New research, published online by the journal Nature Medicine, seems to overturn a widely-accepted biological principle governing female fertility, raising hopes for women who have trouble becoming pregnant.
For a half-century or so, women were presumed to be born with a supply of eggs that could not be replenished.
In fact, that was thought to be true of all mammals until 2004, when Massachusetts General Hospital researcher Jonathan L. Tilly, PhD, found that adult female mice could produce new eggs. And now, Tilly has extended his work to humans.
"We've isolated, essentially, the female equivalent of the stem cells that we know exist in men that actively make new sperm," said Tilly. "So having these cells now isolated, I think, opens up a lot of opportunities to consider that we simply couldn't fathom before."
Tilly and his colleagues took human ovaries and extracted the cells, by grabbing onto a particular protein on the surface, and doing laboratory tests to ensure they had the right cells.
"Once we had isolated these cells, we could place the cells in culture outside the body," he said. "And we could start with perhaps 100 cells, and over several months' time, take those 100 cells and make hundreds of thousands of cells. And interestingly, we noticed that these cells would spontaneously generate immature eggs, all on their own, in these cultures."
And to further confirm the ability of these stem cell-like cells to make eggs, the researchers placed some of the cells into human ovary tissue, which they then implanted under the skin of laboratory mice.
"And what we found when we did those types of studies, [is] these human cells, once reintroduced back into the environment we originally took them from, were more than happy to create brand new human egg cells," he explained.
Growing eggs in the lab could improve prospects for women undergoing in vitro fertilization, during which a woman's egg is fertilized in an external medium and then returned to her womb to develop.
But Tilly said his work could also lead to fertility treatments that might improve prospects for more traditional fertilization methods.
"We can also think about, perhaps, targeting these cells in the ovaries with hormones that these cells like, and thereby increasing their activity and perhaps increasing the size of the egg cell reserve in the ovary, when it would be desirable to do so."
Tilly's work in the past with mice was greeted with skepticism, and independent experts are cautious about this study, too. As is often the case in science, the real proof may come when other researchers try to duplicate these findings.