South Korean scientists have announced that they cloned several human embryos and managed to extract valuable stem cells from one, but experts cautioned the hope of tailored medical treatments from such techniques is still far off.
The Korean team was not trying to make a human being, but aiming at a technique called therapeutic cloning. In essence, it would eventually involve taking a plug of skin or a little blood from a patient and using it to grow perfectly matched tissue, organs or batches of cells.
These could, in theory, be used to treat diabetes by replacing damaged pancreatic cells, brain disease such as Parkinson's or Alzheimer's or even to patch a severed spinal cord.
"Our approach opens the door for the use of these specially developed cells in transplantation medicine," Woo Suk Hwang of Seoul National University in Korea, who led the study, said in a statement.
Hwang and colleagues were scheduled to hold a news conference later on Thursday to detail their experiment.
Writing in Science, they described how they created several clones using eggs and cumulus cells donated by Korean women.
Cumulus cells are found in the ovaries and, in some species, have been found to work especially well in cloning experiments.
The researchers removed the nuclei from the egg cells and replaced them with nuclei from the cumulus cells. The nucleus contains 99 percent of a person's DNA.
Then they used a chemical trigger to start the egg growing as if it had been fertilised by sperm.
LIMITED SUCCESS: The Korean team managed to get stem cells from just one of 30 blastocysts - stem cells taken from days-old embryos - they grew in the experiment. They do not know why.
But the stem cells they extracted grew into several different kinds of tissues, including muscle and cartilage.
Stem cells are found throughout the body and are a kind of master cell. But adult stem cells are difficult to find and to work with.
Many scientists believe blastocysts have much greater potential. Each one, when grown correctly, can be directed to become any kind of cell or tissue at all.
Dr Robert Lanza of Massachusetts-based Advanced Cell Technology, which has claimed to have made human clones but not to have removed stem cells from them, said the process was difficult and would take years to perfect.
"We know it's do-able," Lanza said in a telephone interview. "But it isn't easy."
Neal First, an animal cloning expert at the University of Wisconsin, said their difficulty also shed doubt on how easy it would be to create a human baby through reproductive cloning.
What they did comes as no surprise to scientists working in the field. Animals have been cloned for nearly a decade now and several teams have extracted stem cells from animal embryos.
Several teams have also been working to create human embryos for stem cell research. But in the United States, this work has been slowed by opposition from President George W. Bush to the Catholic Church.
Bush has banned the use of federal funds for human stem cell research, with the exception of a few batches of cells that had already been removed from embryos left over from fertilisation attempts.
Opponents say making a human embryo for medical research purposes is unethical and the Bush administration has sought, so far without success, a national and international ban.
Word of the South Korean group's work had been leaking out, despite attempts to keep it quiet.
It takes months to put together a report that can be published in a prestigious international scientific journal - in this case, Science. During this time experts in the field are asked to take a look at the report, ask questions and suggest changes and further research.
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