Bold claim: a single gene therapy can deliver five years of durable, bleed-free living for adults with hemophilia B. But here's where it gets controversial: how lasting and safe is a one-time infusion really, and does it suit everyone? The latest five-year data from the HOPE-B study, published in the New England Journal of Medicine and presented at ASH, addresses these questions with impressive, though nuanced, findings.
CSL announced five-year results from HOPE-B, a pivotal Phase 3 trial evaluating HEMGENIX® (etranacogene dezaparvovec-drlb) in adults with hemophilia B. The study shows sustained factor IX activity and continued protection from bleeds after a single infusion, reinforcing HEMGENIX as the only gene therapy currently available for adults with this condition, with or without AAV5 neutralizing antibodies.
Key outcomes at five years include:
- Durable factor IX activity: Across five years post-infusion, mean factor IX activity stayed above 36%, with year-by-year means of 41.5 IU/dL at year 1, 36.7 at year 2, 38.6 at year 3, 37.4 at year 4, and 36.1 at year 5 (n varying from 47 to 50). This demonstrates sustained biochemical activity from a single treatment.
- Strong, long-term bleed protection: The adjusted annualized bleeding rate (ABR) for all bleeds dropped roughly 90% from lead-in to year five (4.16 to 0.40; n=54 to n=51). Joint bleeds decreased 93% (2.34 to 0.16) and spontaneous bleeds declined 94% (1.52 to 0.09).
- Prophylaxis freedom: 94% of participants remained off continuous factor IX prophylaxis five years after a one-time gene therapy, with only one patient resuming prophylaxis at month 30.
- Safety profile: No serious treatment-related adverse events were attributed to HEMGENIX. A total of 100 treatment-related adverse events occurred, mostly in the first four months; only five occurred in years four to five. The most common event was elevated liver enzymes (ALT), with nine participants needing supportive corticosteroid therapy for about 81 days on average.
These five-year results underscore the potential of HEMGENIX to transform care for adults with hemophilia B by delivering durable bleed control after a single treatment and reducing reliance on ongoing prophylaxis. Still, this remains a nuanced picture: a small number of participants required later intervention, and the long-term experience beyond five years is still being explored in the IX-TEND 222-3003 extension study, which will follow patients for up to 15 years post-treatment.
Additional context: HOPE-B enrolled 54 adult men with severe or moderately severe hemophilia B, regardless of preexisting AAV5 antibodies. Fifty completed five years of follow-up. The trial’s primary endpoint compared annual bleed rates during steady-state factor IX expression (months seven to 18) with the six-month lead-in period. Secondary endpoints included factor IX activity. There were two non-treatment-related fatalities during the study, and one investigator-assessed possible treatment-related myelodysplastic syndrome was later deemed not treatment-related after comprehensive review.
What does this mean for patients and clinicians? A one-time therapy offering sustained biochemical activity and reduced bleeding offers the promise of a more autonomous daily life, fewer hospital visits, and less treatment burden. Yet opinions vary on long-term safety, equity of access, and the applicability of these results to broader patient populations. Does this data justify a shift toward routine use of gene therapy in hemophilia B, or should caution guide ongoing adoption and monitoring? How should real-world experience, registries, and extended follow-up shape future practice and guidelines? Share your perspectives in the comments.
