The immunogenicity of a virus-induced rat osteosarcoma was studied
utilizing the lymphocyte microcytotoxicity test. Intratibial injection of
murine sarcoma virus (Moloney) resulted in the development of palpable
tumors at the injection site which on histopathological examination
appeared to be osteosarcomas. In 73 per cent of animals injected these
tumors progressed and metastasized to the lungs. Lymphocytes from these
"progressor" animals demonstrated an ability to kill osteosarcoma cells in
vitro (as quantitated in the microcytotoxicity test) while serum from these
animals abrogated or blocked the cell-mediated cytotoxicity. In the
remaining animals the tumors either failed to develop or regressed
spontaneously. Lymphocytes from these "regressor" animals also demonstrated
cytolytic activity against osteosarcoma cells in vitro, but serum failed to
block the lymphocyte-mediated cytolysis. Both regressor and progressor
groups demonstrated humoral cytotoxic antibodies to tumor antigen on the
basis of the ability of their serum to kill tumor cells in vitro.