2022-12-30| Trials & Approvals

Pfizer’s Hemophilia B Gene Therapy Meets Phase 3 Endpoints

by Joy Lin
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Pfizer has announced positive Phase 3 results for fidanacogene elaparvovec, an experimental gene therapy for hemophilia B. The company has said that it will discuss the data with regulatory authorities and present additional data at a scientific conference in early 2023. 

Fidanacogene elaparvovec holds breakthrough, regenerative medicines advance therapy (RMAT), and orphan drug designations from the US FDA. The gene therapy is also an orphan drug and priority medicine under the European Medicines Agency’s PRIME scheme.
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Fidanacogene Elaparvovec Reduced Annual Bleeds

Pfizer’s gene therapy contains a bioengineered AAV capsid and a high-activity human coagulation Factor IX (FIX) gene. The therapy treats hemophilia B by instructing the body to self-produce FIX, a blood clotting factor, after a one-time treatment. 

In the Phase 3 trial called BENEGENE-2, patients had to complete a minimum of six months of routine exogenous FIX prophylaxis before receiving a one-time 5e11vg/kg infusion of fidanacogene elaparvovec. They were also screened for neutralizing antibodies to the gene therapy vector. The participants will be followed as part of a long-term study spanning 15 years. 

According to the latest readout, patients treated with the gene therapy had a 71% reduction in annualized bleeding rate (ABR). Treated patients had a mean ABR for all bleeds of 1.3 in a one-year period compared to an ABR of 4.43 during the six-month pre-treatment period. This showed the non-inferiority and superiority of the gene therapy versus the prophylaxis regimen with FIX. 

The trial also met secondary endpoints showing a 78% reduction in treated ABR and a 92% reduction in annualized infusion rate. The mean FIX activity in treated patients was 27% at 15 months and 25% at 24 months. 

On the safety side, the gene therapy is well-tolerated with a safety profile consistent with results from earlier studies. 14 serious adverse events were reported in seven (16%) patients, with two events linked to the treatment. This included a duodenal ulcer hemorrhage during corticosteroid use and an immune-mediated elevation of liver aminotransferase levels. No deaths, allergic reactions, thrombotic events, or FIX inhibitors were reported. 

In hemophilia B, Pfizer is also investigating marstacimab, a subcutaneously-administered antibody for hemophilia A and B with and without inhibitors. Beyond the disease, the company is investigating giroctocogene fitelparvovec for hemophilia A and fordadistrogene movaparvovec for Duchenne muscular dystrophy. Both gene therapies are in Phase 3.

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