Inhibition of CML progenitor cells growth after exposure to PHA-739358. CD34⁺ cells from patients diagnosed in the untreated chronic phase of CML (A,D; n = 4), in IM-resistant CML-blast crisis (B,E; n = 3), or from a patient with blast crisis with a confirmed T315I mutation (C,F; n = 1) were exposed to the indicated concentrations of PHA-739358 or IM for 9 days in serum-free medium supplemented with growth factors. Cell proliferation was assessed at day 3 (■), day 6 (▩), and day 9 (□). Bar graphs represent the mean percentage of cellular expansion plus or minus SD in relation to untreated control cells. The antiproliferative effects of PHA-739358 on CD34⁺ cells were found to be more pronounced in untreated CML patients at diagnosis compared with patients with IM-resistant CML-blast crisis; however, they seemed to be largely unaffected by the T315I BCR-ABL mutation.