Characterization of T lymphocytes mediating in vivo protection against RSV‐induced murine sarcomas

Tumors induced by Rous sarcoma virus (RSV) in different mouse strains share a common tumor‐associated transplantation antigen, whose expression is controlled both by the viral transforming srcgene and by cellular gene(s) (Prat et al., 1981). The mechanism(s) responsible for the in vivo protective immune response against two RSV‐induced sarcomas has now been investigated. In the “Winn assay” the growth of both tumors was specifically prevented or significantly reduced by the simultaneous administration of lymphocytes isolated from immunized donors. The effector cells were radiosensitive (2,500 rad), Lyt‐l+, Lyt‐2,3+ Thy.l+ cells. Better protection was afforded by transfer of immune spleen cells from mice pre‐treated with cyclophosphamide, which is known to abrogate T‐cell suppressor activity. In a 5‐day mixed lymphocyte/tumor cell culture specific anti‐RSV‐induced sarcoma cytotoxic activity was barely detected, while a good production of interferon‐gamma (IFN‐y) was observed. The cells involved showed the same functional and surface phenotype as displayed by the effectors of the “Winn” assay. It is concluded that in the immune rejection of RSV‐induced sarcomas, Lyt‐l+, Lyt‐2,3+ T cells, rather than cytotoxic T lymphocytes, and lymphokines such as IFN‐γ are involved.