Pfizer announces topline results from Phase 3 study of fidanacogene elaparvovec

Pfizer announced top-line results from the Phase 3 BENEGENE-2 study evaluating fidanacogene elaparvovec, an investigational gene therapy, for the treatment of adult males with moderately severe to severe hemophilia B. The BENEGENE-2 study met its primary endpoint of non-inferiority and superiority in the annualized bleeding rate of total bleeds post-fidanacogene elaparvovec infusion versus prophylaxis regimen with Factor IX, administered as part of usual care. The results demonstrated superiority with a mean ABR for all bleeds of 1.3 for the 12 months from week 12 to month 15 compared to an ABR of 4.43 during the lead-in pre-treatment period of at least six months, resulting in a 71% reduction in ABR after a single dose of 5e11 vg/kg of fidanacogene elaparvovec. Key secondary endpoints demonstrated a 78% reduction in treated ABR and a 92% reduction in annualized infusion rate. Mean FIX activity was 27% at 15 months by one-stage SynthASil assay and 25% at 24 months. The mean steady-state FIX:C was significantly higher than the pre-specified threshold of 5%/ Fidanacogene elaparvovec was generally well-tolerated, with a safety profile consistent with Phase 1/2 results. Fourteen serious adverse events were reported in seven patients, with two assessed as related to treatment, a duodenal ulcer hemorrhage occurring in the setting of corticosteroid use, and an immune-mediated elevation of liver aminotransferase levels. No deaths, SAEs associated with infusion reactions, thrombotic events, or FIX inhibitors were reported. Fidanacogene elaparvovec is a novel, investigational vector that contains a bio-engineered adeno-associated virus capsid and a high-activity human coagulation FIX gene. The goal of this gene therapy for people living with hemophilia B, once treated, is that they will be able to produce FIX via this one-time treatment rather than having to regularly receive exogenous FIX. In this Phase 3 trial, eligible study participants completed a minimum six months of routine exogeneous FIX prophylaxis therapy during the lead-in study and then received one intravenous dose of fidanacogene elaparvovec at a dose of 5e11 vg/kg. Participants in the BENEGENE-2 study were screened with a validated assay designed to identify individuals who test negative for neutralizing antibodies to the gene therapy vector. Clinical trial participants will be evaluated as part of a long-term study over the course of 15 years. Pfizer currently has three Phase 3 programs investigating gene therapy in populations where there is a high unmet need: hemophilia B, hemophilia A, and Duchenne muscular dystrophy. A Phase 3 trial is also ongoing investigating marstacimab, a potential novel subcutaneous therapy option being studied for the treatment of people with hemophilia A and B with and without inhibitors. Fidanacogene elaparvovec has been granted breakthrough, regenerative medicines advance therapy, and orphan drug designations from the US Food and Drug Administration, as well as PRIority MEdicines and orphan drug designation from the European Medicines Agency. Pfizer will discuss these data with regulatory authorities in early 2023. Additional key data will be presented at a scientific conference in early 2023 as well.