[Effect of preliminary administration of cyclophosphamide and pretransplantation irradiation on the growth of syngeneic tumors in mice].

The growth of the syngeneic tumor Acatol was retarded and the minimal number of tumor cells necessary for inoculation was increased in BALB/c mice preinjected with cyclophosphamide (100 mg/kg) and/or totally irradiated (5 Gy). Administration of spleen cells from intact mice abolished the antitumor effect of the above factors. The natural killer activity of spleen cells was estimated within 2-9 days after tumor inoculation. The natural killer activity in intact recipients was elevated on the 2nd day and then decreased to the control level. In irradiated recipients, the natural killer activity remained high throughout the entire observation period.