Female Fertility Preservation through Stem Cell-based Ovarian Tissue Reconstitution In Vitro and Ovarian Regeneration In Vivo

Abstract

Historically, approaches designed to offer women diagnosed with cancer the prospects of having a genetically matched child after completion of their cytotoxic treatments focused on the existing oocyte population as the sole resource available for clinical management of infertility. In this regard, elective oocyte and embryo cryopreservation, as well as autologous ovarian cortical tissue grafting posttreatment, have gained widespread support as options for young girls and reproductive-age women who are faced with cancer to consider. In addition, the use of ovarian protective therapies, including gonadotropin-releasing hormone agonists and sphingosine-1-phosphate analogs, has been put forth as an alternative way to preserve fertility by shielding existing oocytes in the ovaries in vivo from the side-effect damage caused by radiotherapy and many chemotherapeutic regimens. This viewpoint changed with the publication of now numerous reports that adult ovaries of many mammalian species, including humans, contain a rare population of oocyte-producing germ cells-referred to as female germline or oogonial stem cells (OSCs). This new line of study has fueled research into the prospects of generating new oocytes, rather than working with existing oocytes, as a novel approach to sustain or restore fertility in female cancer survivors. Here, we overview the history of work from laboratories around the world focused on improving our understanding of the biology of OSCs and how these cells may be used to reconstitute "artificial" ovarian tissue in vitro or to regenerate damaged ovarian tissue in vivo as future fertility-preservation options.

Keywords: chemotherapy; fertility; folliculogenesis; oocyte; oogenesis; ovary; stem cell.

Figure 1.

Specification of primitive ovarian granulosa cells from ESCs in vitro, which are capable of interacting with early germ cells to initiate folliculogenesis. Differentiation of mouse ESCs engineered to express green fluorescent protein (GFP) driven by a ΔPE-Pou5f1 gene promoter (germ cell marker) and DsRed driven by a Foxl2 gene promoter (primitive granulosa cell marker) leads to the in-vitro formation of ovarian follicle-like structures containing GFP-positive oocytes surrounded by DsRed-expressing granulosa cells. Reproduced from Woods et al.

Figure 2.

Working model for ex-vivo reconstitution of autologous human ovarian tissue. Aggregation of OSCs with primitive granulosa cells, specified from iPSCs or isolated from ovarian tissue during OSC purification, enables de-novo oogenesis and folliculogenesis in the reconstituted tissue in vitro. The tissue containing new follicles is then used for orthotopic grafting to the ovaries for in-vivo growth to produce maturing follicles for oocyte aspiration or for in-vitro follicle culture to generate oocytes. Oocytes obtained from either approach are subjected to in-vitro maturation and in-vitro fertilization to generate blastocysts for embryo transfer and establishment of successful pregnancies.