Btk⁺ B cells exhibit progressive selective advantage. (A-B) PB, BM, spleen, and peritoneal cells were stained for surface markers and intracellular Btk and analyzed by flow cytometry. (A) Representative data showing Btk expression in PB B cells analyzed at weeks 5, 17, and 24 after transplantation. FACS plots show representative mice from WT mock (n = 7), KO mock (n = 8), MOI 3 (n = 3), and MOI 15 to 25 (n = 12) experimental groups. (B) Btk⁺ cells in various B-cell subsets displayed according to increasing maturity in BM and periphery in MOI 15 to 25 LV-treated mice. (C) gDNA derived from total BM, splenic non-B (CD43⁺), and B (CD43⁻) cell populations was evaluated for viral copy number. Data represent 4 independent experiments. ***P < .001; **P = .001-.01; *P = .01-.05.