US: Two teams of scientists in Massachusetts have provided the first definitive evidence that embryonic stem cells can be grown in laboratory dishes without harming healthy embryos, an advance that some scientists and philosophers believe could make the medically promising field more politically and ethically acceptable.
The work, done with mouse cells, generated several colonies of mouse embryonic stem cells without destroying any embryos that otherwise could have developed into mice.
If the new approaches were to work with human cells, as many scientists suspect, they could help defuse a moral maelstrom that has raged since human embryonic stem cells were discovered seven years ago.
But the new techniques raise ethical issues of their own.
Stem cells from days-old human embryos can morph into virtually every kind of tissue, including nerves to replace those destroyed by spinal injuries and cardiac muscle to fill in for cells lost in a heart attack.
Until now, however, the only way to get these cells was to destroy young embryos-which are deemed by some people as "the youngest members of the human family" and deserving of certain human rights.
The new work suggests an alternative might be possible.
"This establishes the scientific feasibility of the idea that you can obtain fully functional embryonic stem cells from an entity that is not a natural, normal embryo," said William B Hurlbut, of Stanford University, who is a member of President Bush's Council on Bioethics.
But few scientists are convinced the new methods transcend the problems inherent in traditional stem cell approaches.
Many say the new work only reveals how intractable the problem remains and how unlikely it is that science will resolve what is essentially a matter of spiritual belief.
That is because one of the new methods still subjects a human embryo to a small added risk, and, even more controversially, the other approach involves deliberately creating an embryo with a disabled version of a gene that is crucial to normal development.
Although some people condone experiments on such gene-altered embryos because they have no potential to grow into babies, others see the work as the purposeful creation of fatally hobbled beings to use as research subjects.
Alexander Meissner and Rudolf Jaenisch of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, created those altered embryos by first disabling a gene called Cdx2 in a skin cell taken from a mouse.
That gene is not normally active in skin, but during early embryo development it governs the creation of the placenta, which allows a developing foetus to feed and survive in the womb.
As described in Sunday's online issue of the journal Nature, the team fused that cell with a mouse egg whose own genetic material had been removed. In this case, though, with every new cell in the growing embryo lacking Cdx2, the embryo had no hope of growing a placenta.
That raises the tricky philosophical question of what moral standing, if any, such balls of cells have in their first days, and whether their creation is a mere experiment in cell biology or an act of cruelty. "Nobody should be speaking too quickly here on either side," said Robert George, a Princeton professor of jurisprudence. "It's not a spiritual question. We're not looking for a soul. The question is, 'Does it have the (biological basis) for self-construction and self-organisation, or is it a fundamentally disordered growth'?"
Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts, describes a different approach. It involved the removal of a single cell from an even younger, eight-cell mouse embryo. But in the new work, Lanza showed that under the right culture conditions, the single removed cell can be prompted to grow into a colony of embryonic stem cells.
Several researchers said Lanza's technique is the less useful of the two, because Jaenisch's cloning step allows researchers to design stem cells specifically matched to a patient's needs.
Others expressed concern that the single cell that Lanza starts with might itself have the potential to become a new embryo. Scientists do not know whether that is true, but if so, the approach would not pass muster with those who insist embryos must not be created for research purposes. "It would be tragic," Lanza said, "not to pursue all the opportunities and methods available to us to get this technology to the bedside as soon as possible."