Experimental protocol.

After CFSE staining, CD34-enriched cells were cultured overnight before FACS to obtain viable (PI⁻), CD34⁺, homogeneously CFSE-stained cells. These cells were then cultured for 3 days in SFM, supplemented or not with GFs (see “Materials and methods”) and with or without the addition of 10 μM STI571. At the end of the culture period, cells were labeled with PI and CD34-PE, and viable divided versus undivided cells were isolated by FACS. These cell populations were then processed for FISH and RT-PCR to determine their genotype.