Tumor-specific suppressor cells induced by immunization with spleen cells from tumor-bearing animals.

Spleen cells from Fischer rats immunized with syngeneic spleen cells immune to the syngeneic 13762A mammary adenocarcinoma inhibited in vitro generation of lymphocytes cytolytic to the tumor. Spleen cells from rats immunized with nonimmune spleen cells were not suppressive. The suppressive property was first detected 10 days after immunization, persisted through the 17th day, and generally correlated with the appearance of an immunoglobulin G (IgG) factor blocking cell-mediated cytotoxicity to the tumor. Suppression was mediated chiefly by T-lymphocytes, but IgG-bearing lymphocytes also had some suppressive ability. Suppression was induced by IgG-positive cells or by serum or IgG from rats immunized to the 13762A mammary adenocarcinoma. The suppressor cells in the spleens of serum-immunized rats appeared earlier (3 days) than after immunization with immune spleen cells (10 days). These results suggest that certain IgG-positive spleen cells, as well as IgG present in the same tumor-bearing animals, induce one type of suppressor cell modulating cytolytic lymphocyte activity to this mammary adenocarcinoma.