The abrogation of in vivo resistance to parental bone marrow transplantation and of in vitro natural cell-mediated cytotoxicity to the YAC lymphoma by in vivo growth of a transformed thymus-derived cell culture.

A thymus-derived monolayer culture, referred to as E1, from (C57Bl/6 X A)F1 hybrid mice was continuously passaged in vitro for over three years and formed rapidly growing, non-metastasizing tumors when injected s.c. into syngeneic mice. The spleens of tumor-bearing mice were greatly enlarged, but no tumor cells were detected in these spleens. The natural cell-mediated cytotoxic activity of spleen cells of tumor-bearing mice decreased with increasing tumor size. In addition, the expression of genetic resistance to transplantation of C57Bl/6 parental bone marrow cells was decreased in the spleens of irradiated tumor-bearing mice. This correlation between the expressions of natural cell-mediated cytotoxicity and of genetic resistance to bone marrow transplantation is consistent with the hypothesis that both of these responses are mediated by the same population of effector cells.