Major ethical concerns over human stem cell research could be circumvented if the cells came from embryos produced through parthenogenesis, a process by which unfertilized eggs undergo embryonic development. Because human parthenotes cannot develop into viable fetuses, so the argument goes, the harvesting of stem cells from parthenotes does not pose ethical problems. Previous experiments involving primate parthenotes have produced embryos, but none of these have yielded stem cells. To that end, research described today in the journal Science represents an important new advance.

Starting with 77 macaque monkey eggs, Jose B. Cibelli of Advanced Cell Technology and colleagues tricked four into becoming embryos. One of these yielded a stable line of "pluripotent" stem cells. The researchers managed to coax a variety of cell types from those stem cells, including neurons, smooth muscle cells and heart-like cells. Particularly encouraging, they say, is the development of the dopamine-producing neurons, which, if replicated in humans, could potentially help treat Parkinson's disease.

In addition to providing a way around thorny ethical issues, deriving stem cells through parthenogenesis could hold another advantage over so-called therapeutic cloning. According to Don Wolf of the Oregon Regional Primate Research Center in Beaverton, the former would be a simpler means of producing genetically compatible tissue for a patient. "Of course, with this approach," he told Science, "you could not produce your own stem cells unless you could also provide your own eggs." Still, as promising as the macaque-based results may seem, whether scientists will be able to derive stem cells from human parthenotes remains to be seen.