Mammary tumorigenesis and mammary tumor transplantation immunogenicity were examined in breeding females of 2 syngeneic sublines of the C3H strain: in mammary tumor virus (MTV) plus nodule-inducing virus-infected C3H/Sed mice; and in MTV-free, nodule-inducing virus-infected C3Hf/Sed mice.

Ninety-seven % of the C3H mice (29 of 30) developed mammary tumors at an average age of 280 days. Of 43 different C3H tumors tested for transplantation immunogenicity in the C3H strain of origin, 13 (30%) had non-MTV-associated tumor-specific transplantation antigens (TSTA). Of 5 primary C3H hosts that developed multiple mammary tumors, 4 animals developed both TSTA-positive and TSTA-negative tumors. All C3H tumors tested (20 of 20) for antigenicity in the C3Hf strain had MTV-associated transplantation antigens.

Sixty-nine % of the C3Hf mice (34 of 49) developed mammary tumors at an average age of 708 days. Of 16 different C3Hf tumors tested for antigenicity in the C3Hf strain of origin, 1 (6%) had TSTA.

Mammary tumorigenesis and mammary tumor transplantation immunogenicity were examined in explants of 2 separate MTV-free C3Hf/Ki hyperplastic alveolar nodule (HAN) outgrowth lines transplanted to the cleared mammary fat pads of syngeneic MTV-free C3Hf/Ki mice and transplanted to the cleared mammary fat pads of syngeneic MTV-infected C3H/Ki mice. Tumor development in HAN line 1 was 44% at 297 days in C3Hf recipients and 100% at 175 days in C3H recipients. Tumor development in HAN line 2 was 75% at 225 days in C3Hf recipients and 87% at 142 days in C3H recipients. One of 9 HAN line 1 tumors acquired TSTA during development in the C3Hf/Ki strain: 0 of 10 acquired TSTA during development in the C3H/Ki strain. Each tumor tested had acquired virus-associated transplantation antigens during development in the C3H/Ki strain. One of 14 HAN line 2 tumors acquired TSTA during development in the C3Hf/Ki strain; 0 of 15 acquired TSTA during development in the C3H/Ki strain.

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This work was supported in part by USPHS Grants CA 13018, CA11944, and CA13261.

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