Ex vivo gene therapy of an SCID-X1 mouse model with either the Revgen vector or the EF1α vector potently restores lymphocyte development. (A) Counts of peripheral blood lymphocyte subpopulations (CD4⁺ or CD8⁺ T lymphocytes and B220⁺ B lymphocytes) and natural killer (NK1.1⁺) cells at 18 weeks after transplantation. The Revgen vector and the EF1α vector were evaluated in 2 separate transplantation experiments with their own negative mock and positive MSCV-hγc vector controls (experiment 1 on the left and experiment 2 on the right). Each dot represents data from a single mouse. EF1α* indicates 4 of 10 mice transplanted with cells transduced with the EF1α vector at a lower MOI of 3.3 showed significant reconstitution; and WT, data from nontransplanted wild-type C57BL/6J mice to serve as reference. (B) Relative proportions (percentage) of lymphoid subpopulations in spleen, bone marrow, and thymus of transplanted mice analyzed at 21 weeks. (C) Proliferation of peripheral blood T lymphocytes taken from recipient mice at 14 weeks in response to concanavalin A and interleukin-2 stimulation. The number of cells was counted on day 6 for the left panel (n = 3 for WT, n = 4 for the other groups) and on day 5 for the right panel (n = 3 for WT, n = 5 for other groups). (D) Plasma immunoglobulin levels of recipient mice at 14 weeks after transplantation. Each dot represents data for a single mouse. The 3 panels on the left and the 3 panels on the right represent data from transplantation experiments 1 and 2, respectively. P values were obtained by t test.