Massachusetts General Hospital researchers find new lead on stem cells, study new egg production

For more than 60 years, scientists believed that women are born with a set number of egg cells, but Massachusetts General Hospital researchers recently discovered stem cells in human ovaries could be isolated to produce new eggs.

Following experimentation with mice and with human ovaries, the scientists concluded the rare cells, found in the ovaries of reproductive-age women, could be propagated into viable egg cells either in vitro or in life, according to the study released Sunday in Nature Medicine.

The MGH scientist who led the research, Jonathon Tilly, works as the director of the Vincent Center for Reproductive Biology at MGH and as a professor at Harvard Medical Center.

“We . . . demonstrated that human egg precursor cells not only exist in ovaries of reproductive-age women, but that these newly discovered cells possess . . . features that permit maturation into eggs,” Tilly said in press release published by OvaScience, a fertility clinic he co-founded.

Tilly has been conducting research directly related to the formation of oocytes, or cells that mature into egg cells in females, since 2004, when he and several colleagues proposed that female mammals may be capable of producing egg cells even after they have been born.

Contrary to longstanding tradition, which held that egg cell production in any one female stopped before she was born, researchers found that oocyte production could be stimulated in adult mouse ovaries under certain rare conditions.

In the latest MGH study, Tilly sought to connect the 2004 findings to human reproduction, testing whether or not women’s ovaries hold the same type of egg-producing cells researchers said they found in mouse ovaries.

To do so, MGH researchers used ovaries surgically removed from women in their 20s and early 30s who were undergoing sex reassignment operations at the Saitama Medical Center in Japan.

They injected human germline cells into ovarian biopsies, which they implanted into mice tissue. After about one to two weeks, according to the study, “follicles containing . . . occytes” began to form within the grafts.

“In addition to opening a new research field in human reproductive biology that was inconceivable less than 10 years ago, clear evidence for the existence of these [egg-producing] cells in women may offer new opportunities to expand on and enhance current fertility-preservation strategies,” according to the study.

Tilly partnered with scientists from the Saitama Medical Center and with colleagues from the VCRB to conduct the research.

“The results presented in this new study confirm and extend our previous work on egg precursor cells in adult ovaries,” he said in the release, “opening the prospect that human assisted reproduction may be provided with new tools to combat infertility caused by aging or insults.”