Regulation of immune responses against the syngeneic ADJ-PC-5 plasmacytoma in BALB/c mice. IV. Tumor-specific T suppressor cells, induced at early stages of tumorigenesis, act on the induction phase of the tumor-specific cytotoxic T cell response.

The BALB/c plasmacytoma ADJ-PC-5 induces specific non-cytolytic T suppressor (Ts) cells under experimental conditions which closely resemble early stages of tumorigenesis. The phenotype of these Ts cells is Thy-1.2+, Lyt-1.2-, Lyt-2.2+, I-Ad-. They inhibit the induction of the cytotoxic T cells in a primary mixed lymphocyte tumor culture (MLTC) against the ADJ-PC-5 plasmacytoma. Specificity of suppression can be demonstrated by testing them in MLTC against a panel of syngeneic control tumor. Only the induction phase of a primary MLTC can be suppressed, and within 24 h of MLTC, cytotoxic T (Tc) cells become resistant towards suppression. ADJ-PC-5-specific Tc cell clones are also resistant to suppression. The fact that Ts cell-mediated specific suppression can be overcome by addition of semipurified IL2 to the MLTC suggests that Th cells, and not Tc cell precursors, are the target. The findings are discussed with respect to the potential use of Tc effector cells in cancer therapy.