Correlation of differences in antigenicity of four 3-methyl-cholanthrene-induced tumors in syngeneic mice with the susceptibility of tumors to an immunopotentiator, PS-K.

Eleven syngeneic tumors were induced by 3-methylcholanthrene in DDD mice. Their antigenicity in vivo was examined by measuring growth inhibition of transplanted tumors in mice immunized by implanting tumors into their tail and then cutting off the tail. Four tumors with different antigenicity were selected from them for study. The growth-suppressive effect of an immunotherapeutic agent, PS-K, on the four tumors was examined. The growth of highly antigenic tumors in mice was inhibited by PS-K, but that of weakly antigenic tumors was not, and a close correlation was found between the antigenicity of tumors and the antitumor activity of PS-K against them. No similar correlation was found between their antigenicity and their sensitivity to a mitotic poison, 6-mercaptopurine. These results suggest that the antitumor effect of an immunopotentiator depends greatly on the antigenicity of tumors.