Cryopreservation and xenotransplantation of human ovarian tissue: an ultrastructural study

Objective: To analyze the ultrastructure of human ovarian follicles after cryopreservation and short-term xenografting. Design: Prospective experimental study. Setting: Academic gynecology and anatomy research units. Patient(s): Ovarian cortical biopsy specimens were obtained from 13 patients. Intervention(s): Each ovarian biopsy specimen was dissected into pieces of 1 mm(3) and divided into three groups: [1] fresh tissue, [2] frozen-thawed tissue, and [3] frozen-thawed tissue xenografted onto the peritoneum of nude mice for 3 weeks. Main Outcome Measure(S): Follicular ultrastructure was assessed by light and transmission electron microscopy in [1] fresh, [2] frozen, and [31 frozen-grafted tissue. Result(s): Thirty-five ovarian follicles were analyzed by light and transmission electron microscopy. Twenty-five primordial and primary ovarian follicles were found. Most of them exhibited ultrastructurally well preserved features (fresh [N = 8/10], frozen [N = 7/10], and frozen-grafted [N = 4/5] tissue). Ten secondary follicles were present in xenografts. By transmission electron microscopy, all the healthy-looking secondary follicles (70%) were shown to contain intact oocytes, with features typical of earlier developmental stages, surrounded by several layers of follicular cells. Conclusion(S): The present study demonstrates, for the first time, that cryopreservation and xenotransplantation do not appear to greatly affect human primordial/primary follicle ultrastructure. Interestingly, in frozen-thawed xenografts, secondary human ovarian follicles presented a well preserved ultrastructure, but asynchrony between oocyte and granulosa cell development was detected. The possible causes for this asynchrony are discussed.