Enhancing T lymphocytes from tumor‐bearing mice suppress host resistance to a syngeneic tumor

Abstract

Abstract The cell‐mediated immune response of animals to a lethal syngeneic tumor was investigated by inoculating C57BL mice with Lewis lung carcinoma (3LL) cells T lymphocytes, obtained from the enlarged spleens of the tumor‐bearing mice were found to be cytotoxic to 3LL target cells in vitro . However, we found that such spleen cells enhanced tumor growth in vivo when mice were injected with a mixture of spleen cells and tumor cells. Removal of T lymphocytes by treatment of the spleen cells with anti‐Θ serum plus complement reduced the enhancement of tumor growth. Hence, the tumor enhancing cells, like the cytotoxic cells, appeared to be T lymphocytes. Removal of T lymphocytes from normal mice by adult thymectomy before tumor inoculation led to a reduction in the number of tumor metastases. Thus, enhancing T lymphocytes appear to exist in normal as well as in tumor‐bearing mice. Investigation of this mechanism of tumor enhancement suggested that the enhancing T lymphocytes act as suppressor T cells inhibiting natural immune resistance to tumor growth.