The effects of cyclophosphamide and irradiation singly and in combination upon SaI growth in A/J mice.

The effects of various doses of cyclophosphamide and low-dose (15 rads) radiation upon the size of tumors caused by 10(4) Sarcoma I (SaI) cells was determined. In intact A/Jax (A/J) recipients, the effect of the two agents singly and in combination was found to be dependent especially upon the dosage of cyclophosphamide and the time of its administration in relation to tumor inoculation. In cell transfer experiments to adult thymectomized, lethally irradiated, bone-marrow-restored (ATxXBM) mice, the effects of cyclophosphamide and irradiation appeared to be either overlapping (low dosages of cyclophosphamide) or additive (dosages of cyclophosphamide greater than or equal to 50 mg/kg), suggesting that the two agents exert their influence in dissimilar fashion, perhaps by injuring different cell types with the same basic function. The most pronounced conjoint effects are seen when low dosages of cyclophosphamide are given 3 days after the adoptive transfer of spleen cells from mice pretreated with low-dose irradiation. The implications of this observation with respect to immunotherapy are discussed.