aAPC-mediated stimulation of mHag-specific CTL clones. Proliferation (A) and IFN-γ production (B) of various HA-1–specific CTL clones (2.12, 3HA15, 5W38) and HA-2–specific CTL clones (1.7, 1.9) incubated for 48 hours with medium only, with aAPCs coated with the costimulatory molecules CD80 and CD54, with aAPCs coated with costimulatory molecules and either HLA-A2/HA-1 or HLA-A2/HA-2 complexes, or with HA-1⁺/HA-2⁺ EBV-LCLs. Cytotoxic activity (C) of 2 CTL clones (2.12, 1.7) was determined after incubation for 7 days with medium only, with HA-1⁺/HA-2⁺ EBV-LCLs, or with aAPCs coated with specific ligand. Cytotoxic activity is shown for an effector-target ratio of 8:1. Data are presented as the mean percentage of lysis ± SD.