(A) Percentage of CD34⁺ cells in G0, G1, S, and G2/M as assessed by flow cytometry up to 4 days following cytokine stimulation. Following mobilization with low-dose cyclophosphamide and G-CSF, CD34⁺ cells were isolated from peripheral blood and then resuspended in growth medium. Proliferation was stimulated by the addition of cytokines IL-3, IL- 6, and SCF. Cell samples were taken at 24-hour intervals, fixed in 70% ethanol, and flow cytometry was performed. The proportion of cells in G0 decreases with time, progressively more enter G1 by day 1 and then S and G2/M by day 3. The values plotted are % ± SD (n = 4). (B) Percentage of CD34⁺ cells in G0, G1, S/G2/M as assessed by flow cytometry in the first 24 hours following cytokine stimulation. Cells were stimulated as described above and samples were taken at 4-hour intervals, fixed in 70% ethanol, and flow cytometry was performed. Some cells were detected entering G1 as early as 8 hours following cytokine stimulation. The values plotted are % ± SD (n = 3). (C) Cell cycle analysis of the CD34⁺ cells by flow cytometry on the day of purification (day 0) and 3 days after cytokine stimulation (day 3). On day 0, there is a single (2n) DNA peak (>95%). By day 3, 60% of cells are in G1, 26% of cells are in S-phase, and 14% of cells are in G2/M with doubling of the DNA content.