Effect of hypoxia on BM progenitor activity. The CFC (a) and LTC-IC (b) activity of BM Lin^–CD34⁺CD38^– cells was evaluated before (day 0; white bars) and after culture for 4 days under normoxic (gray bars) or hypoxic (1.5% O₂; black bars) conditions. Data shown represent the number (mean ± SD) of BFU-E (E), granulocyte (G), monocyte (M), granulocyte-monocyte (GM), mixed (MIX, i.e., GM colonies with erythroid cells), and total number of colonies from three separate experiments. The paired Student t test was performed to compare day 0 with day 4 cells (*P < 0.05) and to compare hypoxic to normoxic conditions after 4 days of culture (^†P < 0.05).