The advancement of AAV gene therapy for hemophilia B has also expedited the approvals of clinical trials for hemophilia A. In 2017, BioMarin Pharmaceutical reported the success of their first phase 1/2 clinical trial using AAV5 to deliver the codon-optimized B domain-deleted F8 cDNA (BDD-FVIII) (BMN 270) into patients with severe hemophilia A and achieved FVIII activity at around 77% of the normal level in the high-dose (6 × 1013 vg/kg)-treated group [23]. Here, F8 is linked to hemophilia A.