Correlation of antitumor chemoimmunotherapy with serum inhibition of tumor cell destruction

The administration of cyclophosphamide and Corynebacterium parvum in combination results in tumor growth inhibition greater than that resulting from the use of either agent alone. The precise mechanism(s) by which this chemoimmunotherapy combination results in a synergistic inhibiting effect is not known. The possibility was entertained that the tumor effect might be related to a greater decrease in serum-mediated interference with cellular cytotoxicity, i.e., "blocking" activity, by both agents in combination rather than by either alone. The present findings fail to support such an explanation. C. parvum by itself failed to decrease serum inhibition and in conjunction with cyclophosphamide resulted in an effect that was no greater than that produced by cyclophosphamide alone.