HA-1 CTLs lyse tumor cells in vitro. The in vitro killing efficacy of CTLs was determined in a chromium⁵¹ release assay. All target cells are HLA-A2⁺. The allo–HLA-A2 CTL clone lyses all target cells, the HA-1 CTL clones lyse only HA-1⁺ target cells, and the H-Y CTL clone lyses only H-Y⁺ target cells. X-axis represents the mean percentage specific lysis (2 measurements per condition); y-axis, CTL clones each in 2 different effector to target ratios. EBV LCL indicates Epstein-Barr virus/lymphoid cell line.