Clinical grade vitrification of human ovarian tissue: an ultrastructural analysis of follicles and stroma in vitrified tissue

BACKGROUND Cancer therapy is one of many conditions which may diminish the ovarian reserve. Banking of human ovarian tissue has become an option for the preservation of female fertility. We have shown that vitrification is an excellent method to cryopreserve ovarian tissue. To carry out vitrification in a clinical setting, we have developed a clinical grade closed system to avoid direct contact of ovarian tissue with liquid nitrogen. METHODS Ovarian tissue was obtained by biopsy from 12 consenting women undergoing Caesarean section. Tissues were vitrified in cryotubes, using dimethyl sulphoxide, 1,2-propanediol, ethylene glycol and polyvinylpyrrolidon as cryoprotectants. Non-vitrified and warmed-vitrified tissue was compared by light and electron microscopic morphology of the follicles within the tissues. RESULTS We did not see any differences in the light or electron microscopic ultrastructure of oocytes between non-vitrified and vitrified tissues. No irreversible subcellular alterations in vitrified tissues were seen. CONCLUSIONS The ultrastructure of follicles within the vitrified human ovarian tissue was well preserved using cryotube in a closed vitrification system to avoid direct contact of liquid nitrogen. The system is compatible with the European tissue directive.