Antitumor immunity, V.BCG-induced growth inhibition of murine tumors. Effect of hydrocortisone, antiserum against theta antigen, and gamma-irradiated BCG.

Dimethylbenzdithionsaphthene (DBDN)-induced fibrosarcoma transplantable in syngeneic Swiss mice was a weakly immunogenic tumor and did not regress spontaneously. BCG from India, when incubated with the lethal dose of DBDN-induced fibrosarcoma and subsequently inoculated sc into the susceptible animal markedly inhibited growth of the tumor. Animals that did not show any tumors developed tumor-specific immunity. BCG, if administered separately and not inoculated with the tumor cells, did not show similar response. The close contact between the BCG organism and the tumor cell seemed to be an essential requirement for BCG-induced tumor-growth inhibition. Hydrocortisone-treated animals showed tumor growth even when a BCG-tumor admixture was incorporated, indicating the immunologic nature of the phenomenon. Animals preinoculated with anti-O-serum also showed tumor growth when the BCG-tumor admixture was given. This, however, pointed out a major role of O-bearing lymmphocytes in BCG-induced-tumor-growth inhibition.