Monoclonal antibodies against murine IFN-gamma abrogate in vivo tumor immunity against RSV-induced murine sarcomas.

Previous work has shown that immunization of syngeneic mice with v-src-induced sarcomas gives rise to specific protection against a lethal dose of v-src-transformed fibroblasts. This immune response is mediated by Lyt-1+, Lyt-2,3+ T lymphocytes, with no apparent involvement of cytotoxic T cells, as shown in Winn-type assays. Immune cells mediating tumor rejection in this system have now been further characterized, and it was found that L3T4+ T lymphocytes alone provided full protection against v-src-induced sarcomas. Moreover, the role of interferon-gamma (IFN-gamma) in the tumor rejection was analyzed. A monoclonal antibody directed against this lymphokine was able to reverse the protective effect displayed by immune T lymphocytes, by eliciting highly effective T suppressor cells. It was thus concluded that T cells with L3T4 surface marker are the main thing responsible for the adoptive immunity in this tumor system, and the activity of these cells is positively modulated by lymphokines such as IFN-gamma.