Follow-up of More Than 5 Years in a Cohort of Patients with Hemophilia B Treated With Fidanacogene Elaparvovec Adeno-Associated Virus Gene Therapy
Highlights From the 63rd ASH Annual Meeting

Follow-up of More Than 5 Years in a Cohort of Patients with Hemophilia B Treated With Fidanacogene Elaparvovec Adeno-Associated Virus Gene Therapy

Ben J. Samelson-Jones, MD, PhD1, Spencer K. Sullivan, MD2, John E.J. Rasko, BSc (Med), MBBS (Hons), PhD, MAICD, FFSc (RCPA), FRCPA, FRACP, FAHMS3*, Adam Giermasz, MD, PhD4, Lindsey A. George, MD1,5, Jonathan M. Ducore, MD, MPH6, Jerome M. Teitel, MD, FRCPC7, Catherine E. McGuinn, MD8, Amanda O'Brien9*, Ian Winburn, MBBS, PhD, MRCS10*, Lynne M Smith, MBA9*, Amit Chhabra, MBBS, MPH11, and Jeremy Rupon, MD9

1The Children's Hospital of Philadelphia, Philadelphia, PA
2Mississippi Center for Advanced Medicine, Madison, MS
3Cell & Molecular Therapies, Royal Prince Alfred Hospital, SLHD, Australia
4University of California Davis, Sacramento, CA
5Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA
6Hemophilia Treatment Center, UC Davis, Sacramento, CA
7University of Toronto, St. Michael's Hospital, Toronto, Canada
8Columbia University, New York, NY
9Pfizer Inc, Collegeville, PA
10Pfizer Ltd, Tadworth, Surrey, United Kingdom
11Pfizer Inc, New York, NY

Key Data Points

FIX Activity Over Time After Infusion of Fidanacogene Elaparvovec

FIX activity (as of the December 2020 cutoff date) for the 15 participants in the phase 1/2 clinical trial of fidanacogene elaparvovec who received a dose of 5e11 vg/kg. FIX activity was determined using the central laboratory Actin FSL-based one-stage clotting assay. Mean FIX activity levels have remained in the mild hemophilia severity range: 22.8%, year 1 (n = 15); 25.4%, year 2 (n = 14); 22.9%, year 3 (n = 14); 24.9%, year 4 (n = 9); and 19.8%, year 5 (n = 7).

ABR Over Time After Infusion of Fidanacogene Elaparvovec

ABR for 14 of the 15 phase 1/2 participants who participated in the long-term follow-up study. Only 9 and 5 participants have reached the 5 year and 6 year follow-up time points, respectively. Since pre-vector infusion, mean ABR has ranged from 0.1–0.9 per year over the course of follow-up, and no participants have resumed FIX prophylaxis.

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Supported by educational grants from Bayer, BioMarin, CSL Behring, Freeline Therapeutics Limited, Pfizer Inc., Spark Therapeutics, and uniQure, Inc.

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