Blind mice can now see where they run

[Angel]

British scientists have restored vision to blind mice in a stem-cell research breakthrough that could one day help reverse human blindness.

Researchers transplanted specially-selected photoreceptor cells into the retinas of animals which had eye damage similar to many human eye diseases.

All previous attempts to transplant photoreceptors — the light-sensitive nerve cells lining the back of the eye — had failed.

But this time, the researchers from the University College London Institute of Ophthalmology and Child Health and Moorfields Eye Hospital used retina stem-cells harvested at a key stage of development: the cells were on the path to become light-detecting retina rods, but had not yet taken full form. At this stage, they are known as precursors.

It worked. By using precursor cells from days-old mice, the transplanted cells linked up to the animals own retina, and the blind adult mice could see again.

But when it comes to duplicating the method in humans, there is one very big catch. In humans, the early-stage retinal rods are at their optimal harvesting stage in a second-trimester fetus.

“This is clearly not feasible,” University of Washington eye researcher Thomas Reh wrote in an article accompanying the research to be published in Nature magazine on Thursday.

As an alternative, the researchers are working out ways to grow the retinal precursors in a lab using cells taken from the adult human eye.

Lead author on the report, Dr. Robert MacLaren, said changing that adult cells to become the transplant-friendly precursors would also help avoid rejection.

“We are now confident that this is the avenue to pursue to uncover ways of restoring vision to thousands who have lost their sight,” Dr. MacLaren said.

Blindness may not be the only affliction that could benefit from the research. Dr. Reh noted that the timing-theory could be used in many other areas of the central nervous system.

“It may be that the specific time at which the particular cell is harvested will make all the difference,” Dr. Reh wrote. “Sometimes, timing is everything.”

Once the cone and rod photoreceptors in a retina are lost, they cannot be replaced. Photoreceptor loss accounts for more blindness in the developed world than all other eye diseases combined.

The researchers tweaked the transplanted cells to make them fluorescent green. That way they could tell when the transplants took hold and actually connected to the host cells, which was the crucial stage where previous retinal transplants had failed.

“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,” said Dr. Jane Sowden, one of the leading scientists in the study.

Each human eye has over a hundred-million rod- and cone-shaped photoreceptor cells — equivalent to the dots of a thousand television screens — which convert light energy into signals that travel to the brain.

Damage to those nerve cells destroys the vision of people with age-related macular degeneration, which affects 30 million people worldwide, and eye other diseases.

But the scientists warn people not to get too carried away by their findings just yet. Human trials are likely to be at least a decade away.