Concanavalin A-inducible suppressor cells in regional lymph nodes of cancer patients

Regional tumor-draining lymph nodes of 11 of 14 patients with urological tumors and one of four controls studied contained suppressor cell precursors that could be activated by concanavalin A (Con A) to suppress the proliferative response of autologous lymphocytes to Con A. In contrast, no suppression of lymphocyte proliferation by lymph node cells that were not activated with Con A was observed in four patients tested. The suppressive effect was not due to decreased viability or increased release of cold thymidine by Con A-activated cells nor to alteration in the time course of the proliferative response of Con A-activated cells. Mitomycin C treatment of lymph node cells 24 hr after activation did not abrogate their suppressive activity. Peak suppression was observed after 72 hr in culture. The amount of suppression measured could be maximized by treatment of suppressor cells with mitomycin C 24 hr after activation and by washing the cells immediately before pulse labeling with tritiated thymidine. The concentration of Con A required to produce peak suppression varied from patient to patient with optimal doses ranging from 5 to 25 microgram/ml.