Stem Cell Advances Offer Hope to Back Up the Hype
for National Geographic News
|December 4, 2006|
Recent weeks have seen major breakthroughs in stem cell research, including the restoration of vision in blind mice and the use of human stem cells to produce insulin "naturally" in diabetic mice.
Human stem cell treatments for these and other diseases may in some cases be at least a decade away. But each new discovery has added to the notion that stem cell research is showing increasing signs of living up to the hype surrounding it.
"I think it was an act of faith a couple of years ago that [something like the vision-restoration process] should work, but now we have some clear examples that it really is working," said Thomas Reh, a professor in the University of Washington's Department of Biological Structure in Seattle.
Stem cells are primal cells that have the potential to transform into various cells and tissues found in the human body.
They could potentially be used to repair tissue, grow new organs, or lead to treatments for a wide range of ailments.
There are many types of stem cells, from adult stem cells derived from umbilical cord blood or bone marrow, to stem cells taken from human embryos.
Most scientists say embryonic stem cells have the greatest research potential, because they can develop into more cell types than other stem cells. But embryonic stem cell research is controversial, because starting a stem cell line in most cases requires the destruction of a human embryo. (Related: "Stem Cells Can Be Collected Without Destroying Embryos, Scientists Show" [August 23, 2006].)
Some of the recent studies, however, highlight the potential for treating illness with adult stem cells, which are not fraught with the same ethical concerns as embryonic stem cells.
In a study published in November in the journal Proceedings of the National Academy of Sciences, researchers reported that stem cells derived from human bone marrow and transplanted into diabetic mice stimulated the animals' pancreases to produce insulin, repairing damage caused by diabetes.
"This fits with a large body of evidence that these cells have this remarkable ability to go to injured tissues and repair them," said the study's lead author, Darwin Prockop, the director of the Center for Gene Therapy at the Tulane University Health Sciences Center in New Orleans, Louisiana.
In the future, Prockop said, "the therapeutic idea would be to take small amounts of marrow from patients, then grow a large number of these cells, and give them back to the same patient to heal tissue."
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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