Activation of specific suppressor cells with heat-treated allogeneic tumor cells

The ability of heat-treated allogeneic cells to induce suppressor cells was examined. The tumor cell lines EL-4 (H-2^b) and P815-X2 (H-2^d), were heated to 56 °C for 10 min and injected intravenously into mice of the DBA/2J (H-2^d) and C57BL/6J (H-2^b) strains, respectively. After 4 days, the splenocytes of the treated mice were mixed with normal spleen cells and cultured for 5 days with allogeneic tumor cells. The cytotoxic T-cell response was reduced in cultures of these cell mixtures. An allogeneic difference was required to induce suppression because the syngeneic combination did not induce suppressor cell activity. Furthermore, the induction of cytotoxic T cells to the C118 cell line (H-2^k) was not suppressed by this procedure, which suggests that the suppression was haplotype specific. These suppressor cells were sensitive to anti-Thy 1.2 and complement, cortisone, and cyclophosphamide, but insensitive to irradiation. These are characteristics similar to suppressor cells activated by intact cells. Heat treatment abrogated the tumor cell's ability to induce a proliferative and a primary, but not a secondary, cytotoxic T-cell response. The heat-treated cells also lost their ability to function as cold target inhibitor cells, but retained the same quantity of serologically detected antigens as the intact cells. These results suggest that the serologically detected antigens are responsible for the activation of the suppressor cells of the cytotoxic T-cell response.