Augmentation of antitumor cytotoxicity of MOPC-315 tumor bearer spleen cells by depletion of dinitrophenol-adherent cells prior to in vitro immunization.

In vitro immunization of spleen cells from normal BALB/c mice with mitomycin C-treated MOPC-315 tumor cells resulted in high levels of in vitro antitumor cytotoxicity, whereas in vitro immunization of spleen cells from mice bearing large s.c. MOPC-315 tumors resulted in virtually no antitumor cytotoxic ity. The inability of immunized tumor bearer spleen cells to mediate in vitro antitumor cytotoxicity appeared to be due to the presence of metastatic tumor cells and an increased per centage of macrophages in the spleen. Partial recovery of antitumor potential of tumor bearer spleen cells was achieved by depletion of dinitrophenol-adherent cells prior to in vitro immunization. Such a depletion included the removal of most tumor cells with a minimal reduction in the percentage of macrophages. The ability of tumor cells to inhibit the generation of antitumor cytotoxicity was confirmed by the reduced levels of antitumor cytotoxicity obtained when viable tumor cells were added to the immunization mixture of normal spleen cells and mitomycin C-treated tumor cells. Tumor cells appeared to inhibit at the effector stage of antitumor cytotoxicity, since reduced levels of antitumor cytotoxicity were exhibited by immunized normal spleen cells when admixed with immunized tumor bearer spleen cells just prior to their evaluation in the 51Cr release assay. Depletion of glass-adherent cells from tumor bearer spleen cells prior to in vitro immunization, resulted in much greater augmentation in the level of antitumor cytotox icity than that obtained with the same spleen cells that were depleted of dinitrophenol-adherent cells prior to immunization. Depletion of glass-adherent cells included not only the removal of most tumor cells, as did depletion of dinitrophenol-adherent cells, but also the removal of most macrophages.