Gene Therapy Shows Promise Restoring Sight In Patients With Rare Inherited Blindness : Report

More than two years after receiving an intra-ocular injection of an experimental gene therapy agent, 14 people with a rare, previously untreatable form of inherited blindness have achieved sustained improvements in vision.

The landmark findings, published in the journal Nature Medicine, are the latest update in University of Oxford ophthalmologist Robert MacLaren’s decade-long quest to preserve sight in individuals with choroideremia, a condition characterized by progressive vision loss that begins in childhood. Choroideremia is caused by mutations in the gene on the X chromosome that encodes a protein called REP1. Without this protein, the non-regenerating photosensitive cells within the retina cannot function properly, and they begin to die prematurely as the individual ages.

As early leaders in the emerging field of gene-based ophthalmic medicine, Dr MacLaren’s team saw the potential of using a modified virus to deliver a working copy of the REP1 gene into the genome within choroideremia patients’ retinal cells, therefore theoretically restoring REP1 production permanently. (Eye diseases were a great place to perfect early gene therapy platforms because the organ’s tissues are separated from the rest of the body yet easily accessible.)

After a long process of perfecting their candidate treatment, the group began human trials back in 2011. An initial group of six patients received a single surgical injection of the REP1 gene-carrying viral vector into the tissue under the retina; their fellow eye was left untreated as a control. In 2016, Dr MacLaren and his colleagues – who formed the biotech company Nightstar Therapeutics to advance the candidate’s development – announced that two of the six not only showed a cessation of disease progression but also demonstrated significant improvement in vision in the treated eye: they were able to read three or more additional lines on a standardized vision chart than they had been able to before the injection.

These sight gains were maintained for at least 3.5 years.

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