Modulation of Immune Response against Tumor Cells by the in vivo Administration of an Autoreactive Th Clone

The immunization of C3H mice with irradiated syngeneic MM48 tumor cells induced specific tumor‐neutralizing cells (TNC). The TNC activity was mediated by the L3T4(+), Ly‐2(−) T cell population, and the generation of TNC coincided with the appearance of delayed‐type hypersensitivity response against MM48 antigen. The administration of an auto‐I‐A(k) reactive T helper cell clone MS202 to normal C3H mice resulted in the facilitation of growth of MM48 tumor due to the induction of T suppressor (Ts) cells. Splenic T cells from animals given this T cell clone inhibited the TNC activity of immunized mice resulting in the escape of MM48 from the TNC effect. The surface phenotype of the Ts cells was L3T4(+), Ly‐2(−). The Ts cells induced by the clone MS202 were totally antigen‐nonspecific, and were able to suppress both the effector and inductive processes of TNC. The results suggest the presence of a physiological MHC‐restricted T cell circuit that regulates immune responses against the growing tumors.