Can prepubertal human testicular tissue be cryopreserved by vitrification?

Advancements in fertility preservation strategies for pediatric male cancer patients: a review of cryopreservation and transplantation of immature testicular tissue

Recently, there has been increasing emphasis on the gonadotoxic effects of cancer therapy in prepubertal boys. As advances in oncology treatments continue to enhance survival rates for prepubertal boys, the need for preserving their functional testicular tissue for future reproduction becomes increasingly vital. Therefore, we explore cutting-edge strategies in fertility preservation, focusing on the cryopreservation and transplantation of immature testicular tissue as a promising avenue. The evolution of cryopreservation techniques, from controlled slow freezing to more recent advancements in vitrification, with an assessment of their strengths and limitations was exhibited. Detailed analysis of cryoprotectants, exposure times, and protocols underscores their impact on immature testicular tissue viability. In transplantation strategy, studies have revealed that the scrotal site may be the preferred location for immature testicular tissue grafting in both autotransplantation and xenotransplantation scenarios. Moreover, the use of biomaterial scaffolds during graft transplantation has shown promise in enhancing graft survival and stimulating spermatogenesis in immature testicular tissue over time. This comprehensive review provides a holistic approach to optimize the preservation strategy of human immature testicular tissue in the future.

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.

A comprehensive review and update on human fertility cryopreservation methods and tools

The broad conceptualization of fertility preservation and restoration has become already a major concern in the modern western world since a large number of individuals often face it in the everyday life. Driven by different health conditions and/or social reasons, a variety of patients currently rely on routinely and non-routinely applied assisted reproductive technologies, and mostly on the possibility to cryopreserve gametes and/or gonadal tissues for expanding their reproductive lifespan. This review embraces the data present in human-focused literature regarding the up-to-date methodologies and tools contemporarily applied in IVF laboratories' clinical setting of the oocyte, sperm, and embryo cryopreservation and explores the latest news and issues related to the optimization of methods used in ovarian and testicular tissue cryopreservation.

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.

Morphometric and immunohistochemical analysis as a method to identify undifferentiated spermatogonial cells in adult subjects with Klinefelter syndrome: a cohort study

OBJECTIVE

To study the prevalence of spermatogonia in adult subjects with Klinefelter syndrome (KS) using MAGE-A4 and UCHL1 (PGP9.5) immunohistochemistry as markers for undifferentiated spermatogonial cells. We aimed to compare this method to the gold standard of hematoxylin and eosin (H & E) staining with histologic analysis in the largest reported cohort of adult subjects with KS.

DESIGN

A retrospective cohort study.

SETTING

Infertility Clinic and Institute for Regenerative Medicine.

PATIENT(S)

This study consisted of 79 adult subjects with KS and 12 adult control subjects.

INTERVENTION(S)

The subjects with KS (n = 79) underwent bilateral testicular biopsy in an initial effort to recover spermatozoa for in vitro fertilization and intracytoplasmic sperm injection. The institutional review board approved the use of a portion of the archived diagnostic pathology paraffin blocks for the study. The samples were superimposed onto microscopic slides and labeled with the PGP9.5 and MAGE-A4 antibodies. Subjects (n = 12) who had previously consented to be organ donors via the National Disease Research Interchange were selected as controls. Dedicated genitourinary pathologists examined the H & E-, PGP9.5-, and MAGE-A4-stained tissue for presence of undifferentiated spermatogonia and spermatozoa with the use of a virtual microscopy software.

MAIN OUTCOME MEASURE(S)

The primary outcome was the presence of MAGE-A4-positive or UCHL1-positive tubules that indicate undifferentiated spermatogonia. Supportive outcomes include assessing the biopsy specimen for the following: total surface area; total seminiferous tubule surface area; total interstitium surface area; the total number of seminiferous tubules; and MAGE-A4- negative or UCHL1-negative tubules. Additionally, clinical information, such as age, karyotype, height, weight, mean testicle size, and hormonal panel (luteinizing hormone, follicle-stimulating hormone, and testosterone), was obtained and used in a single and multivariable analysis with linear regression to determine predictive factors for the number of UCHL1-positive tubules.

RESULT(S)

The mean age of the subjects in the KS group was 32.9 ± 0.7 years (range, 16-48). UCHL1 (PGP9.5) and MAGE-A4 staining showed that 74.7% (n = 59) and 40.5% (n = 32) of the subjects with KS, respectively, were positive for undifferentiated spermatogonia compared with 100% (n = 12) of the control subjects who were positive for both the markers. Hematoxylin and eosin with microscopic analysis showed that only 10.1% (n = 8) of the subjects were positive for spermatogonia. The mean number of positive tubules per subject with KS was 11.8 ± 1.8 for UCHL1 and 3.7 ± 1.0 for MAGE-A4. Secondary analysis showed 7 (8.9%) adult subjects with KS as positive for spermatozoa on biopsy. The population having negative testicular sperm extraction results (n = 72) showed a spermatogonia-positive rate of 1.4%, (n = 1), 72.2% (n = 52), and 34.7% (n = 25) using H & E, UCHL1, and MAGE-A4, respectively. Further analysis showed that 54 (75.0%) subjects were either positive for UCHL1 or MAGE-A4. Twenty (27.8%) subjects were positive for both UCHL1 and MAGE-A4. Multivariate analysis with linear regression showed no significant correlation between clinical variables and the number of UCHL1-positive tubules found on biopsy specimens.

CONCLUSION(S)

We report a cohort of adult subjects with KS undergoing analysis for the presence of undifferentiated spermatogonia. UCHL1 and MAGE-A4 immunostaining appear to be an effective way of identifying undifferentiated spermatogonia in testicular biopsy specimens of subjects with KS. Despite observing deterioration in the testicular architecture, many patients remain positive for undifferentiated spermatogonia, which could be harvested and potentially used for infertility therapy in a patient with KS who is azoospermic and has negative testicular sperm extraction results.

Tracking Immature Testicular Tissue after Vitrification In Vitro and In Vivo for Pre-Pubertal Fertility Preservation: A Translational Transgenic Mouse Model

Pediatric cancer survivors experiencing gonadotoxic chemoradiation therapy may encounter subfertility or permanent infertility. However, previous studies of cryopreservation of immature testicular tissue (ITT) have mainly been limited to in vitro studies. In this study, we aim to evaluate in vitro and in vivo bioluminescence imaging (BLI) for solid surface-vitrified (SSV) ITT grafts until adulthood. The donors and recipients were transgenic and wild-type mice, respectively, with fresh ITT grafts used as the control group. In our study, the frozen ITT grafts remained intact as shown in the BLI, scanning electron microscopy (SEM) and immunohistochemistry (IHC) analyses. Graft survival was analyzed by BLI on days 1, 2, 5, 7, and 31 after transplantation. The signals decreased by quantum yield between days 2 and 5 in both groups, but gradually increased afterwards until day 31, which were significantly stronger than day 1 after transplantation (p = 0.008). The differences between the two groups were constantly insignificant, suggesting that both fresh and SSV ITT can survive, accompanied by spermatogenesis, until adulthood. The ITT in both groups presented similar BLI intensity and intact cells and ultrastructures for spermatogenesis. This translational model demonstrates the great potential of SSV for ITT in pre-pubertal male fertility preservation.

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.

Rescue and Conservation of Male Adult Alpacas (Vicugna pacos) Based on Spermatogonial Stem Cell Biotechnology Using Atomized Black Maca as a Supplement of Cryopreservation Medium

This is the first time that testicular tissue (n = 44) and isolated testicular cells (n = 51) were cryopreserved from alpaca testes 24 h postmortem. For this purpose, internally designed freezing media and cryopreservation protocols were used. Testicular tissue fragments (25 mg) and isolated testicular cells were frozen in MTDB (trehalose and black maca), MTD (trehalose), MSDB (sucrose and black maca), and MSD (sucrose) media. Isolated spermatogonial cells were cryopreserved in two ways, before and after proliferation in vitro. After cryopreservation, the percentage of cell viability in Group 1 (>50% of cell viability) by trypan blue did not show differences within each group (p > 0.05) but showed significant differences when comparing fragments with isolated cells (p < 0.05). Spermatogonial stem cells (SSC) were identified by flow cytometry as strong Dolichos biflorus agglutinin (sDBA) and mitochondrial activity of SSC as strongly positive for MitoSense (sMitoSense+) in intact mitochondria cells, weakly positive for MitoSense (wMitoSense+) in early apoptosis, and necrosis with 7-Aminoactinomycin-D positive (7-AAD). After freezing, in Group 1M (≥30% sMitoSense+), the fragments did not show differences between the media (p > 0.05), but in the isolated cells frozen in MSDB medium, 63.68 ± 8.90% (p < 0.05). In Group 2M (<30% sMitoSense+), necrosis (7AAD+) in MSDB medium was 27.03 ± 5.80%, and necrosis in isolated cells was 14.05 ± 9.3% with significant differences between these groups (p < 0.05); in sMitoSense+, the isolated cells (34.40 ± 23%) had a higher percentage than the fragments (12.4 ± 5.2) (p < 0.05). On the other hand, MSDB and MSD media were significantly higher for isolated cells than for fragments in sDBA+ (p < 0.05). On the other hand, the SSC (sDBA+) had significant differences (p < 0.05) between fresh cells 7.43 ± 1.3% (sDBA+) compared with those cryopreserved in MSDB medium 1.46 ± 0.34% (sDBA+). Additionally, the proliferated and cryopreserved SSC 6.29 ± 1.17% (sDBA+) did not show significant differences concerning the fresh cells (p > 0.05). In conclusion, the black maca showed antioxidant properties when it was included in the freezing medium and, therefore, improved the SSC's conservation of the alpaca. Furthermore, the proliferation of isolated cells in vitro produces a higher amount of SSC after thawing them for further preclinical or clinical work.

A prospective study on the long-term outcome of prepubertal and pubertal boys undergoing testicular biopsy for fertility preservation prior to hematologic stem cell transplantation

BACKGROUND

Few studies have reported the long-term outcomes of prepubertal and pubertal boys undergoing testicular biopsy for fertility preservation (FP).

PROCEDURE

This prospective longitudinal study examined 21 boys (aged 1.5-14.5 years) who underwent testicular biopsy for FP prior to allogeneic (n = 20) or autologous (n = 1) hematological stem cell transplantation (HSCT) between 2003 and 2010. During counseling, pubertal boys were encouraged to produce a sperm sample by masturbation , while prepubertal boys were presented with surgical testicular tissue retrieval as an option for experimental FP. Clinical outcomes included postoperative complications, pubertal development, and sex-hormone levels. Survivors approaching adulthood were encouraged to provide semen samples.

RESULTS

Twenty boys, including 14 in prepuberty and six in early puberty (Tanner stage 2-3), underwent open testicular biopsies. Two pubertal biopsies contained mature sperms, which were cryopreserved. Testicular tissue was vitrified in the remaining 18 cases. One pubertal boy (Tanner stage 4) underwent percutaneous testicular sperm aspiration and sperms obtained were cryopreserved. Postoperative complications (hematoma or infection) were rare. Overall, 14 boys survived >5 years (mean follow-up after HSCT, 7.2 years) and 11 showed advanced puberty. Semen samples were provided by five boys and obtained sperm were cryopreserved from two. Individuals at adulthood had normal testosterone levels but subnormal testicular size, high follicle stimulating hormone, and low inhibin B and anti-Müllerian hormone levels.

CONCLUSION

No long-term risks were detected during continuous clinical follow-up. Experimental testicular biopsies for FP were well accepted by the patients and families, despite the absence of methods to use prepubertal tissue for fertility treatment.

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.

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.

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.

Haploid Germ Cells Generated in Organotypic Culture of Testicular Tissue From Prepubertal Boys

While in mice various studies have described the completion of spermatogenesis in vitro using either organotypic culture of prepubertal testicular tissue or 3D culture of isolated cells, in humans it has not been possible to achieve germ cell differentiation from immature testicular tissue (ITT). In our study, we evaluated the ability of human ITT to differentiate via a long-term organotypic culture of frozen–thawed 1 mm³ testicular fragments from five prepubertal boys in two different culture media. Tissue and supernatants were analyzed at regular intervals up to day 139. Sertoli cell (SC) viability and maturation was evaluated using immunohistochemistry (IHC) for SOX9, GDNF, anti-Mullerian hormone (AMH) and androgen receptor (AR), and AMH concentration in supernatants. Spermatogonia (SG) and proliferating cells were identified by MAGE-A4 (for SG) and Ki67 (for proliferating cells) via immunohistochemistry (IHC). Apoptotic cells were studied by active caspase 3. To evaluate Leydig cell (LC) functionality testosterone was measured in the supernatants and steroidogenic acute regulatory protein (STAR) IHC was performed. Germ cell differentiation was evaluated on Hematoxylin-Eosin histological sections, via IHC for synaptonemal complex 3 (SYCP3) for spermatocytes, Protein boule-like (BOLL) for spermatocytes and round spermatids, angiotensin-converting enzyme (ACE), protamine 2 and transition protein 1 (for elongated spermatids) and via chromogenic in situ hybridization (CISH). We reported the generation of meiotic and postmeiotic cells after 16 days of culture, as shown by the histological analyses, the presence of differentiation markers and the increase of haploid germ cells. We showed SC viability and maturation by a decrease of AMH secretion in the supernatants (p ≤ 0.001) while the number of SOX9 positive cells did not show any variation. A decrease of spermatogonia (p ≤ 0.001) was observed. The number of apoptotic cells did not vary. LC functionality was shown by the increase in STAR expression (p ≤ 0.007) and a peak in testosterone secretion, followed by a reduction (p ≤ 0.001) with stabilization. According to our knowledge, this is the first report of generation of haploid cells in human ITT. Differentiating germ cells have to be further evaluated for their ability to complete differentiation, their fecundability and epigenetic characteristics.

Cryostorage of immature and mature human testis tissue to preserve spermatogonial stem cells (SSCs): a systematic review of current experiences toward clinical applications

While the survival rate of children with cancer is increasing, preserving fertility for prepubertal boys is still a challenge. Although intracytoplasmic sperm injection (ICSI) using frozen sperms has revolutionized infertility treatment, it is not applicable for the patients who undergo chemotherapy before puberty since spermatogenesis has not begun. Therefore, preserving spermatogonial stem cells (SSCs) as an experimental option can be provided to prepubertal patients at a risk of damage or loss of their SSCs due to cancer treatments and developmental or genetic disorders. Using frozen SSCs in testicular tissue, successful SSC autotransplantation in mouse and nonhuman primates has shown a promising future for SSC-based cell therapy. Cryopreservation of testicular tissue containing SSCs is the first step to translate SSC-based cell therapy into clinical male infertility treatment, and in the investigation into SSCs, it is very important to evaluate their quantity and functionality during this process. This systematic review summarizes the published data on cryopreservation techniques in human testis tissue for potential utilization in future clinical applications.

A comparison between a new vitrification protocol and the slow freezing method in the cryopreservation of prepubertal testicular tissue

OBJECTIVE

This study aimed to compare a new vitrification protocol with reduced cryoprotectant exposure to the slow freezing method in the cryopreservation of prepubertal rat testicular tissue.

METHODS

Five sexually immature male Wistar rats were submitted to bilateral orchiectomy. Tissue samples from each testicle were fragmented into small pieces and randomly assigned to three groups: Group A, fresh tissue (control); Group B, slow programmable freezing (SPF); and Group C (vitrification). Frozen/thawed, vitrified/warmed, and fresh testicular tissue were histologically compared. A pathologist blinded to the procedures assessed the morphology (cell differentiation, nuclei, and epithelium) of 10 seminiferous tubules from each testicle (100 tubules per Group).

RESULTS

Sertoli and spermatogonial stem cells were easily differentiated, and the nucleoli were easily viewed in the tubules assessed in all three groups. Small alterations in tissue architecture were observed in the control group as a result of tissue handling. Moderate alterations of the epithelium with the formation of small gaps and cell detachment from the basement membrane were observed in 28% of the frozen and 9% of the vitrified tubules. Condensed nuclei involving a small proportion of cells were observed in six and three tubules of the frozen and vitrified group, respectively. Despite the alterations, 97% of the frozen and 99% of the vitrified tubules were considered well preserved.

CONCLUSIONS

The findings indicate that the vitrification protocol tested in this study adequately preserved the morphological integrity of prepubertal testicular tissue in a rat model. Further studies are required to confirm testicular tissue function after grafting.

Fertility preservation through gonadal cryopreservation

Fertility preservation is an area of immense interest in today's society. The most effective and established means of fertility preservation is cryopreservation of gametes (sperm and oocytes) and embryos. Gonadal cryopreservation is yet another means for fertility preservation, especially if the gonadal function is threatened by premature menopause, gonadotoxic cancer treatment, surgical castration, or diseases. It can also aid in the preservation of germplasm of animals that die before attaining sexual maturity. This is especially of significance for valuable, rare, and endangered animals whose population is affected by high neonatal/juvenile mortality because of diseases, poor management practices, or inbreeding depression. Establishing genome resource banks to conserve the genetic status of wild animals will provide a critical interface between ex-situ and in-situ conservation strategies. Cryopreservation of gonads effectively lengthens the genetic lifespan of individuals in a breeding program even after their death and contributes towards germplasm conservation of prized animals. Although the studies on domestic animals are quite promising, there are limitations for developing cryopreservation strategies in wild animals. In this review, we discuss different options for gonadal tissue cryopreservation with respect to humans and to laboratory, domestic, and wild animals. This review also covers recent developments in gonadal tissue cryopreservation and transplantation, providing a systematic view and the advances in the field with the possibility for its application in fertility preservation and for the conservation of germplasm in domestic and wild species.

Cryopreservation of testicular tissue or testicular cell suspensions: a pivotal step in fertility preservation

BACKGROUND

Germ cell depletion caused by chemical or physical toxicity, disease or genetic predisposition can occur at any age. Although semen cryopreservation is the first reflex for preserving male fertility, this cannot help out prepubertal boys. Yet, these boys do have spermatogonial stem cells (SSCs) that able to produce sperm at the start of puberty, which allows them to safeguard their fertility through testicular tissue (TT) cryopreservation. SSC transplantation (SSCT), TT grafting and recent advances in in vitro spermatogenesis have opened new possibilities to restore fertility in humans. However, these techniques are still at a research stage and their efficiency depends on the amount of SSCs available for fertility restoration. Therefore, maintaining the number of SSCs is a critical step in human fertility preservation. Standardizing a successful cryopreservation method for TT and testicular cell suspensions (TCSs) is most important before any clinical application of fertility restoration could be successful.

OBJECTIVE AND RATIONALE

This review gives an overview of existing cryopreservation protocols used in different animal models and humans. Cell recovery, cell viability, tissue integrity and functional assays are taken into account. Additionally, biosafety and current perspectives in male fertility preservation are discussed.

SEARCH METHODS

An extensive PubMED and MEDline database search was conducted. Relevant studies linked to the topic were identified by the search terms: cryopreservation, male fertility preservation, (immature)testicular tissue, testicular cell suspension, spermatogonial stem cell, gonadotoxicity, radiotherapy and chemotherapy.

OUTCOMES

The feasibility of fertility restoration techniques using frozen-thawed TT and TCS has been proven in animal models. Efficient protocols for cryopreserving human TT exist and are currently applied in the clinic. For TCSs, the highest post-thaw viability reported after vitrification is 55.6 ± 23.8%. Yet, functional proof of fertility restoration in the human is lacking. In addition, few to no data are available on the safety aspects inherent to offspring generation with gametes derived from frozen-thawed TT or TCSs. Moreover, clarification is needed on whether it is better to cryopreserve TT or TCS.

WIDER IMPLICATIONS

Fertility restoration techniques are very promising and expected to be implemented in the clinic in the near future. However, inter-center variability needs to be overcome and the gametes produced for reproduction purposes need to be subjected to safety studies. With the perspective of a future clinical application, there is a dire need to optimize and standardize cryopreservation and safety testing before using frozen-thawed TT of TCSs for fertility restoration.

Spermatogonial stem cell autotransplantation and germline genomic editing: a future cure for spermatogenic failure and prevention of transmission of genomic diseases

BACKGROUND

Subfertility affects approximately 15% of all couples, and a severe male factor is identified in 17% of these couples. While the etiology of a severe male factor remains largely unknown, prior gonadotoxic treatment and genomic aberrations have been associated with this type of subfertility. Couples with a severe male factor can resort to ICSI, with either ejaculated spermatozoa (in case of oligozoospermia) or surgically retrieved testicular spermatozoa (in case of azoospermia) to generate their own biological children. Currently there is no direct treatment for azoospermia or oligozoospermia. Spermatogonial stem cell (SSC) autotransplantation (SSCT) is a promising novel clinical application currently under development to restore fertility in sterile childhood cancer survivors. Meanwhile, recent advances in genomic editing, especially the clustered regulatory interspaced short palindromic repeats-associated protein 9 (CRISPR-Cas9) system, are likely to enable genomic rectification of human SSCs in the near future.

OBJECTIVE AND RATIONALE

The objective of this review is to provide insights into the prospects of the potential clinical application of SSCT with or without genomic editing to cure spermatogenic failure and to prevent transmission of genetic diseases.

SEARCH METHODS

We performed a narrative review using the literature available on PubMed not restricted to any publishing year on topics of subfertility, fertility treatments, (molecular regulation of) spermatogenesis and SSCT, inherited (genetic) disorders, prenatal screening methods, genomic editing and germline editing. For germline editing, we focussed on the novel CRISPR-Cas9 system. We included papers written in English only.

OUTCOMES

Current techniques allow propagation of human SSCs in vitro, which is indispensable to successful transplantation. This technique is currently being developed in a preclinical setting for childhood cancer survivors who have stored a testis biopsy prior to cancer treatment. Similarly, SSCT could be used to restore fertility in sterile adult cancer survivors. In vitro propagation of SSCs might also be employed to enhance spermatogenesis in oligozoospermic men and in azoospermic men who still have functional SSCs albeit in insufficient numbers. The combination of SSCT with genomic editing techniques could potentially rectify defects in spermatogenesis caused by genomic mutations or, more broadly, prevent transmission of genomic diseases to the offspring. In spite of the promising prospects, SSCT and germline genomic editing are not yet clinically applicable and both techniques require optimization at various levels.

WIDER IMPLICATIONS

SSCT with or without genomic editing could potentially be used to restore fertility in cancer survivors to treat couples with a severe male factor and to prevent the paternal transmission of diseases. This will potentially allow these couples to have their own biological children. Technical development is progressing rapidly, and ethical reflection and societal debate on the use of SSCT with or without genomic editing is pressing.

Developmental Potential of Vitrified Mouse Testicular Tissue after Ectopic Transplantation

Objective

Cryopreservation of immature testicular tissue should be considered as an important factor for fertility preservation in young boys with cancer. The objective of this study is to investigate whether immature testicular tissue of mice can be successfully cryopreserved using a simple vitrification procedure to maintain testicular cell viability, proliferation, and differentiation capacity.

Materials and Methods

In this experimental study, immature mice testicular tissue fragments (0.5-1 mm²) were vitrified-warmed in order to assess the effect of vitrification on testicular tissue cell viability. Trypan blue staining was used to evaluate developmental capacity. Vitrified tissue (n=42) and fresh (control, n=42) were ectopically transplanted into the same strain of mature mice (n=14) with normal immunity. After 4 weeks, the graft recovery rate was determined. Hematoxylin and eosin (H&E) staining was used to evaluate germ cell differentiation, immunohistochemistry staining by proliferating cell nuclear antigen (PCNA) antibody, and terminal deoxynucleotidyl transferase (TdT) dUTP Nick- End Labeling (TUNEL) assay for proliferation and apoptosis frequency.

Results

Vitrification did not affect the percentage of cell viability. Vascular anastomoses was seen at the graft site. The recovery rate of the vitrified graft did not significantly differ with the fresh graft. In the vitrified graft, germ cell differentiation developed up to the secondary spermatocyte, which was similar to fresh tissue. Proliferation and apoptosis in the vitrified tissue was comparable to the fresh graft.

Conclusion

Vitrification resulted in a success rates similar to fresh tissue (control) in maintaining testicular cell viability and tissue function. These data provided further evidence that vitrification could be considered an alternative for cryopreservation of immature testicular tissue.

Experimental methods to preserve male fertility and treat male factor infertility

Infertility is a prevalent condition that has insidious impacts on the infertile individuals, their families, and society, which extend far beyond the inability to have a biological child. Lifestyle changes, fertility treatments, and assisted reproductive technology (ART) are available to help many infertile couples achieve their reproductive goals. All of these technologies require that the infertile individual is able to produce at least a small number of functional gametes (eggs or sperm). It is not possible for a person who does not produce gametes to have a biological child. This review focuses on the infertile man and describes several stem cell-based methods and gene therapy approaches that are in the research pipeline and may lead to new fertility treatment options for men with azoospermia.

A European perspective on testicular tissue cryopreservation for fertility preservation in prepubertal and adolescent boys

STUDY QUESTION

What clinical practices, patient management strategies and experimental methods are currently being used to preserve and restore the fertility of prepubertal boys and adolescent males?

SUMMARY ANSWER

Based on a review of the clinical literature and research evidence for sperm freezing and testicular tissue cryopreservation, and after consideration of the relevant ethical and legal challenges, an algorithm for the cryopreservation of sperm and testicular tissue is proposed for prepubertal boys and adolescent males at high risk of fertility loss.

WHAT IS KNOWN ALREADY

A known late effect of the chemotherapy agents and radiation exposure regimes used to treat childhood cancers and other non-malignant conditions in males is the damage and/or loss of the proliferating spermatogonial stem cells in the testis. Cryopreservation of spermatozoa is the first line treatment for fertility preservation in adolescent males. Where sperm retrieval is impossible, such as in prepubertal boys, or it is unfeasible in adolescents prior to the onset of ablative therapies, alternative experimental treatments such as testicular tissue cryopreservation and the harvesting and banking of isolated spermatogonial stem cells can now be proposed as viable means of preserving fertility.

STUDY DESIGN, SIZE, DURATION

Advances in clinical treatments, patient management strategies and the research methods used to preserve sperm and testicular tissue for prepubertal boys and adolescents were reviewed. A snapshot of the up-take of testis cryopreservation as a means to preserve the fertility of young males prior to December 2012 was provided using a questionnaire.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A comprehensive literature review was conducted. In addition, survey results of testis freezing practices in young patients were collated from 24 European centres and Israeli University Hospitals.

MAIN RESULTS AND THE ROLE OF CHANCE

There is increasing evidence of the use of testicular tissue cryopreservation as a means to preserve the fertility of pre- and peri-pubertal boys of up to 16 year-old. The survey results indicate that of the 14 respondents, half of the centres were actively offering testis tissue cryobanking as a means of safeguarding the future fertility of boys and adolescents as more than 260 young patients (age range less than 1 year old to 16 years of age), had already undergone testicular tissue retrieval and storage for fertility preservation. The remaining centres were considering the implementation of a tissue-based fertility preservation programme for boys undergoing oncological treatments.

LIMITATIONS, REASONS FOR CAUTION

The data collected were limited by the scope of the questionnaire, the geographical range of the survey area, and the small number of respondents.

WIDER IMPLICATIONS OF THE FINDINGS

The clinical and research questions identified and the ethical and legal issues raised are highly relevant to the multi-disciplinary teams developing treatment strategies to preserve the fertility of prepubertal and adolescent boys who have a high risk of fertility loss due to ablative interventions, trauma or genetic pre-disposition.

Cryopreservation of testis tissues and in vitro spermatogenesis

Cancer treatments, either chemo‐ or radiotherapy, may cause severe damage to gonads which could lead to the infertility of patients. In post‐pubertal male patients, semen cryopreservation is recommended to preserve the potential to have their own biological children in the future; however, it is not applicable to prepubertals. The preservation of testis tissue which contains spermatogonial stem cells (SSCs) but not sperm would be an alternative measure. The tissues or SSCs have to be transplanted back into patients to obtain sperm; however, this procedure remains experimental, invasive, and is accompanied with the potential risk of re‐implantation of cancer cells. Recently, we developed an organ culture system which supports the spermatogenesis of mice up to sperm formation from SSCs. It was also shown that the tissues could be frozen for later sperm production, which resulted in the generation of offspring. Thus, it could be useful as a clinical application for preserving the reproductive potential of male pediatric cancer patients. The establishment of an optimized cryopreservation method and the development of a culture system for human testis tissue are expected in the future.

In Search of Better Spermatogonial Preservation by Supplementation of Cryopreserved Human Immature Testicular Tissue Xenografts with N-acetylcysteine and Testosterone

Controlled slow-freezing is the procedure currently applied for immature testicular tissue (ITT) cryobanking in clinical practice. Vitrification has been proposed as a promising alternative, with a view to better preserve the spermatogonial stem cells for future fertility restoration by autografting in young boys suffering from cancer. It appears that besides the potential influence of the cryopreservation technique used, the transplantation procedure itself has a significant impact on spermatogonial loss observed in ITT xenografts. Eighteen ITT pieces issued from 6 patients aged 2–15 years were used. Fragments of fresh tissue (serving as ungrafted controls), frozen-thawed tissue, frozen-thawed tissue supplemented with N-acetylcysteine (NAC), and frozen-thawed tissue supplemented with testosterone xenografted to nude mice for 5 days were compared. Upon graft removal, histological and immunohistochemical analyses were performed to evaluate spermatogonia, intratubular proliferation, and intrinsic and extrinsic apoptosis. A significant decrease in the integrity of intact seminiferous tubules was found in all three grafted groups. Spermatogonia were observed by immunohistochemistry in all grafted groups, with recovery rates of 67, 63, and 53%, respectively, for slow-frozen tissue, slow-frozen tissue supplemented with NAC, and slow-frozen tissue supplemented with testosterone. Apoptosis evidenced by active caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was similar in all grafts. The study is limited by the low availability of ITT samples of human origin, and no clear impact of graft supplementation was found. The mouse xenotransplantation model needs to be refined to investigate human spermatogenesis in human ITT grafts.

Optimizing cryopreservation of human spermatogonial stem cells: comparing the effectiveness of testicular tissue and single cell suspension cryopreservation

OBJECTIVE

To determine whether optimal human spermatogonial stem cell (SSC) cryopreservation is best achieved with testicular tissue or single cell suspension cryopreservation. This study compares the effectiveness between these two approaches by using testicular SSEA-4+ cells, a known population containing SSCs.

DESIGN

In vitro human testicular tissues.

SETTING

Academic research unit.

PATIENT(S)

Adult testicular tissues (n=4) collected from subjects with normal spermatogenesis and normal fetal testicular tissues (n=3).

INTERVENTION(S)

Testicular tissue versus single cell suspension cryopreservation.

MAIN OUTCOME MEASURE(S)

Cell viability, total cell recovery per milligram of tissue, as well as viable and SSEA-4+ cell recovery.

RESULT(S)

Single cell suspension cryopreservation yielded higher recovery of SSEA-4+ cells enriched in adult SSCs, whereas fetal SSEA-4+ cell recovery was similar between testicular tissue and single cell suspension cryopreservation.

CONCLUSION(S)

Adult and fetal human SSEA-4+ populations exhibited differential sensitivity to cryopreservation based on whether they were cryopreserved in situ as testicular tissues or as single cells. Thus, optimal preservation of human SSCs depends on the patient's age, type of samples cryopreserved, and end points of therapeutic applications.

Spermatogonial stem cell preservation and transplantation: from research to clinic

STUDY QUESTION

What issues remain to be solved before fertility preservation and transplantation can be offered to prepubertal boys?

SUMMARY ANSWER

The main issues that need further investigation are malignant cell decontamination, improvement of in vivo fertility restoration and in vitro maturation.

WHAT IS KNOWN ALREADY

Prepubertal boys who need gonadotoxic treatment might render sterile for the rest of their life. As these boys do not yet produce sperm cells, they cannot benefit from sperm banking. Spermatogonial stem cell (SSC) banking followed by autologous transplantation has been proposed as a fertility preservation strategy. But before this technique can be applied in the clinic, some important issues have to be resolved.

STUDY DESIGN, SIZE DURATION

Original articles as well as review articles published in English were included in a search of the literature.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Relevant studies were selected by an extensive Medline search. Search terms were fertility preservation, cryopreservation, prepubertal, SSC, testis tissue, transplantation, grafting and in vitro spermatogenesis. The final number of studies selected for this review was 102.

MAIN RESULTS AND THE ROLE OF CHANCE

Cryopreservation protocols for testicular tissue have been developed and are already being used in the clinic. Since the efficiency and safety of SSC transplantation have been reported in mice, transplantation methods are now being adapted to the human testes. Very recently, a few publications reported on in vitro spermatogenesis in mice, but this technique is still far from being applied in a clinical setting.

LIMITATIONS, REASONS FOR CAUTION

Using tissue from cancer patients holds a potential risk for contamination of the collected testicular tissue. Therefore, it is of immense importance to separate malignant cells from the cell suspension before transplantation. Because biopsies obtained from young boys are small and contain only few SSCs, propagation of these cells in vitro will be necessary.

WIDER IMPLICATIONS OF THE FINDINGS

The ultimate use of the banked tissue will depend on the patient's disease. If the patient was suffering from a non-malignant disease, tissue grafting might be offered. In cancer patients, decontaminated cell suspensions will be injected in the testis. For patients with Klinefelter syndrome, the only option would be in vitro spermatogenesis. However, at present, restoring fertility in cancer and Klinefelter patients is not yet possible.

STUDY FUNDING/COMPETING INTEREST(S)

Research Foundation, Flanders (G.0385.08 to H.T.), the Institute for the Agency for Innovation, Belgium (IWT/SB/111245 to E.G.), the Flemish League against Cancer (to E.G.), Kom op tegen kanker (G.0547.11 to H.T.) and the Fund Willy Gepts (to HT). E.G. is a Postdoctoral Fellow of the FWO, Research Foundation, Flanders. There are no conflicts of interest.

Developing a clinical-grade cryopreservation protocol for human testicular tissue and cells

Recent work in preservation of female fertility as well as new information on the nature of spermatogonial stem cells has prompted an investigation into the possibility of an effective clinical-grade procedure for the cryopreservation of testicular cells and/or tissue. Clinical-grade reagents, validated equipment, and protocols consistent with cGTP/cGMP standards were used in developing a procedure suitable for the safe and effective cryopreservation of human testicular cells and tissues. These procedures were designed to be compliant with the relevant FDA regulations. The procedure proved to effectively cryopreserve both testicular cells and tissue. The cryopreservation of testicular tissue was comparable in most aspects we measured to the cryopreservation of isolated cells, except that the viability of the cells from cryopreserved testicular tissue was found to be significantly higher. On the other hand, cryopreservation of cells is preferred for cell analysis, quality control, and sterility testing. This study demonstrates that testicular tissue and cells from sexual reassignment patients can be successfully cryopreserved with a clinical-grade procedure and important cell populations are not only preserved but also enriched by the process. Further studies will determine whether these findings from hormone-treated patients can be generalized to other patients.