New Light-Sensing Protein Restores Vision in Mice via Gene Therapy, Study Says

New gene therapy treatment causes retinal neurons to assist vision

Opsins are proteins capable of signaling other cells during a cascade of signals vital to visual acuity and perception. In ordinary eyes, opsins take the form of rod and cone photoreceptors in the retina — and when activated via light, they pulse to send signals through other retinal neurons, the optic nerve, and finally reaching brain-dwelling neurons.

Several common eye diseases — including age-related macular degeneration, in addition to retinitis pigmentosa — can cause significant damage to photoreceptors, reducing visual acuity. But even when photoreceptors no longer work, other retinal neurons — including an interesting class of cells called bipolar cells — remain functional.

Gene therapy sees widespread success in retinal regeneration

The investigating researchers found a novel way to cause bipolar cells to assume some of the work of damaged photoreceptors.

"The beauty of our strategy is its simplicity," said Samarendra Mohanty, corresponding author of the mouse study report and founder of Nanoscope. "Bipolar cells are downstream from the photoreceptors, so when the MC01 opsin gene is added to bipolar cells in a retina with nonfunctioning photoreceptors, light sensitivity is restored."

This strategy might help overcome serious challenges other approaches to retinal regeneration face, say the scientists. Gene replacement therapy has seen success in rare diseases known to leave photoreceptors intact — like Luxturna, for example, for Leber congenital amaurosis.

Vision of mice restored with no implants, no side-effects, with one injection

Bionic eyes like the Argus II retinal prosthesis are implanted via invasive surgery and wearable hardware. Additional opsin replacement therapies don't work without the intensification of real light to achieve the necessary threshold for signal transduction.

However, if light is too intense it can risk further damage to the retina. Nanoscope's therapy requires just one injection into the eye — with no hardware. Additionally, MC01 reacts to ambient light, which means no one needs to shine a bright light into the patient's eye. MC01 therapy could also treat a wider range of serious degenerative retinal diseases — because photoreceptor survival isn't necessary.

Researchers responsible for the study found no critical safety issues in mice treated with MC01, and no signs of inflammation were noted. Most notably, there appear to be no side effects from the one-shot procedure.

New vision treatment could serve as valuable alternative

In the best scenarios, the therapy might help blind patients gain 20/60 vision — but no one is sure how well restored vision will compare to normal, fully-functional vision.

"A clinical study in people will help us understand how signaling through bipolar cells affects vision quality; for example, how well treated eyes can pick out fast-moving objects," said lead author of the study Subrata Batabyal. The therapy will probably only see limited application to patients suffering from severe retinal disease.

"If this optogenetic approach using cells spared in degenerated retina can prove to be effective in vision restoration in humans, beyond light perception, it could offer a valuable alternative to the retinal prosthesis approach for people with late-stage retinitis pigmentosa," said the NEI's program manager for the Small Business Innovation Research program PaekGuu Lee.

With so much hype around bionic implants and futuristic conceptions of the body as a potential cyberscape like Elon Musk's Neuralink, it's refreshing to hear of a one-shot policy capable of restoring vision without any mechanical parts whatsoever.