Medical Microbiology

useofinactivatedvaccinesagainsttherespiratorysyncytialvirus(RSV)inthe

sixties,andexperiencewithcertainso-calledsubunitvaccinesandrecombi-

nantvaccinesagainstnoncytopathicviralinfectionsinraremodelsituations.

Generally,itshouldbekeptinmindthatmostofthesuccessfulimmunization

programsdevelopedtodatehavemediatedprotectionviaantibodies.Thispar-

ticularlyappliestotheclassicprotectivevaccineslistedinTable 1. 13 (p.33)for

children,andexplainswhyantibodiesnotonlyareresponsiblefortheprotec-

tionofneonatesduringtheimmuno-incompetentearlypostnatalperiod

whereimmunologicalexperienceispassedonfromthemotherviaantibodies,

butalsoattenuateearlychildhoodinfectionstobecomevaccine-like.Thisex-

plainswhysuccessfulvaccinesallprotectvianeutralizingantibodies,because

thispathwayhasbeenselectedbyco-evolution.Asmentionedearlier,with

regardtoimmunologicalmemory,memoryTcellsappeartobeessentialto

hostimmuneprotection,particularlyinthosesituationswhenantigenper-

sistenceiscontrolledefficientlybymeansofinfection-immunity(e.g.,tuber-

culosis,HIV).

TumorImmunity..........................................

Ourknowledgeconcerningtheimmunecontroloftumorsisstillmodest.

Sometumortypesbeardefinedtumor-associated,ortumor-specific,anti-

gens.Howeverthisisapparentlynotsufficientforinductionofanefficient

immunedefense.Thereisalsotheproblemoftumordiagnosis;thepresence

oftumorsissometimesconfirmedusingafunctionalorimmunological

basis,yetthetumorcannotbelocatedbecauseconventionalexaminations

areoftenunabletodiscoverthemuntiltheyreachasizeofabout 109 cells

(i.e.,about 1 ml)oftumortissue.

Factorsimportantinimmunedefensereactionsincludethelocationand

rateofproliferation,vascularizationorthelackthereof,andnecrosiswithpha-

gocytosisofdisintegratingtumortissue.Weneveractuallygettoseethose

raretumorsagainstwhichimmunecontrolmighthavebeensuccessfullyeli-

cited,insteadweonlyseethoseclinicallyrelevanttumorsthathaveunfortu-

natelybecomesuccessfultumorswhichhaveescapedimmunecontrol.

Evidenceoftheimmunesystem’sroleintumorcontrolincludes:

&Greaterthan 85 %ofalltumorsarecarcinomasandsarcomas,thatisnon-
lymphohematopoietictumorswhichariseintheperiphery,outsideoforga-
nizedlymphoidtissues.Theimmunesystem,inamannersimilartothatseen
formanystrictlyextra-lymphaticselfantigens,ignoressuchtumorsatfirst.

&Lymphohematopoietictumorsoftenpresentimmunologicalodditiessuch
asunusuallylow,orentirelyabsent,MHCand/orlowtumorantigenconcen-
trations,plustheyfrequentlylackaccessorymoleculesandsignals.

ImmuneDefensesagainstInfectionandTumorImmunity 107

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