BMP2 and BMP4 amplify leukemic myeloid progenitors. Selected CD34⁺ cells (6 × 10⁵/mL) were incubated in serum-free medium for 7 days in the presence of either BMP2 or BMP4 (50 ng/mL). The progenitor content of the treated cells was analyzed using the CFC assay. (A) We scored them as indicated as early or late erythroid-E and granulo-monocytic-GM (as defined in supplemental Figure 4). Results represent the mean value ± SEM of 12 or 15 experiments for healthy donors and CML patients, respectively, and are expressed as ratio of treated to untreated cells (none). (B) CFC values obtained from CD34⁺ cells treated in the same experiments with BMP2 or BMP4 and isolated from 12 or 18 different healthy or CP-CML patients at diagnosis, respectively, are expressed as a percentage of the total number of colonies obtained and are presented as pie charts. P < .05 indicates differences between treated and untreated cells. (C) Sorted CD34⁺CD38⁻ cells from healthy and CML samples were plated at 1 cell/well in serum-free medium in the presence of 50 ng/mL BMP2 or BMP4. After 7 days, methylcellulose was added to the wells, and single cell–derived colonies were scored 2 weeks later. We scored all colonies (total CFC) as well as CFU-GM content. Results are expressed as percentage of wells that give rise to colonies and represent the mean value ± SEM of 5 experiments for healthy donors and CML patients.