Abstract
We have studied whether specific immunization administered intraperitoneally can augment the activity ofC. parvum (0.25 mg intraperitoneally or intravenously) against intravenously injected cells of a syngeneic fibrosarcoma in C~3~Hf/Bu mice as expressed by the reduction of pulmonary metastases (nodules, colonies) and/or by the prolongation of the survival of recipients. Combination of specific immunization and C. parvum, applied either before or after IV inoculation of viable tumor cells, was more effective than the single treatments. IV injection of a mixture of heavily irradiated and viable tumor cells gave more tumor nodules in the lungs of normal mice than injection of viable cells alone. The metastasis‐enhancing effect of admixed irradiated cells was not found in mice previously treated with C. parvum, and was abolished if the immunostimulant was injected after tumor cells. Generation of lung metastases by IV inoculation of fibrosarcoma cells was reduced in mice already having this tumor in the leg. This concomitant immunity to metastases was increased by treating the recipients with C. parvum, but not with irradiated cells: also, the injection of irradiated cells together with C. parvum did not augment the efficiency of the latter. C. parvum was not as effective in T‐cell deprived as in control mice, which suggests that in this system, T‐cells are required for optimal anti‐tumor activity of this immunostimulant. Specific immunization was not effective in T‐cell‐deprived mice and did not augment the efficiency of C. parvum.