Ever since human embryonic stem (ES) cells were first isolated in 1998, a debate over their use has raged. Proponents of ES cell research say that the promise of the cells in treating diseases ranging from heart failure to paralysis is invaluable. Critics, on the other hand, argue that the ethical cost of using ES cells, which are derived from human embryos, is too high. Scotland-based PPL Therapeutics hopes to end the debate once and for all by developing an unlimited source of stem cells-without ever creating or destroying an embryo.

The potential of ES cells to treat a spectrum of diseases lies in the fact that the cells are "pluripotent," meaning they can form any tissue in the adult body. In October, PPL's labs in Blacksburg, Va., won a $1.9 million grant from the National Institute of Standards and Technology (NIST) for research on reprogramming adult cells to be pluripotent. If PPL succeeds, it will free researchers and eventually doctors from their reliance on a relatively rare commodity: aborted fetuses and embryos left over from in vitro fertilization. "The benefits are ethical on the one hand, and they could be practical on the other," says Ron James, PPL's chief executive.