Suppression of the immune response to antigenic tumors in isogenic mice by whole-body irradiation.

It is known that sarcomas induced in mice with 3-methylcholanthrene (MCA) bear tumor-specific antigens which evoke specific immune responses when transplanted to isogenic animals. In this study, MCA-induced sarcomas were transplanted to iso genic C3H mice and the effect of immune suppression by wholebody X-irradiation on tumor growth was examined. The role of radiation dose, interval between irradiation and transplantation, and age was evaluated in animals irradiated before trans plantation. The results obtained in animals irradiated before transplantation were compared with those in animals irradiated after transplantation. Whole-body irradiation prior to transplantation resulted in marked acceleration of tumor growth. The degree of acceleration varied with the size of the dose—within certain limits; 200 rads given 24 hours before transplantation resulted in significant accel eration of growth compared to tumor growth in nonirradiated controls. The rate of growth further increased with a dose of 300 rads; additional increases in dose did not result in further accel eration of tumor growth. However, above 400 rads, a predictable increase in radiation mortality was encountered. The effect of irradiation with 400 rads on tumor growth varied inversely with the time between irradiation and tumor transplantation. The maximum effect was observed with a 24-hour interval; the degree of acceleration of tumor growth decreased as the interval was lengthened—some acceleration was still noted at a 4-month inter val. No age related differences in effect were evident in the range 2-15 months of age; however, only a few animals older than 12 months were included in the study. In contrast to these findings, tumor growth was not accelerated when irradiation followed transplantation.