F9 and hemophilia B: In 2014, we reported successful gene therapy in severe hemophilia B patients (NCT00979238) following a single intravenous infusion of a self-complementary, serotype-8 pseudotyped adeno-associated virus (AAV) vector encoding the wild-type, codon-optimized factor IX gene (scAAV2/8-LP1-hFIXco).2,3 We demonstrated that glucocorticoids effectively suppressed immune responses against AAV-transduced hepatocytes, preserving transgenic factor IX levels.