Prometheus's Vulture and the Stem-Cell Promise

Embryonic stem cells have been the focus of intense study over the past two decades. Embryonic stem cells originate from undetermined early embryos, with no possible history of differentiation, whereas the provenance of adult stem cells found in mature tissues is far less well understood. The possibility that a population of reserve stem cells, perhaps set aside during gestation, might be coerced into renewed regenerative service later in life holds great promise. This review considers the status of stem-cell research.