Junying Yu/University of Wisconsin-Madison
Genetic modifications in skin cells (above) induced the cells into what scientists call a pluripotent state — a condition that is essentially the same as that of embryonic stem cells.
Two teams of scientists have independently discovered a way to turn ordinary human skin cells into stem cells with the same characteristics as those derived from human embryos, a breakthrough that could open the door for advanced medical therapies.
If the work holds true to its promise, it would largely bypass ethical issues that have dogged research on human embryonic stem cells. It could also allow scientists to tailor the cells to specific individuals, eliminating the possibility of rejection.
The crux of the discovery, published online Tuesday by the journals Cell and Science, is a "direct reprogramming" technique that adds a cocktail of four genetic factors to run-of-the-mill human skin cells.
The Cell paper is from a team led by Dr. Shinya Yamanaka of Kyoto University; the Science paper is from a team led by Junying Yu, working in the lab of stem-cell pioneer James Thomson of the University of Wisconsin-Madison.
The discovery builds on work presented in 2006 by Yamanaka in which the same technique was demonstrated for skin cells from mice.
The two teams have been able to isolate cells that look and behave like embryonic stem cells. The researchers caution that there are still many steps to take before the cells are useful for human therapies.
Yamanaka said he knew that the real payoff would be if his work on mouse cells could be translated to human cells.
"We started working on human cells more than a year ago, but in the beginning, the four factors didn't work," he told NPR.
He said it was unclear whether the cells he produced from skin were identical to embryonic stem cells, but "all I can say is they are very similar."
While Yamanaka was working on mice to find the critical factors for transforming skin cells to embryonic stem cells, Thomson was already working on human cells. His team also reports four factors that can transform skin cells, but two of them are different from those Yamanaka found.
"It does seem that there are multiple paths to the same outcome," Thomson said. "How divergent those paths are remains to seen."
Thomson, 48, made headlines in 1998 when he announced that his team had isolated human embryonic stem cells.
Since then, the research has pitted groups that question the ethics of harvesting stem cells from human embryos against those that hope the line of research could result in important medical breakthroughs. The latest announcement from the Japanese and American teams could skirt the controversy.
"It changes everything in that these are not cells derived from embryos anymore," Thomson told NPR. But "we are back at the starting point now. These biologically ... appear to be the same as embryonic stem cells, and we still have to figure out how to differentiate them into useful things."
The whole idea of stem-cell based therapies is that the stem cells could be used to replace or repair cells damaged or destroyed by disease or injury, such as new heart cells for people who have had heart attacks or new neurons for patients with Alzheimer's disease.
"This is a huge deal," said Jose Cibelli, a researcher at Michigan State University.
"Anybody can do this procedure. It's a very simple recipe," he said. "A combination of three or four genes, and in a couple of weeks, you go from a skin cell to an embryonic stem cell. It's remarkable."
The first embryonic stem cells were isolated in mice in 1981. But it wasn't until 1998 that researchers managed to derive stem cells from human embryos. That kicked into full gear an ethical debate th