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Skin cell back to embryo stage
WASHINGTON - U.S. researchers said on Monday they have created a new human embryonic stem cell by fusing an embryonic stem cell to an ordinary skin cell. They hope their method could someday provide a way to create tailor-made medical treatments without having to start from scratch using cloning technology. That would mean generating the valuable cells without using a human egg, and without creating a human embryo, which some people, including President George W. Bush, find objectionable. But the team, led by stem cell expert Dr. Douglas Melton, Kevin Eggan and others at Harvard Medical School, stress in a report to be published in next Friday's issue of the journal Science that their method is not yet perfect. Stem cells are the body's master cells, used to continually regenerate tissues, organs and blood. Those taken from days-old embryos are considered the most versatile. They can produce any kind of tissue in the body. Doctors hope to someday use embryonic stem cells as a source of perfectly matched transplants to treat diseases such as cancer, Parkinson's and some injuries. But because some people object to the destruction of or experimentation on a human embryo, U.S. law restricts the use of federal funds for this kind of research. It is a hot debate in Congress and several bills have been offered for consideration when the Senate comes back next month that would either relax the federal restrictions or tighten them even more. Melton has complained about the restraints and, like other experts, has used private funding to pursue stem cell work. REPROGRAMMING CELLS He and other stem cell experts say they only want to understand how to re-program an ordinary cell and hope the use of human embryos would only be a short-term and interim step to learning how to manufacture these cells. The Harvard team say they have taken a big step in this direction. Currently, embryonic stem cells are either taken from embryos left over from fertility clinics, or generated using a cloning technology called nuclear transfer. This requires taking the nucleus out of an egg cell and replacing it with the nucleus of an adult cell, called a somatic cell, from the person to be treated. Done right, this reprograms the egg, which starts dividing as if it had been fertilized by a sperm. "On the basis of previous experiments with (mouse embryonic stem cells) we reasoned that human embryonic stem cells might provide an alternative source of material for the reprogramming of human somatic nuclei," the Harvard team wrote. So they fused embryonic stem cells to human adult skin cells, and managed to reprogram them back to an embryonic state. The new cells acted like stem cells, forming tumors called teratomas when injected into mice -- a classic test for a true embryonic stem cell -- and with hoped for marker genes. The cells also appeared to be very long-lived, another test of a true embryonic stem cell. And when cultured in lab dishes, the cells differentiated, or matured, into the three major basic types of cell. "In conclusion, these findings show that human embryonic stem cells have the capacity to reprogram adult somatic cell chromosomes after cell fusion," the researchers wrote. But there is "a substantial technical barrier" they warned. The newly fused cell contains chromosomes from the original embryonic stem cell. Therefore, it would not be a perfect genetic match to the patient. The researchers hope if they can get around this problem, they will have found a way to generate the valuable cells.
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