Low temperature storage and grafting of human ovarian tissue

A finite stockpile of germ cells forms in the human ovary before birth and is progressively utilised until it is almost exhausted at menopause in mid-life. Currently, there is no proven method for preventing wastage of this irreplaceable store, although cryopreservation provides an opportunity for long-term preservation of oocytes. This technology can potentially be used to conserve fertility in patients undergoing sterilising treatment or otherwise at risk of an early menopause. The structure of the ovary is well-suited to tissue storage because primordial follicles are abundant, developmentally dormant and located peripherally. Thin cortical slices of tissue can be prepared either from biopsies collected laparoscopically or by dissecting the cortex from the whole ovary. To test survival after freezing and thawing, tissues donated from women undergoing Caesarian section or gynaecological surgery were cooled slowly to liquid nitrogen temperatures in various cryoprotectant solutions and thawed rapidly. Three weeks after grafting under the renal capsule of immunodeficient SCID mice the majority of follicles were still viable. To test the procedure in human volunteers, small discs of ovarian tissue were autografted to the anterior uterus. After 3-4 months the tissues still contained follicles, including growing stages with PCNA-positive granulosa cells, but only about a quarter of the original follicle population had survived. In another study using either human xenografts or murine isografts, follicle survival rates were improved by administration of antioxidants to counteract ischaemia-reperfusion injury. Ovarian tissue banking should still be regarded as an experimental procedure, though recent results indicate that it has clinical potential.