Specific cytotoxicity in vitro by T-cell-enriched lymphocyte subpopulations from rats bearing chemically induced but not spontaneous tumors.

Effector cells from inbred BD X and WAB rats bearing either spontaneously arising or chemically induced tumors were cytotoxic for target cells of both kinds of tumor. The level of cytotoxicity of tumor-bearing animals regularly surmounted that of natural cytotoxicity observed in age-matched untreated controls. These findings were obtained by a visual-countin microcytotoxicity assay (48 hr) and by a 51Cr label assay (12 hr). Cytotoxicity by tumor-bearing rat effectors was directed against the homologous tumor target cell line, different tumor cells of the same inbred rat strain, tumor cells derived from allogeneic rats, and fetal fibroblasts, but not against adult fibroblasts. Separation of lymphocytes by rosetting with sheep red blood cells (SRBC) loaded with either antiimmunoglobulin or anti-SRBC or with anti-SRBC and complement revealed that cross-reactive cytotoxiciy was confined to a non-T effector cell population, which was observed with lymphocytes from rats bearing either chemically induced or spontaneous tumors. Cytotoxicity directed exclusively against the tumor of the lymphocyte donors was exerted by the T-cell-enriched fraction. This element was completely absent in lymphocytes from animals bearing spontaneous tumors, but it was detected in lymphocytes from donors with chemically induced (immunogenic) tumors.