Introduction: Patients faced with infertility due to spermatogonial stem cell loss have currently semen cryobanking as only option for fertility preservation. A growing group of patients cannot benefit from this strategy as they are devoid of spermatozoa or even of any spermatogenic cell at the time of diagnosis. We therefore aimed at investigating alternative strategies to preserve or restore fertility. Methods: As fertility preservation strategies, we investigated the reintroduction of spermatogonial stem cells by spermatogonial stem cell transplantation (SCCT) or grafting of testicular tissue pieces. To restore fertility, we explored the germ cell differentiation capacity of human embryonic stem cells (hESC). Moreover, to avoid embryo destruction during hESC derivation, we aimed to derive hESC from single blastomeres of human embryos Results: For the SSCT, we showed that selection protocols based on magnetic and fluorescent cell sorting or selective matrix adhesion result in high germ cell-enriched fractions for transplantation. However, they are not sufficiently efficient to attain a pure germ cell fraction. After xenografting of human testicular testis tissue to immunodeficient mice, we observed long-term survival of spermatogonia within the grafts. In the fertility restoration part, we demonstrated the inductive capacity of sertoli cell-conditioned medium on germ cell differentiation from hESC. Finally, we derived two hESC from single blastomeres of two distinct four-cell stage human embryos. Discussion and Conclusions: The fertility preservation strategies that we investigated are currently on the edge of a clinical application. In the fertility restoration path, however, more extended research will be necessary.
