Making new lines

Stem-cell scientists love a good challenge.Here's one : can you create embryonic stem-cell lines without destroying healthy embryos? Two new reports,released by the journal Nature,say yes.At least,yes in mice.The studies take very different approaches.In the first,scientists at MIT's Whitehead Institute figured out how to derail a gene that is critical to the formation of placenta.The end result : an embryo that is capable of providing stem cells,but is incapable of implanting in the womb.In the second study,led by Advanced Cell Technology in Worcester,Massachusetts,researchers extracted one cell out of eight cell embryos.Each cell was used to generate stem-cell lines;the original "biopsied" embryos survived.After implantation in mice,some even developed into live pups.Mice aren't humans,so nobody knows if the science will translate.An embryo doomed for demise may not quash the ethical debate.And biopsying an embryo is unlikely to be risk-free.New hope,but new challenges,too.