GFP is expressed by cytokine-stimulated CD34⁺⁺Lin⁻ UCB cells transduced with MFG-GFP retroviral supernatant. Flow cytometric analysis of the progeny of CD34⁺⁺Lin⁻ UCB cells after culture for 3 days, either without cytokines and retroviral supernatant (A), without cytokines but with retroviral supernatant (B), or with both cytokines (100 ng/mL SCF and 500 U/mL IL-3) and retroviral supernatant (C). Retroviral supernatant was added after 1 day of culture. Dot plots shows CD34 PE staining versus GFP expression gated on live cells. The values in the crosses indicate the percentage of cells present in the corresponding quadrant. Quadrants were set to include 99.5% of the cells from staining showed in (A) in the upper left quadrant. The data shown are representative of six independent experiments.