South Korean scientists recently described how they cloned several human embryos and extracted valuable stem cells from one, and said their achievement showed an immediate need for a global ban on cloning to make babies.
They are the first researchers to prove they cloned a human being and said they did it not to make a baby but for the purposes of therapeutic cloning.
It could eventually involve taking a plug of skin from a patient and using it to grow perfectly matched tissue or even organs to treat diseases ranging from diabetes to Alzheimer's.
Woo Suk Hwang of Seoul National University, who led the study, and his colleagues said it was clearly wrong to use the technique for making an embryo that would be put into a woman's womb to grow into a baby.
"We call for a ban on reproductive cloning," Shin Yong Moon of Seoul National University, director of the center where the research was done, told a news conference in Seattle.
"To prevent reproductive cloning we would like to ask every country or every nation to have a law to prohibit reproductive cloning," added Moon, whose team's work was featured at the annual meeting of the American Association for the advancement of Science.
US President George Bush opposes all forms of cloning and his administration has pressed for bans in Congress and in the United Nations, without success. Supporters of therapeutic cloning say the battle has left the entire field unregulated and allowed renegade scientists a legal opening to try to clone a human baby.
Ethicist Laurie Zoloth of Northwestern University said the Korean report showed it was time for lawmakers around the world to agree on what to do about cloning. "No one religion, no one moral authority, can claim to be the final arbiter of this work," she told the news conference.
Scientists welcomed the work as a breakthrough but stressed it would be years before any patient benefited from the technique. Disease researchers were also cautious in their welcome.
"If it turns out be true, it's a nice step forward," said Dr. Bob Goldstein of the Juvenile Diabetes Foundation. "It's measured skepticism only in the sense that, until these things are repeated (by other scientists), it always makes us nervous."
Opponents condemned the report.
"Cloning research is impossible to do without exploiting women. It should be banned immediately," said Daniel McConchie, a spokesman for the Chicago-based Center for Bioethics and Human Dignity.
"Cloning human beings is wrong. It is unethical to tinker with human life," said U.S. Rep. Joe Pitts, a Pennsylvania Republican who supports efforts to ban the technique.
Hwang's team created several clones using eggs and cumulus cells donated by Korean women who had independently approached them.
Kansas Republican Sen. Sam Brownback, who has led efforts to ban all human cloning, said using adult stem cells was the only acceptable route.
Cloning expert Dr. Irving Weissman of Stanford University disputed that work with adult stem cells showed as much promise as embryonic stem cells and said both avenues of research need to be pursued.