EFFECT OF CYCLOPHOSPHAMIDE AND METHYLPREDNISOLONE ON IN VITRO CELLULAR IMMUNE RESPONSE TO ALLOGENEIC TUMOR CELLS CORRELATION WITH IN VIVO REJECTION

Abstract

SUMMARY The immunosuppressive effects of methylprednisolone (MP) (5 mg/kg) and cyclophosphamide (CY, 180 and 48 mg/kg) on cellular immune responses to allogeneic tumor cells were evaluated using in vitro tests. The variations in the number of splenocytes and the in vivo response to the injection of allogeneic tumor cells (rejection or facilitation) were recorded. The drugs were administered at different times in relation to immunization. Polyclonal stimulation essentially reflected T cell recovery, whereas monoclonal stimulation was depressed when the drugs were administered at the time of immunization, suggesting a defect at the level of sensitization. MP had little effect on cytotoxicity but was nevertheless associated with allograft facilitation. CY however strongly inhibited the specific activity of cytotoxic lymphocytes when administered at the time of inoculation, but this was associated with normal graft rejection. Reduced numbers of T cells and increased cytotoxicity was recorded when both drugs were administered 2 days prior to immunization. Thus, this study (1) has shown that MP-induced facilitation does not correlate with the levels of in vitro cytotoxicity; (2) has demonstrated a dissociation of the effect of CY on in vitro cytotoxicity and the in vivo response when given at the time of immunization; and (3) confirmed the hypothesis that CY enhances T cell responses when given 2 days before immunization and similar observations being extended to MP treatment. It also suggested that the cytotoxicity observed at that time was responsible for graft rejection. SUMMARY Methylprednisolone (MP) and cyclophosphamide (CY) are widely used as immunosuppressors to induce graft acceptance. Cytotoxic lymphocytes (CTL) are thought to be responsible for graft rejection because they express lytic activity against H-2-incompatible cells (7). However, other components of the immune system play an important role in allograft rejection and facilitation. In particular, B cells and antibodies that may have either cytotoxic or enhancing effects mediated through different mechanisms such as the protection of target cells from cytotoxic effectors (16) or in provoking the formation of antigen-antibody complexes, “defusing” CTL from their targets (24). Suppressor T cells may also participate in graft facilitation and they may be present as such or may be induced by the presence of antigen-antibody complexes (12). However, because of the strong relationship between cytotoxicity and allograft rejection, we wanted to verify whether these immunosuppressive drugs had any effect on the T cell population as evaluated by nonspecific tests (polyclonal stimulation) and specific tests (mixed lymphocyte cultures (MLC) and chromium release test) and to correlate this effect with in vivo graft rejection.