Freezing protocols for the cryopreservation of immature testicular tissue - a systematic review.

Increasing numbers of childhood cancer survivors reach adulthood making therapy induced infertility a growing concern. Sperm cryopreservation is not possible prior to puberty. Testicular tissue cryopreservation has been proposed as an alternative fertility preservation method for prepubertal males but no standardised cryopreservation procedure for immature tissue has been agreed to date. Here we review the current literature of cryopreservation protocols to determine which method best preserves the morphology and function of immature testicular tissue; and to examine which tissue intervention, grafting or tissue culture, is mostly likely to restore fertility. Embase, Medline, and Web of Science were systematically searched using relevant MeSH headings and search terms for testis, cryopreservation, and fertility preservation. This systematic search returned 4748 unique entries which were screened for relevance. Eleven studies were found to be eligible and were included in the systematic review. We found that cryopreservation protocols differ in freezing rate and cryoprotectant media, the optimum combination of which for ITT has yet to be determined. Further investigations must be carried out to decipher which method best preserves tissue integrity and function and which application method is most likely to induce spermatogenesis.

The effect of thawing protocols on follicle conservation in human ovarian tissue cryopreservation.

BACKGROUND: Ovarian tissue cryopreservation has the potential to improve fertility preservation for a growing number of patients undergoing sterilising therapy, particularly where oocyte or embryo cryopreservation is not suitable. However, its success is limited by significant follicular apoptosis upon thawing, and there is wide variation in thawing protocols used with little evidence of efficacy. OBJECTIVE: To determine the best warming rates to maintain tissue viability. MATERIALS AND METHODS: Ovarian tissue biopsies from 11 patients were taken with informed consent and divided into four pieces, which were allocated to either fresh assessment or to one of several freeze-thaw protocols. Cryopreservation was undertaken using a Stirling cycle cryo-cooler and cryopreserved samples were exposed to different warming protocols. Tissue conservation was then assessed using a marker, neutral red, to identify viable follicles. RESULTS: The results showed greatest follicle conservation rates in fresh samples, followed by those thawed using a rapid thawing protocol (Protocol 1). Tissue thawed using an ultra fast protocol (Protocol 2) and slow warming (Protocol 3) resulted in greater follicle loss. CONCLUSION: These preliminary results indicate thawing conditions significantly affect follicle conservation in cryopreserved human ovarian tissue.