human embryonic stem cells Our ability to control human fertility is astounding. The numerous advances made in assisted reproductive technology allow “infertile” couples to have biological children. While assisted reproductive technology has been vastly expanding, certain dogmas regarding female fertility have remained constant throughout the past 60 years. In particular, the concept that females carry a finite supply of oocytes (egg cells) hasn't been challenged. This means that unlike males, females have a limited non-renewing supply of eggs; once her oocytes are gone, a female will be infertile.

This dogma has limited the therapeutic options for preserving fertility and normal ovarian function in females. Particularly, sterility resulting from cancer therapies has been problematic. Although current treatments of cryopreservation of oocytes allow many cancer patients to save their fertility, these techniques are invasive and require hormonal therapy. The use of hormonal therapy might not be medically advisable in instances of hormonally responsive tumors or in instances with prepubescent females. If oocyte production cannot be stimulated, the ovarian cortex can be frozen for later transplant, but this is not guaranteed to work, as freezing may damage the ovarian cortex. These limitations require further innovation in methods to preserve female fertility.

The controversial work of Dr. Jonathan Tilly and his team at Harvard Medical School challenges the notion of non-renewing female fertility. In 2004, Dr. Tilly’s team reported that adult female mice possess the ability to continue to generate new oocytes. Like other research that goes completely against long-term commonly held scientific beliefs, the report in mice met great criticism, specifically in regards to whether or not this would apply to humans. Recently, this team reported that human female ovaries contain oogonial stem cells that can generate oocytes. (Check out this video about their discovery.)

Pregnant woman While the buzz surrounding this latest report suggests that the general public is willing to change their understanding of female fertility, scientists may not be ready to rewrite this chapter in biology textbooks. Individuals in the field caution that further replication must occur. Even if the results can be replicated, the generation of usable oocytes from female germ line cells is not as straight foreword as it may seem. Cells grown in laboratories often contain abnormalities. This means that producing oocytes by oogonial stem cells does not equal suitable oocytes for implantation. Despite these limitations, Dr. Tilly feels confident in the work and has patented the methods of using female germ line stem cells and progenitor cells as a way to produce oocyte reserves to restore fertility in females.

Aside from the exciting potential of this method for helping restore fertility in females, the implications of this study go beyond clinical therapeutics. This study questions a core belief in our understanding of female fertility. In doing so, it opens a previously closed case about the renewability of female fertility. The self-correcting nature of science, though often slow and filled with skepticism, has shown that “scientific facts” do not exist. Over the years, numerous accepted “scientific facts” have been shown to be incorrect. It will definitely be interesting to see how this study plays out in terms of our understanding of female fertility.