A novel virus-based gene therapy, fidanacogene elaparvovec, appears to be effective at reducing bleeding risk compared with prophylaxis among male patients with moderately severe or severe hemophilia B, according to research presented at the International Society of Thrombosis and Haemostasis (ISTH) 2023 Congress.

Fidanacogene elaparvovec was designed to encode a high-activity factor IX (FIX) variant. The aim of using this therapy is to enable endogenous FIX expression among patients with hemophilia B.

A previous phase 1/2a study suggested that a single dose of fidanacogene elaparvovec may improve FIX levels in this patient population, lowering annualized bleeding rates (ABRs). For the ongoing phase 3 BENEGENE-2 study (ClinicalTrials.gov Identifier: NCT03861273), researchers are evaluating the safety and efficacy of fidanacogene elaparvovec among male patients with moderately severe or severe hemophilia B.

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Overall, 45 patients had been enrolled through data cutoff for inclusion in this presentation. The average patient age was 33.2 years, 100% of patients were male, and 73.3% of patients were White. All 45 patients received a fidanacogene elaparvovec dose; 41 patients completed 15-month follow-up.

Analysis showed that the mean total ABR was reduced by 71%, which met the study’s primary endpoint of non-inferiority to prophylaxis; the reduction was, in fact, superior to prior prophylaxis (P <.0001). Furthermore, 64.4% of patients had 0 bleeding events from week 12 through month 15 after infusion.

A total of 6 (13.3%) patients resumed FIX prophylaxis, 5 because of low FIX activity. Furthermore, 205 adverse events were observed in 84.4% of patients. Fourteen serious events were noted in 15.6% of patients, which included anemia (2.2%).

“Fidanacogene elaparvovec yielded endogenous FIX expression in participants with moderately severe to severe hemophilia B, resulting in significant decreases in bleeding and was generally well tolerated,” the study presenter noted.

Disclosures: This research was supported by Pfizer. Some study authors declared affiliations with biotech, pharmaceutical, or device companies. Please see the original reference for a full list of disclosures.


Cuker A, Alzahrani H, Astermark J, et al. Efficacy and safety of fidanacogene elaparvovec in adults with moderately severe or severe hemophilia B: results from the phase 3 BENEGENE-2 gene therapy trial. ISTH 2023 Congress; June 24-28, 2023. Abstract OC 52.3.