In vitro reactivity of splenic lymphocytes from normal and UV-irradiated mice against syngeneic UV-induced tumors.

Skin tumors induced in mice by chronic ultraviolet (UV) irradiation are highly antigenic and are frequently immunologically rejected upon transplantation to normal syngeneic recipients. In this study we characterized this immune response with an in vitro microcytotoxicity test. Cytotoxic activity was present in the spleen cells of mice given a single injection of syngeneic UV-induced fibrosarcoma cells. After removal of adherent spleen cells, the remaining splenic lymphocytes were specifically cytotoxic for the immunizing tumor and showed no cross-reactivity with other syngeneic UV-induced or methylcholanthrene-induced tumors of similar histologic type. The level of cell-mediated reactivity against UV-induced tumors was quite high compared to that obtained with syngeneic tumors induced by methylcholanthrene, and the cytotoxicity was attributable to a population of theta antigen-bearing lymphocytes. With this in vitro test, we compared the response of normal mice, which reject a syngeneic tumor challenge, with that of UV-irradiated mice, in which the syngeneic UV-induced tumors grow progressively. After tumor cell inoculation, lymphocytes form the unirradiated (regressor) mice showed a high degree of cytotoxicity that reached a maximum level 8 days after injection. In contrast, no reactivity could be detected in the spleens of tumor-challenged UV-irradiated (progressor) mice.