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.

PPL’s three-year grant from NIST allows the company to work only with cells from livestock and nonhuman primates. But if the initial research goes well, the company could privately fund efforts toward its ultimate goal: human-derived cells that can be used in a number of therapeutic applications.

When it comes to explaining just how they plan on reprogramming adult cells to behave like ES cells, PPL executives are understandably tight-lipped–after all, such a trick is the Holy Grail of developmental biology. And the company faces competition not only from those working with ES cells, but also from a growing number of firms that are focusing instead on isolating stem cells from adult tissues such as blood and brain (see table below).

Because they have traveled further on a pathway of differentiation than an embryo’s cells have, such tissue-specific stem cells are believed by many to have more limited potential than ES cells or those that PPL hopes to create. Some researchers, however, are beginning to argue that these limitations would actually make tissue-specific stem cells safer than their pluripotent counterparts. University of Pennsylvania bioethicist Glenn McGee is one of the most vocal critics on this point: “The emerging truth in the lab is that pluripotent stem cells are hard to rein in. The potential that they would explode into a cancerous mass after a stem cell transplant might turn out to be the Pandora’s box of stem cell research.”

So far, the ethical debate on deriving stem cells from embryos has obscured such vital scientific questions. Perhaps advances like PPL’s will, at the very least, make discussion of these issues possible.

Companies Researching Adult Stem Cells COMPANY LOCATION STEM CELL TYPE Aastrom Biosciences Ann Arbor, Mich. Blood Neuronyx Malvern, Pa. Nerve Nexell Therapeutics Irvine, Calif. Blood Osiris Therapeutics Baltimore, Md. Connective tissue StemCells Sunnyvale, Calif. Nerve, blood