In search of the most efficient fertility preservation strategy for prepubertal boys

Fertility preservation strategies are currently being developed for boys facing spermatogonial stem cell (SSC) loss. However, it is not clear yet which transplantation strategy would be the best choice. Therefore, the aim of the work presented in this thesis was both to compare these strategies and to study how to improve their efficiency. The efficiency to restore spermatogenesis after transplantation of SSCs or testicular tissue was evaluated. In addition, we investigated the potential of transplanted adult bone marrow stem cells (BMSCs) to repopulate the testis. We aimed to improve the efficiency of human intratesticular xenografting by exogenous administration of FSH. Since spermatogonial loss was observed in human intratesticular xenografts, we finally evaluated whether early cell death was the cause of this loss. Compared to SSC transplantation, more donor-derived spermatogenesis was observed after intratesticular tissue grafting. Human SSCs were able to survive for at least 12 months inside the mouse testis and meiotic activity was observed. However, the attempt to improve germ cell survival and induce full differentiation by the exogenous administration of FSH failed. Spermatogonia-specific apoptosis could not explain the SSC loss. Differentiation towards the germ line was not observed after intra-testicular injection of BMSCs, neither did we observe any protective effect for SSC loss. Intra-testicular tissue grafting seems to be the most efficient fertility preservation strategy. However, this strategy can not be applied in patients at risk of malignant contamination. For these patients SSC transplantation should be performed after decontamination of the cell suspension.