Amit Nathwani at the University College London Cancer Institute and his colleagues tested a gene therapy approach for hemophilia B using an adenovirus-associated virus vector — one that's different from previously used adenovirus vectors — to deliver a corrected coagulation factor IX, or FIX, gene. As they report in the New England Journal of Medicine, Nathwani and his team performed a combined phase 1 and 2 clinical trial of their approach on six male patients with hemophilia B.