cFIX expression and anti-cFIX humoral responses in an HB dog with preexisting anti-hFIX inhibitors after administration of AAV-cFIX-Padua. Wiley, a University of Alabama HB dog with a history of inhibitors against hFIX, was assessed for (A) cFIX antigen and activity, (B) anti-cFIX IgG2 and Bethesda units, (C) whole blood clotting time, and (D) anti-hFIX IgG2 and Bethesda units after administration of 3 × 10¹² vg/kg AAV8-cFIX-Padua. Black line, closed circles, cFIX activity, cFIX Bethesda units, and hFIX Bethesda units; gray line, open circles, cFIX antigen, anti-cFIX IgG2 and anti-hFIX IgG2; horizontal dashed lines, positive levels of Bethesda units and IgG2; vertical dashed lines, time of challenge with recombinant cFIX; dark gray bar, WBCT of hemophiliac dogs (>45 minutes); light gray bar, WBCT of normal dogs (<8 minutes).