Blind mice see after cell transplant
Study suggests newborn cells best for transfer.
Using a technique that may one day help blind people to see, researchers have shown in mice that retinal cells from newborns transplanted into the eyes of blind adults wire up correctly and help them to detect light.
The finding challenges conventional biological thinking, because it shows that cells that have stopped dividing are better for transplantation than the stem cells that normally make new cells.
For decades, researchers have sought a way to replace the light-detecting cells that carpet the back of our eyes and which break down in diseases such as retinitis pigmentosa and macular degeneration. But they have struggled to find cells that will work normally after being transplanted into the eye.
To find the best cell type, researchers led by Anand Swaroop at University of Michigan, Ann Arbor, and Robin Ali at University College London, UK, extracted cells from the retinas of mice at various times when photoreceptors are normally being generated, as embryos and after they are born. They then injected these cells into adult mouse retinas and counted how many new photoreceptors were generated.
Injecting these cells into the eyes of partially blind mice improved the animals' sight, making their pupils react to light. "For us ophthalmologists it's very, very, very exciting," says Robert MacLaren, one of the study's authors at Moorfields Eye Hospital, London. "We can suddenly see in our minds a potential treatment."
From mice to man
It would be difficult to obtain equivalent human cells for transplantation, because they would have to come from fetuses in the first or second trimester of pregnancy. But Maclaren says that it may soon be possible to grow the correct retinal cells from adult stem cells or embryonic stem cells.
In the past there have been many attempts at transplanting tissue into the adult retina. Some researchers have transferred whole sheets of fetal retina into animals a method that is now showing good results in tests on humans, says Robert Aramant of the company Ocular Transplantation in Louisville, Kentucky.
But these sheets do not join properly to the rest of the retina, says Thomas Reh, who studies retinal development at the University of Washington, Seattle. And transplanted stem cells have not efficiently generated new photoreceptors or restored sight. "This new work is head and shoulders above most of the other studies," Reh says.
MacLaren thinks that his cells are well suited to transplantation, because they are only one step from being adaptable stem cells and can tolerate being moved from one eye to another. Also, they are newly committed to becoming photoreceptors, so that they continue to grow into photoreceptors even after the move.
Researchers will now want to test whether newborn cells, rather than stem cells, are successful in other transplants, Reh says: "We've been doing it all wrong". Grafting new spinal neurons, for example, might help treat spinal-cord injuries.
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- MacLaren R. E. , et al. Nature, 444 . 203 - 207 (2006).