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Dennis Turner's Parkinson's disease had become so severe by 1999 that he could not use his right arm. That was the year he underwent an experimental treatment with his own brain adult stem cells. "Soon after having the cells injected, my Parkinson's symptoms began to improve," Turner testified in 2004 before the U.S. Senate. "My trembling grew less and less, until to all appearances it was gone."

He also said this: "I can't say with certainty what my condition would have become if Dr. Levesque had not used my own adult stem cells to treat me. But I have no doubt that because of this treatment, I've enjoyed five years of quality life that I feared had passed me by."

Turner is not alone in benefiting from adult stem-cell therapy. Thousands of other patients have experienced relief from conditions that include leukemia, multiple sclerosis, lupus, sickle-cell anemia, and heart damage. Adult stem cells have grown new blood vessels to prevent amputation from gangrene, new corneas to restore sight, new cartilage and bone to replace those lost through accident or disease. They've prevented life-threatening problems from genetic diseases for children. Spinal cord injuries have also shown improvement; Laura Dominguez, testifying at the same hearing as Turner, told of regaining feeling and movement after treatment with her own nasal adult stem cells.

British doctors are starting trials to test bone marrow adult stem cells to treat liver disease. And a Harvard team now has FDA approval to begin patient trials for juvenile diabetes, after scientists showed in mice that adult stem cells could achieve "permanent reversal" of diabetes.

Adult stem cells have now helped patients with at least 65 different human diseases. It's real help for real patients. For embryonic stem cells the score is zero—not a single patient has benefited from embryonic stem cells. After 24 years of research with embryonic stem cells, they are still risky even for experimental animals, all too often forming tumors or misplaced tissue in rats and mice.

Why then the obsession with embryonic stem cells? One reason is the claim that only embryonic stem cells are pluripotent, meaning they have the flexibility, or plasticity, to form most or all tissues of the body. This ability to morph into virtually any tissue type would make a stem cell useful for treating a host of diseases, slipping into any organ to replace damaged or missing cells. This is certainly a characteristic of embryonic stem cells if left in the intact embryo. But scientists have not been successful at directing the same range of tissue formation from embryonic stem cells in the lab dish.

For adult stem cells, the dogma has been that they are not as flexible, only forming the tissue from which they originated. They have been useful for decades at replacing bone marrow and forming blood, but it was thought that they were limited in forming other tissues.

Not so. Since the mid-1990s, a rapidly growing volume of scientific evidence has documented that adult stem cells possess much greater abilities than scientists imagined, and some show the same pluripotent flexibility as embryonic stem cells. Within the last four years, researchers from around the world have documented that adult stem cells from bone marrow, blood, amniotic fluid, placenta, umbilical cord blood, and nasal tissue show this same remarkable plasticity, but without the problems of tumors seen with embryonic stem cells.

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October 2005, Vol. 49, No. 10