Myeloid leukemic CD34⁺ progenitor cells from accelerated-phase CML Pt1 are efficiently lysed by LRH-1–specific CTLs under inflammatory conditions and with relatively high E/T ratios. (A) Subpopulations of CD34⁺ cells in relapse samples 1 and 2 from CML Pt1 were phenotyped with antibodies directed against CD38, CD117, CD33, CD13, and CD133. (B) Survival of sorted CD34⁺ leukemic cells from relapses 1 and 2 from Pt1 was determined in flow cytometry–based cytotoxicity assays 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 in the absence or presence of CTLs at an E/T ratio of 3:1. Data are depicted as mean plus or minus SD of triplicate wells. (C)usb Pretreatment with IFN-γ increases susceptibility to LRH-1 CTL-mediated lysis. Percentage survival of CD34⁺ cells from relapse 2 with or without preincubation with inflammatory cytokine IFN-γ in the presence of LRH-1–specific CTL RP1 was determined in flow cytometry–based cytotoxicity assays. Survival is calculated compared with medium after coculture at an E/T ratio of 10:1. Data are depicted as mean plus or minus SD of triplicate wells. (D) Higher E/T ratios result in improved lysis of IFN-γ–pretreated CD34⁺ cells from relapse 2. Survival of sorted CD34⁺ leukemic cells from relapse 2 from Pt1 was determined in flow cytometry–based cytotoxicity assays after incubation with LRH-1–specific CTL RP1 at E/T ratios 10:1 (■), 3:1 (▴), and 0.5:1 (●) or medium (♦) in the presence of growth factors. Data are depicted as mean plus or minus SD of triplicate wells.