CTL response not affected in IFN-γ knockout tumors. (A) CTL lysis of Tax⁺IFN-γ^+/+ and Tax⁺IFN-γ^-/- tumors by in vitro-stimulated Tax⁺ splenocytes. In vitro-restimulated splenic lymphocytes from 3 mice were used to measure the ability of Tax-specific CTLs to lyse specific targets from IFN-γ⁺ and knockout Tax tumor cells at different target-effector ratios, in triplicate in a 24-hour LDH release CTL assay, as described in “Materials and methods.” MHC-matched EL-4 and Tax-transfected EL-4 targets were used as controls in a similar CTL lysis assay. Standard error of the mean (SEM) is represented as error bars. (B) CTL lysis of Tax⁺IFN-γ^+/+ and Tax⁺IFN-γ^-/- tumors by in vitro-stimulated splenocytes from IFN-γ[ϵν] deficient Tax mice. Graph represents the cytolytic T-cell profile in Tax⁺IFN-γ^-/- (spleen T) cells upon in vitro stimulation with Tax expressing EL-4 cells. Vector DNA-transfected EL-4 cells were used as targets to measure background lysis. Error bars correspond to SEM of triplicate samples from 3 mice.