Using a person's own cells, rather than foreign cells, in regenerative therapies would avoid the transplantation of stem cells that the body's immune system might reject.
(See photos on stem cell research from National Geographic magazine.)
For a retina-repair study reported in a November issue of the journal Nature, scientists developed a novel approach.
Many forms of blindness are caused by the degeneration of cone and rod photoreceptors, the cells that convert light into brain signals.
In previous studies, stem cells transplanted into the retinas of mice had failed to make the right connections with the brain.
Rather than injecting undifferentiated stem cells into the retina in the hope that they would develop into photoreceptors, researchers this time introduced the cells at a later stage in their development.
"Our reasoning was that it would be great if we could put these stem cells onto a certain path" before they were transplanted, said Anand Swaroop, a professor of ophthalmology and visual sciences at the University of Michigan in Ann Arbor, who was involved in the study.
"These precursor cells were not really stem cells," he said. "They were immature cells programmed to be rod photoreceptors but not yet functional rods."
Once transplanted into the eyes of blind mice, the photoreceptor "precursor" cells became integrated into the retinas and restored vision in the mice.
The results suggest that precursor cells grown from human adult or embryonic stem cells might also restore sight in humans. The study also hints that, in some cases, "pure" embryonic stem cells may need a little prodding before they are implanted in a host.
"The immediate impact of this study will be to show people working on stem cell research that it's important for them to start thinking of using not only stem cells, pure and simple, as they are, but trying to really push them in specific directions that they would like these cells to go," Swaroop said.
Reh, the University of Washington scientist, wrote an accompanying Nature article about the study. He says embryonic stem cells are unpredictable.
"You don't want to take embryonic stem cells and hope that they will do the right thing when put into an injured region of the body. You want to make sure they make exactly what you want and nothing else," he said.
Reh believes the retina study may further galvanize scientists working in other areas of the nervous system to "really make attempts at neural repair, where they might have been skeptical before that reconstructing neural circuits would basically be impossible because of their complexity."
He says stem cell researchers will be able to learn from one another.
"Treating one issue will have its unique challenges. But it will follow largely along the same lines as treating a different disease," he said.
The challenges of developing stem cell treatments for humans are daunting, Reh admitted.
"But we are optimists," he said. "We are constantly discovering new things. And we wouldn't be in this field if we didn't think we could solve some of these problems."
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