Rejection of retrovirus-infected tumor cells in guinea pigs: effect on bystander tumor cells.

We studied the basis of rejection of retrovirus-infected tumor cells in guinea pigs by evaluating host response to injection of mixtures containing retrovirus-infected tumor cells and, antigenically and biologically distinct, uninfected tumor cells (line 10). After intradermal injection, line 10 grew progressively, metastasized to regional lymph nodes, and led to death of animals; line 107C3 4070A, a murine leukemia virus-infected fibrosarcoma cell line, grew for approximately 1 week and then regressed. Growth of the line 10 hepatoma was suppressed when the hepatoma cells were mixed with viable 107C3 4070A cells before injection into strain 2 guinea pigs. Viable virus-infected 107C3 cells were more effective than irradiated virus-infected cells in suppressing line 10 growth; mixture of line 10 with murine leukemia virus 4070A alone did not inhibit line 10 growth. Suppression of growth of line 10 cells by admixed murine leukemia virus 4070A-infected cells was less effective in animals with established viral immunity. Cyclophosphamide inhibited suppression of line 10 at sites of injection of virus-infected cells. Infection of line 10 with murine leukemia virus in vitro required cocultivation of line 10 cells with murine leukemia virus-infected fibrosarcoma cells; virus alone did not lead to acquisition of murine leukemia virus antigens by line 10 cells.