiodegradableparticleshaebeenshowntosuccessfullyinducepeptide-andpathogen-specificimmuneresponses.eralmethodsforidentificationofpeptidesmi-mickingpolysaccharideshaebeenused.Oneistheanti-idiotypicantibodytechnology.Duringthegenerationofanantibody-mediatedimmuneresponse,eitherafterinfectionoraccination,anindiidualwilldeantibodiestoanantigenaswellasanti-idiotypeanti-bodies,whoseimmunogenicbindingsite(idiotype)mimicstheantigen.Inthiscontext,anti-idiotypicantibodiesdirectedattheariabledomainsofanti-carbohydratebindingantibodiescanactasimmunogensandinduceananti-polysaccharideimmuneresponse.Amonoclonalanti-idiotypicantibodythatmimicsmeningococcalserogroupCpolysaccharidehasbeendescribed.Theanti-idiotypicmonoclonalantibodycouldinhibitthebindingofhumananti-Cpolysacchar-ideseratoC-polysaccharide.Thesameauthorsshowedthatthismonoclonalanti-idiotypicantibodycouldinduceprotectieanti-meningococcalserogroupCpoly-saccharideantibodiesinmice.Anti-idiotypicantibodytechnologyhasalsobeenusefultodeelopimmunogensmimickingdisialogan-gliosideGD2fortreatmentofmelanomaandgang-liosideGD3fortreatmentofsmallcelllungcancer.Anothermethodforidentificationofpeptidemimicsisthephage-displaylibrarytechnology.Usinganti-polysaccharidemonoclonalantibodiesorpolyclonalantisera,aphagelibraryisscreenedbysuccessiecyclesofselectionandamplification.Phageexpressingpep-tidesthatbindthespecificanti-polysaccharideantibodycanbeselected.Iftheinteractionbetweenthephageandtheantibodycanbeinhibitedbythepolysaccharide,thepeptidemaymimicthepolysaccharideantigen.ThistechnologyhasbeenusedtoidentifypeptidescapableofinducingantibodiesagainstaarietyofcarbohydrateepitopespresentonthesurfaceofS.flexnericoccusneoformansN.meningitidisserogroupA,abortusandgroupBstreptococci.antageofphagedisplaylibrariesisthattheyallowrapidscreeningandidentificationofreactiepeptides.Thus,theuseofphagedisplaylibrariesisanefficientandeffectiewaytoidentifypotentialaccinecandi-datescapableofinducingfunctional,anti-polysacchar-ideantibodies.AlistofpeptidesmimickingcarbohydratestructuresisshowninTable24.2.DNAvaccinesaccinesrepresentanoaccineapproach,whichemploysgenesencodingproteinsofpathogens,ratherthantheproteinsorpathogensthemselesasinmoreconentionalapproaches.Theaccinesconsistofbacterialplasmidscontainingastrongpromoter,whichwillfunctioninmammaliancellsandageneencodingtheproteinantigen.Afterinjection,theproteinantigenisproducedinsituandcanelicitimmuneresponses.Fromanimmunologicalstandpoint,theadantageofthistechnologyisthatbothhumoralandcellularimmuneresponsesaregenerated,withtheproductionofantibodies,andTcellresponses.Howeer,DNA-basedaccineswerenotconsideredasanoptionfordeelopmentofaccinesagainstdiseasescausedbybacteriapossessingpolysaccharidesasprotectieantigens,sincethecarbohydrateantigensaresecondarygeneproducts.Howeer,thefieldofpeptidesmimickingcarbohydratestructuresopenedthepossibilitytousethistechnologytoinduceanti-poly-saccharideimmunity.TheDNAaccinesmayhaeraladantagescomparedtoconentionalaccines;(i)DNAaccinesareeasilyconstructedbystandardmolecularcloningtechniques;(ii)theaccinesarestableandheatresistant,whichmakethemespeciallysuitableaccinedelieryindeelopingcountries;(iii)they Table2ListofpeptidesmimickingcarbohydrateantigensAntigenMethodReferenceB.abortusLPSPhagedisplay79,83S.flexneri5aLPSPhagedisplayC.neoformansPhagedisplayC.neoformansPhagedisplayAntiidiotypePhagedisplayCarbohydratesonadeno-carcinomacellsPhagedisplayPhagedisplayBlood-groupantigenPhagedisplayTumourassociatedPhagedisplayA.Weintraub/CarbohydrateResearch338(2003)2539 shouldbecheaperinproductionandpurificationcomparedtopolysaccharideorneoglycoconjugatecines;(i)theyhaethecapacityofinducinganimmuneresponsewithapredominanceofIgG2aisotype.IgG2aisotypeshaebeenreportedtobeparticularlyeffectieinconferringprotectionagainstencapsulatedorganismsbecauseoftheirabilitytoopsoniseandfixcomplement.Finally,DNAaccinesallowadminis-trationofmultipleDNA-encodedantigens.Thistech-nologyhasrecentlybeendemonstratedbyKieber-EmmonswhoconstructedaDNAaccineencodingapeptidemimicofthebloodgrouprelatedantigenLewisY(LeY).DNAimmunizationofmiceresultedinananti-LeYantibodyresponseoftheIgG2aisotype.ThestudiesshowedthatDNAaccinationprimesforacarbohydrateinducibleIgGantibodyresponse,andthatinducedanti-LeYIgG2aantibodymediatescellkill-ThisisthefirstreportofDNAaccinationinducingTDimmunityagainstacarbohydrateantigenandopensacompletelynewfieldforthedeelopmentofanewgenerationofaccinesagainstpolysaccharidespresentonthesurfaceofpathogenicmicroorganisms.5.ConcludingremarksBacterialpolysaccharidesarethemajorsurfacecompo-nentsandtheimmunityconfersprotection.Theuseofpolysaccharidesinaccineshasbeenpartiallysuccessful,er,seeralproblemsremaintobesoled.PurepolysaccharidesarepoorimmunogensandmostofthemareTIantigens.PolysaccharideneoglycoconjugatesasaccinescouldbeawaytoconertaTItoTDantigen.eralexamplesaredescribedwiththeHibconjugateaccineasthebestexample.Peptidemimicsofcarbohy-dratestructuresisanewapproachthatmayhaegoodpotentialinthedeelopmentofnewaccines.Theantagesanddisadantagesofthesethreeapproachesforanti-polysaccharideaccinesarelistedinTable3References1.Finland,M.;Dowling,H.F.J.Immunol.,2852.Lister,S.;Ordman,D.SouthAfricanInst.Med.Res.3.MacLeod,C.M.;Hodge,S.R.G.;Heidelberger,M.;Bernhard,W.G.J.Exp.Med.,4454.Ruegsegger,J.M.;Finland,M.J.Clin.In5.Daies,J.A.V.J.Immunol.6.Fothergill,L.D.;Wright,J.J.J.Immunol.,2737.Sutliff,W.D.;Finland,M.J.Exp.Med.,8378.Ward,H.K.;Lyons,C.J.Exp.Med.,515 Table3antagesanddisadantagesofpolysaccharidebasedTypeofaccineAdantagesDisadCapsularpolysaccharideElicitantibodiessimilartothoseinnaturalresponse;safeandefficacious;microbialproducts;canbeeasilypurifiedPoorlyimmunogenicTI-type2antigens:donotelicitimmunologicalmemoryorisotypeswitching;poorlyimmunogenicinpatientswithB-lymphocytedefects;potentialfordeleteriousimmunomodulation;CPSareCapsularpolysaccharide-proteinconjugateElicitantibodiessimilartothoseinnaturalresponse;conertTItoTDresponsesininfantsandchildren;increasedimmunogenicityininfantsandyoungchildren;safeandefficaciousDonotelicitclassicalTDresponsesintheelderly;mostopsonicIgGsubclassesmightnotbeproduced;poorlyimmunogenicinpatientswithunderlyingB-lymphocytedefects;protectieandnon-protectieantibodiescanbeproduced;conjugatesfromCPSpreparationsareheterogeneous;possibleundesiredimmunityagainstthecarrierprotein;PeptidemimotopeofpolysaccharideantigenBiochemicallydefined;TDantigens,canelicitimmunologicalmemory,affinitymaturationandisotypeswitching;mightbeabletofocusresponseontheproductionofprotectieantibodiesPoorlyimmunogenicifnotconjugatedtoacarriermolecule;tdantigen,mightrequireintactcell-mediatedimmunitytobeimmunogenic;noexperienceforefficacyinhumans*AdaptedfromRef.A.Weintraub/CarbohydrateResearch338(2003)2539 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