EμB29-Btk-LV restores calcium flux in Btk-deficient B cells. (A) Schematic of the LV EμB29-Btk used for all murine transplantation experiments. Expression of the human BTK cDNA transgene is driven by a B29 (Igβ) minimal promoter in conjunction with an Ig heavy chain enhancer (Eμ). (B) Schematic of EμB29-Btk-2A-GFP (Btk-GFP) vector used in DT40 transduction experiments. Btk-deficient DT40 chicken B cells were transduced at limiting MOI and evaluated for GFP and Btk expression by FACS (left panels). Transduced cells were stimulated with anti-IgM and analyzed for calcium flux within the GFP⁺ vs GFP⁻ fractions (right panel).