Transduced CD34⁺⁺Lin⁻ UCB cells generate dendritic cells expressing high levels of GFP in FTOC. Flow cytometric analysis of thymocytes recovered from FTOC initiated with transduced CD34⁺⁺Lin⁻ UCB cells that were not selected for GFP expression (in this experiment, 30% GFP⁺ cells at initiation of FTOC) and used to initiate FTOC. After 14 days of culture, thymocytes were recovered from FTOC and prestained with antimouse CD45 Cychrome (see the Materials and Methods). Subsequently, aliquots were stained with IgG1 PE and IgG2a BIO/SA-TC (not shown) or CD4 PE and HLA-DR BIO/SA-TC and analyzed by flow cytometry. The left dot plot shows the forward scatter (FSC) versus TC + Cychrome staining of all cells recovered. R1 is set to include less than 1% of the human cells in isotypic control antibody staining and contains the HLA-DR⁺ human cells. Above R1, the cluster of Cychrome⁺ murine cells is seen, which are at 14 days of FTOC still more numerous than human cells. The right dot plot shows CD4 staining versus GFP expression gated on HLA-DR⁺ human cells (R1). The values in the crosses indicate the percentage of cells present in the corresponding quadrant. Quadrants were set to include 99% of cells stained, with isotypic control antibody in lower quadrants, gated on all human cells. The data shown are representative of two independent experiments.