Erythroid progenitors can be grown from CD34⁺ and CD34⁻ cell fractions. Mononuclear bone marrow cells were fractionated into CD34⁻ and CD34⁺ fractions using Minimacs columns. The CD34⁻ fraction was repurified using the same columns (A and B). Cells were stained for CD34 to verify the purity of the CD34⁻ and CD34⁺ fraction by FACS. The CD34⁺ cells were costained with CD71 (horizontal axis) and CD38 (vertical axis; C). Only CD34⁺ cells were gated (A and B; gate R2). Fractions highly enriched for BFU-E (C; R4, high CD71, medium CD38) or immature blast cells (C; R3; medium-low CD71, medium-low CD38) were purified by sorting. CD34⁻ cells (▴), the sorted BFU-E progenitors (○), and the sorted immature blast cells (□) were cultured in CFU-E medium supplemented with Epo, SCF, IGF-I, and Dex. Cumulative cell numbers were calculated (D).