A one-stage clotting assay was used to determine FIX coagulation activity at prespecified time points (arrows) after the administration of the AAV vector (scAAV2/8-LP1-hFIXco). Panels A and B show FIX levels in Participants 1 and 2, respectively, who received the low dose of vector (2×1011 vector genomes [vg] per kilogram of body weight). Panels C and D show FIX levels in Participants 3 and 4, respectively, who received the intermediate dose of vector (6×1011 vg per kilogram). Panels E and F show both FIX levels and alanine aminotransferase (ALT) levels in Participants 5 and 6, respectively, who received the high dose of vector (2×1012 vg per kilogram). The duration of treatment with prednisolone (Pred), which was initiated at a dose of 60 mg per day and then gradually tapered, is also shown.