By David | Biotech News Today
Hemophilia gene therapy is a one-time treatment that gives liver cells a working copy of the gene needed to make a missing blood clotting protein. In the United States, the FDA has approved gene therapies for adults with hemophilia A (Roctavian) and hemophilia B (Hemgenix). The goal is to let the body make its own clotting factor, so patients bleed less and may need fewer regular factor infusions.
This guide explains what hemophilia is, how gene therapy for hemophilia works, which treatments are approved, and what risks and limits patients should understand.
What Is Hemophilia?
Hemophilia is an inherited bleeding disorder in which blood does not clot properly. Because of this, even small injuries can cause long bleeding, and some patients have bleeding inside joints and muscles without any clear injury. Repeated joint bleeds can lead to lasting joint damage and pain.
There are two main types:
- Hemophilia A: The body does not make enough clotting factor VIII. It is caused by changes in the F8 gene.
- Hemophilia B: The body does not make enough clotting factor IX. It is caused by changes in the F9 gene.
Both genes are on the X chromosome, so the condition is much more common in males. Severity depends on how much clotting factor a person has. Those with very low levels have the most frequent bleeding.
Standard Hemophilia Treatments Today
Most patients are treated by replacing the missing factor with regular infusions, or in hemophilia A, with a non-factor medicine that helps blood clot. These treatments work well for many people, but they are usually needed for life. Some patients also develop inhibitors, which are antibodies that stop the replacement factor from working.
Gene therapy aims to reduce this burden by changing the underlying cause. It is part of the wider progress in biotech medicine, and the general science is covered in our guide on how gene therapy works.
How Hemophilia Gene Therapy Works
Hemophilia gene therapy is an in vivo treatment, meaning the gene is delivered directly into the patient’s body rather than into cells modified in a lab. The process works like this:
- Screening: Doctors check whether the patient is suitable. They test for existing antibodies to the viral vector and review liver health.
- The vector: A harmless, modified virus called AAV (adeno-associated virus) is used as the delivery vehicle. It carries a working copy of the F8 gene (for hemophilia A) or an F9 gene (for hemophilia B).
- Infusion: The vector is given as a single infusion into a vein, usually over a few hours in a specialist center.
- Reaching the liver: The vector travels to liver cells. The liver is the main place where clotting factors are made.
- Making the missing protein: Liver cells read the new gene and begin making factor VIII or factor IX. The gene mostly stays separate from the cell’s own DNA.
- Monitoring: Patients have frequent blood tests for several months, mainly to check clotting factor levels and liver enzymes.
Approved Hemophilia Gene Therapies
| Feature | Roctavian | Hemgenix |
|---|---|---|
| Generic name | valoctocogene roxaparvovec | etranacogene dezaparvovec |
| Condition | Severe hemophilia A | Hemophilia B |
| Developer | BioMarin | CSL Behring and uniQure |
| Gene delivered | Factor VIII gene | Factor IX gene (a more active variant) |
| Vector | AAV5 | AAV5 |
| FDA approval | June 2023 | November 2022 |
| Patient group | Adults | Adults |
| List price at launch | About $2.9 million | About $3.5 million |
A third therapy for hemophilia B, Pfizer’s Beqvez, was approved by the FDA in 2024. Pfizer later announced that it would stop commercial development and sales of the product, which shows how uncertain the market for these treatments still is.
Gene Therapy for Hemophilia B
Hemophilia B is often seen as a good target for gene therapy. The factor IX gene is small enough to fit inside an AAV vector, and even a modest rise in factor IX levels can reduce bleeding in many patients. The approved therapy, Hemgenix, uses a modified factor IX gene that is more active than the natural version. In clinical studies, many patients had fewer bleeding episodes and many were able to stop regular factor IX infusions.
Hemophilia A is harder because the factor VIII gene is large, which makes it difficult to fit in a vector. For this reason, results and the durability of factor levels can differ between the two conditions.
Gene Therapy vs. Regular Treatment
| Feature | Regular factor or non-factor treatment | Gene therapy |
|---|---|---|
| Frequency | Ongoing infusions or injections | One-time infusion |
| Source of clotting factor | Given from outside the body | Made by the patient’s own liver |
| Cost over time | Continuing yearly cost | Very high one-time cost |
| Who can use it | Most patients | Adults who pass screening tests |
| Long-term evidence | Many years of experience | Still growing |
Who Can Receive It?
Not everyone with hemophilia can have gene therapy. Doctors usually look at:
- Pre-existing antibodies: Many people already have antibodies to AAV that could block the vector, and these patients may not be able to receive treatment.
- Liver health: Because the liver is the target, patients with serious liver disease may be excluded.
- Age and type: Current approvals are for adults with specific types and severity of hemophilia.
- Inhibitors and other history: Doctors review a patient’s treatment history before deciding.
Risks and Limitations
- Liver reactions: Raised liver enzymes are a common side effect. Patients are monitored closely and may be given corticosteroids to protect the liver.
- Immune response: The immune system may react to the vector, and it is usually not possible to receive the same AAV therapy twice.
- Variable results: Clotting factor levels differ between patients, and in some patients they fall over time.
- Uncertain long-term safety: Regulators ask for years of follow-up to see how long benefits last and whether late problems appear.
- Cost and access: These are among the most expensive medicines ever approved, and few treatment centers offer them.
Products like these are part of the growing field of biologics, and making them at scale is a major challenge for manufacturers.
Frequently Asked Questions
Is there a gene therapy for hemophilia?
Yes. In the United States, Hemgenix is approved for hemophilia B and Roctavian for severe hemophilia A, both for adults.
Can gene therapy cure hemophilia?
Gene therapy can raise the body’s own clotting factor levels and reduce bleeding, but it is not yet clear how long the effect lasts for every patient. Doctors therefore describe the results as long-lasting benefit rather than a guaranteed cure.
How is hemophilia gene therapy given?
It is given as a single infusion into a vein at a specialist treatment center, followed by regular monitoring of clotting factor levels and liver tests.
What is the difference between hemophilia A and B gene therapy?
Hemophilia A therapy delivers the factor VIII gene, and hemophilia B therapy delivers the factor IX gene. The two conditions have different genes, products and results.
Can children get hemophilia gene therapy?
Current approvals in the United States are for adults. Research in children is ongoing.
Key Takeaways
- Hemophilia is caused by missing factor VIII (type A) or factor IX (type B), and the genes involved are on the X chromosome.
- Gene therapy uses an AAV vector to help liver cells make the missing clotting factor.
- Hemgenix (hemophilia B) and Roctavian (hemophilia A) are approved for adults in the United States.
- Liver monitoring, patient selection, cost and uncertainty about long-term results remain important limits.
This article is for general information only and is not medical advice. Patients should speak to their hematologist about treatment options.
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