Samuel Wood, a coauthor of the new paper and chief executive of Stemagen Corp. of La Jolla, Calif., said he and his colleagues are now attempting to produce stem cell lines from the embryos.
The work was published online Thursday by the journal Stem Cells.
Scientists say stem cells from cloned embryos could provide a valuable tool for studying diseases, screening drugs and, perhaps someday, creating transplant material to treat conditions like diabetes and Parkinson's disease.
But critics raise objections. The process "involves creating human lives in the laboratory solely to destroy them for alleged benefit to others," said Richard Doerflinger, spokesperson for the U.S. Conference of Catholic Bishops.
Citing the earlier work in Britain, he also said that as a scientific advancement, the new work was "very limited."
Other objections to cloning include concerns about health risks and exploitation if large numbers of women are asked to provide eggs.
Different Approaches
Those objections are one reason that an alternative route to stem cells made headlines last November. Scientists reported a relatively simple way to turn skin cells directly into stem cells.
This direct reprogramming carries a theoretical risk of cancer for the recipients of tissue from these cells, however, and many scientists have urged that work continue on the cloning technique as well.
The cloning approach involves inserting DNA from a person into an egg, and then growing the egg into an embryo about five days old before extracting the stem cells. At that stage, the embryo is a sphere of about 150 cells.
In the new work, researchers took skin cells from coauthor Wood and another volunteer and produced three embryos with DNA matching the men's. Further DNA testing on one of these embryos strengthened the case that it was a clone, researchers said.
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