Cross-immunity among allogeneic tumors in rats immunized with gamma-irradiated ascites tumors.

Non-inbred rats of the Gifu strain were intraperitoneally challenged with Hirosaki sarcoma (tetraploid type, 10(5) cells) after repeated immunization with gamma-irradiated (13,000 rads 60Co) allogeneic non-viral tumors of ascites type (tetraploid or diploid type of Hirosaki sarcoma, Usubuchi sarcoma or AH130). In rats immunized not only with the same tumor as the immunizing tumor but also with a different tumor, the growth of the challenge tumor was markedly inhibited as compared with the control in non-immunized rats. It is considered that these tumors retained common antigen(s) by the resistance to irradiation because of their form of ascites tumor. The marked cross-immunity in rats immunized with AH130 may be explained by the fact that gamma-irradiated AH130 cells were alive longer in the peritoneal cavity than other tumors on account of its high resistance to irradiation.