Effect of heat treatment on tumor cells and antitumor effector cells.

We examined the effects of heat treatment on tumor cells and antitumor effector cells in order to investigate the combined effects of hyperthermia and immunotherapy including adoptive immunotherapy. Plasmacytoma MOPC104E syngeneic to BALB/c mice was used as the tumor cell line, while fresh spleen cells immunized to MOPC104E (IM-FSC) and interleukin-2-cultured lymphocytes induced in vitro from IM-FSC (CL) were used as the effector cells. Tumor cells or effector cells were heat-treated in a water bath at 42 degrees C for 30 or 60 min. Tumor cells heat-treated at 42 degrees C for 30 min grew temporarily and then regressed in the tumor transfer test, whereas untreated tumor cells showed no regression under any conditions. Furthermore, fresh spleen cells of mice inoculated with heat-treated tumor cells from regressed tumors showed marked tumor-neutralizing activity. The antitumor effects of CL were markedly inhibited by heat treatment according to the results of the tumor-neutralizing test and the 51Cr release assay, whereas heat treatment had little influence on the antitumor activity of IM-FSC. However, the neutralizing activity of effectors and the killing activity of CL against heat-treated tumor cells were both markedly augmented, since the susceptibility of the tumor cells to the antitumor effector cells was augmented by heat treatment. These results suggest that heat treatment of tumor cells augments the antitumor effects of IM-FSC and CL, hence we speculate that hyperthermia augments the effects of immunotherapy including adoptive immunotherapy.