Pfizer's Hemophilia B Therapy Succeeds in Late-Stage Study

Pfizer said that the overall results in a new moderate-to-severe hemophilia B gene therapy were ideal.

Key takeaways:
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    Positive results of an experimental gene treatment for adult males with moderate-to-severe hemophilia B were released by Pfizer.
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    Hemophilia B is a rare blood disorder in which the blood doesn't clot properly. This is caused by a lack of factor IX (FIX).
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    Fidanacogene elaparvovec, an experimental gene therapy, helped hemophilia B patients make their own FIX in Phase 3 of the BENEGENE-2 trial.

Pfizer announced positive topline results of investigational gene therapy for adult males with moderate-to-severe hemophilia B.

The results, featured in the U.S. National Library of Medicine, showed promise in Phase 3 of the BENEGENE-2 trial of fidanacogene elaparvovec, an investigational gene therapy.

Fidanacogene elaparvovec, licensed under Pfizer as SPK-9001, is a new gene therapy still being tested. It has a bio-engineered AAV capsid (protein shell) and a high-activity human coagulation FIX gene.

Researchers found the primary endpoint of non-inferiority and superiority in the annualized bleeding rate (ABR) of total bleeds post-fidanacogene elaparvovec infusion versus another FIX treatment given as part of usual care.

Non-inferiority trials are carried out to show that a new treatment is "not significantly worse" than the current standard therapy. This is in contrast to superiority trials, which aim to demonstrate that one treatment is superior to another.

Since this study met its goal for both, researchers find that the BENEGENE-2 trial may actually work better than existing FIX treatments for hemophilia B.

“The BENEGENE-2 data demonstrate the promise of this gene therapy candidate as a potential one-time option for people living with hemophilia B as a means of reducing the clinical and treatment burden over the long term,” said Dr. Adam Cuker, Director at the Penn Comprehensive Hemophilia and Thrombosis Program.

The trial also showed a 78% decrease in treated ABR and a 92% decrease in annual infusion rates. This is especially helpful for those with severe hemophilia B, who tend to experience the most internal and random bleeding.

The goal of this treatment for people with hemophilia B is that once treated they can produce FIX instead of getting FIX from outside their bodies.

Hemophilia B, also called Christmas disease, is a rare blood disorder that causes improper blood clotting. Over 60% of hemophilia B cases are genetic and passed down from parent to child.

Hemophilia B is caused by a lack of the FIX enzyme. FIX in a person's plasma determines how often and much they bleed. Plasma is the fluid part of blood that is just a little bit yellow.

It can occur in people of any race or ethnicity but is mainly found in men or people with XY chromosomes.

Normal plasma FIX blood levels are 50-150 percent. When blood clotting factors drop below 50%, hemophilia B symptoms appear. Symptoms include internal bleeding after serious injury, trauma, or surgery, and spontaneous bleeding episodes. The lower the FIX levels, the more hemophilia B symptoms.

Fidanacogene elaparvovec was generally well-tolerated by participants. However, fourteen serious side effects were reported in 16 percent of patients. Some side effects, also known as serious adverse events (SAEs), were bleeding from duodenal ulcers and elevated liver enzymes, which often indicate inflammation or damage to liver cells.

There were no deaths or serious adverse events (SAEs) linked to infusion reactions, thrombotic events, or FIX inhibitors or blockers.

Chris Boshoff, CEO of Pfizer’s Oncology and Rare Disease Department, expressed goals to continue to study gene therapy for people with hemophilia B.

“We are extremely appreciative of those who are participating in the trial and to the investigators contributing to this innovative research as we work to unlock the full potential of gene therapies for people living with hemophilia,” said Boshoff.


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