Reprogramming damaged retinal cells to detect light again could form basis of a general gene-therapy. 

The majority of gene therapies for blindness this far have concentrated on replacing the faulty genes responsible for a number of highly specific, and much rarer conditions. One of the first successful gene therapy trials examined a condition called Leber’s congenital amaurosis, which affects approximately 3 out of 100,000 people. Last week researchers from the University of Manchester, UK, published a method to treat all blindness caused by damaged or missing retinal cells that they have successfully tested in mice.

The treatment works by inserting the human gene for rhodopsin, the light-sensing pigment in the eye, via a virus into the eyes of mice whose rod and cone cells had been destroyed. After treatment, Dr Rob Lucas and his team found that mice could tell objects apart by their size, although not as well as sighted mice. “The treated mice could discriminate black and white bars, but only ones that were 10 times thicker than what sighted mice could see,” says Lucas.

Treated mice ran for cover when played a video of an approaching owl, just as a moue with normal vision would. “You could say they were trying to escape, but we don’t know for sure,” says Dr Lucas. “What we can say is that they react to the owl in the same way as sighted mice, whereas the untreated mice didn’t do anything.”

“This is the most effective example yet of the use of genetic therapy to treat advanced retinal degeneration,” says Robin Ali, whose team at University College London were behind the successful gene therapy trial for Leber’s congenital amaurosis.

This is the first time that a human gene has been tested in this way. The virus used by Dr Lucas’ team to deliver the gene therapy has already been approved for use in humans, leading to the possibility of a human trial for the treatment in about five years.

While this news is another promising step towards the clinic for gene therapy treatments, there are still concerns. Earlier this year evidence emerged that sight has begun to deteriorate again in patients with Leber’s congenital amaurosis who were involved in the initial gene therapy trial. Any new treatment continuing to clinical trials will now have to prove its longevity as well as initial effectiveness.