BaEV-LV GPs confer efficient gene transfer into in vitro–generated early T-cell progenitors. CB CD34⁺ cells were plated on Dll4-coated culture wells in the presence of a cytokine cocktail (IL-7, TPO, Flt3-L) for 24 hours, and they were subsequently transduced with VSV-G-, RD114TR-, BaEVTR-, BaEVRless- and H/F-LVs encoding the GFP reporter at an MOI of 10, except for VSV-G-LVs for which a higher vector dose (MOI of 50) was applied. (A-B) At day 3 of culture, the cells were analyzed by FACS for surface expression of CD34 and CD7. The gating strategy to determine GFP expression in the subpopulations of ELP, ETP, and proT cells are shown for differentiation at day 3 in panel A for a representative experiment. The transduction levels for day 3 of differentiation toward T-cell lineage in these subpopulations are summarized in the histograms in panel B (mean ± SD; n = 3). (C) At day 14 of culture, the cells were analyzed by FACS for surface expression of CD34, CD7, CD5, and CD1a (for gating strategy, see supplemental Figure 6). GFP expression in the subpopulations ELP, ETP, proT1, proT2, and preT cells at day 14 of differentiation toward T-cell lineage is shown for the different pseudotypes (mean ± SD; n = 3; VSV-G vs other pseudotypes). **P < .01.