In vitro generation of cytotoxic lymphocytes against radiation- and radiation leukemia virus-induced tumors. III. Suppression of anti-tumor immunity in vitro by lymphocytes of mice undergoing radiation leukemia virus-induced leukemogenesis

Adult C57BL/6 mice exposed to fractionated irradiation or inoculated with the radiation leukemia virus (RadLV), develop high incidence (80-100%) of lymphatic leukemias within 3-6 mo. RadLV-induced lymphomas can elicit cytotoxic responses in vitro in lymphocytes of preimmunized syngeneic mice, a reaction that is dependent on the expression of membrane-associated viral antigenicity. As soon as 5 d after RadLV inoculation, and during the entire leukemogenic process, suppressor T cells are detectable in the spleen that are capable of specifically abrogating generation of syngeneic anti-tumor cytotoxic cells in vitro. Mice exposed to fractionated x irradiation do not develop suppressor cells and their splenocytes may be stimulated in vitro to generate cytotoxicity toward RadLV-induced leukemias. These findings suggest that although RadLV has been isolated from radiation-induced leukemias, x-ray- and RadLV-induced leukemogenesis do not seem to involve a common viral etiology, and that induction of suppressor cells during RadLV leukemogenesis may be essential for tumor progression.