British scientists have managed to make blind mice see, a breakthrough that could open the way to treating millions of people who lose their sight.

A team successfully transplanted retinal cells into mice that were blind as a result of a genetic defect, the effects of which are very similar to the human disease retinitis pigmentosa.

The treated mice regained some vision, and the team responsible showed that the transplanted cells integrated into the retina and formed new photoreceptors, the cells that are sensitive to light. The loss of photoreceptors underlies many causes of blindness in human beings, from macular degeneration to diabetes.

The team, from University College London (UCL), Moorfields Eye Hospital, London, and the University of Michigan, achieved its results by using cells that had already begun the transformation from stem cells into dedicated retinal cells. They believe that this is the key to their success.

Previous attempts using stem cells — they have the capacity to develop into all the specialised cells of the body — had failed. There was little evidence in these experiments that stem cells can integrate into the retina and become photoreceptors, perhaps because they lack the signals needed to bring this change about. Robin Ali, of the Institute of Ophthalmology at UCL, said: “We worked on the theory that cells at a later stage of development might have a higher probability of success upon transplantation.”

The cells used by the team have been programmed to be, but have yet to become, mature photoreceptors. This means that once transplanted, they are primed and ready to integrate with the retina.

A second encouraging feature of the research, reported in Nature, is that the retina accepted the new cells.

Jane Sowden, co-leader of the research, said: “Remarkably, we found that the mature retina, previously believed to have no capacity for repair, is in fact able to support the development of new functional photoreceptors.”

It seems possible that the eye already possesses a source of such cells. On the margin of the retina there are cells with stem cell-like properties — that is, cells capable of self-renewal.

“These could be harvested through minor surgery and grown in the lab to become photoreceptor precursors before being reimplanted on the retina,” Professor Ali said.

Robert MacLaren, an eye surgeon at Moorfields Eye Hospital, and a member of the team, said: “We are now confident that this (photoreceptor transplantation) is the avenue to pursue to uncover ways of restoring vision to thousands who have lost their sight.”

The evidence that the blind mice could see is indirect, but the team carried out two tests that convinced them. They took measurements of the electrical signals triggered in the next layer of cells when the eyes of the treated mice were exposed to light, and found that there were such signals, unlike untreated mice. They also showed that the pupils of the eyes of the treated mice responded to light, shrinking as the light became brighter. This showed that their eyes were sensitive to light, which was not the case with untreated mice.

An ophthalmologist unconnected with the research, Andrew Dick, of the University of Bristol, said that it was “a stunning piece of research that may in the distant future lead to transplants in humans to relieve blindness”.

• Mice vaccinated with stem cells have proved to be resistant to lung cancer. The findings, announced at a conference in Prague, suggest the possibility of developing embryonic stem-cell vaccines that prevent cancers in human beings.

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