Scientists Claim to Find Cells That Restore Egg Production

After tests indicated the source of the cells may lie in the animals' bone marrow, the researchers infused marrow from healthy mice into those that were either genetically engineered to be infertile or had been made infertile with chemotherapy. Two months later, the recipients' ovaries looked normal, whereas those that had not received the transplants remained barren, the researchers reported. Blood transfusions produced similar results, they said.

The researchers then infused blood into infertile mice from animals that had been genetically engineered so that their reproductive stem cells glowed fluorescent green. Within two days, green egg cells appeared in the recipients' ovaries, which the researchers said indicated the cells had traveled through the blood to the ovaries.

Finally, the researchers screened human bone marrow and blood from healthy women and found that both tested positive for biological markers indicating the presence of immature reproductive cells.

"Mice and humans appear to be the same -- they appear to have a set of genes in bone marrow consistent with . . . cells that can make themselves a new egg," Tilly said.

The findings could help explain previously mysterious cases of women sterilized by cancer treatment who spontaneously became pregnant after receiving bone marrow transplants, Tilly said. This may happen only rarely because some, but not all, techniques used to process bone marrow before transplantation may destroy the cells in some cases, he speculated.

The research triggered a mixture of excitement, caution and deep skepticism.

"It's quite amazing," said Hans Schoeler of the Max Planck Institute in Germany. "The idea that cells from bone marrow may be a reservoir for egg cells would be quite astonishing."

But Schoeler and other researchers cautioned that many crucial questions remained. Several researchers had doubts about some of the techniques the researchers used. Others were puzzled by the speed with which the ovaries appeared to be repopulated with eggs. Many pointed out that the researchers had failed to show the eggs were viable, the mice were ovulating or that they could give birth to healthy offspring.

"I'm very skeptical," said David F. Albertini of the University of Kansas Medical Center in Kansas City, Kan. "There are a lot of holes in the research."

Tilly attributed the skepticism to the radical nature of the findings and said he already had work underway to address the concerns, including breeding studies aimed at producing healthy offspring.

"We hope we will have the answers very soon," Tilly said.