Enhancement of Naturally Occurring Human Spontaneous Monocyte-mediated Cytotoxicity by c/s-Diamminedichloroplatinum(ll)

The effect of the antineoplastic agent c/s-diamminedichloroplatinum(ll) (c/s-DDP) on spontaneous cytotoxicity of human mononuclear cells in vitro was assessed. c/s-DDP enhanced spontaneous monocyte-mediated cytotoxicity 300% compared to control values. Further, this spontaneous monocyte killing developed earlier (3 to 4 days) than did that of untreated cells (5 to 7 days). Since monocyte cytotoxicity is under the control of lymphocyte suppressor cells, the effect of c/s-DDP on sep arated populations of lymphocytes and monocytes was exam ined. Unlike X-irradiation which enhanced monocyte cytotox icity through the indirect pathway of inactivation of lymphocyte suppressors, c/s-DDP directly stimulated the monocyte popu lation. Direct stimulation of killer monocytes may be an impor tant mechanism of the antitumor effect of c/s-DDP.