By Dr Ananya Mandal, MD
Researchers in Britain have successfully renewed a level of sight in visually impaired mice, opening the possibility that the same can be achieved in humans.
The University College London researchers transplanted immature vision cells directly into the mouse retina. They noted that within weeks the cells began to integrate into the retina and the researchers, led by Prof Robin Ali in the university’s Institute of Ophthalmology, were able to show that vision began to return to the mice.
The cells in question are known as photoreceptors and are lost in very common degenerative diseases such as retinitis pigmentosa, age-related macular degeneration and diabetic retinopathy, said Anna Moran, external affairs manager at Irish medical charity Fighting Blindness. At least 100,000 people here are affected by these conditions. Prof Ali receives funding from Fighting Blindness and is also the body’s associate director of research. This work was funded directly by the UK Medical Research Council and details are published today in the journal Nature.
The team explains that the eye has two types of photoreceptors: rod cells and cone cells. The UCL team collected immature rod photoreceptor cells from healthy donor mice and transplanted them into the retinas of the vision-impaired mice. The undeveloped precursor cells used in the study were taken from week-old mice. Up to 32,000 of the cells were integrated into the retinas of recipient animals.
After four to six weeks the transplanted cells had formed connections to the optic nerve and were working almost as well as rod cells in healthy mice, the researchers found.
To see how the transplants affected behavior, mice were placed in a dimly lit Y-shaped water maze in which one of two routes led to escape. This required swimming towards a visual cue, a grating pattern. Mice with transplanted cells were able to find a raised platform much more quickly than mice without the transplanted cells. Untreated mice swam in circles, proving the treated ones could see the way out.
“We have shown for the first time that transplanted photoreceptor cells can integrate successfully with the existing retinal circuitry and truly improve vision,” Prof Ali said. Researchers were taken aback by the results. “It is restoring visual function and to a much higher degree than they expected,” Ms Moran said. “Fighting Blindness has been supporting vision research for 30 years and this is probably the most important finding in that time,” Ms Moran said.
David Head, chief executive at the retinitis pigmentosa charity RP Fighting Blindness, which part-funded the research, said, “This is fantastic progress and exciting for patients faced with sight loss as a result of retinitis pigmentosa. To read that cells appeared to be functioning almost as well as normal rod-photoreceptor cells and had formed the connections needed to transmit visual information to the brain is truly amazing. This is a great step forward.”