• Adam Cuker, Kaan Kavakli, Laurent Frenzel, Jiaan-Der Wang, Jan Astermark, Monica H Cerqueira, Alfonso Iorio, Olga Katsarou-Fasouli, Robert Klamroth, Amy D Shapiro, Cédric Hermans, Akira Ishiguro, Andrew D Leavitt, Johannes B Oldenburg, Margareth C Ozelo, Jerome Teitel, Francesca Biondo, Annie Fang, Joanne Fuiman, John McKay, Pengling Sun, John E J Rasko, Jeremy Rupon, and BENEGENE-2 Trial Investigators.
• From the Departments of Medicine and of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia (A.C.), and Pfizer, Collegeville (J.F., J.R.) - both in Pennsylvania; the Division of Hematology, Department of Pediatrics, Ege University Faculty of Medicine, Izmir, Turkey (K.K.); the Department of Hematology, Hemophilia Care and Research, Necker Hospital, Institut Imagine, Paris (L.F.); the Center for Rare Disease and Hemophilia, Taichung Veterans General Hospital, Taichung, Taiwan (J.-D.W.); the Department of Translational Medicine, Lund University, Lund, and the Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Malmö - both in Sweden (J.A.); Instituto de Hematologia do Estado do Rio de Janeiro, Rio de Janeiro (M.H.C.), and Hemocentro UNICAMP, Department of Internal Medicine, School of Medical Sciences, University of Campinas, Campinas (M.C.O.) - both in Brazil; the Departments of Health Research Methods, Evidence, and Impact and of Medicine, McMaster University, Hamilton, ON (A. Iorio), and the Division of Hematology, St. Michael's Hospital, University of Toronto, Toronto (J.T.) - both in Canada; the Blood Transfusion Center, National Reference Center for Congenital Bleeding Disorders, Laiko General Hospital, Athens (O.K.-F.); Vivantes Hospital in Friedrichshain, Berlin (R.K.), and the Institute of Experimental Hematology and Transfusion Medicine, University Hospital Bonn, and the Center for Rare Diseases Bonn, University Clinic Bonn, Bonn (J.B.O.) - all in Germany; Indiana Hemophilia and Thrombosis Center, Indianapolis (A.D.S.); the Hemostasis and Thrombosis Unit, Division of Hematology, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Brussels (C.H.); the Division of Hematology, National Center for Child Health and Development, Tokyo (A. Ishiguro); the Departments of Medicine and of Laboratory Medicine, University of California, San Francisco, San Francisco (A.D.L.); the Faculty of Medicine and Health, Central Clinical School, and the Gene and Stem Cell Therapy Program, Centenary Institute, University of Sydney, and the Department of Cell and Molecular Therapies, Royal Prince Alfred Hospital - all in Sydney (J.E.J.R.); Pfizer, New York (A.F.); Pfizer, Groton, CT (J.M.); Pfizer, Rome (F.B.); and Pfizer, Cambridge, MA (P.S.).
• N. Engl. J. Med. 2024 Sep 26; 391 (12): 110811181108-1118.

BackgroundFidanacogene elaparvovec, an adeno-associated virus (AAV) gene-therapy vector for hemophilia B containing a high-activity human factor IX variant (FIX-R338L/FIX-Padua), was associated with sustained factor IX activity in a phase 1-2a study.MethodsWe conducted a phase 3 open-label study of fidanacogene elaparvovec at a dose of 5×1011 vector genome copies per kilogram of body weight. Men 18 to 65 years of age with hemophilia B and a factor IX level of 2% or less were eligible for screening if they had received at least 6 months of therapy with prophylactic factor IX concentrate. The primary end point, tested for noninferiority, was the annualized bleeding rate (treated and untreated bleeding episodes) from week 12 to month 15 after treatment with fidanacogene elaparvovec as compared with the prophylaxis lead-in period. Superiority, additional efficacy end points, and safety were also assessed.ResultsOf 316 men who underwent screening for the lead-in study, 204 (64.6%) were not eligible; 188 (59.5%) of those were ineligible owing to the presence of anti-AAV neutralizing antibodies. Of the 45 participants who received fidanacogene elaparvovec, 44 completed at least 15 months of follow-up. The annualized rate of bleeding for all bleeding episodes decreased by 71%, from 4.42 (95% confidence interval [CI], 1.80 to 7.05) at baseline to 1.28 (95% CI, 0.57 to 1.98) after gene therapy, a treatment difference of -3.15 episodes (95% CI, -5.46 to -0.83; P = 0.008). This result shows the noninferiority and superiority of fidanacogene elaparvovec to prophylaxis. At 15 months, the mean factor IX activity was 26.9% (median, 22.9%; range, 1.9 to 119.0) by one-stage SynthASil assay. A total of 28 participants (62%) received glucocorticoids for increased aminotransferase levels or decreased factor IX levels (or both) starting between 11 and 123 days. No infusion-related serious adverse events, thrombotic events, development of factor IX inhibitors, or malignant conditions were observed.ConclusionsFidanacogene elaparvovec was superior to prophylaxis for the treatment of participants with hemophilia B, leading to reduced bleeding and stable factor IX expression. (Funded by Pfizer; BENEGENE-2 ClinicalTrials.gov number, NCT03861273.).Copyright © 2024 Massachusetts Medical Society.

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