Gene therapy shows promise at treating immunodeficiency

Two patients enrolled in a clinical trial of a gene therapy to treat severe congenital immunodeficiency have shown signs of substantial improvements in their condition.

The study is being carried out by researchers working for the US National Institutes of Health to test the safety and effectiveness of gene therapy combined with low-dose chemotherapy in five patients aged seven to 24 affected by X-linked severe combined immunodeficiency (SCID-X1).

SCID-X1 is a rare condition caused by a mutation in the IL2RG gene, affecting the body's ability to produce several types of white blood cell. Those affected by the condition have little or no immune system and are highly susceptible to infectious diseases.

The existing treatment for SCID-X1 typically involves transplanting stem cells from a tissue-matched sibling or from the affected infant's parents, which can then develop into white blood cells. However, gene therapy would remove the need for a donor as the cells come from the patients themselves. It also reduces the risk of graft-versus-host disease (GVHD), where the transplanted immune cells ending up attacking the recipient's tissues.

The trial uses genetically engineered viruses to insert functional copies of the IL2RG gene into a patient's own stem cells, which are then reintroduced to allow them to develop into the various types of blood cell needed by the immune system. While this technique has been employed successfully in babies (see BioNews 775), this is the first report of it also appearing to work in older children and young adults.

Two of the five patients currently enrolled in the study, both of whom are in their 20s, are reported to be showing signs of long-term improvement. The researchers have observed a positive response to vaccinations and a reduction in some of their SCID symptoms, such as chronic warts and norovirus infections, suggesting an improvement in their immune status. The other three patients have only undergone the treatment within the last few months, making it too early to measure effectiveness.

However, the interim results are consistent with other similar studies and, should these results bear out, it could give hope to patients with this and similar genetic diseases.

The trial is being conducted by the National Institute of Allergy and Infectious Diseases, and the findings were presented at a conference of the American Society of Hematology.