Hemophilia B Trial Shows that Gene Therapy Is Here to Stay

Diseases can have many causes and can be complex. But some diseases, like genetic diseases, can be caused by just one faulty gene that we get from our parents. We can often treat the symptoms of genetic diseases, but fixing the real cause is much harder. 

Hemophilia B is a genetic disease. This means it is passed down through families. People with hemophilia B bleed for a long time because their blood does not clot well. This happens because they are missing a gene for a blood-clotting protein called Factor IX (9), or because the gene does not work right. Without this protein, the body cannot stop bleeding easily.

Symptoms of hemophilia B include: 

• Bruising more easily and often 
• Bleeding a lot after injuries, during surgery, or for no clear reason (like nosebleeds) 
• Blood in the joints, which can cause pain and swelling 

Doctors can treat these symptoms by giving the person Factor IX (9). This can be done routinely or after a bleeding event. But the treatment can be hard, inconvenient, and expensive. It also does not fix the faulty gene.

Gene therapy is a new and promising way to treat hemophilia B. With gene therapy, scientists can give patients a working copy of the Factor IX (9) gene. This means their bodies can start producing Factor IX (9) and reduce the impact of their symptoms. 

How gene therapy works

Gene therapy begins in the lab. Scientists put the working Factor IX (9) gene into the DNA of a virus “cargo ship.” The virus has been designed to be completely harmless. Once given to a patient, the virus moves to the liver cells, which make Factor IX (9). The DNA “cargo” is moved inside the cell. Once inside, the Factor IX (9) gene begins to work. This means that the cell, and future copies of the cell, can produce Factor XI (9). 

Until recently, scientists were not sure whether hemophilia B gene therapy would continue to work for decades or lose its effect over time. This was important to know, as gene therapy is expensive.  

A hemophilia B gene therapy clinical trial began more than 13 years ago at St. Jude Children’s Research Hospital. This trial helped to answer this question. 

A long-term study

For the trial, 10 adults got Factor IX (9) gene therapy in a single dose, given through a vein. St. Jude researchers then tracked the group’s bleeding rates, immune responses, how well the therapy worked, and any health concerns.  

The impact was quickly felt by people in the trial. Bleeding events dropped significantly. This, along with other similar studies, helped gene therapy to become available for adults with moderate to severe hemophilia B.  

Two such Factor IX (9) gene therapy drugs have been approved by the FDA, which brand names are Hemgenix (2022) and Beqvez (2024). 

Gene therapy is built to last

The long-term follow-up of these 10 adults on the St. Jude trial showed that patients had nearly 10 times fewer bleeding episodes per year after treatment. This greatly improved their quality of life. And 13 years after the trial began, the Factor IX (9) gene was as active as ever in their bodies.  

“Amazingly, there hasn’t been a difference between short-term and long-term results,” says Adrian, one participant in the trial. 

Equally important is the consistency and safety of the therapy.  

“For these 10 patients, the Factor IX (9) levels are stable and have been at the same level across these 13 years,” says the trial’s co-leader, Ulrike Reiss, MD, of St. Jude. 

 “We have also not seen any side effects or toxic events in the long-term follow-up.” 

Gene therapy research continues

While this research shows the long-term safety and benefit of gene therapy to treat hemophilia B, available treatments are still new. So, people may not fully understand how it works.  

Clinical trials at St. Jude and other hospitals help patients, families, and scientists better understand gene therapy and its effects.  

One clinical trial at St. Jude seeks to understand how hemophilia affects how children and teens think and feel. This study focuses on attention span, anxiety, understanding, and transition to adult care. The trial is named HEMOCOG: Neurocognitive Functions, Health Literacy, and Transition Readiness in Pediatric Hemophiliacs.

To find other clinical trials for hemophilia, visit: