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 for cancer immunotherapy since (1) the expression of many MiHA is tissue specific and (2) they can trigger potent T lymphocyte responses. A primary objective of our research program is to characterize T cell responses to cells displaying multiple incompatible MiHA. Early in the course of this work, we observed in various stimulator/responder combinations that immunization versus multiple MiHA generated cytotoxic effectors that killed not only stimulator cells but also a large panel of MHC-identical and MHC-different targets. To characterize the cells responsible for this cytotoxic activity and their specificity, we expanded polyclonal and clonal CD3+ CD4- CD8+ LP anti-C57BL/6 effectors. LP anti-C57BL/6 polyclonal effectors (LPTc cell line) showed strong cytotoxic activity when tested against several H-2b and non-H-2b targets, but displayed, respectively, weak or absent cytotoxicity against MHC class I-deficient cells and syngeneic cells. When used as cold targets, C57BL/6 cells inhibited the lysis of all H-2b and non-H-2b cells. Some H-2b, but no H-2d or H-2k, cold targets inhibited the lysis of C57BL/6 targets. With the exception of LP and C57BL/6, all types of H-2b cells (A.BY, D1.LP and C3H.SW) showed complete reciprocal inhibition of lysis. The same observation was made for non-H-2b targets. The cytotoxicity profile of 12/14 LP anti-C57BL/6 clones was identical to that of the LPTc cell line, while 2/14 clones recognized only H-2b cells. Cytotoxicity was inhibited by incubation of effector cells with anti-CD3 or anti-CD8 antibodies and by incubation of target cells with specific anti-MHC class I antibodies. These results show 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 recognized MHC-peptide complexes on allogeneic MHC-different targets. This observation has significant implications concerning the use of anti-MiHA T cells in cancer immunotherapy.