Gene therapy for blindness

The Daily Express today reported that the “Blind will ‘see’ within few days of gene therapy.” It said trials have shown that a revolutionary new therapy cures a form of inherited blindness within days. The Daily Mail also covered the story and said that an injection of genes directly into the retina could “reverse blindness in hundreds of thousands of patients”. The newspapers report that within two years it could treat other inherited diseases of the retina and in five years could be ready for testing on those who have age-related macular degeneration.

This small study builds on scientists’ understanding of the effects of gene therapy for a particular form of blindness called Leber congenital amaurosis (LCA). More studies are needed to fully understand the process and its longer-term effects and safety before it can be used more widely. It is important to note that the particular gene therapy described in this study would only work for this type of LCA, as it replaces the specific gene that is mutated in this condition. In theory, this technique could be adapted to treat some other forms of blindness, but it is likely to be less useful in forms of blindness where multiple genetic and environmental factors play a role.

Where did the story come from?

Dr Artur V. Cideciyan and colleagues from the University of Pennsylvania and other universities in the US and Canada carried out the research. The study was funded by the National Eye Institute, the Macula Vision Research Foundation, the Foundation Fighting Blindness, Research to Prevent Blindness, and Hope for Vision.

Some of the authors of the study and the University of Florida reported having a financial interest in the use of the type of gene therapy used and owning equity in a company (AGTC Inc.) might commercialise some aspects of this work in the future. One of the authors and some of the universities hold patents involving or related to gene therapy.

The study was published in the peer-reviewed scientific journal: Proceedings of the National Academy of Sciences of the USA.

What kind of scientific study was this?

This was a case series looking at the effects of gene therapy in three people with LCA, a severe and incurable form of blindness. In these people, LCA had been caused by mutations in a gene called RPE65. These mutations lead to the cells in the retina not being able to regenerate their light-sensing pigment, and to some of the cells dying off. Preliminary studies in humans have shown that using gene therapy to restore RPE65 function carries no short-term safety concerns, and that there can be some increase in visual function. This study aimed to look at exactly which light-sensing cells in the retina were restored by this therapy – rods (which are sensitive to light and dark, shape and movement) or cones (which are sensitive to colours) or both, and to further investigate the extent of vision improvement.

The researchers recruited three young adult volunteers (aged 21, 23, and 24 years old), who had LCA and had experienced severe loss of vision since childhood. Their sight was tested before the study began. The researchers then used a technique whereby a virus called AAV was used to introduce a normal form of the RPE65 gene into human cells. In this technique, the DNA of the virus was removed and then replaced with DNA containing the desired gene (RPE65 in this case). The virus carrying the RPE65 gene was then injected into the retinas of one eye in each of the volunteers. Their sight was measured 30 and 90 days after the injection and this included a test of how their eyes adapted to the dark. In this test, the light in the room was diminished and the volunteer’s vision assessed at up to eight hours after the change in light level to see whether they had adapted to the reduced light conditions and if so, how much. The researchers also tested how low long it took for the volunteers’ vision to recover after a bright flash of light.

What were the results of the study?

The researchers found that all three volunteers had an improvement in their sensitivity to light 30 days after the injection of the RPE65 gene, with two volunteers reporting improvements as early as seven to 10 days after the treatment. The areas that were treated had regained both rod and cone vision. There was an up to 50-fold increase in cone vision, and up to 63,000-fold increase in rod vision, with the extent of improvement differing in the three volunteers. The rods and cones were as sensitive as normal rods and cones. However, the rods were slow to adapt to dark conditions or after a flash of bright light, requiring about eight hours for full sensitivity, compared to less than an hour in normal eyes. In contrast, cones regained light sensitivity quickly.

What interpretations did the researchers draw from these results?

The researchers concluded that their results showed, “dramatic, albeit imperfect, recovery of rod- and cone-photoreceptor-based vision after RPE65 gene therapy.”

What does the NHS Knowledge Service make of this study?

This research continues to build scientists’ understanding of the effects of gene therapy for LCA. These small studies are needed to fully understand the process and its longer-term effects and safety before it can be used more widely.

It is important to note that this particular gene therapy is specifically for LCA caused by mutations in the RPE65 gene. The technique could be adapted for some other inherited forms of blindness, but it is likely to be less useful in blindness where multiple genetic and environmental factors play a role.