• Savita Rangarajan, Liron Walsh, Will Lester, David Perry, Bella Madan, Michael Laffan, Hua Yu, Christian Vettermann, Glenn F Pierce, Wing Y Wong, and K John Pasi.
• From Hampshire Hospitals NHS Foundation Trust, Basingstoke (S.R.), University Hospitals Birmingham NHS Foundation Trust, Edgbaston (W.L.), Cambridge University Hospital NHS Foundation Trust, Addenbrooke's Hospital, Cambridge (D.P.), and the Centre for Haemostasis and Thrombosis, St. Thomas' Hospital (B.M.), Imperial College London and NIHR Clinical Research Facility at Imperial College Healthcare NHS Trust (M.L.), and Barts and the London School of Medicine and Dentistry (K.J.P.), London - all in the United Kingdom; and BioMarin Pharmaceutical, Novato (L.W., H.Y., C.V., W.Y.W.), and private consultant, La Jolla (G.F.P.) - both in California.
• N. Engl. J. Med. 2017 Dec 28; 377 (26): 2519-2530.

BackgroundPatients with hemophilia A rely on exogenous factor VIII to prevent bleeding in joints, soft tissue, and the central nervous system. Although successful gene transfer has been reported in patients with hemophilia B, the large size of the factor VIII coding region has precluded improved outcomes with gene therapy in patients with hemophilia A.MethodsWe infused a single intravenous dose of a codon-optimized adeno-associated virus serotype 5 (AAV5) vector encoding a B-domain-deleted human factor VIII (AAV5-hFVIII-SQ) in nine men with severe hemophilia A. Participants were enrolled sequentially into one of three dose cohorts (low dose [one participant], intermediate dose [one participant], and high dose [seven participants]) and were followed through 52 weeks.ResultsFactor VIII activity levels remained at 3 IU or less per deciliter in the recipients of the low or intermediate dose. In the high-dose cohort, the factor VIII activity level was more than 5 IU per deciliter between weeks 2 and 9 after gene transfer in all seven participants, and the level in six participants increased to a normal value (>50 IU per deciliter) that was maintained at 1 year after receipt of the dose. In the high-dose cohort, the median annualized bleeding rate among participants who had previously received prophylactic therapy decreased from 16 events before the study to 1 event after gene transfer, and factor VIII use for participant-reported bleeding ceased in all the participants in this cohort by week 22. The primary adverse event was an elevation in the serum alanine aminotransferase level to 1.5 times the upper limit of the normal range or less. Progression of preexisting chronic arthropathy in one participant was the only serious adverse event. No neutralizing antibodies to factor VIII were detected.ConclusionsThe infusion of AAV5-hFVIII-SQ was associated with the sustained normalization of factor VIII activity level over a period of 1 year in six of seven participants who received a high dose, with stabilization of hemostasis and a profound reduction in factor VIII use in all seven participants. In this small study, no safety events were noted, but no safety conclusions can be drawn. (Funded by BioMarin Pharmaceutical; ClinicalTrials.gov number, NCT02576795 ; EudraCT number, 2014-003880-38 .).

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