An open-label, non-investigational product, multi-center, lead-in study to evaluate at least 6 months of prospective efficacy and selected safety data of current factor IX (FIX) or factor VIII (FVIII) prophylaxis replacement therapy in the usual care setting of moderately severe to severe adult hemophilia B subject (FIX:C≤2%) who are negative for neutralizing antibodies to adeno-associated virus vector-SPARK100 (BENEGENE-1) and moderately severe to severe hemophilia A adult subjects (FVIII:C≤1%) who are negative for neutralizing antibodies to adeno-associated virus vector SB-525 CAPSID (AAV6), prior to the respective therapeutic phase 3 gene therapy studies)