Life After Life

Twenty-five days. That's how long it took Dr. Shinya Yamanaka of Kyoto University to undo more than 30 years of exquisitely programmed biology packed into a woman's cheek cell — and just maybe change the world. In a procedure that some scientists thought could take decades to discover, Yamanaka tricked the cheek cell into acting like an embryonic stem cell — capable of dividing, developing and maturing into any of the body's more than 200 different cell types. And he wasn't alone: on the same day that he published his milestone in the journal Cell, James Thomson, a pioneering University of Wisconsin molecular biologist, reported similar success in Science.

Their papers cap a year of remarkable research, in which scientists have surged ahead of ethicists and politicians in finding ever more clever ways to generate stem cells. But where other breakthroughs relied on using cells from living embryos — tiny bits of inchoate life, fraught with ethical issues — the work by Yamanaka and Thomson sidesteps that abyss by nursing adult cells into a state in which their cellular destiny is yet to be fulfilled. No embryos, no eggs, no hand-wringing over where the cells come from and whether it is ethical to make them in the first place.

Stem cells generated by this method are ideal not just because they are free of political and moral baggage. They can also be coaxed into becoming any type of tissue, and then be transplanted back into the donor with little risk of rejection. Still, these cells are far from ready for medical use. The viruses used to ferry the genes that manipulate the cells can introduce genetic mutations and cancer. And with myriad ways to reprogram a cell, sorting out the best ones will take time — meaning that stem cells from embryos will remain useful (and controversial) for a while. Both Yamanaka and Thomson admit that we still know too little about how the process works to exploit the method's full potential. Nevertheless, their discovery has moved stem-cell research back to an embryonic state of its own — in which anything, it seems, is possible.