BALB/c mice were inoculated subcutaneously with 10(6) cells from either of two syngeneic sarcomas 1315 and 1425. 6--8 days later, the mice were randomized into groups which were left untreated or given 400 rads of whole body irradiation. Irradiation significantly retarded the growth of both sarcomas, and complete regressions were seen of approximately equal to 30% of the small, established 1315 tumors. The anti-tumor effect of irradiation was abolished if the irradiated mice were inoculated with a T-cell-enriched (but not with a T-cell deprived) suspension of syngeneic spleen cells, suggesting that the irradiation inhibited tumor growth by affecting a radiosensitive population of host suppressor T cells.

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