Deoxyspergualin, a novel immunosuppressant, markedly inhibits human mixed lymphocyte reaction and cytotoxic T-lymphocyte activity in vitro.

Deoxyspergualin (DSG) has demonstrated potent immunosuppressive activities in vivo. However, because of its lability in culture medium, the mechanism of activity has not yet been identified in vitro. In this study, a more stable analogue, deoxymethylspergualin (MeDSG), was used to investigate the in vitro immunosuppressive activity of DSG. MeDSG suppressed both human mixed lymphocyte reaction (MLR) and cytotoxic T-lymphocyte (CTL) activity at doses greater than 0.1 micrograms/ml in vitro. In kinetics studies, MeDSG was found to suppress a MLR when added on day 3 of a 7 day MLR incubation but cyclosporin A (CYA) suppressed a MLR only when added during the initial stage of a MLR (i.e. on day 1). In studies of cell surface phenotype in the MLR, MeDSG treatment decreased the numbers of CD8+ lymphocytes but those of CD4+ lymphocytes were not affected. In addition, MeDSG had no significant effect on interleukin-2 (IL-2) receptor expression or IL-2 production. These results suggest that MeDSG suppresses the T-cells which are proliferating competent cells such as cytotoxic T-cells (CD8+), but has a different mode of immunosuppressive action compared with CYA.