Human WT1.37-specific CTL kill WT1-expressing tumor cell lines and WT1-positive primary leukemia cells in a HLA-class I–dependent manner. WT1.37-specific CTLs were tested in a chromium release assay for lytic activity against (A) 697 and RS 4,11 cell lines (both HLA-A*0201⁺WT1⁺) and primary WT1⁺ leukemia cells from 4 different HLA-A*0201⁺ patients (I-IV) alone at the effector/target (E/T) ratios indicated or (B) in the presence of an antibody specific for HLA-class I (W6.32), alone (without Ab) or with an isotype control (+ isotype) at an effector/target cell ratio of 60:1 (targets 697, RS 4,11 and sample III) or 100:1 (sample II). (C) WT1.37-specific CTL were tested for lytic activity against target cells from 2 different WT1⁺ and HLA-A*0201⁻ patients (V and VI). Data are a combination of 2 experiments with 2 different WT1.37-specific CTL lines, differentiated by □ or .