DIRECT EVIDENCE FOR IN-VIVO INDUCTION OF CD8(-CELLS DIRECTED TO DONORMHC CLASS-I PEPTIDES FOLLOWING MOUSE ALLOTRANSPLANTATION() CYTOTOXIC T)

There is accumulating evidence indicating that the T cell response to donor major histocompatibility complex (MHC) peptides plays a crucial role in graft rejection. We and others previously demonstrated the in volvement of MHC class-II-restricted recognition of donor MHC class I and II peptides by alloreactive CD4(+) T helper cells in graft rejecti on. Here we studied the in vivo induction of CD8(+) cytotoxic T lympho cytes (CTL) directed to donor MHC class I peptides following allotrans plantation in the mouse. To address this question, BALB/c irradiated s plenocytes (H-2(d)) (K-d, A(d), E(d) L(d), D-d) were injected into L(d )-deficient BALB/c-dm2 (dm2) mutant mice (K-d, A(d), E(d) -, D-d). Nin e days after allogeneic cell transplant, recipient lymph node T cells were tested for cytolytic activity using peritoneal macrophages as tar gets. We observed that in addition to BALB/c targets, dm2 macrophages could also be lysed but only when incubated with a dominant peptide on donor L(d) molecule, L(d) 61-80. This response was abolished by anti- CD8 but not anti CD4 monoclonal antibodies. In addition, after immuniz ation of dm2 mice with the peptide L(d) 61-80, alloreactive CTL were g enerated in vivo and shown to destroy allogeneic donor BALB/c target c ells in the absence of exogenously added peptide. We conclude that aft er allotransplantation, concomitant in vivo priming of alloreactive CD 8(+) CTL by donor MHC class I peptides occurs through both direct and indirect pathways of allorecognition.