A reproductive quirk of some reptiles, insects, and other species may help stem cell researchers sidestep ethical debates over the use of human embryos. In the 1 February issue of Science, researchers report they have isolated the first stem cell lines from primate parthenotes, embryos grown from unfertilized eggs that, in mammals, can't develop into viable fetuses.
In October, scientists at the Institute for Reproductive Medicine and Genetics in Los Angeles showed they could derive stem cells, which later developed into neurons, from mouse parthenotes. Then in November, Advanced Cell Technology (ACT) in Worcester, Massachusetts, grabbed headlines with the news that it had created human parthenotes--although the cell clusters died before reaching the blastocyst stage, well before stem cells could be extracted (ScienceNOW 26 November 2001).
Now, ACT's Jose Cibelli and colleagues relate that they have cultured a variety of cell types from stem cells taken from monkey parthenotes. The scientists treated 28 macaque ova with chemicals that prevent eggs from ejecting half their chromosomes--as they do when fertilized--and instead spur the eggs to begin dividing. Four eggs developed into blastocysts, and the team established the first stable stem cell line from a primate parthenote.
The implication is that the same could be accomplished in humans, says Don Wolf of the Oregon Regional Primate Research Center in Beaverton. But every mammal has its own quirks, notes developmental biologist Davor Solter of the Max Planck Institute for Immunobiology in Freiburg, Germany. "If you want to figure out how to make [parthenotes] in humans, you have to make them in humans."
Ethically, however, the option is attractive, says bioethicist Glenn McGee of the University of Pennsylvania in Philadelphia. Human parthenotes cannot develop to full-term babies, so researchers could avoid the problem posed by therapeutic cloning, in which a potentially viable embryo is created as a source of stem cells and then destroyed.
Wolf says parthenogenesis would actually be simpler than therapeutic cloning for producing genetically compatible material for a patient--at least one with oocytes. "Of course, with this approach," he adds, "you could not produce your own stem cells unless you could also provide your own eggs. Sorry, guys."