EF1α-driven human common γ_c vectors for clinical gene therapy. (A) Schematic map of the EF1α-hgcOPT vector expressing codon-optimized human γ_c cDNA. (B-D) In vitro correction of ED7R cells after transduction with EF1α-driven common γ_c vector containing the 400-bp insulator. (B) Staining with antibody specific for human common γ_c after transduction with vector (gray line) or mock (black line) supernatants. Staining with antibody specific for phosphorylated Stat5 is shown for mock (C) and vector-transduced (D) cells either with (gray line) or without (black line) stimulation by IL-2. (E-G) In vivo correction of SCID-X1 mouse bone marrow with EF1α vector containing 2 × 250-bp insulator elements. Absolute lymphocyte cell counts determined by staining for the indicated antigen for B cells (E), CD4⁺ T cells (F), and CD8⁺ T cells (G) at 10 weeks post transplantation are shown for both vector (+V) and mock (KO) transduced IL2RG^−/− bone marrow–transplanted mice, compared with wild-type (wt) mice. Each diamond represents 1 mouse.