Fruitful progress to fertility: Male fertility in the test tube

Advances of three-dimensional (3D) culture systems for in vitro spermatogenesis

The loss of germ cells and spermatogenic failure in non-obstructive azoospermia are believed to be the main causes of male infertility. Laboratory studies have used in vitro testicular models and different 3-dimensional (3D) culture systems for preservation, proliferation and differentiation of spermatogonial stem cells (SSCs) in recent decades. The establishment of testis-like structures would facilitate the study of drug and toxicity screening, pathological mechanisms and in vitro differentiation of SSCs which resulted in possible treatment of male infertility. The different culture systems using cellular aggregation with self-assembling capability, the use of different natural and synthetic biomaterials and various methods for scaffold fabrication provided a suitable 3D niche for testicular cells development. Recently, 3D culture models have noticeably used in research for their architectural and functional similarities to native microenvironment. In this review article, we briefly investigated the recent 3D culture systems that provided a suitable platform for male fertility preservation through organ culture of testis fragments, proliferation and differentiation of SSCs.

Fertility Preservation in Childhood Cancer: Endocrine Activity in Prepubertal Human Testis Xenografts Exposed to a Pubertal Hormone Environment

Simple Summary

Substantial strides have been made in treating childhood cancers; however, as a result of chemotherapy and radiotherapy, young males experience long-term side effects, including impaired fertility. Whilst prepubertal testicular tissue can be cryopreserved prior to gonadotoxic treatments, it remains to be determined how to generate mature gametes from the immature human testis tissue. Development of immature germ cells into sperm is a complex process, which is supported by mature Sertoli cells and testosterone produced from Leydig cells. We used an established testicular xenotransplantation model to investigate the effect of puberty hormones, known as gonadotrophins, on functional maturation of the spermatogonial stem cell (SSC) niche. Limited testosterone production and partial maturation of Sertoli cells occurred in prepubertal testis grafts, suggesting that longer periods of grafting and/or identification of additional factors are required to develop testicular transplantation as a model for fertility preservation in male survivors of childhood cancer.

Abstract

Survivors of childhood cancer are at risk for long-term treatment-induced health sequelae, including gonadotoxicity and iatrogenic infertility. At present, for prepubertal boys there are no viable clinical options to preserve future reproductive potential. We investigated the effect of a pubertal induction regimen with gonadotrophins on prepubertal human testis xenograft development. Human testis tissue was obtained from patients with cancer and non-malignant haematological disorders (n = 6; aged 1–14 years) who underwent testis tissue cryopreservation for fertility preservation. Fresh and frozen-thawed testis fragments were transplanted subcutaneously or intratesticularly into immunocompromised mice. Graft-bearing mice received injections of vehicle or exogenous gonadotrophins, human chorionic gonadotrophin (hCG, 20 IU), and follicle-stimulating hormone (FSH, 12.5 IU) three times a week for 12 weeks. The gross morphology of vehicle and gonadotrophin-exposed grafts was similar for both transplantation sites. Exposure of prepubertal human testis tissue xenografts to exogenous gonadotrophins resulted in limited endocrine function of grafts, as demonstrated by the occasional expression of the steroidogenic cholesterol side-chain cleavage enzyme (CYP11A1). Plasma testosterone concentrations (0.13 vs. 0.25 ng/mL; p = 0.594) and seminal vesicle weights (10.02 vs. 13.93 mg; p = 0.431) in gonadotrophin-exposed recipient mice were comparable to vehicle-exposed controls. Regardless of the transplantation site and treatment, initiation and maintenance of androgen receptor (AR) expression were observed in Sertoli cells, indicating commitment towards a more differentiated status. However, neither exogenous gonadotrophins (in castrated host mice) nor endogenous testosterone (in intact host mice) were sufficient to repress the expression of markers associated with immature Sertoli cells, such as anti-Müllerian hormone (AMH) and Ki67, or to induce the redistribution of junctional proteins (connexin 43, CX43; claudin 11, CLDN11) to areas adjacent to the basement membrane. Spermatogonia did not progress developmentally but remained the most advanced germ cell type in testis xenografts. Overall, these findings demonstrate that exogenous gonadotrophins promote partial activation and maturation of the somatic environment in prepubertal testis xenografts. However, alternative hormone regimens or additional factors for pubertal induction are required to complete the functional maturation of the spermatogonial stem cell (SSC) niche.

Donor-derived spermatogenesis following stem cell transplantation in sterile NANOS2 knockout males

Spermatogonial stem cell transplantation (SSCT) is an experimental technique for transfer of germline between donor and recipient males that could be used as a tool for biomedical research, preservation of endangered species, and dissemination of desirable genetics in food animal populations. To fully realize these potentials, recipient males must be devoid of endogenous germline but possess normal testicular architecture and somatic cell function capable of supporting allogeneic donor stem cell engraftment and regeneration of spermatogenesis. Here we show that male mice, pigs, goats, and cattle harboring knockout alleles of the NANOS2 gene generated by CRISPR-Cas9 editing have testes that are germline ablated but otherwise structurally normal. In adult pigs and goats, SSCT with allogeneic donor stem cells led to sustained donor-derived spermatogenesis. With prepubertal mice, allogeneic SSCT resulted in attainment of natural fertility. Collectively, these advancements represent a major step toward realizing the enormous potential of surrogate sires as a tool for dissemination and regeneration of germplasm in all mammalian species.

Ethics of fertility preservation for prepubertal children: should clinicians offer procedures where efficacy is largely unproven?

Young children with cancer are treated with interventions that can have a high risk of compromising their reproductive potential. 'Fertility preservation' for children who have not yet reached puberty involves surgically removing and cryopreserving reproductive tissue prior to treatment in the expectation that strategies for the use of this tissue will be developed in the future. Fertility preservation for prepubertal children is ethically complex because the techniques largely lack proven efficacy for this age group. There is professional difference of opinion about whether it is ethical to offer such 'experimental' procedures. The question addressed in this paper is: when, if ever, is it ethically justifiable to offer fertility preservation surgery to prepubertal children? We present the ethical concerns about prepubertal fertility preservation, drawing both on existing literature and our experience discussing this issue with clinicians in clinical ethics case consultations. We argue that offering the procedure is ethically justifiable in certain circumstances. For many children, the balance of benefits and burdens is such that the procedure is ethically permissible but not ethically required; when the procedure is medically safe, it is the parents' decision to make, with appropriate information and guidance from the treating clinicians. We suggest that clinical ethics support processes are necessary to assist clinicians to engage with the ethical complexity of prepubertal fertility preservation and describe the framework that has been integrated into the pathway of care for patients and families attending the Royal Children's Hospital in Melbourne, Australia.

Testicular Tissue Cryopreservation and Ethical Considerations: A Scoping Review

Testicular tissue cryopreservation (TTCP) aims to preserve the future option of genetic reproduction for prepubescent cancer patients who are at risk of infertility as a result of their cancer therapies. This technology is experimental and currently only offered in the research context. As TTCP moves towards becoming more widely available, it is imperative that healthcare providers recognize the complex ethical issues surrounding this technology. This scoping review study identifies and assesses the range and depth of ethical concerns related to this testicular tissue cryopreservation technology. At present, no such scoping review of ethical concerns exists in the TTCP literature. The forty-three full-text articles included in this study yielded twenty-two different ethical considerations discussed in relation to TTCP. It was observed that these ethical considerations fit within a mainstream Principlism approach to bioethics. Accordingly, there are ethical gaps in the TTCP literature that can be identified with alternative moral lenses. In particular, it was found that ethical concerns related to context and relational aspects of identity were absent in nearly all ethical examinations of TTCP. Furthermore, only 9 per cent of articles reviewed in this study focused primarily on the ethics of TTCP, thus demonstrating a need for further in depth ethical analyses of this technology. The results of this study are important for supporting the ethical provision of TTCP and can contribute to policy and guideline development. The findings of this study demonstrate the need for greater depth and diversity in analyses of ethical considerations related to this technology.

Granulocyte colony-stimulating factor (G-CSF) promotes spermatogenic regeneration from surviving spermatogonia after high-dose alkylating chemotherapy

BACKGROUND

The lifesaving chemotherapy and radiation treatments that allow patients to survive cancer can also result in a lifetime of side-effects, including male infertility. Infertility in male cancer survivors is thought to primarily result from killing of the spermatogonial stem cells (SSCs) responsible for producing spermatozoa since SSCs turn over slowly and are thereby sensitive to antineoplastic therapies. We previously demonstrated that the cytokine granulocyte colony-stimulating factor (G-CSF) can preserve spermatogenesis after alkylating chemotherapy (busulfan).

METHODS

Male mice were treated with G-CSF or controls before and/or after sterilizing busulfan treatment and evaluated immediately or 10-19 weeks later for effects on spermatogenesis.

RESULTS

We demonstrated that the protective effect of G-CSF on spermatogenesis was stable for at least 19 weeks after chemotherapy, nearly twice as long as previously shown. Further, G-CSF treatment enhanced spermatogenic measures 10 weeks after treatment in the absence of a cytotoxic insult, suggesting G-CSF acts as a mitogen in steady-state spermatogenesis. In agreement with this conclusion, G-CSF treatment for 3 days before busulfan treatment exacerbated the loss of spermatogenesis observed with G-CSF alone. Reciprocally, spermatogenic recovery was modestly enhanced in mice treated with G-CSF for 4 days after busulfan. These results suggested that G-CSF promoted spermatogonial proliferation, leading to enhanced spermatogenic regeneration from surviving SSCs. Similarly, there was a significant increase in proportion of PLZF+ undifferentiated spermatogonia that were Ki67+ (proliferating) 1 day after G-CSF treatment.

CONCLUSIONS

Together, these results clarify that G-CSF protects spermatogenesis after alkylating chemotherapy by stimulating proliferation of surviving spermatogonia, and indicate it may be useful as a retrospective fertility-restoring treatment.

Preserved seminiferous tubule integrity with spermatogonial survival and induction of Sertoli and Leydig cell maturation after long-term organotypic culture of prepubertal human testicular tissue

STUDY QUESTION

Is an organotypic culture system able to provide the appropriate testicular microenvironment for in-vitro maturation of human immature testicular tissue (ITT)?

SUMMARY ANSWER

Our organotypic culture system provided a microenvironment capable of preserving seminiferous tubule (ST) integrity and Leydig cell (LC) functionality and inducing Sertoli cell (SC) maturation.

WHAT IS KNOWN ALREADY

Cryopreservation of human ITT is a well-established strategy to preserve fertility in prepubertal boys affected by cancer, with a view for obtaining sperm. While spermatogenesis in mice has been replicated in organotypic culture, yielding reproductively efficient spermatozoa, this process has not yet been achieved in humans.

STUDY DESIGN, SIZE, DURATION

The aim of this study was to in vitro mature frozen-thawed ITT. To this end, 1 mm³ tissue fragments from three prepubertal patients aged 2 (P1), 11 (P2) and 12 (P3) years were placed in organotypic culture for 139 days. Culture media, supplemented with either testosterone or hCG, were compared.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ST integrity and tissue viability were assessed by histological score and lactate dehydrogenase (LDH) levels in supernatants. Spermatogonia (SG), proliferating cells and proliferating SG were identified by the use of MAGE-A4 and Ki67 immunohistochemical markers. Glial cell line-derived neurotrophic factor (GDNF) was used as a marker of SC functionality, while SC maturation was evaluated by androgen receptor (AR), anti-Müllerian hormone (AMH) immunohistochemistry (IHC) and AMH immunoenzymatic assay. LC functionality was determined by testosterone levels in supernatants and by 3β-hydroxysteroid dehydrogenase (3β-HSD) IHC. Apoptosis was studied by IHC with active caspases 3 and 8 and by TUNEL (terminal deoxynubocleotidyl transferase-mediated dUTP nick end labeling) analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Tissue viability was preserved, as demonstrated by the decrease in and stabilization of LDH release, and evolution of ST scoring, with the percentage of well-preserved STs showing no statistical differences during culture in either medium. GDNF was expressed until Day 139, demonstrating SC functionality. Moreover, a significant reduction in AMH expression and release indicated SC maturation. Testosterone concentrations in supernatants increased in both culture media, demonstrating LC functionality with paracrine interactions. SG were present up to Day 139, although the ratio between MAGE-A4-positive cells and well-preserved tubules was significantly reduced over the course of culture (P ≤ 0.001). SCs exhibited a decreased proliferation rate over time (P ≤ 0.05). The proliferation rate of SG remained stable until Day 64, but over the total culture period (139 days), it was found to have decreased (P ≤ 0.05). The number of apoptotic cells did not vary during culture, nor was any statistical difference observed between the two culture media for any of the studied parameters.

LARGE SCALE DATA

N/A LIMITATIONS, REASONS FOR CAUTION: Loss of SG constitutes a limitation for evaluating full functionality of spermatogonial stem cells and warrants further investigation. The scarcity of human immature material is the reason for the limited amount of tissue available for experiments, precluding more comprehensive analysis.

WIDER IMPLICATIONS OF THE FINDINGS

Our culture system, mimicking the peripubertal testicular microenvironment with SC maturation, LC functionality and preserved paracrine interactions, and the first to use human ITT, opens the door to a deeper understanding of niche and culture conditions to obtain sperm from cryostored ITT, with the ultimate goal of restoring fertility after gonadotoxic treatments.

STUDY FUNDING/COMPETING INTERESTS

This project was supported by a grant from the Fond National de la Recherche Scientifique de Belgique (grant Télevie N° 7.4554.14F and N° 7.4512.15F) and the Fondation Salus Sanguinis. No conflict of interest is declared.

Seminiferous epithelium damage after short period of busulphan treatment in adult rats and vitamin B12 efficacy in the recovery of spermatogonial germ cells

Several different strategies have been adopted in attempt to recover from chemotherapy-damaged spermatogenesis that is often seen in oncologic patients. In this study, we have evaluated the impact of short period of exposure to busulphan on the haemogram and seminiferous epithelium of adult rats, focusing on spermatogonial depletion and Sertoli cell (SC) integrity. We then examined whether vitamin B₁₂ supplementation improves the haematological parameters and spermatogonia number. The animals received 10 mg/kg of busulphan (BuG) or busulfan+vitamin B₁₂ (Bu/B₁₂ G) on the first and fourth days of treatment. In H.E.-stained testicular sections, the areas of the seminiferous tubule (ST) and seminiferous epithelium were measured. The number of spermatogonia in H.E-stained and PCNA-immunolabelled testicular sections was quantified. The frequency of tubules with abnormal SC nuclei or TUNEL-positive SC was evaluated. Vimentin immunofluorescence in ST was also evaluated. In BuG and Bu/B₁₂ G, the animals showed leukopenia and thrombocytopenia, but the body weight reduced only in BuG. The areas of ST and seminiferous epithelium decreased in Bu/B₁₂ G and BuG. In BuG, the number of H.E.-stained and PCNA-immunolabelled spermatogonia reduced significantly. The frequency of tubules containing abnormal SC nuclei and TUNEL-positive SC increased and the vimentin immunoexpression pattern changed. In Bu/B₁₂ G, the number of H.E.-stained or PCNA-immunolabelled spermatogonia increased fourfold in comparison with BuG. The structural changes in ST after 6 days of busulphan exposure may be associated with the potential effect of this anti-neoplastic agent on SC. The increased number of spermatogonia in the busulphan-treated animals receiving vitamin B₁₂ indicates that this vitamin can be an adjuvant therapy to improve the fertility in male cancer patients.

Granulocyte colony-stimulating factor prevents loss of spermatogenesis after sterilizing busulfan chemotherapy

OBJECTIVE

To determine whether granulocyte colony-stimulating factor (G-CSF) could prevent loss of spermatogenesis induced by busulfan chemotherapy via protection of undifferentiated spermatogonia, which might serve as an adjuvant approach to preserving male fertility among cancer patients.

DESIGN

Laboratory animal study.

SETTING

University.

ANIMAL(S)

Laboratory mice.

INTERVENTION(S)

Five-week-old mice were treated with a sterilizing busulfan dose and with 7 days of G-CSF or vehicle treatment and evaluated 10 weeks later (experiment 1) or 24 hours after treatment (experiment 2).

MAIN OUTCOME MEASURE(S)

Experiment 1: testis weights, epididymal sperm counts, testis histology. Experiment 2: PLZF immunofluorescent costaining with apoptotic markers. Molecular analysis of G-CSF receptor expression in undifferentiated spermatogonia.

RESULT(S)

Ten weeks after treatment, busulfan-treated mice that also received treatment with G-CSF exhibited significantly better recovery of spermatogenesis and epididymal sperm counts than animals receiving busulfan alone. G-CSF led to increased numbers of PLZF+ spermatogonia 24 hours after treatment that was not accompanied by changes in apoptosis. To address the cellular target of G-CSF, mRNA for the G-CSF receptor, Csf3r, was found in adult mouse testes and cultured THY1+ (undifferentiated) spermatogonia, and cell-surface localized CSF3R was observed on 3% of cultured THY1+ spermatogonia.

CONCLUSION(S)

These results demonstrate that G-CSF protects spermatogenesis from gonadotoxic insult (busulfan) in rodents, and this may occur via direct action on CSF3R+ undifferentiated spermatogonia. G-CSF treatment might be an effective adjuvant therapy to preserve male fertility in cancer patients receiving sterilizing treatments.

Testicular tissue cryopreservation in prepubertal male children: an analysis of parental decision-making

BACKGROUND

Infertility is an unfortunate treatment-related consequence for some pediatric malignancies as well as some non-malignant conditions treated with stem cell transplant. Unlike pubertal males, prepubertal males cannot produce semen for cryopreservation. This manuscript reports on the acceptability and safety of a multi-institutional protocol for offering testicular tissue cryopreservation to families of prepubertal male children at highest risk for infertility. Data on decision influences, decision-making control, and emotional state when considering this option are described.

PROCEDURE

Prepubertal males facing gonadotoxic therapy were offered testicular cryopreservation. Post-biopsy, patients were followed for acute side effects. In addition, parents and patients were asked to complete questionnaires, whether or not they chose to cryopreserve tissue.

RESULTS

Seventy-four prepubertal male children were approached. Fifty-seven families (77%) consented to the testicular biopsy; 48 of 57 underwent the procedure. There was one post-operative side effect. Parents who agreed to testicular cryopreservation and those that did not felt in control of this decision. Parents who consented to the biopsy and refusers were not deterred by the experimental nature of the protocol. An important decision-making influence was the risk of the biopsy.

CONCLUSION

Biopsy and cryopreservation of testicular tissue from prepubertal male children was performed successfully and safely at three institutions. Parents faced with this option at diagnosis can make an informed decision and weigh carefully the risks and benefits. Although asked to make a decision soon after they were given a difficult diagnosis, parents uniformly felt in control of this decision.

Adult somatic cells to the rescue: nuclear reprogramming and the dispensability of gonadal germ cells

With advances in cancer therapies, survival rates in prepubescent patients have steadily increased. However, a number of these surviving patients have been rendered sterile owing to their rigorous oncologic treatment regimens. In addition to cancer treatments, men and women, who are genetically fertile, can become infertile owing to immune suppression treatments, exposure to environmental and industrial toxicants, and injury. Notwithstanding the great emotional burden from an inability to conceive a child with their partner, the financial burdens for testing and treatment are high, and successful treatment of these patients' sterility is rare. Recent advances in pluripotent stem cell differentiation and the generation of patient-specific, induced pluripotent stem cells indicate that stem cell replacement therapies or in vitro differentiation followed by IVF may be on the horizon. Here we discuss these recent advances, their relevance to treating male-factor and female-factor infertility, and what experimental procedures must be carried out in animal models before these exciting new treatments can be used in a clinical setting. The goal of this research is to generate functional gametes from no greater starting material than a mere skin biopsy.

Germline stem cells: toward the regeneration of spermatogenesis

Improved therapies for cancer and other conditions have resulted in a growing population of long-term survivors. Infertility is an unfortunate side effect of some cancer therapies that impacts the quality of life of survivors who are in their reproductive or prereproductive years. Some of these patients have the opportunity to preserve their fertility using standard technologies that include sperm, egg, or embryo banking, followed by IVF and/or ET. However, these options are not available to all patients, especially the prepubertal patients who are not yet producing mature gametes. For these patients, there are several stem cell technologies in the research pipeline that may give rise to new fertility options and allow infertile patients to have their own biological children. We will review the role of stem cells in normal spermatogenesis as well as experimental stem cell-based techniques that may have potential to generate or regenerate spermatogenesis and sperm. We will present these technologies in the context of the fertility preservation paradigm, but we anticipate that they will have broad implications for the assisted reproduction field.

Stem cell therapy for male infertility takes a step forward

The feasibility of using spermatogonial stem cells (SSCs) for cell-based infertility treatment has suffered from a lack of evidence in a preclinical nonhuman primate model. In this issue, Hermann et al. (2012) demonstrate that autologous and allogeneic transplantation of SSCs in testes of rhesus macaques produced functional sperm.

Expanding access to testicular tissue cryopreservation: an analysis by analogy

Researchers are developing a fertility preservation technique--testicular tissue cryopreservation (TTCP)--for prepubescent boys who may become infertile as a result of their cancer treatment. Although this technique is still in development, some researchers are calling for its widespread use. They argue that if boys do not bank their tissue now, they will be unable to benefit from any therapies that might be developed in the future. There are, however, risks involved with increasing access to an investigational procedure. This article examines four methods of expanding access to TTCP: (1) expansion of institutional review board (IRB)-approved research trials; (2) offering TTCP as an innovative procedure in hospitals; (3) offering TTCP as a standard practice in hospitals; and (4) commercialization of TTCP. The ethical and practical implications of each are evaluated through a comparison with umbilical cord blood banking (UCBB), a technology that has achieved widespread use based on similar claims of future benefit.

Spermatogonial stem cell transplantation into rhesus testes regenerates spermatogenesis producing functional sperm

Spermatogonial stem cells (SSCs) maintain spermatogenesis throughout a man's life and may have application for treating some cases of male infertility, including those caused by chemotherapy before puberty. We performed autologous and allogeneic SSC transplantations into the testes of 18 adult and 5 prepubertal recipient macaques that were rendered infertile with alkylating chemotherapy. After autologous transplant, the donor genotype from lentivirus-marked SSCs was evident in the ejaculated sperm of 9/12 adult and 3/5 prepubertal recipients after they reached maturity. Allogeneic transplant led to donor-recipient chimerism in sperm from 2/6 adult recipients. Ejaculated sperm from one recipient transplanted with allogeneic donor SSCs were injected into 85 rhesus oocytes via intracytoplasmic sperm injection. Eighty-one oocytes were fertilized, producing embryos ranging from four-cell to blastocyst with donor paternal origin confirmed in 7/81 embryos. This demonstration of functional donor spermatogenesis following SSC transplantation in primates is an important milestone for informed clinical translation.

Stem cell interaction with somatic niche may hold the key to fertility restoration in cancer patients

The spontaneous return of fertility after bone marrow transplantation or heterotopic grafting of cryopreserved ovarian cortical tissue has surprised many, and a possible link with stem cells has been proposed. We have reviewed the available literature on ovarian stem cells in adult mammalian ovaries and presented a model that proposes that the ovary harbors two distinct populations of stem cells, namely, pluripotent, quiescent, very small embryonic-like stem cells (VSELs), and slightly larger “progenitor” ovarian germ stem cells (OGSCs). Besides compromising the somatic niche, oncotherapy destroys OGSCs since, like tumor cells, they are actively dividing; however VSELs persist since they are relatively quiescent. BMT or transplanted ovarian cortical tissue may help rejuvenate the ovarian niche, which possibly supports differentiation of persisting VSELs resulting in neo-oogenesis and follicular development responsible for successful pregnancies. Postnatal oogenesis in mammalian ovary from VSELs may be exploited for fertility restoration in cancer survivors including those who were earlier deprived of gametes and/or gonadal tissue cryopreservation options.