Myeloid leukemic CD34⁺ progenitor cells from AML patients are efficiently lysed by LRH-1–specific CTLs. Survival of sorted CD34⁺ leukemic cells in flow cytometry–based cytotoxicity assays was determined from 4 HLA-B7⁺ patients after incubation with LRH-1–specific CTL RP1 (▴), HLA-B7-specific CTL KOR18 (▾; ie, positive control), or medium (♦) in the presence of growth factors. Proliferation of viable CFSE-labeled leukemic cells is shown from 2 LRH-1⁺ AML patients (A,B) and from 2 LRH-1⁻ AML patients (C,D) in the absence or presence of CTLs at an E/T ratio of 0.5:1. Data are depicted as mean plus or minus SD of triplicate wells.