Prevention of syngeneic tumor growth in vaccinia virus-primed mice by immunization with vaccinia virus-modulated tumor cells.

Immunization with vaccinia virus-infected and then X-ray-irradiated murine hepatoma MH134 cells provided C3H/He mice with strong resistance to challenge with viable MH134 cells. Male C3H/He mice of 5 to 6 weeks old were primed intraperitoneally (IP) with 1 x 10(7) PFU of live vaccinia virus (Ikeda strain) after irradiation with 250 R of X-ray. Three weeks after priming, the mice were immunized IP 3 times at weekly intervals with 1 x 10(7) X-ray-irradiated MH134 cells that had been infected with vaccinia virus 8 h before irradiation. Over 60% of these cells showed vaccinia virus-induced antigen on their surface (membrane antigen). Challenge with viable MH134 cells was done by inoculating 1 x 10(5) cells IP one week after immunization. During a 4-week observation period, all the untreated control mice died with ascites. On the contrary, all the mice that were X-ray-irradiated, primed and immunized survived challenge with the tumor cells for at least 4 weeks. The mortalities of mice in other groups that were not irradiated, or not primed, or immunized with only X-ray-irradiated tumor cells, were at lowest 50%.