The results of an international Phase III clinical trial published in the New England Journal of Medicine showed that adults with hemophilia B experienced a significant decrease in bleeding episodes after receiving a single infusion of gene therapy. Hemophilia B is a genetic disorder that affects the blood’s ability to clot and is caused by a lack of clotting factor IX. The gene therapy enables the liver to produce factor IX, allowing the blood to clot and reducing the risk of bleeds. Lead author Adam Cuker emphasized that while it may be life-changing for patients, caution should be exercised when using the term “cure” until longer follow-up data is available.
Participants in the study who received the gene therapy experienced a 71 percent reduction in bleed rate after at least one year of follow-up compared to the year prior, when they were receiving standard treatment with prophylactic infusions of factor IX. More than half of the patients did not experience any bleeds after receiving gene therapy. As a result of these positive outcomes, the FDA approved the gene therapy (fidanacogene elaparvovec) in April 2024, making it the second gene therapy approved to treat hemophilia B. Penn Medicine, where the study was conducted, is one of the leading centers offering access to FDA-approved gene therapies for hemophilia B.
The most common adverse effect observed in the study was related to an immune system attack on liver cells targeted by the gene therapy, which could potentially render the therapy ineffective. Patients affected by this immune reaction were treated with steroids to limit its impact. Participants will continue to be monitored for at least five years to assess any potential long-term side effects. The standard of care for hemophilia B involves ongoing prophylactic infusions of factor IX, which can be burdensome for patients. The new gene therapy only requires a single dose, eliminating the need for regular infusions for most patients in the study.
Patients with hemophilia B often find the burden of ongoing prophylactic treatments to be challenging, with regular infusions impacting their quality of life and daily activities. The new gene therapy offers a potential solution to this burden, with patients reporting a new sense of freedom and relief from the constant worry about bleeds and treatments. For many patients, this new treatment represents a significant improvement in their overall well-being and quality of life. The study was supported by Pfizer, with lead author Adam Cuker having previously served as a paid consultant for the company.
In conclusion, the results of the Phase III clinical trial demonstrate the significant impact of gene therapy on reducing bleeding episodes in adults with hemophilia B. The approval of the gene therapy by the FDA provides a new treatment option for patients with this genetic disorder, potentially offering a more effective and convenient alternative to standard prophylactic infusions of factor IX. Ongoing monitoring and research will be essential to further assess the long-term safety and efficacy of gene therapy for hemophilia B.
