Data Published in the New England Journal of Medicine Confirm the Long-term Durability and Safety of HEMGENIX® (etranacogene dezaparvovec-drlb) Over Five Years

- 94% of patients (51 of 54) remained free from the burden of continuous prophylaxis treatment through five years following a single infusion of HEMGENIX, demonstrating sustained therapeutic benefit
- At year five, mean factor IX activity levels remained strong at 36.1% and HEMGENIX continued to demonstrate a favorable safety profile, reinforcing its durable efficacy
- More than 75 individuals across eight countries have received HEMGENIX in real-world settings, reflecting growing global adoption

KING OF PRUSSIA, Pa., Dec. 7, 2025 /PRNewswire/ -- Global biopharma leader CSL (ASX:CSL; USOTC:CSLLY) today announced five-year (60-month) results from the pivotal Phase 3 HOPE-B study, confirming the long-term durability and safety of a one-time infusion of HEMGENIX^® (etranacogene dezaparvovec-drlb) in adults living with hemophilia B. Published in the New England Journal of Medicine (NEJM) and presented simultaneously at the American Society of Hematology (ASH) Annual Meeting, the data reaffirm HEMGENIX's consistent performance over time to deliver durable factor IX activity levels, sustained bleed protection compared to prophylaxis treatment, and continued freedom from routine prophylaxis. HEMGENIX remains the only commercially available gene therapy for adults with hemophilia B and can be used in patients with or without AAV5 neutralizing antibodies.

"The five-year HOPE-B results mark a pivotal milestone for gene therapy, providing clear, long-term data of the ability of HEMGENIX to potentially transform care for adults with hemophilia B," said Steven Pipe, MD, Professor of Pediatrics and Pathology, Hemophilia and Coagulation Disorders Program and the Special Coagulation Laboratory, University of Michigan. "For those who have relied on frequent prophylactic infusions, achieving lasting bleed control from a single treatment offers the potential for greater day-to-day freedom and a life less burdened by the demands of ongoing therapy."

In the Phase 3, open-label, single-dose, single-arm HOPE-B trial, 54 adult male participants with severe or moderately severe hemophilia B, with or without preexisting AAV5 neutralizing antibodies, were infused with a single dose of HEMGENIX. Of the 54 participants, 50 completed five years of follow-up. The five-year follow-up analysis demonstrated:

• Durable Factor IX Activity: Mean factor IX activity levels were sustained at greater than 36% during years one through five post-infusion: mean factor IX levels of 41.5 IU/dL (n=50) at year one, 36.7 IU/dL (n=50) at year two, 38.6 IU/dL (n=48) at year three, 37.4 IU/dL (n=47) at year four, and 36.1 IU/dL (n=48) at year five.
• Sustained Bleed Protection: The mean adjusted annualized bleeding rate (ABR) for all bleeds was reduced by approximately 90% from the lead-in (4.16, n=54) compared to year five (0.40, n=51) post-infusion. Additionally, joint bleeds were reduced by 93% from lead-in (mean ABR of 2.34 at lead-in to 0.16 at year five) and spontaneous bleeds were reduced by 94% (mean ABR of 1.52 during lead-in versus 0.09 during year five).
• Freedom from Prophylaxis: 94% of patients remained free of continuous prophylaxis treatment following their one-time gene therapy infusion. This rate has remained consistent over time, with only one participant resuming continuous factor IX prophylaxis at month 30 post-infusion.
• Favorable Safety Profile: No serious adverse events were related to treatment with HEMGENIX. HEMGENIX was generally well-tolerated, with a total of 100 treatment-related adverse events (TRAEs), most of which occurred in the first four months post-infusion. Only five TRAEs were reported between years four and five. The most common adverse events were an increase in alanine transaminase (ALT), for which nine (16.7%) participants received supportive care with reactive corticosteroids for a mean duration of 81.4 days (standard deviation: 28.6; range: 51-130 days).

"We are incredibly proud to share the five-year results from the HOPE-B study, which reinforce the lasting impact of HEMGENIX as a one-time treatment option for adults with hemophilia B," said Deborah Long, MD, FCCP, Senior Vice President and Head, Medical Affairs, CSL. "These results highlight the meaningful difference HEMGENIX can make—helping people experience fewer bleeds compared to prophylaxis treatment and freeing them from the burden of regular ongoing treatment. We remain committed to expanding access to this important treatment."

Although the five-year data mark the final analysis for the HOPE-B study, participants who consent will continue to be monitored in the IX-TEND 222-3003 extended follow-up study (NCT05962398), which will track patients for up to 15 years post-treatment.

The multi-year clinical development of HEMGENIX was led by uniQure (Nasdaq: QURE) and sponsorship of the clinical trials transitioned to CSL after it licensed global rights to commercialize the treatment. CSL also established a post-marketing registry to generate additional long-term safety, efficacy and durability data.

HEMGENIX has received regulatory approval in the United States, Canada, the UK, Switzerland, Australia, Saudi Arabia, Taiwan, South Korea, Singapore, and Hong Kong, and conditional marketing authorization from the European Commission (EC) for the European Union and European Economic Area. To date, more than 75 individuals across eight countries have received HEMGENIX in real-world settings.

For more information on HEMGENIX, please visit www.Hemgenix.com.

About the Pivotal HOPE-B Trial
The pivotal Phase 3 HOPE-B trial is an ongoing, multinational, open-label, single-arm study to evaluate the safety and efficacy of HEMGENIX. Fifty-four adult male participants with severe or moderately severe hemophilia B, with or without preexisting AAV5 neutralizing antibodies, were enrolled in a prospective, six-month or longer observational period during which time they continued to use their current standard-of-care therapy to establish a baseline ABR. After at least the six-month lead-in period, patients received a single intravenous administration of HEMGENIX at a 2x10^13 gc/kg dose. Patients were not excluded from the trial based on preexisting neutralizing antibodies (NAbs) to AAV5.

A total of 54 patients received a single dose of HEMGENIX in the pivotal trial, with 50 patients completing five years of follow-up. The primary endpoint in the pivotal HOPE-B study was ABR 52 weeks after achievement of stable factor IX expression (months seven to 18) compared with the six-month lead-in period. For this endpoint, ABR was measured from month seven to month 18 after infusion, ensuring the observation period represented a steady-state factor IX transgene expression. Secondary endpoints included assessment of factor IX activity.

No serious treatment-related adverse reactions (TRAEs) were reported. Two deaths occurred during the study due to non-treatment-related TRAEs: one at approximately 15 months post-dose due to cardiogenic shock and urosepsis, and another at approximately 54 months post-dose due to cardiac amyloidosis. A serious adverse event of myelodysplastic syndrome was initially assessed by the investigator as possibly treatment-related; however, following the results of molecular analysis and based on the assessment of risk factors, the investigator reassessed the event as not treatment-related after the five-year clinical database lock for the study. No inhibitors to factor IX were reported.

About Hemophilia B
Hemophilia B is a life-threatening rare disease caused by a mutation on the F9 gene, resulting in low levels of functional clotting factor IX. People with the condition are particularly vulnerable to bleeds in their joints, muscles, and internal organs, leading to pain, swelling, and joint damage. Treatments for moderate to severe hemophilia B typically include life-long prophylactic infusions of factor IX to temporarily replace or supplement low levels of the blood-clotting factor. Beyond the physical burden, many people with hemophilia B are continually confronted with the mental and emotional impact of managing their condition—and rarely have their minds free of hemophilia.

About HEMGENIX
HEMGENIX is a gene therapy that reduces the rate of abnormal bleeding in eligible people with hemophilia B by enabling the body to continuously produce factor IX, the deficient protein in hemophilia B. It uses AAV5, a non-infectious viral vector, called an adeno-associated virus (AAV). The AAV5 vector carries the Padua gene variant of Factor IX (FIX-Padua) to the target cells in the liver, generating factor IX proteins that are 8x more active than normal. These genetic instructions remain in the target cells, but generally do not become a part of a person's own DNA. Once delivered, the new genetic instructions allow the cellular machinery to produce stable levels of factor IX.

Important Safety Information (ISI)

What is HEMGENIX?
HEMGENIX^®, etranacogene dezaparvovec-drlb, is a one-time gene therapy for the treatment of adults with hemophilia B who:

• Currently use Factor IX prophylaxis therapy, or
• Have current or historical life-threatening bleeding, or
• Have repeated, serious spontaneous bleeding episodes.

HEMGENIX is administered as a single intravenous infusion and can be administered only once.

What medical testing can I expect to be given before and after administration of HEMGENIX?
To determine your eligibility to receive HEMGENIX, you will be tested for Factor IX inhibitors. If this test result is positive, a retest will be performed 2 weeks later. If both tests are positive for Factor IX inhibitors, your doctor will not administer HEMGENIX to you. If, after administration of HEMGENIX, increased Factor IX activity is not achieved, or bleeding is not controlled, a post-dose test for Factor IX inhibitors will be performed.

HEMGENIX may lead to elevations of liver enzymes in the blood; therefore, ultrasound and other testing will be performed to check on liver health before HEMGENIX can be administered. Following administration of HEMGENIX, your doctor will monitor your liver enzyme levels weekly for at least 3 months. If you have preexisting risk factors for liver cancer, regular liver health testing will continue for 5 years post-administration. Treatment for elevated liver enzymes could include corticosteroids.

What were the most common side effects of HEMGENIX in clinical trials?
In clinical trials for HEMGENIX, the most common side effects reported in more than 5% of patients were liver enzyme elevations, headache, elevated levels of a certain blood enzyme, flu-like symptoms, infusion-related reactions, fatigue, nausea, and feeling unwell. These are not the only side effects possible. Tell your healthcare provider about any side effect you may experience.

What should I watch for during infusion with HEMGENIX?
Your doctor will monitor you for infusion-related reactions during administration of HEMGENIX, as well as for at least 3 hours after the infusion is complete. Symptoms may include chest tightness, headaches, abdominal pain, lightheadedness, flu-like symptoms, shivering, flushing, rash, and elevated blood pressure. If an infusion-related reaction occurs, the doctor may slow or stop the HEMGENIX infusion, resuming at a lower infusion rate once symptoms resolve.

What should I avoid after receiving HEMGENIX?
Small amounts of HEMGENIX may be present in your blood, semen, and other excreted/secreted materials, and it is not known how long this continues. You should not donate blood, organs, tissues, or cells for transplantation after receiving HEMGENIX.

Please see full prescribing information for HEMGENIX.
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.

You can also report side effects to CSL Behring's Pharmacovigilance Department at 1-866-915-6958. 

About CSL
CSL (ASX:CSL; USOTC:CSLLY) is a leading global biopharma company with a dynamic portfolio of lifesaving medicines, including those that treat hemophilia and immune deficiencies, vaccines to prevent influenza, and therapies in iron deficiency, dialysis and nephrology. Since our start in 1916, we have been driven by our promise to save lives using the latest technologies. Today, CSL – including our three businesses, CSL Behring, CSL Seqirus, and CSL Vifor – provides lifesaving products to patients in more than 100 countries and employs 29,000+ people. Our unique combination of commercial strength, R&D focus and operational excellence enables us to identify, develop, and deliver innovations so our patients can live life to the fullest. For inspiring stories about the promise of biotechnology, visit CSL.com/Vita. 

For more information about CSL, visit CSL.com.

Media Contacts
Etanjalie Ayala, CSL
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Stephanie Fuchs, CSL
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SOURCE CSL