Ovarian stem cells—Potential roles in infertility treatment and fertility preservation

One of the principal beliefs in reproductive biology is that women have a finite ovarian reserve, which is fixed from the time they are born. This theory has been questioned recently by the discovery of ovarian stem cells which are purported to have the ability to form new oocytes under specific conditions post-natally. Almost a decade after their discovery, ovarian, or oogonial, stem cells (OSCs) have been isolated in mice and humans but remain the subject of much debate. Studies in mice have shown that these cells can be cultured to a mature oocyte stage in vitro, and when injected into germ-cell depleted ovary they can form follicles and have resulted in the birth of healthy offspring. There are few data from human OSCs but this finding would open the door to novel fertility preservation strategies for women with both age-related and premature ovarian insufficiency (POI). As the number of girls and young women surviving cancer increases worldwide, POI secondary to gonadotoxic treatments, such as chemotherapy, is becoming more common. The ideal fertility preservation approach would prevent delays in commencing life-saving treatment and avoid transplanting malignant cells back into a woman after treatment: OSCs may offer one route to achieving this. This review summarises our current understanding of OSCs and discusses their potential clinical application in infertility treatment and fertility preservation.