Researchers in South Korea are claiming they created a cloned human embryo that was a genetic replica of a 30-year-old woman.
If true, it would be the first known cloning of a human embryo, and vivid evidence that while nations contemplate the ethics of human cloning, there is little to stop scientists from pursuing the controversial technology.
The Koreans said they destroyed the cloned embryo early in its development. Their goal is to grow human cells for therapeutic purposes, they said, and they have no intention of transferring cloned embryos to any woman's womb without a consensus that it is ethical to grow cloned human babies.
Nonetheless, the announcement -- which came with no scientific evidence to back it up -- sent ripples around the globe as word spread among bioethicists, scientists and legislators.
"Oh my!" said R. Alta Charo, a professor of law and bioethics at the University of Wisconsin and a member of the National Bioethics Advisory Commission, which produced a landmark report on human cloning for President Clinton last year. "This is certainly going to make the debate surrounding cloning and the debate surrounding embryo research ever more urgent."
The work has not been published in a scientific journal, and details remained vague on Wednesday, even as protesters gathered outside the Seoul hospital where the research was done, shouting for a halt to "inhuman research."
Lee Bo-yon, a fertility specialist at Kyunghee University Hospital, said in Korea that he and his colleague, Kim Sung-bo, used the same technique scientists in Hawaii used earlier this year to clone several generations of mice.
Some comments attributed to researchers in Korean news reports were scientifically inaccurate, leading some experts to question the validity of the cloning claim.
For example, Lee said human embryos already had been cloned at Scotland's Roslin Institute, where Dolly the sheep was cloned.
"That's utter nonsense," Ian Wilmut, Dolly's cloner, said on Wednesday. "We don't work with human cells at all."
Lee also said at a news conference on Tuesday that "we can assume that a human child would be formed" if the cloned embryo were placed in a woman's uterus. But other scientists said Lee's experiment does not prove the embryo was truly viable or able to grow into a child, since it was halted before the embryo reached a key developmental milestone.
The Hawaii technique starts with a cell taken from the person to be cloned. Genetic material, or DNA, is removed from that cell and injected into an egg cell that has had its own genes removed.
For cloning to be successful, substances inside the egg cell must "reprogram" the newly inserted genes into a primordial state in which they are able to command the egg to divide repeatedly and develop into an embryo.
The Koreans injected DNA from an unidentified fertility patient's ovarian cell into one of her eggs whose DNA had been removed. They allowed the resulting embryo to divide twice, into a total of four cells, before stopping the experiment to abide by a 1993 national ban that prohibits research on more fully developed embryos.
But in humans, scientists noted, the first four cell divisions happen automatically; only at the 16-cell stage must an embryo's genes kick in to drive further development. Because the Korean experiment was aborted before that, scientists cannot know whether the inserted genes were successfully reprogrammed.
"This experiment provides you with no information at all regarding the question of whether human embryos can be cloned," Wilmut said.
Britain's Human Genetics Advisory Commission criticized the Korean effort, saying in a statement: "The research lacks credibility and does not demonstrate that a viable embryo has been created."
Korea is considering legislation that would restrict the cloning of humans, as are several other nations and about three dozen U.S. states.