Cell cycle status and morphology during erythroid differentiation of CB CD34⁺ cells.

(A) Freshly separated CD34⁺ cells (2 × 10⁴/mL) (day 0), or cells from suspension culture of CD34⁺ cells in the presence of IL-3 (200 units), GM-CSF (200 units), SLF (50 ng) and Epo (1 unit) per milliliter for 3 and 5 days or from BFU-E–derived cells from semisolid cultures after 7, 10, 12, and 14 days of growth in the presence of IL-3, GM-CSF, SLF, Epo, vitamin B12 (10 μg, Sigma), folic acid (15 μg, Sigma), and insulin (10 μg, Sigma) per milliliter were used for cell cycle analysis. Results are the mean ± SEM from 5 experiments. (B) Wright-Giemsa stained day 0 CD34⁺ cells (i) and cells from suspension culture after 4 days (ii), or from BFU-E–derived colonies grown in the presence of cytokines for 7 (iii), 10 (iv), and 14 (v) days (original magnification × 1000). (C) Morphologic classification of BFU-E–derived cells. Cell types were determined by examining 500 cells per time point and are expressed as a percentage. (D) Expression of surface antigen in day 0 CD34⁺ cells and BFU-E–derived cells. Results are the mean percentage of positive cells ± SEM from 5 experiments.