Completely blind mice had their sight restored after having developing cells transplanted into their eyes. The cells reformed the entire light-sensitive layer of the retina, rather like replacing the film in a camera. The researchers believe their cell transplantation therapy might be applied to treat blindness resulting from the progressive condition retinitis pigmentosa.

Led by Robert MacLaren, a professor at the Nuffield Laboratory of Ophthalmology at the University of Oxford in the UK, the team writes about their work in the 3 January online issue of the Proceedings of the National Academy of Sciences.

The idea of using cell replacement to restore vision in retinitis pigmentosa, an inherited condition where the light-sensing or photoreceptor cells in the retina gradually die leading to progressive blindness, and age-related macular degeneration, where vision in the center of the visual field is lost, is not new.

Typically, people with these conditions lose their vision when the outer layer of photoreceptor cells is lost, and researchers are looking for ways to develop treatments that restore vision at this stage.

Other studies that have tried to regenerate a retina have relied on having a pre-existing outer layer of photoreceptor cells in place at the time of treatment.

This study is different because it shows it is possible to regenerate a retina even when that outer layer is lost, say the researchers.

As MacLaren explains in a BBC News report:

“We have recreated the whole structure, basically it’s the first proof that you can take a completely blind mouse, put the cells in and reconstruct the entire light-sensitive layer.”

He says it is like regenerating a whole computer screen rather than repairing individual pixels.

MacLaren and colleagues used mice with severe human retinitis pigmentosa, where the condition had got to the point where there were no photoreceptor cells left. The animals couldn’t tell the difference between light and dark.

The researchers injected precursor cells that develop into cells that then make a retina once inside the eye.

Two weeks later, the mice had formed complete retinas, with a complete structure, with light-sensitive outer segments and connections with host neurons.

“These observations suggest that a cell therapy approach may reconstitute a light-sensitive cell layer de novo and hence repair a structurally damaged visual circuit,” write the researchers, who conclude:

“Rather than placing discrete photoreceptors among preexisting host outer retinal cells, total photoreceptor layer reconstruction may provide a clinically relevant model to investigate cell-based strategies for retinal repair.”

The study is well received in that experts suggest it looks at the most severe, clinically relevant kind of vision loss.

Pete Coffee, a professor of opthalmology at University College London, says in a BBC News report that the study tackles what you would probably “need to do to restore sight in a patient that has lost their vision”.

But he says more needs to be done to determine the quality of the restored vision. McLaren and colleagues carried out brain scans and tested sensitivity to light, but this is not enough to establish, for instance, if treated mice can see the difference between food and predators.

Two studies published recently, report how novel treatments for retinitis pigmentosa are moving closer to clinical trials. One, published in Molecular Medicine, uses skin-derived induced pluripotent stem (iPS) cell grafts, and the other, published in Human Molecular Genetics, uses a gene therapy approach.

Written by Catharine Paddock PhD