In a study published in Nature Medicine, researchers report finding egg-producing stem cells in human ovaries. They also report being able to make some of those ovarian stem cells grow into immature eggs that may someday be useful for reproduction.
At this point, such “seed” eggs can’t be fertilized by sperm. But if scientists are able to entice them to mature and can prove they can be fertilized and grow into embryos -- a feat that has been reported in mice -- it would overturn a long-held scientific belief that women can’t make new eggs as they get older.
“What it does is really open a door into human reproduction that 10 years ago didn’t even exist,” says researcher Jonathan L. Tilly, PhD, director of the Vincent Center for Reproductive Biology at Massachusetts General Hospital, in Boston.
Outside experts agree. They say the findings could have profound importance for reproductive medicine and aging, allowing doctors not only to restore a woman’s fertility but also to potentially delay menopause.
“I think the significance of this work is like reporting that we found microorganisms on Mars,” says Kutluk Oktay, MD, who directs the Division of Reproductive Medicine and the Institute for Fertility Preservation at New York Medical College in Valhalla, N.Y.
Still, It’s a Long Way to Mars
“It’s a proof of principle that they could do it,” says David F. Albertini, PhD, director of the Center for Reproductive Sciences at the University of Kansas Medical Center in Kansas City, Kan.
“The world wants to know today if we’re ready to restore fertility in women, whether they’ve aged or been treated for cancer or whatever,” Albertini says, adding that he doesn’t think that’s on the horizon. “This is an extremely rare event, at best.”
The egg-generating stem cells the researchers were able to extract from ovaries were very rare. The researchers only came across one for every 10,000 or so ovarian cells that they counted.
But when they took those cells and implanted them back into human ovarian tissue, they divided and essentially made young eggs.
Tilly says his team stopped short of trying to make one of the eggs functional because “for a lot of reasons, as it should be,” it is illegal in the U.S. to experimentally fertilize human eggs.
“We think the evidence provided clearly indicates that this very unique, newly discovered pool of cells does exist in women,” he says.
A Lot of Potential
“It’s a really exciting result,” says Evelyn Telfer, PhD, a cell biology expert at the University of Edinburgh in Scotland.
“What we’ve previously believed is that you don’t get new eggs formed during your adult life. This discovery shows that there’s the potential for them to be formed, no question about that,” Telfer says, “but it doesn’t actually show that they’re being formed under normal conditions.”
Indeed, she notes, experience would suggest otherwise. Women, after all, do lose their fertility as they age.
“There are cells there that under certain conditions have the potential to form [eggs]. That’s the really exciting part of this work. And of course they can be used. There’s a practical application,” she says.
Telfer has pioneered a technique that allows her to take immature human eggs and turn them into mature, fertilizable eggs outside the body. She has already partnered with Tilly to try to take his “seed” eggs to the next stage of development. With special government permission, she says, they may even be able to try to experimentally fertilize the eggs.
“It’s actually opening up a whole new field of research, to define these cells, to characterize these cells, and to use them in a practical way,” she says.
Tilly says that by using egg-generating stem cells to make large numbers of viable eggs, doctors might one day be able to cut the expense of in vitro fertilization (IVF), since women would no longer have to go through multiple cycles of treatment to harvest enough eggs to generate a pregnancy.
‘True Emancipation of Women’
“If Dr. Tilly can reverse the biologic clock or halt it, and start making eggs from stem cells, it’s fantastic,” says Avner Hershlag, MD, chief of the Center for Human Reproduction at North Shore University Hospital in Manhasset, N.Y.
“This is the true reproductive emancipation of women,” he tells WebMD. “You will be free to a) not compromise on who you share your life and share your kids with, and b) like any man, you will have the freedom to develop a full professional life and not have to stop everything because you are having children.”
But Hershlag notes that such an advance might still be years away.
For women who are worried they’ll run out of time to have children, Hershlag says there is technology available that helps women buy more time to have a baby. “Her best bet is actually, right now, to freeze her eggs if she wants to delay reproduction.”