Gene Therapy

Gene therapy is currently in clinical trials for both Adrenoleukodystrophy and Metachromatic Leukodystrophy with very promising results.

Gene therapy removes the risk of Graft versus host disease (GvHD), which is a serious complication of Bone Marrow Transplant. GvHD is where the graft reacts against the host. The graft is the donated marrow or stem cells. The host is the person receiving the transplant. GvHD can cause diarrhoea, skin rashes and liver damage.

GvHD happens when particular types of white blood cell (T cells) in the donated bone marrow or stem cells attack your own body cells. This happens because the donated cells (the graft) see your body cells (the host) as foreign and attack them.

Some people have a very mild form which doesn’t last long. For others, GvHD can be severe. It may even be life threatening in a few cases. Some people may have GvHD over many months, or even years.

Gene therapy may also be used for those with Krabbe Disease and is being explored as a possible treatment for Giant Axonal Neuropathy.

Gene therapy is an experimental technique that uses genes to treat or prevent disease. In the future, this technique may allow doctors to treat a disorder by inserting a gene into a patient’s cells instead of using drugs or surgery. Researchers are testing several approaches to gene therapy, including replacing a mutated gene that causes disease with a healthy copy of the gene.

The goal of gene therapy is to address a disease at the genetic level. Many different approaches are being studied, such as:

  • Turning off genes that are causing problems
  • Replacing a defective gene with a functional gene
  • Adding functional genes to help do the work of a defective gene

Gene therapy adds functional copies of a faulty gene to a patient’s own blood stem cells. The functional copies of the gene are delivered into the patient’s blood stem cells outside of the patient’s body. This makes the gene therapy.

The gene therapy is then given to the patient via a Bone Marrow Transplant (BMT), also called stem cell transplant or hematopoietic stem cell transplant.  This takes place in an in-patient hospital setting. As part of the transplant process, the patient will receive chemotherapy to make room in their bone marrow for the gene therapy. After the gene therapy has been infused, the patient’s cells will need time to multiply and produce enough new cells with the functional gene. This process is called engraftment. The patient remains in the hospital until their immune system cells have recovered and their doctor determines that it is safe for the patient to be discharged.

How are Genes added?

Gene addition uses a delivery system, called a vector, to insert the new genes directly into cells. Vectors can be selected parts of viruses that have been genetically modified so they can deliver the new genes into the cells without causing an infectious disease. Viruses are used because they have a natural ability to deliver genetic material into cells.

What happens during gene therapy?

Before a patient begins gene therapy treatment, copies of the functional gene are added to a vector (delivery system) that will carry the gene into the patient’s cells. The copies of the functional gene are the template (or instructions) the patient’s cells will use to create their own gene. This step is done in a laboratory.

Collection of the patient’s cells

Blood stem cells are collected from the patient. Blood stem cells can be collected from a vein in the patient’s arm using a special machine through a process called apheresis. For this process, the patient will first receive medicine to get more of the stem cells into the circulating blood for collection.

There may be some risks with the cell collection and the medicines received during the process. The patient should discuss these and all risks with their doctor. Stem cells can also be collected directly from the patient’s bone marrow through a process called bone marrow harvest.

The stem cell collection procedure used depends on the patient and the type of disease being treated. The collection process is performed in a hospital.

After the collection process is complete, the patient is discharged from the hospital.

Functional Gene added

The copies of the functional gene are then added into the patient’s blood stem cells that were collected to make the gene therapy. The cells that now have functional copies of the gene are referred to as gene-modified cells. After going through several tests to ensure that there are plenty of cells and it is ready for use, the gene therapy can be used in the patient.

Preparing for Gene Therapy Administration

The patient’s body is prepared to receive gene therapy using chemotherapy. This type of chemotherapy is administered in the hospital and may also be referred to as conditioning.

Chemotherapy is used for nearly all types of stem cell transplant. This process clears out the patient’s faulty bone marrow cells to make room for the gene therapy.

This helps the gene therapy engraft successfully and produce a robust number of new cells with copies of the functional gene.

There are serious risks with this type of chemotherapy, so the patient must remain in the hospital following chemotherapy until after the gene therapy has been infused and bone marrow cells and immune system cells have recovered.

The Gene Therapy is infused into the Patient

After chemotherapy is complete and the patient is ready, the gene therapy is usually delivered by intravenous (IV, or into the vein) infusion. This is done at the hospital.

After the gene therapy has been infused, the patient’s cells will need time to multiply and produce new cells, so the patient’s body has enough cells with the functional gene.

This process is called engraftment. There is a risk that the patient’s cells may not multiply. This is known as failure of engraftment. If this occurs, the patient will be given unmodified backup or reserve cells to help them to form blood cells again.

The patient remains in the hospital until they have enough new cells, their key immune cells have returned to adequate levels, and their doctor determines that it is okay for them to be discharged. Until the patient’s cells have recovered, they will have increased risk for bleeding and serious infections. The patient should discuss these and all risks with their doctor.

Follow-up Care

After the patient is ready to be discharged from the hospital, they will require follow-up monitoring. To monitor gene therapy safety, how well the gene therapy is working, and to collect information that may help other patients who are considering gene therapy, follow-up may extend over a period of years. The extent and length of follow-up required for each patient will be determined by the patient’s healthcare team.

Gene Therapy Explanation

Please click here to be taken to YouTube for a video explaining Gene Therapy. provides information and education about gene therapy and is intended for patients, caregivers, relatives and members of the public. describes what it means to have a genetic disease and how the different types of gene therapies available can be used to treat genetic disease. Gene therapy has the potential to treat many diseases, but the science behind it isn’t always easy to understand.