Chemosensitivity of CD34 progenitors⁺ and erythroid precursors. Highly purified populations of erythroid precursors were obtained by unilineage culture of peripheral blood CD34⁺ cells and analyzed at day 7 and day 14 of differentiation. Cells were incubated with erythroid medium alone (▪), with 1.5 μg/mL cisplatin (□) or 50 ng/mL camptothecin (▦) for 24 hours. The percentage of cell death was evaluated by ethidium bromide—acridine orange staining. The results shown are the mean ± SD of 4 independent experiments performed with cells from different donors.