Fertility preservation for prepubertal boys: lessons learned from the past and update on remaining challenges towards clinical translation

Abstract

BACKGROUND Childhood cancer incidence and survivorship are both on the rise. However, many lifesaving treatments threaten the prepubertal testis. Cryopreservation of immature testicular tissue (ITT), containing spermatogonial stem cells (SSCs), as a fertility preservation (FP) option for this population is increasingly proposed worldwide. Recent achievements notably the birth of non-human primate (NHP) progeny using sperm developed in frozen-thawed ITT autografts has given proof of principle of the reproductive potential of banked ITT. Outlining the current state of the art on FP for prepubertal boys is crucial as some of the boys who have cryopreserved ITT since the early 2000s are now in their reproductive age and are already seeking answers with regards to their fertility. OBJECTIVE AND RATIONALE In the light of past decade achievements and observations, this review aims to provide insight into relevant questions for clinicians involved in FP programmes. Have the indications for FP for prepubertal boys changed over time? What is key for patient counselling and ITT sampling based on the latest achievements in animals and research performed with human ITT? How far are we from clinical application of methods to restore reproductive capacity with cryostored ITT? SEARCH METHODS An extensive search for articles published in English or French since January 2010 to June 2020 using keywords relevant to the topic of FP for prepubertal boys was made in the MEDLINE database through PubMed. Original articles on fertility preservation with emphasis on those involving prepubertal testicular tissue, as well as comprehensive and systematic reviews were included. Papers with redundancy of information or with an absence of a relevant link for future clinical application were excluded. Papers on alternative sources of stem cells besides SSCs were excluded. OUTCOMES Preliminary follow-up data indicate that around 27% of boys who have undergone testicular sampling as an FP measure have proved azoospermic and must therefore solely rely on their cryostored ITT to ensure biologic parenthood. Auto-transplantation of ITT appears to be the first technique that could enter pilot clinical trials but should be restricted to tissue free of malignant cells. While in vitro spermatogenesis circumvents the risk linked to cancer cell contamination and has led to offspring in mice, complete spermatogenesis has not been achieved with human ITT. However, generation of haploid germ cells paves the way to further studies aimed at completing the final maturation of germ cells and increasing the efficiency of the processes. WIDER IMPLICATIONS Despite all the research done to date, FP for prepubertal boys remains a relatively young field and is often challenging to healthcare providers, patients and parents. As cryopreservation of ITT is now likely to expand further, it is important not only to acknowledge some of the research questions raised on the topic, e.g. the epigenetic and genetic integrity of gametes derived from strategies to restore fertility with banked ITT but also to provide healthcare professionals worldwide with updated knowledge to launch proper multicollaborative care pathways in the field and address clinical issues that will come-up when aiming for the child’s best interest.

Immature Testicular Tissue Engineered from Weaned Mice to Adults for Prepubertal Fertility Preservation—An In Vivo Translational Study

“…This translational bioengineering study may echo the messages from a cutting-edge review article, entitled "Fertility preservation for prepubertal boys: lessons learned from the past and update on remaining challenges towards clinical translation" [49]. Since there has so far been no live births from various fertility preservation methods in prepubertal boys, partly due to ethical concerns as well as the lack of long-term longitudinal follow-ups, our study may pave the way for future applications.…”

Cellular Therapy via Spermatogonial Stem Cells for Treating Impaired Spermatogenesis, Non-Obstructive Azoospermia

“…On the other hand, VSELs present in humans and mice are pluripotent as they can self-renew and regenerate. Since VSELs are not affected by chemotherapy, they can contribute to germ cell development in men who have received chemotherapy as an infant [ 161 , 162 ].…”

Accelerated and Improved Vascular Maturity after Transplantation of Testicular Tissue in Hydrogels Supplemented with VEGF- and PDGF-Loaded Nanoparticles

“…Fertility impairment induced by anticancer treatments in the pediatric population [ 1 , 2 , 3 , 4 , 5 ] represents a major concern for the quality of life of oncological survivors [ 6 , 7 ], and several fertility preservation (FP) programs have been set up worldwide to preserve patients’ reproductive potential [ 8 , 9 , 10 ]. While for female and post-pubertal male patients FP is at a clinical stage [ 11 , 12 , 13 ], for pre-pubertal boys it is still considered experimental.…”

“…With regard to human tissue, frozen–thawed immature testicular tissue (ITT) xeno-transplanted to nude mice allowed preservation of spermatogonia able to proliferate and initiate differentiation [ 15 , 16 , 24 ]. However, as testicular sampling aimed at FP is usually kept at a minimum to avoid potential harm caused by the procedure, only small amounts of testicular tissue are available for cryostorage and future use [ 4 ].…”