WS1.6 promoter results in limited selection of WASp⁺ cells in vivo. (A) Experimental design for in vivo promoter comparison studies. WASp^−/− congenically marked HSC were transduced with either MND or WS1.6-containing LV and cotransplanted into lethally irradiated WASp^−/− CD45.1⁺CD45.2⁺ recipients. (B) WASp expression in peripheral blood mononuclear subsets was examined by intracellular staining at different time points; monocytes (CD11b⁺GR1^low); B cells (B220⁺CD3⁻); and T cells (B220⁻CD3⁺). (C) Viral copy numbers in sorted CD45.1⁺ or CD45.2⁺ BM CD11b⁺ monocytes were analyzed by qPCR. (D) Representative WASp staining in splenic T-and B-cell subsets, with the summary WASp expression data shown for T cells (E) and for B cells (F). To quantify WASp expression in different subsets, we analyzed MFI of WASp⁺ cells within the T- (G) and B-cell (H) lineages. Data represent 2 unique experiments with error bars showing standard deviation (SD), n = 8 for MND and 7 for WS1.6 (*P < .05; **P < .01; ***P < .001).