Ten years after introducing the world to Dolly the sheep, the
first cloned animal, University of Edinburgh biologist Ian
Wilmut announced last November that he was quitting the cloning
game. He was not going out on a high note—neither Wilmut nor any
of his colleagues had succeeded in cloning an adult human cell
by implanting its nucleus into a properly prepared egg, yielding
precious embryonic stem cells. Rather his announcement heralded
the publication a few days later of a method for directly
transforming human skin cells into a form that was essentially
equivalent to the embryonic kind. Cloning, Wilmut told
reporters, had become obsolete. In principle, if the products of
this transformation—called induced pluripotent stem (iPS)
cells—are sufficiently versatile and defect-free, they could
relatively quickly become the go-to source of stem cells for
modeling disease more realistically, testing drugs and designing
future therapies derived from cell lines matched to a patient’s
immune system. “All this now bec