γc gene transfer restores T-cell differentiation of CD34⁺ SCID-Xl patients’ cells in FTOC. CD34⁺ γc transduced S1 (A), S2 (B) cells as well as untransduced CD34⁺ S1 cells (C) were cultured with the preestablished combination of cytokines (SCF, Flt-3L, IL-7, IL-1, IL-15) into fetal thymic lobes for 35 days. FTOC were harvested and cells were stained for expression of CD4, CD8, CD3, and TCRβ (dot plots) or for γc expression (histograms). T-cell differentiation obtained from CD34⁺ normal CB cells is indicated on panel (D) as a control.