In a world first, South Korean scientists created cloned human embryos to generate stem cells, touted as the miracle material that may one day reverse diabetes, cancer, Alzheimer's and other disorders.
The technique is aimed at disease therapy, not at creating a cloned baby, the scientists said, and in any case has many hurdles to clear before it can ever be used for humans.
Stemcells are nascent cells that can be coaxed by chemical signals in the body into becoming different kinds of tissue.
By far the most versatile of these — 'pluripotent' in scientific jargon — are stem cells that come from embryos, for these cells can grow into almost any part of the body.
The dream is one day to use stem cells to grow replacement tissue in a lab dish, such as brain cells, skin, liver, a kidney, that could be used for human transplants.
But, as decades of conventional organ transplants have shown, transplanted tissue is invariably rejected as foreign by the patient's immune system if it comes from another body.
To get around this, the search is on for cloned embryonic stem cells -- stem cells which have exactly the same DNA as the patient, and thus would be accepted by his or her body as friendly rather than hostile tissue.
This is the achievement reported on Thursday by a team of researchers led by Woo Suk Hwang of Seoul National University.
'Because these cells carry the nuclear genome of the individual, after differentiation they could be expected to be transplanted without immune rejection for treatment of degenerative disorders,' Woo said.
'Our approach opens the door for the use of these specially developed cells in transplantation medicine.'
The study was published online by the US journal Science ahead of a meeting in Seattle of the American Association for the Advancement of Science (AAAS).
Until now, only mouse cells have yielded embryonic stem cells, and there have been many failures to do the same using human and monkey embryos.
The South Korean team used the classic cloning technique, pioneered in Dolly the Sheep, which is to take an egg and remove the nucleus, which contains virtually all of the DNA code for programming the egg into a human being.
They then replaced the nucleus with one taken from an adult non-reproductive cell, fused them together and then cultured the egg in a warm nutrient bath so that it divided and developed into an early embryo.
Where they improved on this technique, though, was on several fronts.
They had access to an extraordinarily large batch of fresh eggs — 242 donated by 16 unpaid volunteers — which enabled them to finetune their work as they went alone.
They also had stringent programmes for timing in the way the eggs were handled, and used a new procedure that gently extruded the nucleus rather than suctioned it out, thus reducing the risk of DNA damage to the egg.
Out of 242 eggs, the team cultured 30 blastocysts, or fertilised eggs, of which 20 developed into embryonic cell clusters.
Only one of these 20 developed into a stem cell line; the scientists suspect that some of the cloned blastocysts may have suffered chromosomal abnormalities seen in other primate cloning attempts.
Science editor Donald Kennedy said the research might fuel the controversy in the United States and elsewhere about reproductive cloning and the use of embryos in medical research.
And he sounded a cautionary note, saying that this work was still at a very preliminary stage.
'The potential for embryonic stem cells is enormous, but researchers still must overcome significant scientific hurdles,' he said. '(...) It may be years yet before embryonic stem cells can be used in transplantation science.'
Science quoted one of the Korean researchers, gynaecologist Shin Yong Moon, as saying that rogue scientists would find it hard to imitate their technique, used in an expensive, well-equipped lab, to bring a cloned human baby into the world.
Reproductive cloning has been universally condemned as dangerous and immoral.
'I don't believe they could adapt our procedure very easily. I don't they would succeed,' he said.
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