Evidence that tumor antigens enhance tumor growth in vivo by interacting with a radiosensitive (suppressor?) cell population.

The growth of a small number of cells from each of two chemically induced BALB/c sarcomas was enhanced when x-irradiated (15,000 rads) cells of the same sarcoma were mixed with the tumor inoculum. This enhancement did not occur if the recipients had been given a total body x-irradiation of 450 rads. Tumor neutralization (Winn) tests showed that tumor cells irradiated in vitro enhanced tumor growth only in the presence of radiosensitive cells present in the spleens of both nonimmune and tumor-bearing mice. On the basis of these findings we postulate that tumor antigen blocks effective tumor immunity by a mechanism that involves a suppressor cell population.