CML neutrophils confer growth advantage to CML cells. Mixtures of 10⁵ normal (HLA-A2) and CML (HLA-A2^-) CD34⁺ cells were cultured in 2 mL serum-free medium supplemented with 10 ng/mL G-CSF, GM-CSF, and SCF in the presence of varying concentrations of CML neutrophils. After 8 days of culture, nucleated cells were counted, harvested, and analyzed for the percentage expression of HLA-A2. (A) Percentage and (B) absolute number of HLA-A2-positive (normal) and HLA-A2^- (CML) cells in the presence of increasing numbers of CML neutrophils (▪, HLA-A2⁺ cells; □, HLA-A2^- cells). (C) Percentage and (D) absolute number of HLA-A2⁺ (normal) and -negative (CML) cells in the presence of CML neutrophils and protease inhibitor (▪, HLA-A2⁺ cells; □, HLA-A2^-). (E) Percentage inhibition induced by CML neutrophils. Data represent mean ± SEM of 3 experiments (•, normal CD34⁺ cells; ○, CML CD34⁺ cells). ^*Indicates significant differences from normal values (^*P < .05).