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Mature Human Embryos Created From Adult Skin Cells
Other critics noted that scientists in Japan and Wisconsin recently discovered a way to "reprogram" stem cells directly from skin cells, without having to make embryos as a middle step.
"In light of the recent cell reprogramming developments, cloning-based stem cell research is less justified than ever," said Marcy Darnovsky of the Center for Genetics and Society in Oakland, Calif.
Wood and others countered that, for now, those approaches require the use of gene-altered viruses, which can trigger tumor growth.
"It's hard to believe the FDA would approve the use of those cells," Wood said.
Criticism also arose on Capitol Hill, where enthusiasm has grown for the newer stem cell methods that do not involve embryos.
"Human cloning is now less about the science and more about the novelty, which makes it all the more nefarious," said Rep. Dave Weldon (R-Fla.), who has sought to ban all kinds of human cloning.
He said he hopes to revive the legislation this year. Previous bills have failed because Congress, though willing to ban the creation of cloned babies, is divided on the issue of banning human embryo cloning for research.
No law bans cloned-baby-making, but the Food and Drug Administration has said that such experiments would require its approval.
Cloning involves fusing an ordinary body cell with a female's egg cell whose DNA has been removed. Chemical factors inside the egg reprogram the body cell's DNA so that the newly created cell develops into an embryo that is a genetic twin of the person or animal that donated the body cell.
The technology has developed rapidly in animals, and scientists have been trying to apply it to human cells. In 2001, scientists at ACT said that they had made cloned human embryos but that they grew for only a day or two.
In 2005, scientists in Britain grew human embryo clones to the fully mature "blastocyst" stage that the California team described yesterday. But the body cells they used were taken from other human embryos, not from adults.
That approach offers no help to patients who are already born.