About Gene Therapy | Gene Therapy Research in Hemophilia

About Gene Therapy

Gene therapy is a novel approach aimed at treating genetic conditions like hemophilia. Learn more about the process, and talk with your doctor to see if it’s an option for you or a loved one.

The goal of gene therapy is to address a genetic disease at its source—the gene. Gene therapy research continues to evolve and progress with the development of different ways to modify genes, create new functional genes, and deliver those genes to a specific cell. Interested in participating in a clinical trial?

Learn about clinical trial considerations.

50 years of research.

Scientists have been investigating gene therapy for more than 50 years, and the science around gene therapy continues to evolve. To date, more than 4,700 gene therapy clinical trials are planned or ongoing or have been completed for different genetic diseases.

What is investigational gene therapy meant to do? A step-by-step overview

One approach of investigational gene therapy is to deliver a functional gene to specific, or target, cells.

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Think of the functional gene as the instruction manual that tells the body how to make a desired protein.

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Once a functional gene is created, there must be a way to deliver it to the right address, or target cell. The functional gene can be inserted into a viral-based shell, creating a delivery package known as a vector.


The vector’s sole purpose is to deliver the functional gene to the correct target cell type—just like an envelope that ensures the instruction manual gets to the right address.

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The envelope (vector) is then placed into the mailbox (body) and mailed to the correct address (target cell type) to deliver the instruction manual (functional gene).

Vectors are chosen because they have an affinity, or preference, for a specific cell type or types, allowing the functional gene to get to the right place. They’re sort of like a preaddressed envelope that is sent to a particular address.

After the gene therapy is delivered, the body disposes of the gene therapy by-products in a process called vector shedding. Saliva, blood, urine, and semen samples will be taken in follow-up appointments to monitor the body until no gene therapy by-products are detected. Semen samples, for example, can be taken up to 10 months postinfusion, maybe longer for some people.

Learn more about follow-up procedures.

In gene therapy research, modified viruses are the most commonly used method for the delivery of genetic material, as they have been proven to be very good at delivering genetic information into other cells. They also have a natural ability to target specific cell types in the body.

To modify a virus for use in gene therapy research, its own genetic information is replaced by the functional gene. It’s now no longer a disease-carrying virus, but a vector, or transporter. Vectors are modified to be nonpathogenic, meaning they cannot reproduce and cause disease.

AAV vectors in gene therapy research

Adeno-associated virus (AAV) is commonly used as a vector in gene therapy research overall, and specifically in gene therapy research for hemophilia.

There are a few reasons why AAV is used:

  • It is not known to cause disease in humans.
  • The likelihood of previous exposure to AAVs and developing neutralizing antibodies is minimal. Therefore, the immune system would not recognize the vector and would not attempt to destroy it before it had a chance to reach the target cells.
  • It can fit the functional factor gene inside.
  • There are a variety of naturally occurring versions of AAV, which prefer, or have an affinity for, different cell types (tropism).

AAV gene therapy for hemophilia

Using AAV vectors in gene therapy research for hemophilia has shown to be the most successful in preclinical and clinical studies. This approach creates new functional genes in a laboratory and delivers them to liver cells in the body.

Frequently asked questions

Other techniques are being investigated to treat or prevent disease at the genetic level. Here are 3 approaches to gene therapy:

Gene transfer, the main gene therapy approach discussed on this site, introduces new genetic material into cells.

Gene editing, sometimes called genome editing or genomic editing, modifies existing genes in a person’s DNA to correct specific mutations.

Cell therapy transplants whole cells capable of adding a new or desired function into a person.

Currently, gene transfer therapy is the approach being most broadly investigated in hemophilia.

Learn more about these gene therapy approaches.

Gene therapy has been studied for over 50 years; however, most gene therapies are still in the research phase. Potential risks associated with gene therapy for hemophilia include reactions related to the immune system and liver, in addition to a theoretical increased risk of cancer. Even for gene therapies that have been approved, patients will be monitored to document the safety and durability of the treatment.

Learn more about the clinical trial process, including potential risks.

The goal in gene therapy research is finding a one-time treatment option.

Learn more about gene therapy research in hemophilia.

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