Solving this problem is an important step before moving on to potential therapies
THURSDAY, Feb. 14 (HealthDay News) -- A major concern with using stem cells to treat disease has been the possibility that the retrovirus used to implant the cells might cause cancer, but now a group of scientists appears to have solved that problem.
In November, two groups of researchers -- one in Japan and one in the United States -- showed that adult human and mouse skin cells could be reprogrammed into stem cells similar to embryonic stem cells, which can be made into any type of cell. These cells, called induced pluripotent stem cells (iPS), could be the key to using stem cells to cure a variety of diseases.
In this latest study, published in the Feb. 14 issue of Science, the Japanese researchers prove these stem cells are made from normal mature adult cells, and they show that these stem cells can be implanted using a retrovirus without fear of causing cancer.
"This is a real nice follow-up and confirmation of the previous papers that looked at inducing normal cells to become stem cells," said Dr. Hugh Taylor, an associate professor at Yale University School of Medicine.
"The question that still existed from the previous paper was whether these stem cells were some sort of adult stem cells," Taylor said. "This paper shows that these stem cells are fully differentiated adult cells, that they can be reprogrammed into stem cells," he added. "You can probably take almost any adult cell and turn it into a stem cell."
In addition, there has been a fear that using a retrovirus to implant stem cells results in an increased risk of cancer. This study showed that doesn't happen, Taylor said. "It proves, without a doubt, that these cells are safe for human use," he noted.
However, Taylor thinks the cells need to be studied over a longer period to ensure they don't have an elevated cancer risk.
"It will still take years of basic research before we become able to use iPS cells to treat patients," said lead researcher Dr. Shinya Yamanaka, from Kyoto University in Japan. "We are doing our best to bring it to clinics as quick as possible."
In experiments with mice, Yamanaka's team reprogrammed adult mouse liver and stomach lining cells into iPS cells. Using a retrovirus, the scientists were able to transplant these cells into mice. Moreover, Yamanaka's team found that these reprogrammed cells avoided sites that are known to trigger tumors. In fact, mice that received the iPS remained tumor-free for six months.
Creating embryonic-like stem cells from adult cells may resolve an ethical dilemma, but whether these cells will act like real embryonic stem cells is yet to be determined.
"Using adult cells to create what appeared to be embryonic stem cells solves the ethical dilemma that some people have in creating or destroying embryos to create stem cells," Taylor said.
"The one thing we can't say yet is that whether these stem cells generated in this way will have the full potential that embryonic stem cells have," Taylor said. "They probably won't. But exactly where that line will be drawn isn't known. If they do almost everything that embryonic stem cells do, that'll be wonderful. If they don't, we may still need to consider using embryonic stem cells."
Another expert thinks this is an important step forward, but it's going to take a long time before cells generated this way can be used to treat people.
"They're one step closer to solving the problem," said Paul Sanberg, director of the University of South Florida Center for Aging and Brain Repair in Tampa. "Now they're going to have to grow the cells, implant them in animals, and show that they work for diseases," he said. "There's a lot of experiments to do between making these cells and putting them in people."
For more about stem cells, visit the International Society for Stem Cell Research.
SOURCES: Shinya Yamanaka, M.D., Ph.D., Kyoto University, Japan; Paul Sanberg, Ph.D., D.Sc., distinguished professor of neurosurgery, and director, University of South Florida Center for Aging and Brain Repair, Tampa; Hugh Taylor, M.D., associate professor, Yale University School of Medicine, New Haven, Conn.; Feb. 14, 2008, Science
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