The enhanced in vivo antitumor efficacy of in vitro programmed T_EM cells is dependent on IFN-γ production but independent of T-cell responsiveness to IFN-γ. WT mice bearing 10 days established B16 melanoma were sublethally irradiated and left untreated as controls (×) or received unprogrammed pmel T_EM cells (●), or pmel T_EM (□) cells, pmel-Ifng^−/− T_EM cells (■), or pmel-Ifngr1^−/− T_EM cells (♦) programmed in vitro with anti-CD3/anti-CD28 for 24 hours before transfer. For mice receiving programmed pmel T_EM, pmel-Ifng^−/− T_EM cells, or pmel-Ifngr1^−/− T_EM cells, cultures were started with 2 × 10⁶ cells per recipient mouse, and the total number of cells present at 24 hours were transferred. Mice treated with nonprogrammed pmel T_EM cells received 2 × 10⁶ cells. All treated mice received rhIL-2 (36 μg/dose × 6 doses). Results from different representative experiments are presented as the mean measurements from 5 mice per group (± SEM).