The present study demonstrates that spermatogonia are able to survive and proliferate after cryopreservation and long-term transplantation. Complete regeneration of normal spermatogenesis was not observed since, beyond the pachytene stage, no adequate characterization of germ cells was obtained. Further studies are thus required to investigate the differentiation potential of cryopreserved germ cells.

While additional evidence is required to define optimal conditions for ITT cryopreservation with a view to transplantation or IVM, the putative indications for such techniques, as well as their limitations according to disease, are outlined.

Through our orthotopic xenografting model, we have demonstrated the survival and proliferative activity of spermatogonia and Sertoli cells in cryopreserved immature human cryptorchid tissue. Testicular tissue banking may thus prove to be a promising technique for the preservation of fertility in prepubertal boys undergoing oncological treatments. As the stem cell niche is maintained, the cryopreserved tissue can potentially be used for future autotransplantation. In addition, whole tissue freezing does not exclude alternative clinical uses, including isolated cell transplantation after dissociation, selection and enrichment. However, as this work was done on cryptorchid tissue, studies on normal immature testicular tissue, involving longer grafting periods, are needed to demonstrate a differentiation capacity before clinical implementation. Ethical and safety issues should also be addressed.

Because of the simplicity of vitrification, many authors have investigated it as an alternative to slow freezing for cryopreserving ovarian tissue. In the last decade, numerous studies have evaluated vitrification of ovarian tissue from both humans and animals.Different vitrification solutions and protocols, mostly adapted from embryo and oocyte vitrification, have been applied. The results have been discrepant from species to species and even within the same species, but lately they appear to indicate that vitrification can achieve similar or even superior results to conventional freezing. Despite the encouraging results obtained with vitrification of ovarian tissue from humans and different animal species, it is necessary to understand how vitrification solutions and protocols can affect ovarian tissue, notably preantral follicles. In addition, it is important to bear in mind that the utilization of different approaches to assess tissue functionality and oocyte quality is essential in order to validate the promising results already obtained with vitrification procedures. This review summarizes the principles of vitrification, discusses the advantages of vitrification protocols for ovarian tissue cryopreservation and describes different studies conducted on the vitrification of ovarian tissue in humans and animal species.