Enhanced Lymphocyte-mediated Killing of Tumour Cells after Tumour Irradiationin Vivo

Abstract

The effect of local X-irradiation of a syngeneic carcinoma or fibrosarcoma growing in the leg of W/Fu rats on the ability of host spleen lymphocytes to kill syngeneic and allogeneic tumor cells in vitro was examined. Lymphocytotoxicity was enhanced (1) day after local X-irradiation (4000 R) when compared with unirradiated tumor-bearing rats (P = 0.05-0.01). This enhancing effect of local irradiation was not observed when the lymphocytes were tested 1 wk or later after X-irradiation, nor when normal legs of non-tumor bearing rats were irradiated. Mechanisms which might possibly explain these results are a reduction in release of tumor-specific antigen which can act as an inhibitor of cell-mediated cytotoxicity, or depletion of suppressor cells in the lymphocyte population. These findings may be relevant to clinical studies of cellular immunity in patients undergoing radiotherapy or malignant tumors.