British scientists have restored vision to blind mice in a breakthrough operation that raises hopes for thousands of people affected by the most common causes of blindness. Doctors at Moorfields Eye Hospital and the Institute of Child Health in London repaired the animals' eyes in the world's first successful transplantation of light-sensitive cells into retinas.
The treatment replaces photoreceptor cells killed off by retinitis pigmentosa, an incurable condition that afflicts one in 3,500 people, and macular degeneration, the most common cause of blindness, which affects up to 15% of people over 75. The success follows a series of failed attempts to cure blindness by transplanting stem cells and adult retinal cells, neither of which formed the right nerve connections to pass signals from eye to brain.
In the latest research, reported in the journal Nature today, Jane Sowden and Robin Ali injected precursors of light-sensitive cells taken from three- to five-day-old mice into the eyes of adult mice bred to have a genetic defect that causes blindness. Of about half a million cells transplanted into each eye, between 300 and 1,000 formed nerve connections. The mice showed signs that their vision was recovering. Their pupils responded normally to bright lights by shrinking and electrical activity in the retina showed the transplanted cells were passing signals on to the optic nerve. The successful animal studies pave the way for trials in humans, although the scientists warn a treatment might be at least 10 years away.
In the experiments the transplanted cells were taken from newborn mice that were genetically matched to the blind animals to minimise the risk of immune rejection. In humans similar precursor cells are believed to grow around the iris, raising the possibility that blind people might be cured by having injections of cells collected from their own eyes.
Robert MacLaren, a consultant at Moorfields Eye Hospital, said: "We are now confident that this is the avenue to pursue to uncover ways of restoring vision to thousands who have lost their sight."
In a related article Thomas Reh, an expert in regenerative medicine at the University of Washington, Seattle, wrote: "These results provide the best evidence so far that cell-replacement therapy may be possible." Barbara McLaughlan, campaigns manager at the Royal National Institute of the Blind, said the news was exciting but many years of further research and trials were needed. "It is important not to raise the hopes of people who have lost their sight until the results of human trials become available."
Andrew Dick, professor of ophthalmology at Bristol University, said: "As with any basic research we have to be careful not to overhype. However, this is a stunning piece of research that may in the distant future lead to transplants in humans to relieve blindness."
