Generation of macaques with sperm derived from juvenile monkey testicular xenografts

Male Infertility: New Developments, Current Challenges, and Future Directions

There have been many significant scientific advances in the diagnostics and treatment modalities in the field of male infertility in recent decades. Examples of these include assisted reproductive technologies, sperm selection techniques for intracytoplasmic sperm injection, surgical procedures for sperm retrieval, and novel tests of sperm function. However, there is certainly a need for new developments in this field. In this review, we discuss advances in the management of male infertility, such as seminal oxidative stress testing, sperm DNA fragmentation testing, genetic and epigenetic tests, genetic manipulations, artificial intelligence, personalized medicine, and telemedicine. The role of the reproductive urologist will continue to expand in future years to address different topzics related to diverse questions and controversies of pathophysiology, diagnosis, and therapy of male infertility, training researchers and physicians in medical and scientific research in reproductive urology/andrology, and further development of andrology as an independent specialty.

Preservation of fertility in female and male prepubertal patients diagnosed with cancer

Over the past two decades, the importance of fertility preservation has grown not only in the realm of medical and clinical patient care, but also in the field of basic and applied research in human reproduction. With advancements in cancer treatments resulting in higher rates of patient survival, it is crucial to consider the quality of life post-cure. Therefore, fertility preservation must be taken into account prior to antitumor treatments, as it can significantly impact a patient's future fertility. For postpubertal patients, gamete cryopreservation is the most commonly employed preservation strategy. However, for prepubertal patients, the situation is more intricate. Presently, ovarian tissue cryopreservation is the standard practice for prepubertal girls, but further scientific evidence is required in several aspects. Testicular tissue cryopreservation, on the other hand, is still experimental for prepubertal boys. The primary aim of this review is to address the strategies available for possible fertility preservation in prepubertal girls and boys, such as ovarian cryopreservation/transplantation, in vitro follicle culture and meiotic maturation, artificial ovary, transplantation of cryopreserved spermatogonia, and cryopreservation/grafting of immature testicular tissue and testicular organoids.

Live birth of chimeric monkey with high contribution from embryonic stem cells

A formal demonstration that mammalian pluripotent stem cells possess preimplantation embryonic cell-like (naive) pluripotency is the generation of chimeric animals through early embryo complementation with homologous cells. Whereas such naive pluripotency has been well demonstrated in rodents, poor chimerism has been achieved in other species including non-human primates due to the inability of the donor cells to match the developmental state of the host embryos. Here, we have systematically tested various culture conditions for establishing monkey naive embryonic stem cells and optimized the procedures for chimeric embryo culture. This approach generated an aborted fetus and a live chimeric monkey with high donor cell contribution. A stringent characterization pipeline demonstrated that donor cells efficiently (up to 90%) incorporated into various tissues (including the gonads and placenta) of the chimeric monkeys. Our results have major implications for the study of primate naive pluripotency and genetic engineering of non-human primates.

Rhesus monkeys exhibiting spontaneous ritualistic behaviors resembling obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic and debilitating psychiatric disorder that affects ∼2%-3% of the population globally. Studying spontaneous OCD-like behaviors in non-human primates may improve our understanding of the disorder. In large rhesus monkey colonies, we found 10 monkeys spontaneously exhibiting persistent sequential motor behaviors (SMBs) in individual-specific sequences that were repetitive, time-consuming and stable over prolonged periods. Genetic analysis revealed severely damaging mutations in genes associated with OCD risk in humans. Brain imaging showed that monkeys with SMBs had larger gray matter (GM) volumes in the left caudate nucleus and lower fractional anisotropy of the corpus callosum. The GM volume of the left caudate nucleus correlated positively with the daily duration of SMBs. Notably, exposure to a stressor (human presence) significantly increased SMBs. In addition, fluoxetine, a serotonergic medication commonly used for OCD, decreased SMBs in these monkeys. These findings provide a novel foundation for developing better understanding and treatment of OCD.

Optimizing Immature Testicular Tissue and Cell Transplantation Results: Comparing Transplantation Sites and Scaffolds

For patients who had testicular tissue cryopreserved before receiving gonadotoxic therapies, transplantation of testicular tissues and cells has been recommended as a potential therapeutic option. There are no studies that indicate the generation of sperm after human immature testicular tissue (ITT) or spermatogonial stem cells (SSCs) transplantation. The use of releasing scaffolds and localized drug delivery systems as well as the optimizing transplantation site can play an effective role in increasing the efficiency and improving the quality of testicular tissue and cell transplantation in animal models. Current research is focused on optimizing ITT and cell transplantation, the use of releasing scaffolds, and the selection of the right transplantation site that might restore sperm production or male infertility treatment. By searching the PubMed and Google Scholar databases, original and review papers were collected. Search terms were relevant for SSCs and tissue transplantation. In this review, we'll focus on the potential advantages of using scaffolds and choosing the right transplantation site to improve transplantation outcomes.

Generation of inactivated IL2RG and RAG1 monkeys with severe combined immunodeficiency using base editing

Severe combined immunodeficiency (SCID) encompasses a range of inherited disorders that lead to a profound deterioration of the immune system. Among the pivotal genes associated with SCID, RAG1 and IL2RG play crucial roles. IL2RG is essential for the development, differentiation, and functioning of T, B, and NK cells, while RAG1 critically contributes to adaptive immunity by facilitating V(D)J recombination during the maturation of lymphocytes. Animal models carrying mutations in these genes exhibit notable deficiencies in their immune systems. Non-human primates (NHPs) are exceptionally well-suited models for biomedical research due to their genetic and physiological similarities to humans. Cytosine base editors (CBEs) serve as powerful tools for precisely and effectively modifying single-base mutations in the genome. Their successful implementation has been demonstrated in human cells, mice, and crop species. This study outlines the creation of an immunodeficient monkey model by deactivating both the IL2RG and RAG1 genes using the CBE4max system. The base-edited monkeys exhibited a severely compromised immune system characterized by lymphopenia, atrophy of lymphoid organs, and a deficiency of mature T cells. Furthermore, these base-edited monkeys were capable of hosting and supporting the growth of human breast cancer cells, leading to tumor formation. In summary, we have successfully developed an immunodeficient monkey model with the ability to foster tumor growth using the CBE4max system. These immunodeficiency monkeys show tremendous potential as valuable tools for advancing biomedical and translational research.

Fertility preservation in pediatric healthcare: a review

Survival rates for children and adolescents diagnosed with malignancy have been steadily increasing due to advances in oncology treatments. These treatments can have a toxic effect on the gonads. Currently, oocyte and sperm cryopreservation are recognized as well-established and successful strategies for fertility preservation for pubertal patients, while the use of gonadotropin-releasing hormone agonists for ovarian protection is controversial. For prepubertal girls, ovarian tissue cryopreservation is the sole option. However, the endocrinological and reproductive outcomes after ovarian tissue transplantation are highly heterogeneous. On the other hand, immature testicular tissue cryopreservation remains the only alternative for prepubertal boys, yet it is still experimental. Although there are several published guidelines for navigating fertility preservation for pediatric and adolescent patients as well as transgender populations, it is still restricted in clinical practice. This review aims to discuss the indications and clinical outcomes of fertility preservation. We also discuss the probably effective and efficient workflow to facilitate fertility preservation.

The Role of Promyelocytic Leukemia Zinc Finger (PLZF) and Glial-Derived Neurotrophic Factor Family Receptor Alpha 1 (GFRα1) in the Cryopreservation of Spermatogonia Stem Cells

The cryopreservation of spermatogonia stem cells (SSCs) has been widely used as an alternative treatment for infertility. However, cryopreservation itself induces cryoinjury due to oxidative and osmotic stress, leading to reduction in the survival rate and functionality of SSCs. Glial-derived neurotrophic factor family receptor alpha 1 (GFRα1) and promyelocytic leukemia zinc finger (PLZF) are expressed during the self-renewal and differentiation of SSCs, making them key tools for identifying the functionality of SSCs. To the best of our knowledge, the involvement of GFRα1 and PLZF in determining the functionality of SSCs after cryopreservation with therapeutic intervention is limited. Therefore, the purpose of this review is to determine the role of GFRα1 and PLZF as biomarkers for evaluating the functionality of SSCs in cryopreservation with therapeutic intervention. Therapeutic intervention, such as the use of antioxidants, and enhancement in cryopreservation protocols, such as cell encapsulation, cryoprotectant agents (CPA), and equilibrium of time and temperature increase the expression of GFRα1 and PLZF, resulting in maintaining the functionality of SSCs. In conclusion, GFRα1 and PLZF have the potential as biomarkers in cryopreservation with therapeutic intervention of SSCs to ensure the functionality of the stem cells.

Perspectives: Methods for Evaluating Primate Spermatogonial Stem Cells

Mammalian spermatogenesis is a complex, highly productive process generating millions of sperm per day. Spermatogonial stem cells (SSCs) are at the foundation of spermatogenesis and can either self-renew, producing more SSCs, or differentiate to initiate spermatogenesis and produce sperm. The biological potential of SSCs to produce and maintain spermatogenesis makes them a promising tool for the treatment of male infertility. However, translating knowledge from rodents to higher primates (monkeys and humans) is challenged by different vocabularies that are used to describe stem cells and spermatogenic lineage development in those species. Furthermore, while rodent SSCs are defined by their biological potential to produce and maintain spermatogenesis in a transplant assay, there is no equivalent routine and accessible bioassay to test monkey and human SSCs or replicate their functions in vitro. This chapter describes progress characterizing, isolating, culturing, and transplanting SSCs in higher primates.

The importance of the urologist in male oncology fertility preservation

OBJECTIVES

To demonstrate that surgical sperm retrieval (SSR) and spermatogonial stem cell retrieval (SSCR) in an oncological context are safe and successful.

PATIENTS AND METHODS

This a retrospective study in a tertiary hospital in the UK. Patients requiring fertility preservation from December 2017 to January 2020 were included. Data were analysed with Microsoft Excel 2016 and the Statistical Package for the Social Sciences (version 20).

RESULTS

Among 1264 patients referred to the Reproductive Medical Unit at the University College of London Hospitals for cryopreservation prior to gonadotoxic treatment, 39 chose to go forward with SSR/SSCR because they presented as azoo-/cryptozoospermic or an inability to masturbate/ejaculate. Interventions were testicular sperm extraction (23 patients) or aspiration (one), electroejaculation (one), and testicular wedge biopsy for SSCR (14). The median (range) age was 15.0 (10-65) years and the median testosterone level was 4.4 nmoL/L. Primary diagnoses were sarcoma in 11 patients, leukaemia in nine, lymphoma in eight, testicular tumour in five, other oncological haematological entities in two, other solid cancers in two, while two patients had non-oncological haematological diseases. SSR/SSCR could be offered within 7.5 days on average. Chemotherapy could follow within 2 days from SSR/SSCR, and bone marrow transplant occurred within 19.5 days (all expressed as medians). The success rate for SSR was 68.0% (at least one vial/straw collected). The mean (SD) Johnsen score of testicular biopsies was 5.23 (2.25) with a trend towards positive correlation with SSR success (P = 0.07). However, age, hormonal profile and type of cancer did not predict SSR outcome.

CONCLUSION

We show that SSR and SSCR in an oncological context are valid treatment options with a high success rate for patients in which sperm cryopreservation from semen is impossible. By providing an effective pathway, fertility preservation is possible with minimal delay to oncological treatment.

Testis and brown adipose tissue xenografts from yellowish myotis (Myotis levis)

Yellowish myotis present a seasonal reproduction, influenced by rainfall distribution, in which the testis mass, germ cell composition, and brown adipose tissue mass change along the reproductive stages. In the present study, tissue xenografts were performed in immunodeficient mice to investigate spermatogenesis development in a stable endocrine milieu and the possible androgenic role of brown adipose tissue. Forty-one adult male bats were captured in the Santuário do Caraça, Minas Gerais, Brazil. The gonads and brown adipose tissue were collected, weighed, and grafted under the mice's back skin. Mice biometric and hormonal data were evaluated after grafting, and the testis grafts and mice gonads were fixed for histological and immunohistochemical analyses. As a result, testis grafts from adult bats presented a continuous germ cell development in all reproductive phases, showing round spermatids in all testis tissues. Furthermore, testis fragments in the Rest stage presented elongating spermatids as the most advanced germ cell type in the seminiferous epithelium after seven months of grafting. These data indicated that yellowish myotis spermatogenesis could be continued (presenting a constant spermatogonial differentiation) in a stable endocrine milieu, as found in mice. In addition, the best spermatogenic development was achieved when testis fragments were transplanted at their lowest activity (Rest stage). Regarding the brown adipose tissue grafts, the adipose tissue consumption by mice increased seminal vesicle mass and testosterone serum levels. This data proved that the brown adipose tissue is related to testosterone synthesis, which may be critical in stimulating the differentiation of spermatogonia in yellowish myotis.

Gene editing monkeys: Retrospect and outlook

Animal models play a key role in life science research, especially in the study of human disease pathogenesis and drug screening. Because of the closer proximity to humans in terms of genetic evolution, physiology, immunology, biochemistry, and pathology, nonhuman primates (NHPs) have outstanding advantages in model construction for disease mechanism study and drug development. In terms of animal model construction, gene editing technology has been widely applied to this area in recent years. This review summarizes the current progress in the establishment of NHPs using gene editing technology, which mainly focuses on rhesus and cynomolgus monkeys. In addition, we discuss the limiting factors in the applications of genetically modified NHP models as well as the possible solutions and improvements. Furthermore, we highlight the prospects and challenges of the gene-edited NHP models.

What should be done in terms of fertility preservation for patients with cancer? The French 2021 guidelines

AIM

To provide practice guidelines about fertility preservation (FP) in oncology.

METHODS

We selected 400 articles after a PubMed review of the literature (1987-2019).

RECOMMENDATIONS

Any child, adolescent and adult of reproductive age should be informed about the risk of treatment gonadotoxicity. In women, systematically proposed FP counselling between 15 and 38 years of age in case of treatment including bifunctional alkylating agents, above 6 g/m2 cyclophosphamide equivalent dose (CED), and for radiation doses on the ovaries ≥3 Gy. For postmenarchal patients, oocyte cryopreservation after ovarian stimulation is the first-line FP technique. Ovarian tissue cryopreservation should be discussed as a first-line approach in case of treatment with a high gonadotoxic risk, when chemotherapy has already started and in urgent cases. Ovarian transposition is to be discussed prior to pelvic radiotherapy involving a high risk of premature ovarian failure. For prepubertal girls, ovarian tissue cryopreservation should be proposed in the case of treatment with a high gonadotoxic risk. In pubertal males, sperm cryopreservation must be systematically offered to any male who is to undergo cancer treatment, regardless of toxicity. Testicular tissue cryopreservation must be proposed in males unable to cryopreserve sperm who are to undergo a treatment with intermediate or severe risk of gonadotoxicity. In prepubertal boys, testicular tissue preservation is: - recommended for chemotherapy with a CED ≥7500 mg/m2 or radiotherapy ≥3 Gy on both testicles. - proposed for chemotherapy with a CED ≥5.000 mg/m2 or radiotherapy ≥2 Gy. If several possible strategies, the ultimate choice is made by the patient.

A synopsis of global frontiers in fertility preservation

Since 2007, the Oncofertility Consortium Annual Conference has brought together a diverse network of individuals from a wide range of backgrounds and professional levels to disseminate emerging basic and clinical research findings in fertility preservation. This network also developed enduring educational materials to accelerate the pace and quality of field-wide scientific communication. Between 2007 and 2019, the Oncofertility Consortium Annual Conference was held as an in-person event in Chicago, IL. The conference attracted approximately 250 attendees each year representing 20 countries around the world. In 2020, however, the COVID-19 pandemic disrupted this paradigm and precluded an in-person meeting. Nevertheless, there remained an undeniable demand for the oncofertility community to convene. To maintain the momentum of the field, the Oncofertility Consortium hosted a day-long virtual meeting on March 5, 2021, with the theme of "Oncofertility Around the Globe" to highlight the diversity of clinical care and translational research that is ongoing around the world in this discipline. This virtual meeting was hosted using the vFairs ® conference platform and allowed over 700 people to participate, many of whom were first-time conference attendees. The agenda featured concurrent sessions from presenters in six continents which provided attendees a complete overview of the field and furthered our mission to create a global community of oncofertility practice. This paper provides a synopsis of talks delivered at this event and highlights the new advances and frontiers in the fields of oncofertility and fertility preservation around the globe from clinical practice and patient-centered efforts to translational research.

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.

Spermatogonial Stem Cell-Based Therapies: Taking Preclinical Research to the Next Level

Fertility preservation via biobanking of testicular tissue retrieved from testicular biopsies is now generally recommended for boys who need to undergo gonadotoxic treatment prior to the onset of puberty, as a source of spermatogonial stem cells (SSCs). SSCs have the potential of forming spermatids and may be used for therapeutic fertility approaches later in life. Although in the past 30 years many milestones have been reached to work towards SSC-based fertility restoration therapies, including transplantation of SSCs, grafting of testicular tissue and various in vitro and ex vivo spermatogenesis approaches, unfortunately, all these fertility therapies are still in a preclinical phase and not yet available for patients who have become infertile because of their treatment during childhood. Therefore, it is now time to take the preclinical research towards SSC-based therapy to the next level to resolve major issues that impede clinical implementation. This review gives an outline of the state of the art of the effectiveness and safety of fertility preservation and SSC-based therapies and addresses the hurdles that need to be taken for optimal progression towards actual clinical implementation of safe and effective SSC-based fertility treatments in the near future.

Fertility preservation in boys facing gonadotoxic cancer therapy

Patient survival following childhood cancer has increased with contemporary radiation and chemotherapy techniques. However, gonadotoxicity associated with treatments means that infertility is a common consequence in survivors. Novel fertility preservation options are emerging, but knowledge about these options amongst urologists and other medical professionals is lacking. Pre-pubertal boys generally do not produce haploid germ cells. Thus, strategies for fertility preservation require cryopreservation of tissue containing spermatogonial stem cells (SSCs). Few centres worldwide routinely offer this option and fertility restoration (including testicular tissue engraftment, autotransplantation of SSCs and in vitro maturation of SSCs to spermatozoa) post-thaw is experimental. In pubertal boys, the main option for fertility preservation is masturbation and cryopreservation of the ejaculate. Assisted ejaculation using penile vibratory stimulation or electroejaculation and surgical sperm retrieval can be used in a sequential manner after failed masturbation. Physicians should inform boys and parents about the gonadotoxic effects of cancer treatment and offer fertility preservation. Preclinical experience has identified challenges in pre-pubertal fertility preservation, but available options are expected to be successful when today's pre-pubertal boys with cancer become adults. By contrast, fertility preservation in pubertal boys is clinically proven and should be offered to all patients undergoing cancer treatment.

OUP accepted manuscript

The pathways of gametogenesis encompass elaborate cellular specialization accompanied by precise partitioning of the genome content in order to produce fully matured spermatozoa and oocytes. Transcription factors are an important class of molecules that function in gametogenesis to regulate intrinsic gene expression programs, play essential roles in specifying (or determining) germ cell fate and assist in guiding full maturation of germ cells and maintenance of their populations. Moreover, in order to reinforce or redirect cell fate in vitro, it is transcription factors that are most frequently induced, over-expressed or activated. Many reviews have focused on the molecular development and genetics of gametogenesis, in vivo and in vitro, in model organisms and in humans, including several recent comprehensive reviews: here, we focus specifically on the role of transcription factors. Recent advances in stem cell biology and multi-omic studies have enabled deeper investigation into the unique transcriptional mechanisms of human reproductive development. Moreover, as methods continually improve, in vitro differentiation of germ cells can provide the platform for robust gain- and loss-of-function genetic analyses. These analyses are delineating unique and shared human germ cell transcriptional network components that, together with somatic lineage specifiers and pluripotency transcription factors, function in transitions from pluripotent stem cells to gametes. This grand theme review offers additional insight into human infertility and reproductive disorders that are linked predominantly to defects in the transcription factor networks and thus may potentially contribute to the development of novel treatments for infertility.

Fertility Preservation and Restoration Options for Pre-Pubertal Male Cancer Patients: Current Approaches

Fertility preservation for prepubertal male patients undergoing gonadotoxic therapies, potentially depleting spermatogonial cells, is an expanding necessity, yet most of the feasible options are still in the experimental phase. We present our experience and a summary of current and novel possibilities regarding the different strategies to protect or restore fertility in young male patients, before proceeding with chemotherapy or radiotherapy for malignances or other diseases. Adult oncological patients should always be counselled to cryopreserve the semen before starting treatment, however this approach is not suitable for prepubertal boys, who aren't capable to produce sperm yet. Fortunately, since the survival rate of pediatric cancer patients has skyrocketed in the last decade and it's over 84%, safeguarding their future fertility is becoming a major concern for reproductive medicine. Surgical and medical approaches to personalize treatment or protect the gonads could be a valid first step to take. Testicular tissue autologous grafting or xenografting, and spermatogonial stem cells (SSCs) transplantation, are the main experimental options available, but spermatogenesis in vitro is becoming an intriguing alternative. All of these methods feature both strong and weak prospects. There is also relevant controversy regarding the type of testicular material to preserve and the cryopreservation methods. Since transplanted cells are bound to survive based on SSCs number, many ways to enrich their population in cultures have been proposed, as well as different sites of injection inside the testis. Testicular tissue graft has been experimented on mice, rabbits, rhesus macaques and porcine, allowing the birth of live offspring after performing intracytoplasmic sperm injection (ICSI), however it has never been performed on human males yet. In vitro spermatogenesis remains a mirage, although many steps in the right direction have been performed. The manufacturing of 3D scaffolds and artificial spermatogenetic niche, providing support to stem cells in cultures, seems like the best way to further advance in this field.

Transplantation of rat frozen-thawed testicular tissues: Does fragment size matter?

Cryopreservation of testicular tissue from pre-pubertal boys before gonadotoxic treatment is an important step in fertility preservation. Yet, this approach remains experimental, and there is still few study measuring the effect of tissue size on the graft after cryopreservation and transplantation. The objective of this study is to detect the effect of varying tissue sizes on the efficacy of rat testicular tissue cryopreservation and transplantation. Varying sizes of rat testicular tissues were frozen-thawed and autografted. At the 30th day after grafting, the grafts were collected for histology assessment and immunohistochemistry assay for MAGE-A4 (germ cell marker) and CD34 (blood vessel marker). The transplant recovery, seminiferous tubule integrity, tubular diameter, spermatogonia number, and microsvessel density in testicular fragments sizing in 3 mm in length, 3 mm wide, and 3 mm in thickness were significantly lower than other groups. Whereas, the absorption rate of graft sizing in 1 mm in length, 1 mm in wide, and 1 mm in thickness was significantly higher than other groups. Testicular fragment sizing in 2-3 mm in length, 2-3 mm in wide, and 2 mm in thickness (8 mm³-18 mm³) is suitable for rat testicular tissue cryopreservation and transplantation.

Analysis of developmental imprinting dynamics in primates using SNP-free methods to identify imprinting defects in cloned placenta

Our knowledge of genomic imprinting in primates is lagging behind that of mice largely because of the difficulties of allelic analyses in outbred animals. To understand imprinting dynamics in primates, we profiled transcriptomes, DNA methylomes, and H3K27me3 in uniparental monkey embryos. We further developed single-nucleotide-polymorphism (SNP)-free methods, TARSII and CARSII, to identify germline differentially methylated regions (DMRs) in somatic tissues. Our comprehensive analyses showed that allelic DNA methylation, but not H3K27me3, is a major mark that correlates with paternal-biasedly expressed genes (PEGs) in uniparental monkey embryos. Interestingly, primate germline DMRs are different from PEG-associated DMRs in early embryos and are enriched in placenta. Strikingly, most placenta-specific germline DMRs are lost in placenta of cloned monkeys. Collectively, our study establishes SNP-free germline DMR identification methods, defines developmental imprinting dynamics in primates, and demonstrates imprinting defects in cloned monkey placenta, which provides important clues for improving primate cloning.

Mammalian in vitro gametogenesis

[Figure: see text].

Establishment of a Pediatric Ovarian and Testicular Cryopreservation Program for Malignant and Non-Malignant Conditions: The Mayo Clinic Experience

STUDY OBJECTIVES

To describe the structure of a pediatric fertility preservation (FP) program and to share safety and patient satisfaction data.

DESIGN

The FP program operates under prospective research protocols approved by the Mayo Clinic Institutional Review Board (IRB).

SETTING

The FP program is a multidisciplinary effort between pediatric gynecology, reproductive endocrinology, pediatric urology, pediatric surgery, and laboratory medicine.

PARTICIPANTS

The FP program enrolls patients between 0-17 years of age who have been diagnosed with a fertility-threatening condition and/or are scheduled to undergo gonadotoxic treatment.

INTERVENTIONS

FP is offered in the form of ovarian tissue cryopreservation (OTC) and testicular (TTC) tissue cryopreservation.

MAIN OUTCOME MEASURES

The outcome measures are the safety of the procedure and results of patient surveys conducted by phone using a standard list of questions to assess attitudes towards FP.

RESULTS

To date, we have enrolled 38 OTC and 37 TTC patients. The median age (range) of OTC and TTC patients was 11 years (0.83-17 years) and 10 years (0.92-17 years) at the time of enrollment, respectively. Childhood cancers currently represent 88% of the fertility-threatening diagnoses. Meanwhile, patients with non-malignant conditions include those with gender dysphoria, aplastic anemia, and Turner's syndrome. To date, no serious adverse events (SAEs) have been reported following surgery. According to n = 34 one-year follow-ups, 100% of parents felt that FP was a good decision.

CONCLUSION

Consistent with the literature, our data suggests FP is safe and improves the quality of care provided to pediatric patients for their fertility-threatening diagnoses and/or treatments.

TRIAL REGISTRATION

NCT02872532, NCT02646384.

Targeting against the activity of the NLRP3 inflammasome is a potential therapy for rat testicular tissue cryopreservation and transplantation

The objective of the present experiment was to explore the role of NLRP3 inflammasome in the testicular tissue freezing, thawing and grafting; furthermore, the potential effect of a NLRP3 inhibitor on the function of testis transplant was explored. Tissues from male Wistar rats in pre-pubertal age were cryopreserved, thawed and auto-transplanted into the scrotum treated or not treated with the MCC950 (a NLRP3 inhibitor). After grafting, cryopreserved tissue was removed and analysed. Quantitative morphometric, immunohistochemical techniques and Western blotting were used to evaluate the survival of spermatogonia and the activation of the NLRP3 inflammasome after freezing/thawing/grafting. Moreover, serum IL-1β level was assessed with ELISA kits. The testicular transplants exhibited upregulated expression of the NLRP3 pathway meditors (NLRP3, IL-1β). In NLRP3 inhibition group, the rate of recovered grafts, the percentage of intact tubules and spermatogonial number were significantly higher than that in cryopreserved graft group. Moreover, serum concentration of IL-1β in NLRP3 inhibition group was significantly lower than that in cryopreserved graft group. Testicular tissue cryopreservation and transplantation exhibited upregulated expression of NLRP3 pathway and NLRP3 inflammasome blockade improves testicular graft function. These finding suggest that NLRP3 inflammasome is a therapeutic target for testicular tissue cryopreservation and transplantation.

Recent advances: fertility preservation and fertility restoration options for males and females

Fertility preservation is the process of saving gametes, embryos, gonadal tissues and/or gonadal cells for individuals who are at risk of infertility due to disease, medical treatments, age, genetics, or other circumstances. Adult patients have the options to preserve eggs, sperm, or embryos that can be used in the future to produce biologically related offspring with assisted reproductive technologies. These options are not available to all adults or to children who are not yet producing mature eggs or sperm. Gonadal cells/tissues have been frozen for several thousands of those patients worldwide with anticipation that new reproductive technologies will be available in the future. Therefore, the fertility preservation medical and research communities are obligated to responsibly develop next-generation reproductive technologies and translate them into clinical practice. We briefly describe standard options to preserve and restore fertility, but the emphasis of this review is on experimental options, including an assessment of readiness for translation to the human fertility clinic.

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

Avascular transplantation of frozen-thawed testicular tissue fragments represents a potential future technique for fertility restoration in boys with cancer. A significant loss of spermatogonia was observed in xeno-transplants of human tissue most likely due to the hypoxic period before revascularization. To reduce the effect of hypoxia-reoxygenation injuries, several options have already been explored, like encapsulation in alginate hydrogel and supplementation with nanoparticles delivering a necrosis inhibitor (NECINH) or VEGF. While these approaches improved short-term (5 days) vascular surfaces in grafts, neovessels were not maintained up to 21 days; i.e., the time needed for achieving vessel stabilization. To better support tissue grafts, nanoparticles loaded with VEGF, PDGF and NECINH were developed. Testicular tissue fragments from 4-5-week-old mice were encapsulated in calcium-alginate hydrogels, either non-supplemented (control) or supplemented with drug-loaded nanoparticles (VEGF-nanoparticles; VEGF-nanoparticles + PDGF-nanoparticles; NECINH-nanoparticles; VEGF-nanoparticles + NECINH-nanoparticles; and VEGF-nanoparticles + PDGF-nanoparticles + NECINH-nanoparticles) before auto-transplantation. Grafts were recovered after 5 or 21 days for analyses of tissue integrity (hematoxylin-eosin staining), spermatogonial survival (immuno-histo-chemistry for promyelocytic leukemia zinc finger) and vascularization (immuno-histo-chemistry for α-smooth muscle actin and CD-31). Our results showed that a combination of VEGF and PDGF nanoparticles increased vascular maturity and induced a faster maturation of vascular structures in grafts.

Pediatric and Adolescent Oncofertility in Male Patients-From Alpha to Omega

This article reviews the latest information about preserving reproductive potential that can offer enhanced prospects for future conception in the pediatric male population with cancer, whose fertility is threatened because of the gonadotoxic effects of chemotherapy and radiation. An estimated 400,000 children and adolescents aged 0–19 years will be diagnosed with cancer each year. Fertility is compromised in one-third of adult male survivors of childhood cancer. We present the latest approaches and techniques for fertility preservation, starting with fertility preservation counselling, a clinical practice guideline used around the world and finishing with recent advances in basic science and translational research. Improving strategies for the maturation of germ cells in vitro combined with new molecular techniques for gene editing could be the next scientific keystone to eradicate genetic diseases such as cancer related mutations in the offspring of cancer survivors.

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.

Generation and Breeding of EGFP-Transgenic Marmoset Monkeys: Cell Chimerism and Implications for Disease Modeling

Genetic modification of non-human primates (NHP) paves the way for realistic disease models. The common marmoset is a NHP species increasingly used in biomedical research. Despite the invention of RNA-guided nucleases, one strategy for protein overexpression in NHP is still lentiviral transduction. We generated three male and one female enhanced green fluorescent protein (EGFP)-transgenic founder marmosets via lentiviral transduction of natural preimplantation embryos. All founders accomplished germline transmission of the transgene by natural mating, yielding 20 transgenic offspring together (in total, 45 pups; 44% transgenic). This demonstrates that the transgenic gametes are capable of natural fertilization even when in competition with wildtype gametes. Importantly, 90% of the transgenic offspring showed transgene silencing, which is in sharp contrast to rodents, where the identical transgene facilitated robust EGFP expression. Furthermore, we consistently discovered somatic, but so far, no germ cell chimerism in mixed wildtype/transgenic litters. Somatic cell chimerism resulted in false-positive genotyping of the respective wildtype littermates. For the discrimination of transgenic from transgene-chimeric animals by polymerase chain reaction on skin samples, a chimeric cell depletion protocol was established. In summary, it is possible to establish a cohort of genetically modified marmosets by natural mating, but specific requirements including careful promoter selection are essential.

Generation of nonhuman primate retinitis pigmentosa model by in situ knockout of RHO in rhesus macaque retina

Retinitis pigmentosa (RP) is a form of inherited retinal degenerative diseases that ultimately involves the macula, which is present in primates but not in the rodents. Therefore, creating nonhuman primate (NHP) models of RP is of critical importance to study its mechanism of pathogenesis and to evaluate potential therapeutic options in the future. Here we applied adeno-associated virus (AAV)-delivered CRISPR/SaCas9 technology to knockout the RHO gene in the retinae of the adult rhesus macaque (Macaca mulatta) to investigate the hypothesis whether non-germline mutation of the RHO gene is sufficient to recapitulate RP. Through a series of studies, we were able to demonstrate successful somatic editing of the RHO gene and reduced RHO protein expression. More importantly, the mutant macaque retinae displayed clinical RP phenotypes, including photoreceptor degeneration, retinal thinning, abnormal rod subcellular structures, and reduced photoresponse. Therefore, we suggest somatic editing of the RHO gene is able to phenocopy RP, and the reduced time span in generating NHP mutant accelerates RP research and expands the utility of NHP model for human disease study.

Fertility preservation for pediatric male cancer patients: illustrating contemporary and future options; a case report

The main aim of current pediatric male fertility preservation programs is storing spermatogonia stem cell (SSC) prior to starting cancer treatment. From July 1st, 2014 to May 1st, 2020; 170 patients have been recruited in Wake Forest Testicular Tissue Banking Program. The existence of multiple testis biopsies in different time points and detailed histological analyses of a unique cancer patient, provided an educational opportunity to investigate testis condition in different phases of cancer management. A pediatric male cancer patient with B-cell acute lymphoblastic leukemia (ALL) had multiple testicular leukemia recurrences and went through several testicular biopsies, to identify leukemic infiltration as well as considering fertility preservation. Infiltration of leukemia cells into both testes was identified. Neither elongated spermatid nor sperm were detected, but germ cells including SSC, spermatocyte and round spermatid could be identified in the stored tissue even after initial cancer treatment. Different germ cells were identified by hematoxylin and eosin (H&E) staining and specific immunohistochemical (IHC) markers including PGP9.5/UCHL1 or MAGE-A4 (spermatogonia), SYCP3 (spermatocyte) and PRM1 (round spermatid). This emphasizes the importance of offering testicular biopsy to pediatric cancer patients at risk of infertility regardless to the stage of cancer treatment, although earlier biopsy is preferred. Promising research on in vitro spermatogenesis and auto-transplantation support the practice of SSC preservation. In addition, finding and storing round spermatids isolated from testicular biopsy provides a currently available option of round spermatid injection (ROSI). Given the complexity of managing cancer while considering fertility preservation, a multidisciplinary collaboration is important to achieve optimal overall outcomes.

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.

Histologic Analysis of Testes from Prepubertal Patients Treated with Chemotherapy Associates Impaired Germ Cell Counts with Cumulative Doses of Cyclophosphamide, Ifosfamide, Cytarabine, and Asparaginase

Cryopreservation of immature testicular tissue is an experimental strategy for the preservation of fertility in prepubertal boys that will be subjected to a gonadotoxic onset, as is the case of oncologic patients. Therefore, the objective of this study was to assess the impact of chemotherapeutic treatments on the testicular histologic phenotype in prepubertal patients. A total of 56 testicular tissue samples from pediatric patients between 0 and 16 years old (28 with at least one previous chemotherapeutic onset and 28 untreated controls) were histologically analyzed and age-matched compared. At least two 5-μm sections from testis per patient separated by a distance of 100 μm were immunostained for the germ cell marker VASA, the spermatogonial markers UTF1, PLZF, UCHL1, and SALL4, the marker for proliferative cells KI67, and the Sertoli cell marker SOX9. The percentage of tubule cross-sections positive for each marker and the number of positive cells per tubule cross-section were determined and association with the cumulative dose received of each chemotherapeutic drug was statistically assessed. Results indicated that alkylating agents, cyclophosphamide and ifosfamide, but also the antimetabolite cytarabine and asparaginase were associated with a decreased percentage of positive tubules and a lower number of positive cells per tubule for the analyzed markers. Our results provide new evidences of the potential of chemotherapeutic agents previously considered to have low gonadotoxic effects such as cytarabine and asparaginase to trigger a severe testicular phenotype, hampering the potential success of future fertility restoration in experimental programs of fertility preservation in prepubertal boys.

Assessment of fresh and cryopreserved testicular tissues from (pre)pubertal boys during organ culture as a strategy for in vitro spermatogenesis

STUDY QUESTION

Can the organ culture method be applied to both fresh and cryopreserved human (pre)pubertal testicular tissue as a strategy for in vitro spermatogenesis?

SUMMARY ANSWER

Although induction of spermatogenesis was not achieved in vitro, testicular architecture, endocrine function and spermatogonial proliferation were maintained in both fresh and cryopreserved testicular tissues.

WHAT IS KNOWN ALREADY

Cryopreservation of a testicular biopsy is increasingly offered as a fertility preservation strategy for prepubertal cancer patients. One of the proposed experimental approaches to restore fertility is the organ culture method, which, in the mouse model, successfully allows for in vitro development of spermatozoa from testicular biopsies. However, complete spermatogenesis from human prepubertal testicular tissue in such an organ culture system has not been demonstrated.

STUDY DESIGN, SIZE, DURATION

Testicular tissue was collected from nine (pre)pubertal boys diagnosed with cancer (ranging from 6 to 14 years of age) admitted for fertility preservation before treatment. Testicular biopsies were either immediately processed for culture or first cryopreserved, using a controlled slow freezing protocol, and thawed before culture. Organ culture of testicular fragments was performed in two different media for a maximum period of 5 weeks, targeting early cellular events (viability, meiosis and somatic differentiation) in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Fresh and cryopreserved-thawed testis fragments (1–2 mm³) were cultured at a gas–liquid interphase (34°C, 5% CO₂) in Minimum Essential Medium alpha + 10% knock-out serum replacement medium containing 10⁻⁷ M melatonin and 10⁻⁶ M retinoic acid, with or without 3 IU/L FSH/LH supplementation. The effect of culture conditions on testicular fragments was weekly assessed by histological evaluation of germ cell development and immunohistochemical identification of spermatogonia (using MAGEA4), proliferative status of spermatogonia and Sertoli cells (using proliferating cell nuclear antigen [PCNA]), intratubular cell apoptosis (by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) and Sertoli cells maturation (using Anti-Müllerian Hormone [AMH] versus Androgen Receptor [AR]). Additionally, Leydig cells’ functionality was determined by measuring testosterone concentration in the culture media supernatants.

MAIN RESULTS AND THE ROLE OF CHANCE

Neither fresh nor cryopreserved human (pre)pubertal testicular fragments were able to initiate spermatogenesis in our organ culture system. Nonetheless, our data suggest that fresh and cryopreserved testicular fragments have comparable functionality in the described organ culture conditions, as reflected by the absence of significant differences in any of the weekly evaluated functional parameters. Additionally, no significant differences were found between the two tested media when culturing fresh and cryopreserved human testicular fragments. Although spermatogonia survived and remained proliferative in all culture conditions, a significant reduction of the spermatogonial population (P ≤ 0.001) was observed over the culture period, justified by a combined reduction of proliferation activity (P ≤ 0.001) and increased intratubular cell apoptosis (P ≤ 0.001). We observed a transient increase in Sertoli cell proliferative activity, loss of AMH expression (P ≤ 0.001) but no induction of AR expression. Leydig cell endocrine function was successfully stimulated in vitro as indicated by increased testosterone production in all conditions throughout the entire culture period (P ≤ 0.02).

LARGE SCALE DATA

N/A

LIMITATIONS, REASONS FOR CAUTION

Although not noticeable in this study, we cannot exclude that if an optimized culture method ensuring complete spermatogenesis in human testicular fragments is established, differences in functional or spermatogenic efficiency between fresh and cryopreserved tissue might be found.

WIDER IMPLICATIONS OF THE FINDINGS

The current inability to initiate spermatogenesis in vitro from cryopreserved human testicular fragments should be included in the counselling of patients who are offered testicular tissue cryopreservation to preserve fertility.

STUDY FUNDING/COMPETING INTEREST(S)

This project was funded by EU-FP7-PEOPLE-2013-ITN 603568 `Growsperm’. None of the authors have competing interests.

TRIAL REGISTRATION NUMBER

Not applicable.

Complete spermatogenesis in intratesticular testis tissue xenotransplants from immature non-human primate

STUDY QUESTION

Can full spermatogenesis be achieved after xenotransplantation of prepubertal primate testis tissue to the mouse, in testis or subcutaneously?

SUMMARY ANSWER

Intratesticular xenotransplantation supported the differentiation of immature germ cells from marmoset (Callithrix jacchus) into spermatids and spermatozoa at 4 and 9 months post-transplantation, while in subcutaneous transplants, spermatogenic arrest was observed at 4 months and none of the transplants survived at 9 months.

WHAT IS KNOWN ALREADY

Auto-transplantation of cryopreserved immature testis tissue (ITT) could be a potential fertility restoration strategy for patients with complete loss of germ cells due to chemo- and/or radiotherapy at a young age. Before ITT transplantation can be used for clinical application, it is a prerequisite to demonstrate the feasibility of the technique and identify the conditions required for establishing spermatogenesis in primate ITT transplants. Although xenotransplantation of ITT from several species has resulted in complete spermatogenesis, in human and marmoset, ITT has not been successful.

STUDY DESIGN, SIZE, DURATION

In this study, we used marmoset as a pre-clinical animal model. ITT was obtained from two 6-month-old co-twin marmosets. A total of 147 testis tissue pieces (~0.8-1.0 mm3 each) were transplanted into the testicular parenchyma (intratesticular; n = 40) or under the dorsal skin (ectopic; n = 107) of 4-week-old immunodeficient Swiss Nu/Nu mice (n = 20). Each mouse received one single marmoset testis tissue piece in each testis and 4-6 pieces subcutaneously. Xenotransplants were retrieved at 4 and 9 months post-transplantation and evaluations were performed with regards to transplant survival, spermatogonial quantity and germ cell differentiation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Transplant survival was histologically evaluated by haematoxylin-periodic acid Schiff (H/PAS) staining. Spermatogonia were identified by MAGE-A4 via immunohistochemistry. Germ cell differentiation was assessed by morphological identification of different germ cell types on H/PAS stained sections. Meiotically active germ cells were identified by BOLL expression. CREM immunohistochemistry was performed to confirm the presence of post-meiotic germ cells and ACROSIN was used to determine the presence of round, elongating and elongated spermatids.

MAIN RESULTS AND THE ROLE OF CHANCE

Four months post-transplantation, 50% of the intratesticular transplants and 21% of the ectopic transplants were recovered (P = 0.019). The number of spermatogonia per tubule did not show any variation. In 33% of the recovered intratesticular transplants, complete spermatogenesis was established. Overall, 78% of the intratesticular transplants showed post-meiotic differentiation (round spermatids, elongating/elongated spermatids and spermatozoa). However, during the same period, spermatocytes (early meiotic germ cells) were the most advanced germ cell type present in the ectopic transplants. Nine months post-transplantation, 50% of the intratesticular transplants survived, whilst none of the ectopic transplants was recovered (P < 0.0001). Transplants contained more spermatogonia per tubule (P = 0.018) than at 4 months. Complete spermatogenesis was observed in all recovered transplants (100%), indicating a progressive spermatogenic development in intratesticular transplants between the two time-points. Nine months post-transplantation, transplants contained more seminiferous tubules with post-meiotic germ cells (37 vs. 5%; P < 0.001) and fewer tubules without germ cells (2 vs. 8%; P = 0.014) compared to 4 months post-transplantation.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although xenotransplantation of marmoset ITT was successful, it does not fully reflect all aspects of a future clinical setting. Furthermore, due to ethical restrictions, we were not able to prove the functionality of the spermatozoa produced in the marmoset transplants.

WIDER IMPLICATIONS OF THE FINDINGS

In this pre-clinical study, we demonstrated that testicular parenchyma provides the required microenvironment for germ cell differentiation and long-term survival of immature marmoset testis tissue, likely due to the favourable temperature regulation, growth factors and hormonal support. These results encourage the design of new experiments on human ITT xenotransplantation and show that intratesticular transplantation is likely to be superior to ectopic transplantation for fertility restoration following gonadotoxic treatment in childhood.

STUDY FUNDING/COMPETING INTEREST(S)

This project was funded by the ITN Marie Curie Programme 'Growsperm' (EU-FP7-PEOPLE-2013-ITN 603568) and the scientific Fund Willy Gepts from the UZ Brussel (ADSI677). D.V.S. is a post-doctoral fellow of the Fonds Wetenschappelijk Onderzoek (FWO; 12M2815N). No conflict of interest is declared.

Fertility preservation in boys: recent developments and new insights †

BACKGROUND

Infertility is an important side effect of treatments used for cancer and other non-malignant conditions in males. This may be due to the loss of spermatogonial stem cells (SSCs) and/or altered functionality of testicular somatic cells (e.g. Sertoli cells, Leydig cells). Whereas sperm cryopreservation is the first-line procedure to preserve fertility in post-pubertal males, this option does not exist for prepubertal boys. For patients unable to produce sperm and at high risk of losing their fertility, testicular tissue freezing is now proposed as an alternative experimental option to safeguard their fertility.

OBJECTIVE AND RATIONALE

With this review, we aim to provide an update on clinical practices and experimental methods, as well as to describe patient management inclusion strategies used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss.

SEARCH METHODS

Based on the expertise of the participating centres and a literature search of the progress in clinical practices, patient management strategies and experimental methods used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss were identified. In addition, a survey was conducted amongst European and North American centres/networks that have published papers on their testicular tissue banking activity.

OUTCOMES

Since the first publication on murine SSC transplantation in 1994, remarkable progress has been made towards clinical application: cryopreservation protocols for testicular tissue have been developed in animal models and are now offered to patients in clinics as a still experimental procedure. Transplantation methods have been adapted for human testis, and the efficiency and safety of the technique are being evaluated in mouse and primate models. However, important practical, medical and ethical issues must be resolved before fertility restoration can be applied in the clinic.Since the previous survey conducted in 2012, the implementation of testicular tissue cryopreservation as a means to preserve the fertility of prepubertal boys has increased. Data have been collected from 24 co-ordinating centres worldwide, which are actively offering testis tissue cryobanking to safeguard the future fertility of boys. More than 1033 young patients (age range 3 months to 18 years) have already undergone testicular tissue retrieval and storage for fertility preservation.

LIMITATIONS REASONS FOR CAUTION

The review does not include the data of all reproductive centres worldwide. Other centres might be offering testicular tissue cryopreservation. Therefore, the numbers might be not representative for the entire field in reproductive medicine and biology worldwide. The key ethical issue regarding fertility preservation in prepubertal boys remains the experimental nature of the intervention.

WIDER IMPLICATIONS

The revised procedures can be implemented by the multi-disciplinary teams offering and/or developing treatment strategies to preserve the fertility of prepubertal boys who have a high risk of fertility loss.

STUDY FUNDING/COMPETING INTERESTS

The work was funded by ESHRE. None of the authors has a conflict of interest.

Engineered reproductive tissues

Engineered male and female biomimetic reproductive tissues are being developed as autonomous in vitro units or as integrated multi-organ in vitro systems to support germ cell and embryo function, and to display characteristic endocrine phenotypic patterns, such as the 28-day human ovulatory cycle. In this Review, we summarize how engineered reproductive tissues facilitate research in reproductive biology, and overview strategies for making engineered reproductive tissues that might eventually allow the restoration of reproductive capacity in patients.

Progress in translational reproductive science: testicular tissue transplantation and in vitro spermatogenesis

Since the birth of the first child conceived via in vitro fertilization 40 years ago, fertility treatments and assisted reproductive technology have allowed many couples to reach their reproductive goals. As of yet, no fertility options are available for men who cannot produce functional sperm, but many experimental therapies have demonstrated promising results in animal models. Both autologous (stem cell transplantation, de novo morphogenesis, and testicular tissue grafting) and outside-the-body (xenografting and in vitro spermatogenesis) approaches exist for restoring sperm production in infertile animals with varying degrees of success. Once safety profiles are established and an ideal patient population is chosen, some of these techniques may be ready for human experimentation in the near future, with likely clinical implementation within the next decade.

Surrogate testes: Allogeneic spermatogonial stem cell transplantation within an encapsulation device may restore male fertility

Toxic insult to the gonads by chemotherapy or radiotherapy can lead to permanent infertility. It's an important health concern because each year more than 4000 male patients are at risk of azoospermia in the United States due to gonadotoxicity of the regimens used. There are also several benign/genetic diseases whose natural course can result in infertility without gonadotoxic therapy. Considering the fact that most of these people are cured and survive with the advent of modern medicine, infertility is related to serious psychological and relationship implications and parenthood is a significant issue for those patients. Semen cryopreservation option is available for postpubertal adolescent and adult men, while children do not have this storing option since they do not have mature spermatozoa. However, their testes contain spermatogonial stem cells (SSCs), which are initiators of spermatogenesis. Promising findings in animal studies and human cell lines have encouraged scientists that SSCs may be hope for restoring fertility option of patients who cannot produce functional sperm and who have no other choice to preserve their future fertility. For this reason, several centers around the world already began to collect and cryopreserve testicular tissue or cells with anticipation that SSC-based therapies will be available in the near future; however, an optimal transplantation design in humans is yet to be developed. Here we propose an allogeneic testicular stem cell transplantation with an encapsulation device to restore fertility in patients with infertility. We endeavor to discuss the reliability of this method with the current literature and bring the evidence on its feasibility.

A fertility preservation toolkit for pediatric surgeons caring for children with cancer

Survival for children with cancer has improved significantly in recent decades, prompting an increasing emphasis on minimizing late effects of therapy, including infertility and premature gonadal insufficiency. The time interval after diagnosis and before therapy initiation can be stressful and overwhelming for patients and their families coming to terms with the implications of the diagnosis, but is also the optimal time to address oncofertility options. Pediatric surgeons are often an integral part of the care team for these patients during this vulnerable time period and play a key role in advocating for and performing oncofertility procedures. Children with cancer have both non-experimental and experimental fertility preservation options available depending on their pubertal status and a risk assessment performed based on their anticipated therapy. This review provides an oncofertility toolkit for pediatric surgeons to perform a risk assessment, counsel families on fertility preservation options, and establish an oncofertility program tailored to the resources available at their institutions.

Oncofertility: Pharmacological Protection and Immature Testicular Tissue (ITT)-Based Strategies for Prepubertal and Adolescent Male Cancer Patients

While the incidence of cancer in children and adolescents has significantly increased over the last decades, improvements made in the field of cancer therapy have led to an increased life expectancy for childhood cancer survivors. However, the gonadotoxic effect of the treatments may lead to infertility. Although semen cryopreservation represents the most efficient and safe fertility preservation method for males producing sperm, it is not feasible for prepubertal boys. The development of an effective strategy based on the pharmacological protection of the germ cells and testicular function during gonadotoxic exposure is a non-invasive preventive approach that prepubertal boys could benefit from. However, the progress in this field is slow. Currently, cryopreservation of immature testicular tissue (ITT) containing spermatogonial stem cells is offered to prepubertal boys as an experimental fertility preservation strategy by a number of medical centers. Several in vitro and in vivo fertility restoration approaches based on the use of ITT have been developed so far with autotransplantation of ITT appearing more promising. In this review, we discuss the pharmacological approaches for fertility protection in prepubertal and adolescent boys and the fertility restoration approaches developed on the utilization of ITT.

Rebuilding the human testis in vitro

Increasing rates of male infertility have led to a greater need for relevant model systems to gain further insight into male fertility and its failings. Spermatogenesis and hormone production occur within distinct regions of the testis. Defined by specialized architecture and a diverse population of cell types, it is no surprise that disruption of this highly organized microenvironment can lead to infertility. To date, no robust in vitro system has facilitated full spermatogenesis resulting in the production of fertilization‐competent human spermatozoa. Here, we review a selection of current in vitro systems available for modelling the human testis microenvironment with focus on the progression of spermatogenesis and recapitulation of the testis microenvironment.

Role of stem cells in fertility preservation: current insights

While improvements made in the field of cancer therapy allow high survival rates, gonadotoxicity of chemo- and radiotherapy can lead to infertility in male and female pre- and postpubertal patients. Clinical options to preserve fertility before starting gonadotoxic therapies by cryopreserving sperm or oocytes for future use with assisted reproductive technology (ART) are now applied worldwide. Cryopreservation of pre- and postpubertal ovarian tissue containing primordial follicles, though still considered experimental, has already led to the birth of healthy babies after autotransplantation and is performed in an increasing number of centers. For prepubertal boys who do not produce gametes ready for fertilization, cryopreservation of immature testicular tissue (ITT) containing spermatogonial stem cells may be proposed as an experimental strategy with the aim of restoring fertility. Based on achievements in nonhuman primates, autotransplantation of ITT or testicular cell suspensions appears promising to restore fertility of young cancer survivors. So far, whether in two- or three-dimensional culture systems, in vitro maturation of immature male and female gonadal cells or tissue has not demonstrated a capacity to produce safe gametes for ART. Recently, primordial germ cells have been generated from embryonic and induced pluripotent stem cells, but further investigations regarding efficiency and safety are needed. Transplantation of mesenchymal stem cells to improve the vascularization of gonadal tissue grafts, increase the colonization of transplanted cells, and restore the damaged somatic compartment could overcome the current limitations encountered with transplantation.

Testicular organoids to study cell-cell interactions in the mammalian testis

BACKGROUND

Over the last ten years, three-dimensional organoid culture has garnered renewed interest, as organoids generated from primary cells or stem cells with cell associations and functions similar to organs in vivo can be a powerful tool to study tissue-specific cell-cell interactions in vitro. Very recently, a few interesting approaches have been put forth for generating testicular organoids for studying the germ cell niche microenvironment.

AIM

To review different model systems that have been employed to study germ cell biology and testicular cell-cell interactions and discuss how the organoid approach can address some of the shortcomings of those systems.

RESULTS AND CONCLUSION

Testicular organoids that bear architectural and functional similarities to their in vivo counterparts are a powerful model system to study cell-cell interactions in the germ cell niche. Organoids enable studying samples in humans and other large animals where in vivo experiments are not possible, allow modeling of testicular disease and malignancies and may provide a platform to design more precise therapeutic interventions.

Three-dimensional testicular organoids as novel in vitro models of testicular biology and toxicology

Organoids are three dimensional structures consisting of multiple cell types that recapitulate the cellular architecture and functionality of native organs. Over the last decade, the advent of organoid research has opened up many avenues for basic and translational studies. Following suit of other disciplines, research groups working in the field of male reproductive biology have started establishing and characterizing testicular organoids. The three-dimensional architectural and functional similarities of organoids to their tissue of origin facilitate study of complex cell interactions, tissue development and establishment of representative, scalable models for drug and toxicity screening. In this review, we discuss the current state of testicular organoid research, their advantages over conventional monolayer culture and their potential applications in the field of reproductive biology and toxicology.

Donor spermatogenesis in de novo formed seminiferous tubules from transplanted testicular cells in rhesus monkey testis

STUDY QUESTION

Can transplanted primate testicular cells form seminiferous tubules de novo, supporting complete spermatogenesis?

SUMMARY ANSWER

Cryopreserved testicular cells from a prepubertal monkey can reorganize in an adult monkey recipient testis forming de novo seminiferous tubular cords supporting complete spermatogenesis.

WHAT IS KNOWN ALREADY

De novo morphogenesis of testicular tissue using aggregated cells from non-primate species grafted either subcutaneously or in the testis can support spermatogenesis.

STUDY DESIGN, SIZE, DURATION

Two postpubertal rhesus monkeys (Macaca mulatta) were given testicular irradiation. One monkey was given GnRH-antagonist treatment from 8 to 16 weeks after irradiation, while the other received sham injections. At 16 weeks, cryopreserved testicular cells from two different prepubertal monkeys [43 × 106 viable (Trypan-blue excluding) cells in 260 μl, and 80 × 106 viable cells in 400 μl] were transplanted via ultrasound-guided injections to one of the rete testis in each recipient, and immune suppression was given. The contralateral testis was sham transplanted. Testes were analyzed 9 months after transplantation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Spermatogenic recovery was assessed by testicular volume, weight, histology and immunofluorescence. Microsatellite genotyping of regions of testicular sections obtained by LCM determined whether the cells were derived from the host or transplanted cells.

MAIN RESULTS AND THE ROLE OF CHANCE

Transplanted testis of the GnRH-antagonist-treated recipient, but not the sham-treated recipient, contained numerous irregularly shaped seminiferous tubular cords, 89% of which had differentiating germ cells, including sperm in a few of them. The percentages of donor genotype in different regions of this testis were as follows: normal tubule, 0%; inflammatory, 0%; abnormal tubule region, 67%; whole interior of abnormal tubules, >99%; adluminal region of the abnormal tubules, 92%. Thus, these abnormal tubules, including the enclosed germ cells, were derived de novo from the donor testicular cells.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The de novo tubules were observed in only one out of the two monkeys transplanted with prepubertal donor testicular cells.

WIDER IMPLICATIONS OF THE FINDINGS

These findings may represent a promising strategy for restoration of fertility in male childhood cancer survivors. The approach could be particularly useful in those exposed to therapeutic agents that are detrimental to the normal development of the tubule somatic cells affecting the ability of the endogenous tubules to support spermatogenesis, even from transplanted spermatogonial stem cells.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by research grants P01 HD075795 from Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD/NIH) to K.E.O and Cancer Center Support Grant P30 CA016672 from NCI/NIH to The University of Texas MD Anderson Cancer Center. The authors declare that they have no competing interests.