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The result will have to be confirmed by others before it's fully accepted, although many scientists are already pretty well convinced. But even if it's true for mice, says Gosden, "you have to beware of extrapolation to humans." Tilly's group does have at least one indication that humans have something similar going on: women treated with busulfan almost always experience premature menopause, compared with fewer than half of women taking other cancer drugs. Says Tilly: "This is definitely a hint that these cells do exist."
Even if they do, it will be a while before anyone benefits from this research. Scientists will have to figure out how to purify ovarian stem cells, then transfer them into depleted ovaries to see if they can restart egg production--first in mice, then, if possible, in humans. But if they can, Tilly envisions all sorts of benefits. You might extract the cells and freeze them, and if a woman got cancer, you could reintroduce them after chemotherapy shut down her ovaries. Or you might freeze some of the vigorous stem cells in a young woman so she would have a reserve supply as those in her body aged and weakened. Or, if you could keep existing stem cells viable longer, says Tilly, you might stave off the discomforts of menopause by staving off menopause itself--without dangerous hormone-replacement therapy. It's all wildly speculative so far. Says Tilly: "This isn't the solution to anything yet. We're on the ground floor. But maybe we're finally in the right building."