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Stem Cell Breakthrough Defuses Debate

"I was surprised when we achieved our results with the mouse," Yamanaka said. "But proving what we could do with human cells really bowled me over."

Thomson said he was surprised it didn't take longer to discover how to reprogram ordinary cells. The technique, he said, is so simple that "thousands of labs in the United States can do this, basically tomorrow."

In contrast, the cloning approach is so complex and expensive that many scientists say it couldn't be used routinely to supply stem cells for therapy.

While the discovery seems likely to shift the direction of research, Thomson and others said it's too soon to give up on studying embryonic stem cells.

He said he believes the ethical turmoil surrounding the embryonic cells set the field back four or five years. The new results are "probably the beginning of the end for that controversy," he said.

But he said his team wasn't trying to find a way around the ethical debate by pursuing the new technique. "We just thought this was a more practical approach," he said.

An official of one group fiercely opposed to destroying embryos saw things differently, saying scientists should thank "pro-life voices" for pushing them to find alternatives.

"The results are groundbreaking studies like these," said Carrie Gordon Earll, bioethics analyst for Focus on the Family, a conservative Christian group.

The controversy over embryonic stem cells has been a touchstone of national politics. It inspired impassioned pleas by Nancy Reagan, the actor Michael J. Fox, who suffers from Parkinson's disease, and countless ordinary citizens arguing in favor of the potential medical benefits.

Equally heartfelt were objections that destroying embryos to extract the stem cells meant destroying human life.

No federal money was available for embryonic stem cell research until 2001, when President Bush allowed very limited funding. Some states like California and Connecticut responded to his restrictions by setting up their own programs to pay for it.

The new work shows that like cloning, "direct reprogramming" can also use ordinary body cells to create versatile cells that are genetically matched.

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© 2007 The Associated Press