Gene therapy is an experimental treatment currently available for children with ADA-SCID, X-linked SCID, and Artemis SCID. Families of children who choose this therapy must enroll in a clinical trial.
There are several clinical trials now taking place at children’s hospitals throughout the United States and at the National Institute of Health. Research clinical trials that are available at https://clinicaltrials.gov/.
In gene therapy, doctors use a corrected copy of the child’s own hematopoietic stem cells to create a working immune system in the child. These are the steps in gene therapy treatment process.
- The hematopoietic stem cells (containing the mutated gene) are extracted from the child through a peripheral bone marrow harvest and transferred to a lab setting.
- Meanwhile, doctors create a corrected copy of the mutated gene in the lab. The corrected gene is put into a virus, which has been deactivated and can no longer spread infection, but is very efficient in penetrating cells.
- In the lab, doctors mix the virus, containing the corrected gene, with the patient’s stem cells. The virus penetrates some of the unhealthy stem cells and provides them with the corrected gene. The cells are then placed into frozen storage.
- The patient may or may not receive conditioning.
- The cells are taken out of storage and infused back into the patient.
- Cells with the corrected gene divide, making copies. In two to three months, the cells with the corrected gene have spread throughout the child’s body. The cells with the corrected genes are the child’s new immune system.
One past concern with gene therapy is that it could cause leukemia, which is a cancer of the blood, or bone marrow. The reason for this concern is because in gene therapy trials conducted in Europe between 1999 and 2006, the virus that carried the corrected gene caused leukemia in five of the 20 boys with X-linked SCID who were treated with gene therapy. Doctors treated the five patients and one died. In 2016, one additional patient on this trial developed lymphoma caused by the gene therapy.
Since those trials, scientists have changed the type of virus, or vector, used to deliver the corrected gene. In trials of X-linked SCID using new modified vectors, leukemia and lymphoma have not been seen. Additionally, patients with ADA SCID who have undergone gene therapy have never been reported to have leukemia.
Scientists think that the chance of developing leukemia from gene therapy using the newer vectors is extremely low, but many more years of follow-up are needed to be sure.
Another risk is that there is a possibility that the gene therapy does not result in a good immune system for the child. Because it is still experimental, the procedure might not work.