Both CD38⁺ and CD38⁻CD34⁺⁺Lin⁻ UCB cells generate T cells expressing high levels of GFP in FTOC. Before FTOC indicates flow cytometric analysis of the progeny of CD38⁺ and CD38⁻ CD34⁺⁺Lin⁻ UCB cells after culture for 3 days in medium with SCF (100 ng/mL) and IL-3 (50 U/mL) supplemented with retroviral supernatant 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 arbitrarily. FTOC day 30 indicates flow cytometric analysis of thymocytes recovered from FTOC initiated with transduced CD38⁺ and CD38⁻ CD34⁺⁺Lin⁻ UCB cells shown before FTOC that were not selected for GFP expression before initiation of FTOC. After 30 days of culture, thymocytes recovered from FTOC were stained with IgG1 PE (not shown), CD1 PE, CD4 TC, and CD3 PE and analyzed by flow cytometry. Dot plots show staining versus GFP expression of live, human cells recovered. 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 stained, with isotypic control antibody in the lower quadrants. The data shown are representative of three independent experiments.