Radiation-induced augmentation of the response of A/J mice to SaI tumor cells.

Whole-body exposure of A/J mice to low doses (5-25 rads) of ionizing radiation immediately prior to the inoculation of 10(4) Sarcoma I (SaI) cells results in smaller tumors than are observed in sham-irradiated control animals. The irradiated group also contains a greater proportion of mice that fail to develop tumors or that demonstrate tumor regression. Low-dose augmentation is 1) less pronounced in recipients that have undergone splenectomy; 2) not evident in adult thymectomized-lethally irradiated-bone-marrow-restored (ATxXBM) animals, where the opposite effect is seen (eg, low-dose enhancement of tumor growth); and 3) abolished by the administration of normal syngeneic spleen cells unless the latter have been depleted of T cells. On this basis, a very radiosensitive T cell with suppressor activity is implicated in this phenomenon. Low-dose exposure at various times prior to tumor inoculation suggests that this cell regenerates in 5-10 days after irradiation.