The spontaneous bleeding phenotype in Dahl-FVIII^−/−rats is rescued by 2bF8 lentivirus-mediated transgenesis. Transgenic Dahl rats were generated by 2bF8 lentivirus-mediated oocyte transduction transgenesis; 2bF8 transgene was then crossed onto the Dahl-FVIII^−/− background. Animals were monitored for bleeding episodes. Platelets and plasmas were isolated from blood samples collected via ventral tail artery blood draws. FVIII expression levels in platelet lysates and plasma were determined by a modified chromogenic assay. Blood samples from WT and FVIII^−/− Dahl rats were used as controls. B-domain–deleted rhFVIII (Xyntha) was used as a reference standard for FVIII:C assays. (A) FVIII expression levels in 2bF8 transgenic rat platelets. (B) FVIII expression levels in 2bF8 transgenic rat plasma. (C) Occurrence of bleeding episodes in 2bF8 transgenic rats. (D) Platelet counts in 2bF8 transgenic rats.