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Trial Testing Gene Therapy for Rare Eye Disorder

Jean Bennett

Jean Bennett (University of Pennsylvania)

20 January 2015. An early-stage clinical trial is underway testing a gene-repair therapy for choroideremia, a rare progressive genetic eye disorder that leads to blindness. The trial, conducted at Children’s Hospital of Philadelphia began enrolling its first patients, according to Spark Therapeutics, also of Philadelphia, the biotechnology company leading the study.

Choroideremia is associated with mutations in the CHM gene that block production of a protein needed to transport other key proteins to various cells in the body, including the retina. The body finds ways to compensate for most of the missing transported proteins, but not those going to the retina. As a result, the lack of these critical proteins leads to damaged cells in the retina and progressive loss of vision.

The CHM gene mutations occur on the X-chromosome, and since males have one X-chromosome, choroideremia is much more likely to occur in males than females. The condition generally begins with night blindness, followed by loss of peripheral vision, leading to tunnel-vision and complete loss of sight. The condition affects about 1 in 50,000 people and no treatment is available for it.

Spark Therapeutics develops gene therapies for inherited diseases based on research conducted at Children’s Hospital of Philadelphia and University of Pennsylvania. The company’s technology uses engineered adeno-associated viruses, benign microbes designed to deliver genetic material into the cells of patients with defective genes. The company began in October 2013, founded by four scientists from Children’s Hospital, including Jean Bennett, a University of Pennsylvania professor who studies the molecular genetics of inherited retinal disorders.

The clinical trial is testing the safety of two dose levels for Spark’s gene therapy code-named SPK-CHM for choroideremia. SPK-CHM is based on research by Bennett at University of Pennsylvania that studies the use of viruses to deliver genetic material that corrects for mutations, in this case in the CHM gene, to specific cells in the retina.

The trial aims to enroll 10 patients with choroideremia, divided between high and low doses of the therapy delivered to the patients’ retinas. The research team will look primarily safety and tolerability of the therapy, but also for changes in visual function and development of an immune response to the treatments.

Spark’s lead product, code-named SPK-RPE65, is an experimental treatment for other inherited retinal disorders — Leber’s congenital amaurosis and retinitis pigmentosa — that use the same adeno-associated virus delivery methods from Bennett’s lab as SPK-CHM. SPK-RPE65 is currently in late-stage clinical trials.

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