October 26, 2004.
By Margaret Munro,
CanWest News Service.
A Canadian-led research team has shown it is not only possible but relatively easy to harvest stem cells from human eyes that could help fight blindness and degenerative eye disorders.
"I was beyond shock," says researcher Brenda Coles of the University of Toronto, describing her surprise at how readily retinal stem cells grew in her petri dishes. "Within seven days, they go from one cell to 7,000 to 10,000 cells," says Coles, lead author of a report on the discovery released Monday in the Proceedings of the National Academy of Sciences.
Not only did the cells proliferate, they were coaxed to differentiate into the seven kinds of cells associated with the retina, the membrane that senses light and images and relays images to the brain. The Toronto researchers and their colleagues in Switzerland also got the human retinal cells to grow inside mouse and chick eyes.
The researchers dream of using retinal stem cells to treat such eye diseases as macular degeneration and retinitis pigmentosa. They talk of transplanting the cells into people's eyes to repair damage. Coles and her boss, University of Toronto professor Derek van der Kooy, stress that a lot more study is needed to find out if it will work, but say the research on animals looks promising.
They injected human retinal stem cells into young chicks and one-day-old mouse pups and found many of the human cells integrated into the animals' retina. The researchers have yet to prove the mice and chicks sporting human retinal cells see normally but say it appears that they can.
"Their eyes look perfectly normal," says Coles.
The next step is to learn if the human stem cells can "make blind mice see," says Coles, who has started breeding mice that are blinded by retinal degeneration for upcoming experiments. If the cells enable the mice to see, the experiment would have to be tried in other animals before moving on to humans, research the scientists say could take another decade.
While stem cells are said to hold great promise for regenerative medicine, there is concern they might grow uncontrollably, like cancer, when reimplanted. The mouse and chick experiments indicate inhibitory factors inside the animals' eyes kept the cells under control. "They didn't take over the eye, or cause any cancerous-type things or sit in inappropriate places," says Coles. "They found their home and responded to the proper signals."
The scientists have been isolating stem cells from human eyes donated to the Eye Bank of Canada and its counterpart in Switzerland. Coles says she drops whatever she's doing when eyes come available because stem cells must be isolated within 24 hours of a donor's death. Typically, the corneas are removed for transplantation before the eyes arrive at the research lab, says Coles.
The scientists have isolated and grown retinal stem cells from the eyes of infants and those up to age 60, indicating people retain retinal stem cells through life. But the cells are under such tight inhibitory control inside the eye that they cannot repair eye damage.
If the scientists can figure out how the cells are controlled, Coles says they might eventually be able to manipulate them while they are still in the eyes. Another option would be to remove a few, tweak them in the lab and reimplant them. The retinal cells are found near where the white of the eye meets the iris.
"If you had to do surgery to get them, it would be easy," says Coles.
Macular degeneration, a retinal degenerative disease that causes progressive loss of central vision, is the most common cause of vision loss in people over age 55. Incidence of the disease and other eye disorders is expected to soar as the population ages.
© Times Colonist (Victoria) 2004.
Copyright © 2004 CanWest Interactive, a division of CanWest Global Communications Corp.
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