news @ nature.com - 'Ethical' routes to stem cells highlight political divide - Split opens over methods to create nonviable embryos.: "Until now, such methods have been purely theoretical, but in work published online by Nature this week, two teams report their successful use in mice. Rudolf Jaenisch and Alexander Meissner of the Massachusetts Institute of Technology describe a variant of therapeutic cloning called altered nuclear transfer (ANT), in which a gene in the patient's donated cell is switched off before the nucleus is transferred into a fertilized egg. The resulting egg grows into a normal ball of cells called a blastocyst from which ES cells can be derived, but the deactivated gene means that the ball lacks the ability to implant in a uterus and so develop into a baby (A. Meissner and R. Jaenisch Nature doi:10.1038/nature04257; 2005).
In the other paper, a team led by Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts, plucked single cells called blastomeres from eight-cell embryos. They derived new ES cell lines from the blastomere, while the embryos went on to form apparently healthy mice (Y. Chung et al. Nature doi:10.1038/nature04277; 2005)."