Progress in Gene Therapy for Immune Deficiency Diseases

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A study showing that gene therapy may provide some benefit to certain older X-linked severe combined immunodeficiency (XSCID) patients, who remain significantly immunodeficient after bone marrow transplantation, will be presented on Saturday, June 3 at the 9th Annual Meeting of the American Society of Gene Therapy (ASGT) in Baltimore.

X-linked severe immunodeficiency (XSCID) is a rare genetic disease caused by defects in an essential immune hormone receptor called the common gamma chain (?c), found on the surface of lymphocytes and other immune blood cells. Patients with XSCID have immune cells that lack this receptor fail to develop and do not function normally to protect patients against infections.

Patients with XSCID develop fatal infections in infancy unless they receive a bone marrow transplant from a healthy donor. Most patients lack a fully tissue-compatible sibling donor and instead receive only a half-matched transplant from a parent donor. Some of these patients fail to achieve a satisfactory level of immune correction. Gene therapy has previously been shown to be successful for XSCID infants.

A research team led by Javier Chinen, MD, PhD, and Jennifer M. Puck, MD, from the National Human Genome Research Institute, and Harry L. Malech, MD, from the National Institute of Allergy and Infectious Disease investigated the safety and efficacy of gene therapy as salvage treatment for these older post-transplant XSCID patients.

The team obtained blood-forming cells from 3 patients aged 10, 11 and 14 years old. The blood forming cells were then exposed in culture to engineered viruses that transferred the correct ?c gene into the patient’s cells. Each patient received their own gene corrected cells by vein.

Over the next few months, the corrected gene appeared in the blood of all 3 patients. One patient showed a majority of the corrected gene; the other two showed 3% and 22%. However, all 3 patients reported improvement in their well-being, with reduced symptoms. In the patient with the majority of the corrected gene, there was clear evidence of correction of immune function tests. The treatment has appeared to be safe during the follow up period that is currently approaching 10 to 27 months.

Foamy viruses for delivering new genes into cells to correct LAD is successful
A study reporting the first successful gene therapy using foamy viruses for delivering new genes into bone marrow stem cells of dogs, and correcting a leukocyte adhesion deficiency (LAD) will be presented on Friday, June 2 at the 9th Annual Meeting of the Society of Gene Therapy (ASGT) in Baltimore.

Children with LAD suffer severe bacterial infections due to the inability of their white blood cells to stick and travel to sites of infection. Mutations in the white blood cell CD18 protein are responsible for LAD.

Dogs with the canine form of LAD, known as CLAD, also have a mutation in CD18 and don’t survive past 6 months due to severe bacterial infections.

Thomas R. Bauer Jr., PhD, from the National Institutes of Health, and colleagues, used an engineered foamy virus to deliver a normal copy of the canine CD18 DNA into the bone marrow stem cells of 5 puppies with CLAD.

Ten to 14 months after the CLAD puppies received the normal copy of canine CD18 DNA, 4 of the 5 puppies have CD18-positive white blood cell levels ranging from 4.5% to 7.4%, and all 4 dogs are alive and well one year after the treatment.

This research demonstrates the safety and effectiveness of foamy viruses for delivering new genes into bone marrow stem cells and correcting a genetic disease in dogs that is identical to the same disease in children.

American Society of Gene Therapy (ASGT)

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