Blind mice see after cell transplant

Researchers announced yesterday that they have restored vision in mice by implanting new light-sensing cells in their eyes, a scientific first that offers hope to millions of blind people.

The team, based in London, said it has discovered a way to transplant the cells that provide night vision, known as "rods," from a healthy mouse into blind ones. The cells took root in the retina, and the mice's pupils then dilated when exposed to light.

A similar approach, the scientists said, might be used to replace the cells that provide daytime color vision.

The finding is dramatic because it offers a way around a devastating biological fact: When the eye's light-sensing cells die, as they do in many forms of blindness, new ones do not grow in their place. The new technique, reported in today's issue of the journal Nature, is not ready to be tried in humans, the researchers cautioned.

But it may eventually lead to treatments for age-related macular degeneration, retinitis pigmentosa, and other retinal diseases that affect more than 9 million Americans, according to the Foundation Fighting Blindness , located just outside Baltimore.

Scientists have worked for decades on ways to regenerate the retina, the layer at the back of the eye where the light-sensing cells are located, but there has been a renaissance brought on by rapid advances in stem cell biology. The new work is a surprise, however, because the team did not use stem cells -- and because the results were significantly better than previous transplant attempts.

"This is promising and encouraging," said Thomas A. Reh , an eye specialist and professor of biology at the University of Washington in Seattle, who was not involved in the research. "They have figured out a way to make retinal cell therapy much more successful than previously thought."

For the experiments, the researchers transplanted cells that were developing into rods, but which had not fully matured . For humans, there is no ready source of cells at this developmental stage, but researchers may discover how to generate them from embryonic stem cells or possibly even from eye cells taken from the patients, according to Dr. Robert E. MacLaren , who led the research. MacLaren is a surgeon at Moorfields Eye Hospital in London and a scientist at the University College London Institute of Ophthalmology .

Earlier this year, a team led by Reh published research showing they could generate cells that look like rods from human embryonic stem cells. These human rod-like cells appear to be very similar to the mouse cells transplanted in the London experiment. Reh said he is currently investigating their potential to become functioning rod cells.

Rod and cone cells, crucial for daytime color vision, are specialized nerve cells known as photoreceptors at the back of the eye. The eye focuses light onto this field of cells. When the rod and cone cells detect the light, they send electrical signals to the brain, which interprets the signals and creates an image. Without these cells, a person cannot see.

MacLaren said that his team wanted to know when would be the best time to transplant cells, and found that it is much later than expected. Early in the mouse's development, rods begin as stem cells that have the ability to become many types of cells. Over time, some of these cells begin to specialize, becoming cells that are fated to become rod cells. These "progenitor cells" are the cells that made for the best transplant, according to MacLaren.

After being transplanted, the cells continued to develop, assuming their proper place in the retina. In the Nature paper, the scientists provided images showing that the cells adopted the distinctive rod shape of photoreceptor cells -- the first time that transplanted cells have done that.

The team, which included scientists at the University of Michigan and in Japan, also provided evidence that the rod cells were functional. They transplanted the cells into mice bred to have cones, but not rods, in their eyes. The pupils of eyes treated with the cells dilated more than untreated eyes when light was shone on them, according to the paper.

The work is impressive, but the team needs to prove more definitively that the rod cells are forming functional connections to the brain, said Michael Young, a neuroscientist at the Schepens Eye Research Institute and Harvard Medical School. Other scientists said they found the evidence convincing.

Young said the work was evidence of the rapid progress being made in the field of eye regeneration. It has proved a difficult problem for the same reason that spinal cord injuries cannot be reversed -- nerve cells don't regenerate. But eventually, many scientists believe, this barrier will be overcome.

"It all points to the eye," Young said, "as probably being the first part of the central nervous system where functional reconstruction is possible."

Gareth Cook can be reached at cook@globe.com.