first results in gene therapy trial for inherited blindness
The first clinical trial of a gene therapy for an inherited cause of progressive blindness called choroideremia has shown very promising initial results, surpassing the expectations of the researchers involved. Professor Robert MacLaren of the Nuffield Laboratory of Ophthalmology (part of the Nuffield Department of Clinical Neurosciences) led the development of the retinal gene therapy and this first clinical trial.
What is choroideremia?
Choroideremia is a rare inherited cause of blindness that affects around 1 in 50,000 people. There is currently no cure. It is caused by defects in the CHM gene on the X chromosome. Without the protein produced by the CHM gene, pigment cells in the retina of the eye slowly stop working, then die off. As the disease progresses, the surviving retina gradually shrinks in size, reducing vision.
The aim of the treatment in this study was to get the gene therapy into the cells in the retina of the eye without causing damage. After six months, however, the patients actually showed improvements in their vision in dim light and two of the six were able to read more lines on the eye chart.
The gene therapy approach
The gene therapy approach developed by Professor MacLaren’s team uses a small, safe virus to carry the missing CHM gene into the light-sensing cells (photoreceptors) in the retina. In an operation similar to cataract surgery, the patient’s retina is first detached and then the virus is injected underneath using a very fine needle.
The aim is for the CHM gene, once delivered into the cells of the retina, to start producing protein and stop the cells dying off. The results suggest that the approach has promise for treating people early on before too many cells in the retina have been lost. The approach also has relevance for other, far more common causes of blindness where these photoreceptors are affected, such as retinitis pigmentosa and age-related macular degeneration.
Results at six months are now reported for the first six patients in The Lancet medical journal. Based on the success of the treatment in the first six patients, three more have recently been tested at a higher dose.
Professor MacLaren says: ‘It is still too early to know if the gene therapy treatment will last indefinitely, but we can say that the vision improvements have been maintained for as long as we have been following up the patients, which is two years in one case. The results showing improvement in vision in the first six patients confirm that the virus can deliver its DNA payload without causing significant damage to the retina. This has huge implications for anyone with a genetic retinal disease such as age-related macular degeneration or retinitis pigmentosa, because it has for the first time shown that gene therapy can be applied safely before the onset of vision loss.’
The first patient to be treated, Jonathan Wyatt, 65, says: ‘My left eye, which had always been the weaker one, was that which was treated as part of this trial...Now when I watch a football match on the TV, if I look at the screen with my left eye alone, it is as if someone has switched on the floodlights. The green of the pitch is brighter, and the numbers on the shirts are much clearer.’
Wayne Thompson, 43, an IT project manager in Staffordshire, was treated in April with a higher gene therapy dose as part of the subsequent trial: ‘One night in the summer, my wife called me outside as it was a particularly starry evening. As I looked up, I was amazed that I was able to see a few stars. I hadn’t seen stars for a long, long time...For a long time I lived with the certainty of losing vision. Now I have uncertainty of whether the trial will work, but it is worth the risk.’
The Phase I clinical trial is funded by the Health Innovation Challenge Fund, a partnership between the Wellcome Trust and the Department of Health. The research has received additional support from the National Institute for Health Research Oxford Biomedical Research Centre and the charity Fight for Sight.
There is a page of further information for patients about the clinical trial.