T2F8 LV-mediated in situ transduction of ECs in FVIII^nullmice. (A) Schematic diagram of EC-specific FVIII transduction. Approximately 1 × 10⁸ IU of T2F8LV in 300 µL of X-VIVO 10 media were administered into each 6-week-old FVIII^null mouse via tail-vein injection to transduce ECs in situ. Blood samples were collected following transduction, and plasmas were isolated for assays. Blood plasma from nontransduced WT C57BL/6 and naive FVIII^null mice served as controls. (B) Functional FVIII activity (FVIII:C) in plasma. Plasma FVIII:C levels in T2F8LV-transduced mice as determined by chromogenic assay. (C) Anti-FVIII inhibitor titers. Anti-FVIII inhibitor titers in WT, FVIII^null, and FVIII^null T2F8LV-transduced mice were determined by Bethesda assay. (D) Anti-FVIII total IgG in plasmas from T2F8LV-transduced mice as determined by ELISA. Data were analyzed using the 1-way analysis of variance followed by the Tukey test.