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The positive results of the world’s first gene therapy trial for a genetic cause of blindness known as choroideremia have been reported in this week’s edition of Nature Medicine.

Gene therapy operation

The trial, led by Professor Robert MacLaren in our Department, involved 14 patients receiving a single injection into the back of the eye of a virus containing the missing gene and began in 2011 at the Oxford Eye Hospital - part of the Oxford University Hospitals NHS Foundation Trust. By the end of the study there was a significant gain in vision across the group of patients as a whole.

Furthermore, of the 12 patients who received the treatment without any complications, 100% either gained or maintained vision in their treated eyes, which was sustained for up to 5 years at the last follow up. During this time only 25% of the untreated eyes which acted as controls maintained vision. The gene therapy treatment was generally well tolerated and there were no significant safety concerns.

The early results of vision improvement we saw have been sustained for as long as we have been following up these patients and in several the gene therapy injection was over five years ago. The trial has made a big difference to their lives.
- Professor Robert MacLaren

The success of the Oxford study has since led to a much larger international gene therapy trial involving over 100 patients across nine countries in the EU and in North America. It is now led by Nightstar Therapeutics, a gene therapy spin-out company established by the University of Oxford and Syncona to develop the treatment further. If successful the follow on trial could result in the gene therapy treatment being formally approved by the relevant regulatory bodies worldwide.

Overall gene therapy is a new treatment that is currently being developed in several trials for a variety of diseases. The concept of gene therapy is to alter or correct inherited diseases at the level of the DNA and if successful, a single treatment might have life-long effects. These early results support the notion that a single gene correction can have long-lasting beneficial effects on nerve cells of the retina to prevent blindness.

Choroideremia is one disease in a spectrum of inherited eye diseases sometimes referred to as ‘retinitis pigmentosa’ and which have now become the most common cause of untreatable blindness in young people. Last month, the European Medicines Agency formally approved its first gene therapy treatment for a different eye disease. Experts predict that other currently incurable diseases are likely to follow and will have approved gene therapy treatments in future years.