Selective Suppression of the Generation of Anti‐tumor L3T4(+) but Not of Lyt‐2(+) T Cell‐mediated Immunity in the Tumor‐hearing State

C3H/He mice hyperimmune against syngeneic MH134 hepatoma were prepared by intradermal (id) inoculation of viable tumor cells followed by surgical resection of the tumor and by repeated id challenges with viable tumor cells. Winn assays performed utilizing spleen cells from these mice have revealed that both Lyt‐2(+) and L3T4(+) T cell subsets from MH134‐hyperimmune mice produced complete tumor protection. The in vivo tumor‐neutralizing activity was also found in spleen cells from tumor‐bearing mice at various times after id implantation of MH134 tumor cells. However, in contrast to comparable tumor‐neutralization by Lyt‐2(+) and L3T4(+) T subsets from hyperimmune mice, only the Lyt‐2(+) T cell subset from tumor‐bearing mice was capable of mediating the in vivo protective immunity. L3T4(+) T cell‐mediated immunity was not detectable in the tumor‐bearing state irrespective of the length of the sensitization period with a primary growing tumor, but emerged in the mice which resisted the first tumor challenge after the resection of the primary tumor. These results indicate that the emergence of L3T4(+) T cell‐mediated anti‐tumor immunity is stage‐dependent and the Lyt‐2(+) T cells represent the main functional subset in the tumor‐bearing state, although both subsets of T cells are potentially capable of effecting anti‐tumor in vivo immunity. The results are discussed in relation to the selective suppression of the L3T4(+) but not of Lyt‐2(+) T cell function in the tumor‐hearing state.