BMPRIb receptor mediates BMP2 and BMP4 effects on LSC and myeloid progenitors. After qPCR analysis of BMPRIb expression, CP-CML samples were divided as low and high BMPRIb-expressing CML samples. CD34⁺ cells were then isolated from healthy donors (open bars) or both groups of CP-CML samples (closed bars) and incubated at 6 × 10⁵/mL in serum-free medium for 7 days in the presence of BMP2 or BMP4 (50 ng/mL). (A) The SC content of the treated cells was analyzed using the LTC-IC cocultured assay; results represent the mean value ± SEM of the indicated number of samples. Results are presented as the total LTC-IC-derived week 5 colonies per 1 × 10⁴ seeded cells. (B) The progenitor content of treated cells was analyzed using the CFC assay. Results are expressed as ratio of treated to untreated cells and represent the mean value ± SEM of the indicated number of samples. (C) BCR-ABL-transduced (closed bars) or empty vector-transduced (open bars) TF1 cells were continuously treated for 4 weeks by 50 ng/mL BMP2 or BMP4 and then assayed by CFC assay for their progenitor content. Results are expressed as the ratio of treated to untreated cells and represent the mean value ± SEM of 5 experiments. (D) Parental TF1 cells (TF1-wild-type) or TF1-BCR-ABL (TF1-BA) cells were transfected with a control empty (gray bars) or a BMPRIb-encoding (dark gray bars) vector. The effect on CFC output was analyzed using the CFC assay. Results are expressed as the total CFC colonies per 1 × 10³ seeded cells and represent the mean value ± SEM of 7 or 3 experiments for TF1-wild-type and TF1-BCR-ABL, respectively. (E) The progenitor content of CD34⁺ cells isolated from healthy donors (open bars) or CP-CML (closed bars) samples. The cells were divided as low- and high-BMPRIb-expressing CML-samples and were treated for 7 days in serum-free medium by BMP2 or BMP4 (50 ng/mL) in the presence or absence of soluble BMPRIa or BMPRIb receptor (4 μg/mL). Results are expressed as ratio of treated to untreated cells and represent the mean value ± SEM of the indicated number of experiments. (F) The progenitor content of parental TF1 cells (TF1-wild-type; open bars) or TF1-BCR-ABL cells (closed bars) was analyzed by CFC assay after 48 hours of treatment by BMP2 or BMP4 (50 ng/mL), with or without soluble BMPRIb receptor (4 μg/mL). Results are expressed as the total CFC colonies per 1 × 10³ seeded cells and represent the mean value ± SEM of 5 experiments. *P < .05 indicates differences between parental TF1 cells transduced with an empty vector and BCR-ABL-transduced TF1 cells.