Kinetics of responses to tumor antigens and mouse mammary tumor virus in BALB/cCrgl and BALB/cfC3H mice.

Spleen cells from BALB/cCrgl mice responded to murine mammary tumor virus (MuMTV) in cell-mediated immune assays at higher levels than did the spleen cells from the syngeneic BALB/cfC3H mice. Implantation in BALB/cCrgl with a chemically induced mammary tumor and in BALB/cfCrgl mice with spontaneous mammary tumors (SMT) arising in the same strain resulted in sensitization of these animals to the antigens of their tumors. Reactivities peaked 3 weeks after transplantation, whereas no positive reactions could be detected when tumors reached maximum size. A kinetic study with the use of MuMTV antigen(s) showed that the responses of lymphocytes from BALB/cfC3H with SMT followed the same pattern as that obtained with tumor antigens, which indicated that this might be a de novo sensitization. In sharp contrast, a steady type of response to MuMTV was observed with the spleen cells from BALB/cCrgl mice; i.e., the levels of responsiveness to MuMTV did not significantly vary at any stage of tumor development. In vivo studies explored the possible relevance of the in vitro cell-mediated immunity to the host defenses. MuMTV-expressing mammary tumor cells were implanted in BALB/cCrgl and BALB/cfC3H mice. The total incidence of tumors was significantly reduced and a delay occurred in their time of appearance in BALB/cCrgl mice in relation to BALB/cfC3H animals. Thus the in vitro reactivity to MuMTV antigen(s) in BALB/cCrgl mice was found to be coincidental with a degree of protection against the development of MuMTV-expressing mammary tumors.