New gene therapy holds promise for restoring vision

U.S. researchers said Monday they have developed a new gene therapy that not only helped blind mice regain enough light sensitivity to distinguish flashing from non-flashing lights, but also restored light response to the retinas of dogs.

The study, published in the U.S. journal Proceedings of the National Academy of Sciences, may set the stage for future clinical trials of the therapy in humans with degenerative eye diseases such as retinitis pigmentosa.

The therapy employs a virus to insert a gene for a common ion channel into normally blind cells of the retina that survive after the light-responsive rod and cone photoreceptor cells die as a result of eye diseases.

Photoswitches, chemicals that change shape when hit with light, are then attached to the ion channels to make them open in response to light, activating the retinal cells and restoring light sensitivity.

Blind mice given the photoswitch therapy regained the ability to navigate a water maze as well as normal mice.

The study also found the treatment worked equally well to restore light responses to the degenerated retinas of mice and dogs, indicating that it may be feasible to restore some light sensitivity in blind humans.

"The dog has a retina very similar to ours, much more so than mice, so when you want to bring a visual therapy to the clinic, you want to first show that it works in a large animal model of the disease," lead researcher Ehud Isacoff, professor from the University of California, Berkeley, said in a statement.

"We've now showed that we can deliver the photoswitch and restore light response to the blind retina in the dog as well as in the mouse, and that the treatment has the same sensitivity and speed of response. We can reanimate the dog retina."

The therapy has several advantages over other sight restoration therapies now under investigation, the researchers said.

It uses a virus already approved by the U.S. Food and Drug Administration for other genetic therapies in the eye; it delivers an ion channel gene similar to one normally found in humans, unlike others that employ genes from other species; and it can easily be reversed or adjusted by supplying new chemical photoswitches.

The researchers said they will continue to study the effects of treatment in both mice and dogs to improve the photoswitch and develop ways of attaching the photoswitch to other receptors, including some that could amplify the signal and allow perception of fainter light, as occurs normally in rods and cones.