Long-term ovarian function in sheep after ovariectomy and autotransplantation of cryopreserved cortical strips

Transplantation of cryopreserved ovarian tissue offers a means of preserving reproductive function in girls/women whose ovarian function is compromised by radio- and/or chemotherapy for cancer. Studies in small laboratory rodents have demonstrated that fertility can be restored by transplanting whole cryopreserved ovaries. In large animals, it is not possible to freeze or transplant ovaries without vascular anastomosis. However, primordial oocytes in cortical strips survive freezing, thawing and culture in vitro. We have used sheep as an experimental model for the human because the size of the ovary and length of folliculogenesis (4-6 months) are similar. Following orthotopic transplantation the grafts, become vascularised within a few days and ovulatory cycles become established by 4 months. Several lambs have been born in ewes after autotransplantation of the grafts which continue to function for up to 2 years. The levels of FSH remain consistently raised after transplantation due to a reduced secretion of inhibin A, reflecting the reduction in the size of the ovarian pool of follicles.