F9 and hemophilia B: We report the 13-year follow-up of gene therapy in 10 adults with severe hemophilia B. A single infusion of scAAV2/8-LP1-hFIXco at one of three dose levels resulted in stable transgenic factor IX activity (mean 1.7, 2.3 and 4.8 IU/dL) leading to a median 9.7-fold (IQR, 3.7 to 21.8) reduction in bleeding rate and a 12.4-fold (IQR, 2.21 to 27.1) decrease in factor IX concentrate usage.