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Gene-Editing Therapy Advances for Rare Immune Disorder

Human T-cell lymphocyte

Scanning electron micrograph of a human T-cell lymphocyte (National Institute of Allergy and Infectious Diseases, NIH)

1 April 2016. A key committee of the European Medicines Agency recommends approval of treatments for a rare children’s immune disease that uses edited genes as therapy. The Committee for Medicinal Products for Human Use, or CHMP, of the European Medicines Agency at its March 2016 meeting recommended approving Strimvelis by GlaxoSmithKline to treat adenosine-deaminase-deficient severe combined immunodeficiency or ADA-SCID.

ADA-SCID is an inherited disorder, where individuals are born without immune system protection from common bacteria, viruses, and fungi, making them susceptible to repeated infections, which can become life-threatening. The rare disorder — 1 case occurs in 200,000 to 1 million newborns worldwide — is usually diagnosed early in life, and without treatment, babies rarely live beyond the age of 2. In 10 to 15 percent of cases, the disease does not appear until after 6 to 24 months. The disorder is a result of a faulty gene inherited from both parents.

The only treatments for ADA-SCID are transplants of blood-forming stem cells, which requires genetically-matched siblings as donors. Unless the match is near-perfect, the individual risks developing graft-versus-host disease, an immune system rejection disorder. Bone-marrow recipients also may need to take drugs that suppress the immune system, which raises the risk for infection.

Strimvelis is the GlaxoSmithKline brand name for therapies where a sample of the individual’s bone marrow is removed and the person’s immature blood-forming cells are harvested. A healthy adenosine deaminase, or ADA, gene, is inserted into genomes of the blood-forming stem cells, carried by a benign virus, which enables the stem cells to produce healthy blood cells. Stem cells with corrected genes are infused back into the patient, where they flow into the bone marrow to produce healthy blood cells, including lymphocytes with normal immune system functions.

GlaxoSmithKline tested Strimvelis in a clinical trial where 12 children received the treatments over a 10-year period in Israel and Italy. The company says all 12 individuals are still alive today, including the first patient treated some 13 years ago. Nearly all of the participants in the trial (92%) did not require any follow-on stem cell transplants or enzyme replacement treatments. The most common side effects were fever, increased liver enzyme levels, and autoimmune reactions, such as anemia.

Strimvelis was given an orphan drug designation by the European Medicines Agency in 2005. The recommendation goes to the European Commission to authorize marketing Strimvelis in EU countries. No date was given for the European Commission to consider CHMP’s recommendation.

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