Enhancement of concomitant immunity after radiation therapy and immunotherapy in a syngeneic murine tumour system.

Concomitant immunity was evaluated in vivo towards a chemically induced epidermoid carcinoma transplanted in a syngeneic situation. Radiation therapy reversed the declining phase of concomitant immunity associated with tumour progression. The rejection rate of a challenge graft amounted to 82 and 95 per cent, respectively, 2 and 8 days after 25 Gy as compared with 55 and 43 per cent in unirradiated controls. Radiation induced immune recovery was dose related and proved to be different from restoration of immunity following surgical removal of the tumour. Immunotherapy with intraperitoneal injection of Corynebacterium parvum significantly improved concomitant immunity. Immunostimulation and irradiation at low dosage act synergistically on host anti-tumour resistance.