Antigenic differences among virus-induced mouse mammary tumors arising spontaneously in the same C3H-Crgl host.

The immunogenicity of multiple, distinct, mammary tumor virus-induced mammary carcinomas which arose spontaneous ly in the same C3H mouse has been surveyed in MTV-infected syngeneic C3H hosts and in MTV-free syngeneic C3Hf hosts. Nineteen different tumors from 4 original hosts were tested. Whereas all tumors tested were immunogenic in C3Hf hosts, only 5 out of 19 tumors were immunogenic in C3H hosts. All tumors tested for antigenic cross-reactivity did cross-react in C3Hf hosts. Two tumors from the same original C3H donor were immunogenic in C3H hosts but did not cross-react. The results also show that one mouse may develop both immunogenic and nonimmunogenic spontaneous tumors at the same time. This excludes the possibility that minor histocompatibility differences between donor and recipient could be the cause of resistance to tumor grafts in syngeneic C3H mice and confirms a previous conclusion that virus-induced tumors may possess individually distinct tumor antigens in addition to virus-associated antigens. It is suggested that the appearance of individually distinct, nonvirus-associated antigens in virusinduced tumors may indicate a similarity in the action of viral and chemical carcinogens.