Neoantigens on spontaneous and carcinogen‐induced rat tumours defined by in vitro lymphocytotoxicity assays

Lymph‐node cells from rats bearing tumours apparently lacking in tumour rejection antigens were cytotoxic in vitro for cultured tumour cells. The specificities of these reactions differed, however, from those demonstrated with immunogenic chemically‐induced rat tumours since cross‐reactivity was observed, especially between tumours of the same histological type. This was most clearly demonstrated in tests with rat mammary carcinomas where tumour‐bearer lymph‐node cells were cytotoxic for a range of mammary carcinomas including spontaneously arising and chemically‐induced tumours. The reactivities of tumour‐bearer lymph‐node cells could be blocked by pre‐treating target cells with serum of tumour‐bearing rats and also by sera of multiparous rats. Conversely, tumour‐bearer sera were highly effective in blocking embryo cells from attack by sensitized LNC from multiparous rats. The results suggest that antigens detected on these tumours by the in vitro assay were embryonic components which were immunogenic in the tumor‐bearing host, although they were not capable of inducing tumour‐rejection reactions in immunized rats.