Ewe Ovarian Tissue Vitrification: A Model for the Study of Fertility Preservation in Women

Emergency in vitro fertilization followed by embryo vitrification is one feasible fertility preservation option for cancer patients. However, its clinical application has several limitations. Hormonal stimulation delays the initiation of oncotherapy and it is contraindicated in hormone-sensitive cancers or for use in pre-pubertal females. Vitrification of ovarian cortical tissue prior to the start of cancer treatment could be utilized for autotransplantation or for in vitro maturation of follicles enclosed in ovarian tissue. Nevertheless, the main concern associated with autotransplantation is the risk of malignant cell re-introduction to the patient, which is non-existent with the use of follicular in vitro culture. Since obtaining ovarian tissues from women for research is challenging and experimental studies are difficult to complete due to ethical issues, exploring the alternative usage of animal models for fertility preservation may provide beneficial insight into the prospects of follicular culture as an alternative for fertility restoration following ovarian tissue vitrification. Similarities between ewe and human ovary structures, as well as in ovarian follicular development dynamics, make the ewe a possible animal model for the study of female fertility preservation. As vitrification of ovarian tissue has the potential to cryopreserve preantral ovarian follicles, the present review will describe the progress of ovarian tissue vitrification studies completed in ewes.