CD8⁺ minor H antigen-specific CTL clones demonstrate cytolytic activity against leukemic blasts in vitro that is blocked by antibody to class I MHC. Activity of HLA-A3–restricted clone DRN-7 (A) and HLA-B7–restricted clones ATT-4 (B) and ATT-7 (C) against panels of leukemic cells in the absence (□) or presence (▪) of anti-pan class I MHC antibody W6/32 at 25 μg/mL. The target cell panel in (A) was derived from 11 different HLA-A3⁺patients: 7 with AML, 2 with ALL, and 2 with CLL. The target cell panel in (B) and (C) was derived from 5 different HLA-B7⁺patients: 4 with AML and 1 with CLL. E:T was 20:1 in all experiments.