Cellular hypersensitivity of gp55 of RIII-murine mammary tumor virus and gp55-like protein of human breast cancers.

Previous studies suggested that immunogenic breast cancer tissues contained a component(s) that is antigenically similar to some component of murine mammary tumor virus (MuMTV) and resembles the glycoprotein, M.W. 55,000 (gp55), of RIII-MuMTV in molecular weight and charge density. This investigation measured in vitro cellular hypersensitivity responses of breast cancer patients to RIII mouse milk, purified RIII-gp55, C3H-MuMTV, autologous and homologous breast cancer tissues, gp50 of A-MuMTV, and preparations of Rauscher leukemia virus and Mason-Pfizer monkey virus. Particular attention was paid to cross-reactivity between gp55 and the other targets. The data indicate that responsiveness to C3H-MuMTV and RIII milk are linearly correlated with responsiveness to gp55. A preferential relationship was demonstrable between responses to gp55 and to those breast cancer tissues containing a gp55-like protein component (S-p50). The critical role of a gp55-like protein as the antigen responded to by breast cancer patients' in leukocytes was also suggested by the ability of anti-gp55 antiserum to decrease leukocyte responsiveness to RIII-gp55, C3H-MuMTV, and breast cancer tissues. In vitro cellular hypersensitivity against RIII-gp55 was preferentially found in prognostically favorable cases with immunogenic lesions. Further studies are needed to test the possibility that gp55 might be of value in the immunodiagnosis of early breast cancer, the monitoring of prognostically significant cellular hypersensitivity, and the induction of such hypersensitivity (immunoprophylaxis).