Suppressor factor secreted by T-lymphocytes from tumor-bearing mice.

Spleen cells from C57BL mice bearing the syngeneic carcinoma 3LL enhanced tumor growth. Tumor growth was also enhanced by a soluble factor found in the media of cultured spleen cells from tumor-bearing animals. This factor suppressed a protective immune response of the host and was found to be a product of T-lymphocytes. Removal of B-lymphocytes and macrophages did not prevent its appearance in the culture media, whereas removal of T-lymphocytes inhibited its appearance. Similar suppressor factors were obtained from C3H mice bearing the 3LL tumor and from mice with other tumors. The suppressing factor produced after the growth of 3LL tumor also enhanced the growth of other tumors. It could act on strains incompatible with the donor of the factor-producing cells. Hence tumor growth was possibly facilitated by soluble products of T-lymphocytes that were found in spleens of tumor-bearing mice and that nonspecifically suppressed immune defense mechanisms.