Restoration of functional sperm production in irradiated pubertal rhesus monkeys by spermatogonial stem cell transplantation

Pediatric Cancer Immunotherapy and Potential for Impact on Fertility: A Need for Evidence-Based Guidance

The use of immunotherapies for the treatment of cancer in children, adolescents, and young adults has become common. As the use of immunotherapy has expanded, including in earlier lines of therapy, it has become evident that several aspects of how these immunotherapies impact longer term outcomes among survivors are understudied. Traditional cancer therapies like alkylating and platin agents carry the greatest risk of infertility, but little is known about the impact of novel immunotherapies on fertility. This topic is of great interest to patients, patient advocates and clinicians. In this paper, we review immunotherapeutic agents used to treat childhood and young adult cancers and discuss potential mechanisms by which they may impact fertility based on the known interplay between the immune system and reproductive organs. We highlight the relative paucity of high-quality literature examining these late effects. We discuss interventions to optimize fertility preservation for our patients. Conducting longitudinal, collaborative, and prospective research on the fertility outcomes of pediatric and young adult patients with cancer who receive immunotherapy is critical to learn how to effectively counsel our patients on long-term fertility outcomes and indications for fertility preservation procedures. Collection of patient-level data will be necessary to draft evidence-based guidelines on which providers can make therapy recommendations.

Advanced isolation, expansion and characterization research study on pig testicular cells during differentiation and proliferation

Spermatogenesis is the complex process of sperm production to transmit paternal genetic information to the subsequent generation. This process is determined by the collaboration of several germ and somatic cells, most importantly spermatogonia stem cells and Sertoli cells. To characterize germ and somatic cells in the tubule seminiferous contort in pig and consequently has an impact on the analysis of pig fertility. Germ cells were extracted from pig testis by enzymatic digestion before being expanded on Sandos inbred mice (SIM) embryo-derived thioguanine and ouabain resistant fibroblasts (STO) feeder layer supplemented with FGF, EGF, and GDNF. Immunohistochemistry (IHC) and immunocytochemistry (ICC) analysis for Sox9, Vimentin, and PLZF markers were performed to examine the generated colonies of pig testicular cells. Electron microscopy was also utilized to analyze the morphological features of the extracted pig germ cells. IHC analysis revealed that Sox9 and Vimentin were expressed in the basal compartment of the seminiferous tubules. Moreover, ICC results showed that the cells have low expression of PLZF while expressing Vimentin. The heterogeneity of the in vitro cultured cells was detected via morphological analysis by the electron microscope. In this experimental study, we tried to reveal exclusive information which obviously could be helpful for future success in the achievement of proper therapies against infertility and sterility as an important global issue.

DAZL Knockout Pigs as Recipients for Spermatogonial Stem Cell Transplantation

Spermatogonial stem cell (SSC) transplantation into the testis of a germ cell (GC)-depleted surrogate allows transmission of donor genotype via donor-derived sperm produced by the recipient. Transplantation of gene-edited SSCs provides an approach to propagate gene-edited large animal models. DAZL is a conserved RNA-binding protein important for GC development, and DAZL knockout (KO) causes defects in GC commitment and differentiation. We characterized DAZL-KO pigs as SSC transplantation recipients. While there were GCs in 1-week-old (wko) KO, complete GC depletion was observed by 10 wko. Donor GCs were transplanted into 18 DAZL-KO recipients at 10-13 wko. At sexual maturity, semen and testes were evaluated for transplantation efficiency and spermatogenesis. Approximately 22% of recipient seminiferous tubules contained GCs, including elongated spermatids and proliferating spermatogonia. The ejaculate of 89% of recipients contained sperm, exclusively from donor origin. However, sperm concentration was lower than the wild-type range. Testicular protein expression and serum hormonal levels were comparable between DAZL-KO and wild-type. Intratesticular testosterone and Leydig cell volume were increased, and Leydig cell number decreased in transplanted DAZL-KO testis compared to wild-type. In summary, DAZL-KO pigs support donor-derived spermatogenesis following SSC transplantation, but low spermatogenic efficiency currently limits their use for the production of offspring.

Fertility Preservation Practices at Pediatric Oncology Institutions in the United States: A Report From the Children's Oncology Group

PURPOSE

Fertility discussions are an integral part of comprehensive care for pediatric, adolescent, and young adult patients newly diagnosed with cancer and are supported by national guidelines. Current institutional practices are poorly understood.

METHODS

A cross-sectional survey was distributed to 220 Children's Oncology Group member institutions regarding fertility discussion practices. Descriptive statistics were calculated for all variables. The association between specific practices and selected outcomes on the basis of sex was examined via multivariable logistic regression.

RESULTS

One hundred forty-four programs (65.5%) returned surveys. Of these, 65 (45.1%) reported routine discussions of fertility with all female patients and 55 (38.5%) all male patients (P = .25). Ninety-two (63.8%) reported no specific criteria for offering females fertility preservation (FP), compared with 40 (27.7%) for males (P < .001). Program characteristics associated with fertility discussions included reproductive endocrinology and infertility on site (females odds ratio [OR], 2.1; 95% CI, 1.0 to 4.3), discussion documentation mandate (females OR, 2.3; 95% CI, 1.0 to 5.5; males OR, 3.5; 95% CI, 1.4 to 8.7), and cumulative institution-based FP infrastructure (which included [1] routine practice of documentation, [2] template for documentation, [3] mandate for documentation, and [4] availability of FP navigation; females OR, 1.6; 95% CI, 1.1 to 2.3; males OR, 2.3; 95% CI, 1.6 to 3.4). Utilization of practices unsupported by guidelines included offering sperm banking after treatment initiation (39/135 programs; 28.9%), gonadotropin-releasing hormone analogs for ovarian suppression/FP (75/144 programs; 52.1%), ovarian tissue cryopreservation at diagnosis for patients with leukemia (19/64 programs; 29.7%), and testicular tissue cryopreservation (23/138 programs; 16.7%) not part of a clinical trial.

CONCLUSION

Despite recommended guidelines, fertility discussions with patients/families before treatment initiation are not routine at Children's Oncology Group institutions. Standard criteria to determine which options should be offered to patients are more common for males than females.

Models and Methods for Evaluating Regeneration of Spermatogenesis After Cytotoxic Treatments

Cytotoxic exposure, predominantly during radiation and/or chemotherapy treatment for cancer, interferes with fertility in men. While moderate doses cause temporary azoospermia allowing eventual recovery of spermatogenesis, higher doses of sterilizing agents can cause permanent sterility by killing the spermatogonial stem cells (SSCs). In this chapter, the methods involved in the following aspects of cytotoxic regeneration are described: (i) designing rodent and non-human primate models for regeneration of spermatogenesis after cytotoxic treatment by radiation and chemotherapy; (ii) analysis of SSCs with respect to the impact of the cytotoxic treatment, including analysis of spermatogonial clones, scoring the testicular section to analyze the extent of spermatogenic recovery, preparation of testicular and epididymal sperm, and collection of semen in non-human primates for sperm analysis; and (iii) preparation and delivery of a GnRH antagonist and steroids for enhancement or induction of spermatogonial differentiation, leading to the regeneration of spermatogenesis, largely applicable in the rat model.

Germline stem cells in human

The germline cells are essential for the propagation of human beings, thus essential for the survival of mankind. The germline stem cells, as a unique cell type, generate various states of germ stem cells and then differentiate into specialized cells, spermatozoa and ova, for producing offspring, while self-renew to generate more stem cells. Abnormal development of germline stem cells often causes severe diseases in humans, including infertility and cancer. Primordial germ cells (PGCs) first emerge during early embryonic development, migrate into the gentile ridge, and then join in the formation of gonads. In males, they differentiate into spermatogonial stem cells, which give rise to spermatozoa via meiosis from the onset of puberty, while in females, the female germline stem cells (FGSCs) retain stemness in the ovary and initiate meiosis to generate oocytes. Primordial germ cell-like cells (PGCLCs) can be induced in vitro from embryonic stem cells or induced pluripotent stem cells. In this review, we focus on current advances in these embryonic and adult germline stem cells, and the induced PGCLCs in humans, provide an overview of molecular mechanisms underlying the development and differentiation of the germline stem cells and outline their physiological functions, pathological implications, and clinical applications.

Male fertility preservation and restoration strategies for patients undergoing gonadotoxic therapies†

Medical treatments for cancers or other conditions can lead to permanent infertility. Infertility is an insidious disease that impacts not only the ability to have a biological child but also the emotional well-being of the infertile individuals, relationships, finances, and overall health. Therefore, all patients should be educated about the effects of their medical treatments on future fertility and about fertility preservation options. The standard fertility preservation option for adolescent and adult men is sperm cryopreservation. Sperms can be frozen and stored for a long period, thawed at a later date, and used to achieve pregnancy with existing assisted reproductive technologies. However, sperm cryopreservation is not applicable for prepubertal patients who do not yet produce sperm. The only fertility preservation option available to prepubertal boys is testicular tissue cryopreservation. Next-generation technologies are being developed to mature those testicular cells or tissues to produce fertilization-competent sperms. When sperm and testicular tissues are not available for fertility preservation, inducing pluripotent stem cells derived from somatic cells, such as blood or skin, may provide an alternative path to produce sperms through a process call in vitro gametogenesis. This review describes standard and experimental options to preserve male fertility as well as the experimental options to produce functional spermatids or sperms from immature cryopreserved testicular tissues or somatic cells.

Progress in germline stem cell transplantation in mammals and the potential usage

Germline stem cells (GSCs) are germ cells with the capacities of self-renewal and differentiation into functional gametes, and are able to migrate to their niche and reconstitute the fertility of recipients after transplantation. Therefore, GSCs transplantation is a promising technique for fertility recovery in the clinic, protection of rare animals and livestock breeding. Though this novel technique faces tremendous challenges, numerous achievements have been made after several decades' endeavor. This review summarizes the current knowledge of GSCs transplantation and its utilization in mammals, and discusses the application prospect in reproductive medicine and animal science.

Maintenance of Sertoli Cell Number and Function in Immature Human Testicular Tissues Exposed to Platinum-Based Chemotherapy-Implications for Fertility Restoration

Background: Retrospective studies in adult survivors of childhood cancer show long-term impacts of exposure to alkylating chemotherapy on future fertility. We recently demonstrated germ cell loss in immature human testicular tissues following exposure to platinum-based chemotherapeutic drugs. This study investigated the effects of platinum-based chemotherapy exposure on the somatic Sertoli cell population in human fetal and pre-pubertal testicular tissues. Methods: Human fetal (n = 23; 14-22 gestational weeks) testicular tissue pieces were exposed to cisplatin (0.5 or 1.0 μg/ml) or vehicle for 24 h in vitro and analysed 24-240 h post-exposure or 12 weeks after xenografting. Human pre-pubertal (n = 10; 1-12 years) testicular tissue pieces were exposed to cisplatin (0.5 μg/ml), carboplatin (5 μg/ml) or vehicle for 24 h in vitro and analysed 24-240 h post-exposure; exposure to carboplatin at 10-times the concentration of cisplatin reflects the relative clinical doses given to patients. Immunohistochemistry was performed for SOX9 and anti-Müllerian hormone (AMH) expression and quantification was carried out to assess effects on Sertoli cell number and function respectively. AMH and inhibin B was measured in culture medium collected post-exposure to assess effects on Sertoli cell function. Results: Sertoli cell (SOX9+ve) number was maintained in cisplatin-exposed human fetal testicular tissues (7,647 ± 459 vs. 7,767 ± 498 cells/mm2; p > 0.05) at 240 h post-exposure. No effect on inhibin B (indicator of Sertoli cell function) production was observed at 96 h after cisplatin (0.5 and 1.0 μg/ml) exposure compared to control (21 ± 5 (0.5 μg/ml cisplatin) vs. 23 ± 7 (1.0 μg/ml cisplatin) vs. 25 ± 7 (control) ng/ml, p > 0.05). Xenografting of cisplatin-exposed (0.5 μg/ml) human fetal testicular tissues had no long-term effect on Sertoli cell number or function (percentage seminiferous area stained for SOX9 and AMH, respectively), compared with non-exposed tissues. Sertoli cell number was maintained in human pre-pubertal testicular tissues following exposure to either 0.5 μg/ml cisplatin (6,723 ± 1,647 cells/mm2) or 5 μg/ml carboplatin (7,502 ± 627 cells/mm2) compared to control (6,592 ± 1,545 cells/mm2). Conclusions: This study demonstrates maintenance of Sertoli cell number and function in immature human testicular tissues exposed to platinum-based chemotherapeutic agents. The maintenance of a functional Sertoli cell environment following chemotherapy exposure suggests that fertility restoration by spermatogonial stem cell (SSC) transplant may be possible in boys facing platinum-based cancer treatment.

Infrastructure of Fertility Preservation Services for Pediatric Cancer Patients: A Report From the Children's Oncology Group

PURPOSE

Fertility preservation (FP) services are part of comprehensive care for those newly diagnosed with cancer. The capacity to offer these services to children and adolescents with cancer is unknown.

METHODS

A cross-sectional survey was sent to 220 Children's Oncology Group member institutions regarding institutional characteristics, structure and organization of FP services, and barriers to FP. Standard descriptive statistics were computed for all variables. The association between site-specific factors and selected outcomes was examined using multivariable logistic regression.

RESULTS

One hundred forty-four programs (65.5%) returned surveys. Fifty-three (36.8%) reported a designated FP individual or team. Sperm banking was offered at 135 (97.8%) institutions, and testicular tissue cryopreservation at 37 (27.0%). Oocyte and embryo cryopreservation were offered at 91 (67.9%) and 62 (46.6%) institutions, respectively; ovarian tissue cryopreservation was offered at 64 (47.8%) institutions. The presence of dedicated FP personnel was independently associated with the ability to offer oocyte or embryo cryopreservation (odds ratio [OR], 4.7; 95% CI, 1.7 to 13.5), ovarian tissue cryopreservation (OR, 2.7; 95% CI, 1.2 to 6.0), and testicular tissue cryopreservation (OR, 3.3; 95% CI, 1.4 to 97.8). Only 26 (18.1%) participating institutions offered all current nonexperimental FP interventions. Barriers included cost (70.9%), inadequate knowledge or training (60.7%), difficulty characterizing fertility risk (50.4%), inadequate staffing (45.5%), and logistics with reproductive specialties (38%-39%).

CONCLUSION

This study provides the most comprehensive view of the current landscape of FP infrastructure for children and adolescents with cancer and demonstrates that existing infrastructure is inadequate to offer comprehensive services to patients. We discuss modifiable factors to improve patient access to FP.

Primary culture of germ cells that portray stem cell characteristics and recipient preparation for autologous transplantation in the rhesus monkey

Fertility preservation for prepubertal cancer patients prior to oncologic treatment is an emerging issue, and non‐human primates are considered to constitute suitable models due to the limited availability of human testicular tissues. However, the feasibility of spermatogonial stem cell (SSC) propagation in vitro and autologous testicular germ cell transplantation in vivo requires further exploration in monkeys. Herein, we characterized germ cells in macaque testes at 6 months (M), 18 M and 60 M of age, and effectively isolated the spermatogenic cells (including the spermatogonia) from macaque testes with high purity (over 80%) using combined approaches of STA‐PUT separation, Percoll gradients and differential plating. We also generated recipient monkey testes with ablated endogenous spermatogenesis using the alkylating agent busulfan in six macaques, and successfully mimicked autologous cell transplantation in the testes under ultrasonographic guidance. The use of trypan blue led to successful intratubular injection in 4 of 4 testes. Although SSCs in culture showed no significant propagation, we were able to maintain monkey testicular germ cells with stem cell characteristics for up to 3 weeks. Collectively, these data provided meaningful information for future fertility preservation and SSC studies on both non‐human primates and humans.

In vitro propagation of XXY human Klinefelter spermatogonial stem cells: A step towards new fertility opportunities

Klinefelter Syndrome (KS) is characterized by a masculine phenotype, supernumerary sex chromosomes (47, XXY), and impaired fertility due to loss of spermatogonial stem cells (SSCs). Early testicular cryopreservation could be an option for future fertility treatments in these patients, including SSCs transplantation or in vitro spermatogenesis. It is critically essential to adapt current in vitro SSCs propagation systems as a fertility option for KS patients. KS human testicular samples (13,15- and 17-year-old non-mosaic KS boys) were donated by patients enrolled in an experimental testicular tissue banking program. Testicular cells were isolated from cryopreserved tissue and propagated in long-term culture for 110 days. Cell-specific gene expression confirmed the presence of all four main cell types found in testes: Spermatogonia, Sertoli, Leydig, and Peritubular cells. A population of ZBTB16⁺ undifferentiated spermatogonia was identified throughout the culture using digital PCR. Flow cytometric analysis also detected an HLA^-/CD9⁺/CD49f⁺ population, indicating maintenance of a stem cell subpopulation among the spermatogonial cells. FISH staining for chromosomes X and Y showed most cells containing an XXY karyotype with a smaller number containing either XY or XX. Both XY and XX populations were able to be enriched by magnetic sorting for CD9 as a spermatogonia marker. Molecular karyotyping demonstrated genomic stability of the cultured cells, over time. Finally, single-cell RNAseq analysis confirmed transcription of ID4, TCN2, and NANOS 3 within a population of putative SSCs population. This is the first study showing successful isolation and long-term in vitro propagation of human KS testicular cells. These findings could inform the development of therapeutic fertility options for KS patients, either through in vitro spermatogenesis or transplantation of SSC, in vivo.

Postpubertal spermatogonial stem cell transplantation restores functional sperm production in rhesus monkeys irradiated before and after puberty

BACKGROUND

Cancer treatment of prepubertal patients impacts future fertility due to the abolition of spermatogonial stem cells (SSCs). In macaques, spermatogenesis could be regenerated by intratesticular transplantation of SSCs, but no studies have involved cytotoxic treatment before puberty and transplantation after puberty, which would be the most likely clinical scenario.

OBJECTIVES

To evaluate donor-derived functional sperm production after SSC transplantation to adult monkeys that had received testicular irradiation during the prepubertal period.

MATERIALS AND METHODS

We obtained prepubertal testis tissue by unilaterally castrating six prepubertal monkeys and 2 weeks later irradiated the remaining testes with 6.9 Gy. However, because spermatogenic recovery was observed, we irradiated them again 14 months later with 7 Gy. Three of the monkeys were treated with GnRH-antagonist (GnRH-ant) for 8 weeks. The cryopreserved testis cells from the castrated testes were then allogeneically transplanted into the intact testes of all monkeys. Tissues were harvested 10 months later for analyses.

RESULTS

In three of the six monkeys, 61%, 38%, and 11% of the epididymal sperm DNA were of the donor genotype. The ability to recover donor-derived sperm production was not enhanced by the GnRH-ant pretreatment. However, the extent of filling seminiferous tubules during the transplantation procedure was correlated with the eventual production of donor spermatozoa. The donor epididymal spermatozoa from the recipient with 61% donor contribution were capable of fertilizing rhesus eggs and forming embryos. Although the transplantation was done into the rete testis, two GnRH-ant-treated monkeys, which did not produce donor-derived epididymal spermatozoa, displayed irregular tubular cords in the interstitium containing testicular spermatozoa derived from the transplanted donor cells.

DISCUSSION AND CONCLUSION

The results further support that sperm production can be restored in non-human primates from tissues cryopreserved prior to prepubertal and post-pubertal gonadotoxic treatment by transplantation of these testicular cells after puberty into seminiferous tubules.

Spermatogonial stem cell transplantation into nonablated mouse recipient testes

Spermatogonial transplantation has been used as a standard assay for spermatogonial stem cells (SSCs). After transplantation into the seminiferous tubules, SSCs transmigrate through the blood-testis barrier (BTB) between Sertoli cells and settle in a niche. Unlike in the repair of other self-renewing systems, SSC transplantation is generally performed after complete destruction of endogenous spermatogenesis. Here, we examined the impacts of recipient conditioning on SSC homing. Germ cell ablation downregulated the expression of glial cell line-derived neurotrophic factor, which has been shown to attract SSCs to niches, implying that nonablated niches would attract SSCs more efficiently. As expected, SSCs colonized nonablated testes when transplanted into recipients with the same genetic background. Moreover, although spermatogenesis was arrested at the spermatocyte stage in Cldn11-deficient mice without a BTB, transplantation not only enhanced donor colonization but also restored normal spermatogenesis. The results show promise for the development of a new transplantation strategy to overcome male infertility.

Survivable potential of germ cells after trehalose cryopreservation of bovine testicular tissues

Germplasm preservation of livestock or endangered animals and expansion of germline stem cells are important. The purpose of this study is to investigate whether supplementation of trehalose to the freezing medium (FM) reduces tissular damage and improves the quality of testicular cells in the cryopreserved bovine testicular tissues. We herein established an optimized protocol for the cryopreservation of bovine testicular tissues, and the isolation as well as culture of bovine germ cells containing spermatogonial stem cells (SSCs) from these tissues. The results showed that FM containing 10% dimethyl sulfoxide (Me₂SO/DMSO), 10% knockout serum replacement (KSR) and 20% trehalose (FM5) combined with the uncontrolled slow freezing (USF) procedures has the optimized cryoprotective effect on bovine testicular tissues. The FM5 + USF protocol reduced the cell apoptosis, maintained high cell viability, supported the structural integrity and seminiferous epithelial cohesion similar to that in the fresh tissues. Viable germ cells containing SSCs were effectively isolated from these tissues and they maintained germline marker expressions in the co-testicular cells and co-mouse embryonic fibroblasts (MEF) feeder culture systems respectively, during the short-term culture. Additionally, upregulated transcriptions of spermatogenic differentiation marker C-KIT and meiotic marker SYCP3 were detected in these cells after retinoic acid-induced differentiation. Together, FM5 + USF is suitable for the cryopreservation of bovine testicular tissues, with benefits of reducing the apoptosis, maintaining the cell viability, supporting the testicular structure integrity, and sustaining the survival and differentiation potential of bovine germ cells containing SSCs.

Is It Possible to Treat Infertility with Stem Cells?

Infertility is a major health problem, and despite improved treatments over the years, there are still some conditions that cannot be treated successfully using a conventional approach. Therefore, new options are being considered and one of them is cell therapy using stem cells. Stem cell treatments for infertility can be divided into two major groups, the first one being direct transplantation of stem cells or their paracrine factors into reproductive organs and the second one being in vitro differentiation into germ cells or gametes. In animal models, all of these approaches were able to improve the reproductive potential of tested animals, although in humans there is still too little evidence to suggest successful use. The reasons for lack of evidence are unavailability of proper material, the complexity of explored biological processes, and ethical considerations. Despite all of the above-mentioned hurdles, researchers were able to show that in women, it seems to be possible to improve some conditions, but in men, no similar clinically important improvement was achieved. To conclude, the data presented in this review suggest that the treatment of infertility with stem cells seems plausible, because some types of treatments have already been tested in humans, achieving live births, while others show great potential only in animal studies, for now.

Strategies for cryopreservation of testicular cells and tissues in cancer and genetic diseases

Cryopreservation of testicular cells and tissues is useful for the preservation and restoration of fertility in pre-pubertal males expecting gonadotoxic treatment for cancer and genetic diseases causing impaired spermatogenesis. A number of freezing and vitrification protocols have thus been tried and variable results have been reported in terms of cell viability spermatogenesis progression and the production of fertile spermatozoa. A few studies have also reported the production of live offspring from cryopreserved testicular stem cells and tissues in rodents but their replication in large animals and human have been lacking. Advancement in in vitro spermatogenesis system has improved the possibility of producing fertile spermatozoa from the cryopreserved testis and has reduced the dependency on transplantation. This review provides an update on various cryopreservation strategies for fertility preservation in males expecting gonadotoxic treatment. It also discusses various methods of assessing and ameliorating cryoinjuries. Newer developments on in vitro spermatogenesis and testicular tissue engineering for in vitro sperm production from cryopreserved SSCs and testicular tissue are also discussed.

Spermatogonial Stem Cell Transplantation in Large Animals

Simple Summary

The spermatogonial stem cell (SSC) is the only adult stem cell in males to transmit genetic information to offspring. SSC transplantation (SSCT) is a laboratory technique to regenerate spermatogenesis in recipient males, thus can be used as a novel breeding tool to benefit animal production. Although successful SSCT in rodent models has been established, progress in realizing SSCT in large animals has been limited. Here we discuss what we learned in this area from past experiments and highlight possible directions in developing effective SSCT protocol in large animals.

Abstract

Spermatogonial stem cell transplantation (SSCT) can restore male fertility through transfer of germline between donor and recipient males. From an agricultural perspective, SSCT could be an important next-generation reproductive and breeding tool in livestock production. Current SSCT approaches in large animals remain inefficient and many technical details need further investigation. This paper reviews the current knowledge on SSCT in large animals, addressing (1) donor spermatogonial stem cell (SSC) preparation, (2) recipient male treatment, and (3) SSC injection, homing, and detection. The major studies showing unequivocal evidence of donor SSC-derived spermatogenesis in large animals (mainly in livestock for breeding purpose) are summarized to discuss the current status of the field and future directions.

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

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.

Approaches and Technologies in Male Fertility Preservation

Male fertility preservation is required when treatment with an aggressive chemo-/-radiotherapy, which may lead to irreversible sterility. Due to new and efficient protocols of cancer treatments, surviving rates are more than 80%. Thus, these patients are looking forward to family life and fathering their own biological children after treatments. Whereas adult men can cryopreserve their sperm for future use in assistance reproductive technologies (ART), this is not an option in prepubertal boys who cannot produce sperm at this age. In this review, we summarize the different technologies for male fertility preservation with emphasize on prepubertal, which have already been examined and/or demonstrated in vivo and/or in vitro using animal models and, in some cases, using human tissues. We discuss the limitation of these technologies for use in human fertility preservation. This update review can assist physicians and patients who are scheduled for aggressive chemo-/radiotherapy, specifically prepubertal males and their parents who need to know about the risks of the treatment on their future fertility and the possible present option of fertility preservation.