The biology, pathology and immunology of a virus induced rat osteosarcoma. II. Immunological studies.

The immunogenicity of a virus-induced rat osteosarcoma was studied utilizing the lymphocyte microcytoxicity test. Lymphocytes from "progressor" animals (in which the tumour progressed and metastasized) demonstrated an ability to kill osteosarcoma cells in vitro, while serum from these animals abrogated or blocked the cell-mediated cytotoxicity. Lymphocytes from "regressor" animals (in which tumours failed to develop or regressed spontaneously) also showed cytolytic activity against osteosarcoma cells in vitro, but their serum failed to block the lymphocyte-mediated cytolysis. Both progressor and regressor animals demonstrated the presence of humoral cytotoxic antibodies to tumour antigens on the basis of the ability of their serum to kill tumour cells in vitro. In an attempt to alter the fatal course of the disease in progressor animals, immunoprophylaxis and immunotherapy of the osteosarcoma in F1 hybrid rats war carried out by injecting them with parentalor, third party, allogeneic lymphoid cells. Injection of parental spleen lymphocytes into F1 hybrids produced a transient graft versus host reaction (GVHR), and prolonged the survival of the animals when lymphocytes were injected three days before, seven days after and on the day of tumour induction. Injection of allogeneic, third party lymphoid cells produced no detectable GVHR and prolonged the survival of F1 hybrids with osteosarcoma only when injected on the day of tumour induction. The prolonged survival of the groups treated with parental lymphoid cells was a result of stimulation of the host's immunological mechanisms during a transient GVHR, whereas the prolongation of survival in the group given allogeneic cells was most likely the result of a direct action of the donor lymphocytes on tumour cells, and not connected to a GVHR.