In vitro growth and maturation of human primordial follicles from cryopreserved tissue

In addition to oocyte and embryo cryopreservation, ovarian tissue banking is now increasingly being considered as a standard of care for preserving the fertility of girls and young women at high risk of sterility. Primordial follicles are the most abundant follicle population in the ovary, and their relatively quiescent metabolism makes them resistant to cryoinjury. This dormant pool represents a key target for fertility preservation strategies as a resource for generating high-quality and fertilizable oocytes. Successful live births after transplantation of frozen-thawed ovarian tissue illustrate the ability of dormant follicles to resume their development and achieve maturation, however for some patients, transplantation presents a risk of reintroducing malignant cells. A safer alternative could be the complete in vitro growth (IVG) and maturation (IVM) of cryopreserved primordial follicles to fertile metaphase II (MII) oocytes. Although challenging, recent breakthroughs in this approach may pave the way to the development of effective culture systems supporting folliculogenesis outside the body and, eventually, revolutionize current ART procedures. This chapter details the progress made in developing human in vitro growth systems and discusses the steps required to be taken before clinical application can be achieved.