T-LYMPHOCYTE RESPONSES TO MULTIPLE MINOR HISTOCOMPATIBILITY ANTIGENS GENERATE BOTH SELF-MAJOR HISTOCOMPATIBILITY COMPLEX-RESTRICTED AND CROSS-REACTIVE CYTOTOXIC T-LYMPHOCYTES

Minor histocompatibility antigens (MiHA) may represent ideal targets f or cancer immunotherapy since (1) the expression of many MiHA is tissu e specific and (2) they can trigger potent T lymphocyte responses. A p rimary objective of our research program is to characterize T cell res ponses to cells displaying multiple incompatible MiHA. Early in the co urse of this work, we observed in various stimulator/responder combina tions that immunization versus multiple MiHA generated cytotoxic effec ters that killed not only stimulator cells but also a large panel of M HC-identical and MHC-different targets. To characterize the cells resp onsible for this cytotoxic activity and their specificity, we expanded polyclonal and clonal CD3(+) CD4(-) CD8(+) LP anti-C57BL/6 effecters. LP anti-C57BL/6 polyclonal effecters (LPTc cell line) showed strong c ytotoxic activity when tested against several H-2(b) and non-H-2(b) ta rgets, but displayed, respectively, weak or absent cytotoxicity agains t MHC class I-deficient cells and syngeneic cells. When used as cold t argets, C57BL/6 cells inhibited the lysis of all H-2(b) and non-H-2(b) cells. Some H-2(b), but no H-2(d) or H-2(k), cold targets inhibited t he lysis of C57BL/6 targets. With the exception of LP and C57BL/6, all types of H-2(b) cells (A.BY, D1.LP, and C3H.SW) showed complete recip rocal inhibition of lysis. The same observation was made for non-H-2(b ) targets. The cytotoxicity profile of 12/14 LP anti-C57BL/6 clones wa s identical to that of the LPTc cell line, while 2/14 clones recognize d only H-2(b) cells. Cytotoxicity was inhibited by incubation of effec tor cells with anti-CD3 or anti-CD8 antibodies and by incubation of ta rget cells with specific anti-MHC class I antibodies. These results sh ow that immunization against multiple MiHA in the context of self-MHC generates 2 types of CTL: some are strictly self-MHC restricted while others are strongly cross-reactive and recognize MHC-peptide complexes on allogeneic MHC-different targets. This observation has significant implications concerning the use of anti-MiHA T cells in cancer immuno therapy.