Modified Gene Therapy May Help Children With SCID

Retrovirus vector for X linked SCID restored immune function and may have decreased leukemia risk

(RxWiki News) Children with SCID have a hard time fighting infections, and, sometimes, treatment for their disease makes them even sicker. But a new therapy for these kids has shown good results in fighting SCID and may prevent one serious side effect of treatment.

Children with one type of severe combined immunodeficiency disease (SCID-X1) who have been treated with gene therapy may have an increased risk of developing leukemiacancer of the white blood cells that usually starts in the bone marrow.

In a new report, a new treatment using a modified gene therapy was shown to restore immune system function in children with SCID-X1. As of October 2014, the children were still free of leukemia.

The report was written by lead authors Salima Hacein-Bey-Abina, PharmD, PhD, and Alain Fischer, MD, PhD, of Necker-Enfants Malades Hospital in Paris, and their colleagues.

Patients with SCID cannot fight off infections and are often referred to as "bubble boys" for the isolation they are often kept in to avoid infections from contact with others. Children with SCID-X1 are born with the genetic disease and usually die before age 1.

One way to treat the disease is with gene therapy. In gene therapy, scientists add genes that might correct the SCID to the genetic material in a type of virus called a retrovirus. The virus carrying the new genes is called a vector — it is the vehicle that brings the new genetic material into the patient's cells.

Once the retroviral vector is injected into the patient, the patient's body multiplies and uses the new genetic material to correct the immune system defect. However, gene therapy has sometimes left the SCID-X1 patients with a raised risk for leukemia.

In the modified gene therapy used in the new study, scientists removed some of the virus's genes — the ones the study team felt were tied to leukemia. The vector still contained the genetic material that could correct the SCID patients' immune systems.

In the current study, nine boys — 8 months old on average — were given the modified gene therapy.

After follow-up that varied from 16 to 43 months, eight of the nine boys were still alive. One boy died from an infection he had before he received the gene therapy.

Seven of the eight boys had working immune systems. Six of the boys had an increased number of immune cells, called T-cells. The T-cells indicated that part of their immune system was restored.

None of the eight boys had developed leukemia at the time the study was published. The research team said it was too early to say whether the boys would remain leukemia-free.

"The efficacy data from our study is clear: The [retroviral vector] does work to correct the disease ... we have improved the treatment's safety, although it's too early to say that we've completely eliminated the long-term risk of leukemia," said David A. Williams, MD, senior author of the study, in a press release.

The researchers planned to monitor the boys for 15 years.

The study was published online Oct. 8 in the New England Journal of Medicine.

The research was funded by the National Institute of Allergy and Infectious Diseases and the National Heart, Lung and Blood Institute, among other sponsors. The authors did not declare any conflicts of interest.


Review Date: 
October 8, 2014