[Cryopreserved ovaries: models of experimental grafting].

Childhood cancers account for 1% of malignant tumors. As a result of advances in treatment, almost 80% of children and adolescents who currently receive a diagnosis of cancer become long-term survivors. Assessment of potential for fertility preservation should thus be a systematic element of care for children treated for a malignant tumor (high-dose chemotherapy with alkylizing agents, radiation therapy including the gonads) or those receiving hematopoietic stem cell grafts for malignant or benign disease (sickle-cell anemia, immune deficit). Potential adverse consequences of treatment include impaired puberty and fertility due to gonadal removal, genital tract injury or damage to germ cells from adjuvant therapy. Advances in assisted reproductive technologies have led to new possibilities for the prevention and treatment of infertility. Among them, cryopreservation of ovarian tissue appears to be the most promising, or perhaps the only one available before puberty with encouraging results. Nevertheless the uncertainties, or even risks, related to these treatments, should not be neglected. We review experimental data in mouse and sheep animal models. The results demonstrate that immature ovarian grafting can restore spontaneous puberty and fertility in both models. This study addresses the very important issue of epigenetics, and provides valuable information for the study of ovarian transplantation, suggesting that these procedures do not perturb normal epigenetic marks. These results are highly relevant to the question of immature cortex reimplantation.