Single Gene Therapy Infusion Cuts Hemophilia B Bleeding by 63% Over Five Years
A phase 3 trial finds etranacogene dezaparvovec delivers stable factor IX expression for 5 years, slashing bleeding rates and prophylaxis needs by 96%.
Summary
A final 5-year analysis of the HOPE-B trial shows that a single infusion of etranacogene dezaparvovec — an AAV5-based gene therapy carrying the high-activity Padua factor IX variant — provided durable disease control in men with severe hemophilia B. Across 54 participants, annualized bleeding rates dropped 63% compared to the lead-in prophylaxis period, and exogenous factor IX consumption fell by 96%. Mean factor IX activity stabilized at 36.1 IU/dL at year five, well above the severe threshold. Crucially, efficacy held regardless of pre-existing AAV5 neutralizing antibodies, and treatment-related adverse events were rare after the first six months, supporting the long-term safety and transformative potential of this one-time therapy.
Detailed Summary
Hemophilia B is a serious bleeding disorder caused by deficiency of clotting factor IX, traditionally managed with lifelong, frequent intravenous infusions. This prophylactic burden is significant in terms of cost, quality of life, and vascular access. Gene therapy promises a paradigm shift — a single treatment capable of enabling the body to produce its own clotting factor indefinitely.
The HOPE-B phase 3 trial enrolled 54 men with severe or moderately severe hemophilia B (factor IX activity ≤2 IU/dL). After a lead-in period of at least six months on standard factor IX prophylaxis, participants received one infusion of etranacogene dezaparvovec, an AAV5 vector encoding the Padua factor IX variant — a naturally occurring mutation that produces roughly 8-fold higher clotting activity than wild-type factor IX.
At the 5-year final analysis, the adjusted annualized bleeding rate dropped from 4.16 during lead-in to 1.52 post-treatment — a 63% reduction. Factor IX activity levels stabilized at a mean of 36.1 IU/dL by year five, placing most participants in the mild-to-normal range. Exogenous factor IX use for prophylaxis and bleed treatment plummeted by 96%, from approximately 257,000 IU/year to under 11,000 IU/year.
A notable finding was that participants with pre-existing AAV5 neutralizing antibodies — historically an exclusion criterion in other gene therapy trials — showed comparable efficacy, broadening the eligible patient population significantly. Adverse events potentially related to treatment were rare after the first six months, suggesting an acceptable long-term safety profile.
These results position etranacogene dezaparvovec as a potentially transformative treatment for hemophilia B, though longer follow-up will be needed to assess whether factor IX expression remains truly permanent and whether late adverse events emerge.
Key Findings
- Single infusion reduced annualized bleeding rates by 63% compared to standard prophylaxis over 5 years.
- Mean factor IX activity reached 36.1 IU/dL at year 5, well above the severe hemophilia threshold of 2 IU/dL.
- Exogenous factor IX consumption declined by 96%, from ~257,000 IU/year to ~11,000 IU/year.
- Efficacy was maintained regardless of pre-existing AAV5 neutralizing antibody status at baseline.
- Treatment-related adverse events were rare after month 6, supporting long-term safety.
Methodology
Open-label, phase 3 single-arm trial (HOPE-B; NCT03569891) enrolling 54 men with severe hemophilia B. Participants underwent ≥6-month lead-in prophylaxis before receiving one IV infusion; outcomes were assessed over 60 months. Prespecified 5-year analyses compared post-treatment bleeding rates, factor IX expression, and safety against the lead-in baseline.
Study Limitations
The study is single-arm and open-label without a randomized control group, limiting causal inference. The cohort is exclusively male and relatively small (n=54), which may limit generalizability. Follow-up beyond 5 years is needed to determine whether factor IX expression is truly permanent.
Enjoyed this summary?
Get the latest longevity research delivered to your inbox every week.
Enter your email to subscribe: