Antigen-specific release of IFN-γ by transduced CD8⁺ T cells is critical for enhanced survival of mice. The scid mice were given intravenous injections of 5 × 106 MDA-MB-435-erbB2 tumor cells followed by combined transfer of transduced CD8⁺ (5 × 106) and CD4⁺ (5 × 106) donor T cells at day 5 from BALB/c wild-type or BALB/c IFN-γ^–/–mice. Mice received either 1:1 transfer of scFv-CD28-ζ–transduced CD8⁺IFN-γ⁺/+/CD4⁺IFN-γ⁺/+ T cells (▪), CD8⁺IFN-γ^–/–/CD4⁺IFN-γ^–/–T cells (▴), CD8⁺IFN-γ^–/–/CD4⁺IFN-γ⁺/+ T cells (○), or CD8⁺IFN-γ⁺/+/CD4⁺IFN-γ^–/–(▵) T cells. Control mice received a 1:1 transfer of wild-type CD8⁺ and CD4⁺ T cells transduced with the scFv-anti-CEA-γ receptor (□). Results are calculated as the percentage of each group surviving and are representative of 2 experiments. Arrows depict the day of T-cell transfer (*P < .05, Mann-Whitney test).