Suppression of cell-mediated antitumor immunity by complete Freund's adjuvant.

The effect of complete Freund's adjuvant (CFA), which is one of the strong immunoadjuvants, on the induction of either cytotoxic or suppressor T-cells against syngeneic tumors was investigated by an in vitro assay system. CFA did not show the apparent augmenting activity in the induction of cytotoxic T-cells against syngeneic tumors when it was administered i.p. to mice receiving s.c. inoculations of mitomycin C-treated tumor cells. The treated animals failed to develop stronger resistance against the second inoculum of the same viable tumor cells. Furthermore, CFA had an effect on the induction of suppressor T-cells in tumor-bearing hosts in which suppressor T-cells had been readily activated. Suppressor T-cells developed in syngeneic tumor-bearing mice treated with CFA was tumor specific. Tumor growth was enhanced when CFA was administered to mice given s.c. inoculations of the homologous tumor.