The team, led by Woo Suk Hwang and Shin Yong Moon of Seoul National University, used a technique called somatic cell nuclear transfer to produce a human blastocyst, a 100- to 200-cell stage in the development of the embryo that occurs before it implants into the wall of the womb. SCNT has been widely used to clone transgenic animals, including Dolly the sheep.
The stem cells produced by the technique seem to retain their ability to form the three basic cell layers - ectoderm, mesoderm and endoderm - from which all cell types in the body are derived. This suggests that, with a lot more work on uncovering the right developmental conditions, they could be used to produce just about any type of tissue, for example insulin-producing cells that could be implanted into diabetics.
Developing new cellular therapies based on cloned tissues will take years, Hwang told a news conference at the American Association for the Advancement of Science annual meeting in Washington DC. However, he also said that the technique used in this study, although intended for therapeutic purposes, could also be used in reproductive cloning, calling for a worldwide ban on the latter application.
Last year, scientific academies from around the world issued a joint statement calling on the United Nations to introduce a ban on human reproductive cloning, whilst arguing that embryonic cloning for research and therapeutic purposes should be exempt from any eventual convention.
In December, a last-ditch effort by conservative members of the UN to ban all human cloning was abandoned Tuesday in lieu of a decision to postpone any action for one year, after it was unable to agree on a means of differentiating therapeutic and reproductive cloning.
The UN had previously voted in early November by a slim margin to postpone the decision for two years, but reduced the deadline in recognition of the urgent need to set down guidelines.
Meanwhile, in the US the Bush administration is firmly opposed to any form of human cloning and only allows research on stem cells harvested from embryos destroyed before 9 August 2001. US researchers say this policy is causing them to fall behind in the development of therapeutic cloning technology.
Low success rate
In any event, the odds of successfully using SCNT to create a healthy baby are slim, given the rate of successful embryo development in the Seoul study and the high risk of genetic abnormalities that may well occur in cloned embryos, leading to miscarriages or birth defects,
The Korean team created the human embryos after collecting 242 eggs from 16 unpaid, anonymous volunteers. They also took from each woman cells from the ovaries. To attempt male embryo cloning, they used cells taken from the ear lobes of adult men. The researchers extracted the nucleus from each of the eggs and then inserted the nucleus from the other cells.
43 per cent of the cells created using the technique survived the procedure, but the team was able to extract stem cells from just one of the embryos, made using the egg and genetic material from the same woman.
This failure rate echoes the experience of controversial US fertility specialist Panos Zavos, who is determined to implant a cloned embryo and bring it to term. Last year he announced to widespread condemnation that he had implanted an embryo into a woman created using genetic material taken from her husband, but revealed earlier this month that the woman did not in fact become pregnant.
The Seoul research is published in the online edition of Science (12 February).