Cross-immunity between syngeneic tumors in mice immunized with gamma-irradiated ascites tumors

C3H/He mice immunized repeatedly with irradiated (13,000 rads 60Co) MM46 or MM48, both transplantable ascites mammary carcinomas of the same strain, were subcutaneously challenged with the identical or the different tumor. In mice immunized with irradiated MM46, the growth of challenges of not only MM46 but also MM48 was inhibited. On the other hand, in mice immunized with irradiated MM48, the growth of challenges of MM48 was inhibited, but the inhibition of the growth of MM46 was not observed. Cross-immunity, therefore, was shown by immunization with MM46 but not with MM48. These findings was considered to indicate that MM46 expressed cross-immunity against MM48 because of its high resistance to the irradiation, and that MM48 did not show cross-immunity to MM46 because of its low resistance to the irradiation.