The IL-2/CD25 axis is a potential target for therapy directed against CML LICs. (A) Survival of CML model mice injected intraperitoneally with an anti-CD25 mAb (n = 12) or isotype IgG (n = 12) every other day from day 1 to day 15 after transplantation. (B) Survival of CML model mice treated with anti–IL-2 mAb (n = 7) or isotype IgG (n = 7) every other day from day 1 to day 15 after transplantation. (C) Frequency and number of CD25⁺F⁻LSK cells in panel A (11 days after transplantation) (means ± SD, n = 7). (D) Representative profiles for CD25 expression in the CD34⁺CD38⁻ (red histogram) and CD34⁺CD38⁺ (blue histogram) fractions of freshly isolated bone marrow from untreated CML CP patients (n = 2) or lymphoma patients without bone marrow involvement (n = 3). (E) CD25 expression in bone marrow or peripheral blood of patients at various stages of CML, based on microarray data derived from the public database. (F-G) GSEA was applied to human leukemia samples. Genes upregulated in mast cells compared with neutrophils were significantly enriched in CML BC (n = 33) relative to CML CP (n = 57) (F), and genes upregulated in mast cells compared with B cells were significantly enriched in CD25⁺ B-ALL (n = 43) relative to CD25-low or -negative B-ALL (n = 151) (G) *P < .05; **P < .01. IgG, immunoglobulin G.