Enhanced proliferation of BCR-ABL⁺ CP CML CD34⁺ cells by retroviral introduction of BMI1. (A) RNA was isolated from CD34⁺ cells of CP-CML patients; one BC-CML patient and normal bone marrow (NBM) and BMI1 expression was determined by quantitative real-time polymerase chain reaction. (B) CD34⁺ cells from CP-CML patients were transduced with control or MiGR1 BMI1 vectors and cells were cultured on MS5 stromal cells, and cumulative cell counts in suspension are shown. Where indicated by the arrows, cultures were harvested and replated onto new stroma. (C) Suspension cells from week 5 cocultures of transduced CP-CML samples were used to perform CFC assays. Progenitor self-renewal was analyzed by replating the cells in secondary CFC assays, and only the BMI1-overexpressing cells had replating ability. (D) CD34⁺ cells from CP-CML patients were transduced with control or MiGR1 BMI1 vectors, transduced cells were sorted by MoFlo, and CFC frequencies as well as CFC replating capacity were determined in methylcellulose assays. (E) CD34⁺ cells from a BC CML sample were transduced with lentivirus encoding shRNA sequences against BMI1 or scrambled and then cultured on MS5 stromal cells.