Medical Microbiology

secondarylymphaticorgans.Indeedthesameforeigntransplantationanti-

gensarehardlyimmunogenicwhenexpressedonfibroblastsoronepithelial

orneuroendocrinecells,unlessthesecellsareabletoreachlocallymphoid

tissue.

ToavoidaGVHreactioninimmunoincompetentorsuppressedbonemar-

rowrecipients,immunocompetentTcellsmustfirstbeeliminatedfromthe

transplantedbonemarrow.Thiscanbeachievedbyusinganti-T-cellantibo-

dies,anti-lymphocyteantisera,andcomplementormagneticbeadcell-se-

parationtechniques.However,itisnoteworthythatcompleteelimination

ofmatureTcellsleadstoareductionintheacceptancerateforbonemarrow

transplants,andthatitmayalsoweakentheanti-tumoreffectofthetrans-

plant(desirableinleukemia).ItseemsthatthesmallnumberofTcellstrans-

plantedwiththebonemarrowcanmediateasubclinicalGVHreaction,thus

preventingrejectionofthetransplantbutretainingtheabilitytodestroythe

recipient’sleukemiacellsandpreventingtumorre-emergence.

BoneMarrowTransplantsToday

&ReconstitutionofimmunedefectsinvolvingBandTcells

&Reconstitutionofotherlymphohematopoieticdefects

&Genetherapyviainsertionofgenesintolymphohematopoieticstemcells

&Leukemiatherapywithlethaleliminationoftumorcellsandreconstitutionwith

histocompatible,purifiedstemcells,eitherautologousorallogenic.

HVGreactions,thatisimmuneresponsesoftherecipientagainsttrans-

plantedcellsororgans,arenotgeneratedinautotransplants(forinstance

transplantationofskinfromonepartofthebodytoanotheronthesame

individual).Thisalsoappliestotransplantsbetweenmonozygotictwinsor

geneticallyidenticalanimals(syngeneictransplants).However,transplants

betweennon-relatedornon-inbredanimalsofthesamespecies(allogeneic

transplants),andtransplantsbetweenindividualsofdifferentspecies(xeno-

geneictransplants)areimmunologicallyrejected.BecauseTcellsrecogni-

tionissubjecttoMHCrestriction,cellularrejectionwithinaspeciesis

evenmorepronouncedthanbetweendifferentspecies,althoughthelatter

procedureinvolvesothertransplantationcomplications.Theseincludethe

occurrenceofnaturalcross-reactiveantibodies,andalackofcomplementin-

activationbyanti-complementfactors(whichareoftenspecies-incompatible

andthereforeabsentinxenogeneictransplants),whichtogetheroftenresults

inhyperacuterejectionwithinminutes,hours,orafewdays—thatisbefore

anyspecificimmuneresponsescanevenbeinduced.

Threetypesoftransplantrejectionhavebeencharacterized:

&Hyperacuterejectionofvascularizedtransplants,occurringwithinmin-

utestohoursandresultingfrompreformedrecipientantibodiesreacting

116 2 BasicPrinciplesofImmunology

2

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Kayser, Medical Microbiology © 2005 Thieme

All rights reserved. Usage subject to terms and conditions of license.