Human T-cell differentiation in ND samples and patients with early T-cell block. (A) Representative analysis of T-cell differentiation in an ND sample at 8 weeks (ND4). Cells were gated on LIVE/DEAD^–CD45⁺CD14^–CD56^– cells to check for the presence of CD34⁺ and CD19⁺ cells and the expression of early and late T-cell commitment markers (CD5, CD7, CD1a, CD4, CD8α, CD8β, CD3, TCRαβ, and TCRγδ). (B-D) T-cell differentiation assay in patients with reticular dysgenesis (RD) (analyzed at 5 weeks) (B), and XSCID, carrying a null (P2) (6 weeks) (C), or a missense mutation (P3) (6 weeks) (D). The fluorescence-activated cell sorting (FACS) plots show expression of CD34, CD19, CD7, CD5, CD1a, CD4, CD8β, TCRαβ, and CD3 upon gating on LIVE/DEAD^–CD45⁺CD14^–CD56^– cells. CD5, CD7, and CD1a plots are obtained upon gating on LIVE/DEAD^–CD45⁺CD14^–CD56^–CD34^– cells. The bar graphs show the absolute cell counts per ATO in the indicated gates in each patient’s sample and in the ND sample (red bars) analyzed in parallel in the T-cell differentiation assay.