Effect of melphalan administration on the activity of natural killer and natural cytotoxic spleen cells of normal and tumor-bearing mice.

The effect of melphalan (L-PAM; L-phenylalanine mustard) administration on natural killer (NK) and natural cytotoxic (NC) activities of spleen cells from normal noninoculated BALB/c mice and mice bearing large MOPC-315 plasmacytoma tumors was investigated. Injection of L-PAM (7.5 or 15.0 mg/kg) had no effect on NK and NC activities of spleen cells from normal mice whereas stimulation by PHA was markedly suppressed. NK activity was markedly suppressed in spleens of tumor-bearing mice whereas NC activity was not affected. Therapy with L-PAM of tumor-bearing mice led to transient recovery of NK activity which was possibly related to the effect of L-PAM on macrophage suppressive activity on NK cells. It is concluded that NK and NC cell activities and the response to PHA stimulation are selectively affected by L-PAM administration.