EYE RECEPTOR TRANSPLANT PROMISES THERAPY FOR BLINDNESS
For the first time, the light-sensing cells found in the retina have been grown from scratch in the lab, and then successfully transplanted into the eyes of blind mice.
The transplanted cells successfully matured and connected with nerves that transmit visual signals to the brain.
The researchers say that if the procedure can be repeated with human stem cells, they believe they can cure most forms of blindness that result from degeneration of these photoreceptor cells, due to either the effects of ageing or diseases like diabetes.
"We can treat a really broad range of patients," says Robin Ali of University College London, head of the team that performed the transplant.
Another experimental stem-cell treatment, one involving a transplant of cells that support and nourish photoreceptors in the eye, has restored the sight of a man blinded by the degeneration of his retinal cells. But Ali says that this treatment will only work in people with some surviving photoreceptor cells, whereas the new therapy would work even where these cells have completely degenerated.
3D jelly
Ali and his colleagues made the photoreceptors using a relatively new procedure that allows embryonic stem cells to self-organise into retina-like structures within a three-dimensional glob of jelly.
Crucially for developing human treatments, they also identified the optimal stage in the cells development – at around 24 days – to transplant them into the eyes of mice. At that point, the photoreceptor cells are still relatively immature, but when implanted they find their own way to the correct sites in the eye where they mature fully. If the cells had already started to become fully mature photoreceptor structures called outer segments, they would not have been able to do this when transplanted, says Ali.
"We now have a route map for doing this with human embryonic stem cells," he says. The team has already grown the precursors to human retinal photoreceptor cells. "The challenge is to get [the procedure] efficient enough for transplants," he says.
In the meantime, the team wants to carry out more transplants and show that the treated mice can see. They say that although the transplanted cells developed and connected up successfully in their first attempt, not enough of the cells were implanted to restore the mouses vision. "Its a numbers game," says Ali.
"Until recently, photoreceptor loss was thought to be irreversible, but with this paper, theres now enough evidence to think we might be able to reverse blindness in the future," says Robert Lanza, medical director of Advanced Cell Technology, a company in Marlborough, Massachusetts, that is evaluating whether implanting retinal pigment epithelial cells that nourish other types of retinal cells can prevent age-related blindness. "But it needs to be repeated using human cells, and there are lots of technical issues that need to be addressed, such as scaling up the three-dimensional culture system."