Similarly, studies in the canine model of hemophilia A have demonstrated persistent therapeutic expression of FVIII of over a decade following AAV vector infusions.50 Somewhat in contrast, the results of the longest duration human FVIII gene transfer trial using an AAV5 vector has shown a significant decline in FVIII levels over the first 4 years postvector delivery. The gene discussed is F8; the disease is hemophilia A.