For 60 years, doctors have believed women were born with all the eggs they'll ever have. Now Harvard scientists are challenging that dogma, saying they've discovered the ovaries of young women harbor very rare stem cells capable of producing new eggs.

If Sunday's report is confirmed, harnessing those stem cells might one day lead to better treatments for women left infertile because of disease or simply because they're getting older.

"Our current views of ovarian aging are incomplete. There's much more to the story than simply the trickling away of a fixed pool of eggs," said lead researcher Jonathan Tilly of Harvard's Massachusetts General Hospital, who has long hunted these cells in a series of controversial studies.

Tilly's previous work drew fierce skepticism, and independent experts urged caution about the latest findings.

A key next step is to see whether other laboratories can verify the work. If so, then it would take years of additional research to learn how to use the cells, said Teresa Woodruff, fertility preservation chief at Northwestern University's Feinberg School of Medicine.

Still, even a leading critic said such research may help dispel some of the enduring mystery surrounding how human eggs are born and mature.

"This is going to spark renewed interest, and more than anything else it's giving us some new directions to work in," said David Albertini, director of the University of Kansas' Center for Reproductive Sciences. While he has plenty of questions about the latest work, "I'm less skeptical," he said.

Scientists have long taught that all female mammals are born with a finite supply of egg cells, called ooctyes, that runs out in middle age. Tilly, Mass General's reproductive biology director, first challenged that notion in 2004, reporting that the ovaries of adult mice harbor some egg-producing stem cells. Recently, Tilly noted, a lab in China and another in the U.S. also have reported finding those rare cells in mice.

But do they exist in women? Enter the new work, reported Sunday in the journal Nature Medicine.

First Tilly had to find healthy human ovaries to study. He collaborated with scientists at Japan's Saitama Medical University, who were freezing ovaries donated for research by healthy 20-somethings who underwent a sex-change operation.

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Women Have Egg-Producing Stem Cells

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