Hemophilia B is an inherited bleeding disorder caused by low levels of a blood-clotting protein called factor IX. Without enough factor IX, bleeding may last longer than usual and can happen inside the joints, muscles, or other parts of the body.
People with severe hemophilia B often use regular factor IX infusions to prevent bleeding. These treatments can work well, but they usually need to be repeated throughout life.
In 2022, the FDA approved Hemgenix (etranacogene dezaparvovec-drlb). It is a gene therapy given as a one-time treatment to help the body make its own factor IX.
This article covers how Hemgenix works, who may benefit from it, and how it was studied for hemophilia B.
How Does Hemgenix Work?
Genes give cells instructions for making proteins. In hemophilia B, a change in the F9 gene keeps the body from making enough working factor IX, a protein that helps blood clot.
Hemgenix carries a working copy of a gene into liver cells, allowing them to make factor IX. It uses a modified virus called adeno-associated virus type 5 (AAV5) to carry the gene into the liver. This virus cannot cause an infection.
The process works in three steps:
- Hemgenix carries a working factor IX gene to liver cells.
- The liver cells use the gene’s instructions to make factor IX.
- The factor IX enters the bloodstream and helps the blood clot.
The factor IX made after Hemgenix is a naturally occurring form called the Padua variant, which has greater clotting activity than standard factor IX.
Hemgenix does not repair the gene change that caused hemophilia B. Instead, it gives the liver new instructions to make factor IX, which may reduce bleeding and the need for routine factor IX infusions.
Hemgenix does not work right away. In clinical trial participants, factor IX made by the body was first detected after the third week. Some people may still need factor IX replacement infusions during the first few weeks after receiving Hemgenix until their factor IX levels become more stable.
Is Hemgenix Right for Me?
Hemgenix may be an option if you have hemophilia B and meet at least one of the following conditions:
- Regular use of factor IX treatment to prevent bleeding
- A past or current life-threatening bleed
- Repeated, serious bleeding episodes that happen on their own (spontaneously)
Before recommending Hemgenix, your health care provider will review your health history and order several tests. The following tests help show whether Hemgenix may be safe for you and whether it is likely to work:
- Factor IX inhibitor testing. Some people make antibodies called factor IX inhibitors, which block factor IX. Your health care provider will test for these antibodies before treatment. You should not take Hemgenix if you have factor IX inhibitors now or have had them in the past.
- Liver testing. You will also have blood tests and liver imaging to check for liver damage or scarring, along with testing for active hepatitis B and active hepatitis C. Hemgenix treatment should be delayed if you have an active hepatitis infection.
Your health care provider will also consider your overall health, bleeding history, current factor IX treatment, and ability to complete follow-up testing.
How Is Hemgenix Given?
Hemgenix is given once as an IV infusion, meaning it flows through a needle into a vein, usually in the arm. The dose is based on your body weight, with your treatment center preparing a customized dose for you.
The infusion usually takes about one to two hours. A health care provider will monitor you closely during treatment and for at least three hours afterward to watch for allergic or infusion-related reactions. If a reaction happens, your health care team may slow or stop the infusion and give you medicines to treat your symptoms. Once the symptoms go away, the infusion may be restarted at a slower rate.
In clinical studies, infusion-related reactions happened in about one-third of participants. Most improved on the day of the infusion, the next day, or within several days. Read this article to learn more about potential side effects of Hemgenix.
How Was Hemgenix Studied for Hemophilia B?
Hemgenix was studied in the HOPE-B clinical trial. The study included 54 men aged 19 to 75 with severe or moderately severe hemophilia B. All participants had been using standard factor IX treatment to prevent bleeding.
Before receiving Hemgenix, participants were followed for at least six months while continuing their usual preventive factor IX treatment. Researchers recorded their bleeding episodes and use of factor IX during this period. Each participant then received one Hemgenix infusion and had regular check-up visits for up to five years afterward.
The study did not compare Hemgenix with a separate group of people. Instead, researchers compared each participant’s results before and after Hemgenix treatment.
The main goal of the study was to compare the average number of bleeds per year before treatment with the number of bleeds after treatment (months 7-18). Researchers started this comparison at month 7 to give factor IX levels time to stabilize.
What Benefits Were Seen With Hemgenix In Studies?
During months 7-18 after Hemgenix treatment, the average number of bleeds per year fell from 4.1 to 1.9. The percentage of participants with no bleeding episodes went up from 26% before Hemgenix to 63% after treatment.
Hemgenix also reduced spontaneous bleeds and bleeds into the joints. These types of bleeds can cause pain and lasting joint damage.
Most participants were able to stop routine factor IX treatment. At 18 months, 96% were no longer using preventive factor IX infusions. Of the people who did not stop preventive factor IX infusions, one did not respond to Hemgenix, and another received only part of the planned dose due to a reaction.
Average factor IX levels rose to about 37%-42% of normal during the first two years and remained about 36% at five years. This is generally within the mild hemophilia range, although levels varied widely between participants.
Keep in mind that your results may differ from those seen in the study.
How Long Does Hemgenix Last?
Hemgenix is designed to provide long-lasting results after one infusion. In the HOPE-B study, average factor IX levels remained generally steady through five years after treatment.
However, it is not yet known exactly how long the benefits last. Results can also differ between people. Some may still have bleeding episodes or need factor IX treatment for surgery, injuries, or breakthrough bleeding.
Is There Any Cost Assistance Available for Hemgenix?
CSL Behring, the maker of Hemgenix, offers financial support services, including copay assistance for eligible patients. Whether you qualify to enroll may depend on your insurance status and type. To learn more, visit this website or call 833-436-0021.