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Increasing numbers of patients are now surviving previously fatal malignant diseases, so for women of childbearing age, fertility concerns are paramount once they are cured. However, the treatments themselves, namely chemo- and radiotherapy, can cause considerable damage to endocrine and reproductive functions, often leaving these women unable to conceive. When such gonadotoxic therapy cannot be postponed due to the severity of the disease or for prepubertal girls, the only way to preserve fertility is cryobanking their ovarian tissue for future use. Unfortunately, with some types of cancer, there is a risk of reimplanting malignant cells together with the frozen-thawed tissue, so it is not recommended. A safer approach involves grafting isolated preantral follicles back to their native environment inside a specially created transplantable artificial ovary for their protection. This bioengineered ovary must mimic the natural organ and therefore requires an appropriate scaffold to encapsulate not only isolated follicles, but also autologous ovarian cells, which are needed for follicles to survive and develop. Here we review the indications for use of this artificial ovary and advances in the field that are bringing us ever closer to clinical implementation.

This study was designed to evaluate follicular survival and growth after short-term transplantation of fresh isolated human follicles and ovarian cortical tissue to nude mice. Ovarian biopsies were obtained from nine women undergoing laparoscopy. Twelve nude mice were xenografted with an ovarian cortical fragment in the right ovarian bursa, and a clot containing isolated follicles in the left, for a period of 7 days. One ungrafted fragment was used as a control. Histological sections were analyzed to determine follicle number and stage. The proliferative status of follicular cells was assessed by Ki-67 immunostaining. A total of 659 follicles was analyzed by histology and 545 follicles by immunohistochemistry. The percentage of primordial follicles was found to be markedly reduced 1 week post-grafting when compared with ungrafted tissue, while the percentage of primary follicles had significantly increased. Only 8% of follicles showed Ki-67-positive granulosa cells before grafting, whereas 1 week after grafting, 71% of follicles in fragments and 67% of isolated follicles were Ki-67-positive (P<0.001). Moreover, the histological aspect of isolated follicle grafts was similar to that of grafted fragments: follicles were surrounded by vimentin-positive stroma-like tissue of human origin, as confirmed by fluorescent in situ hybridization with human-specific probes. Our results demonstrate, for the first time, that isolated human follicles are able to survive and grow after xenografting. This study also shows massive in vivo follicular activation after transplantation of grafted fragments and isolated follicles. One week after grafting, well-structured stroma-like tissue of human origin was observed around the isolated follicles. The potential origin of this stroma is discussed.