In a breakthrough treatment that holds promise for treating some forms of blindness, night-blind mice had their vision boosted by implants of light-sensing nerve cells in a laboratory, scientists said Wednesday.
The cells, rod-type photoreceptors required for vision in dim light, were taken from the retinas of baby mice and implanted into adults who did not have any such photoreceptors, researcher Robin Ali told AFP.
"This is the first evidence that the transplantation of photoreceptor cells can result in correct connectivity and improved vision," he said.
"It is just a proof of concept. We are a long way from clinical application, but it is a first step."
Ali, from University College London, said his team transplanted about 30,000-40,000 rod cells into each eye of the test mice and then used brain imaging to confirm that the visual cortex responded to the impulses.
This still did not confirm that the mice could actually see, so the animals were put through a behavioural test of their vision.
The mice, before their transplants, had been taught to follow visual signs directing them to a surface platform in a small bath.
As soon as the lights were turned down, the night-blind mice became unable to find their way and started swimming around in circles.
In the test, "the treated mouse swims straight for the platform and that is dependent on the cells we transplanted," said Ali of the study published in Nature.
The scientist said further studies will be done, also to determine whether transplants could restore vision in subjects who had lost all their photoreceptor cells and had become completely blind.
"We suspect it might (be possible), but we don't know for how long and we don't know under what circumstances."
Trials with cone photoreceptors, which are used for seeing in daylight, had proved less successful in the past, said Ali.
"Transplantation of cones would actually really increase the potential usefulness of this treatment because humans rely more on cones than on rods."
Most causes of blindness in the Western world were caused by the loss of photoreceptor cells, said Ali.
He did not expect there to be a human trial within five years, "but we would expect within the next five years to have a much clearer idea of which types of human conditions may be appropriate to treat with this sort of transplantation."
The study adds to encouraging reports from the first use of embryonic stem cells in humans to ease degenerative forms of blindness called dry age-related macular degeneration and Stargardt's macular dystrophy.
First trials have been carried out on two volunteers in the United States by Massachusetts biotech firm Advanced Cell Technology (ACT). It began European trials in January.