In search of an efficient injection technique for future clinical application of spermatogonial stem cell transplantation: infusion of contrast dyes in isolated cadaveric human testes

Ultrasonographic evaluation of the rete testis thickness: a promising approach to differentiate obstructive from nonobstructive azoospermia

This study aimed to evaluate the ability of rete testis thickness (RTT) and testicular shear wave elastography (SWE) to differentiate obstructive azoospermia (OA) from nonobstructive azoospermia (NOA). We assessed 290 testes of 145 infertile males with azoospermia and 94 testes of 47 healthy volunteers at Shanghai General Hospital (Shanghai, China) between August 2019 and October 2021. The testicular volume (TV), SWE, and RTT were compared among patients with OA and NOA and healthy controls. The diagnostic performances of the three variables were evaluated using the receiver operating characteristic curve. The TV, SWE, and RTT in OA differed significantly from those in NOA (all P ≤ 0.001) but were similar to those in healthy controls. Males with OA and NOA were similar at TVs of 9-11 cm 3 ( P = 0.838), with sensitivity, specificity, Youden index, and area under the curve of 50.0%, 84.2%, 0.34, and 0.662 (95% confidence interval [CI]: 0.502-0.799), respectively, for SWE cut-off of 3.1 kPa; and 94.1%, 79.2%, 0.74, and 0.904 (95% CI: 0.811-0.996), respectively, for RTT cut-off of 1.6 mm. The results showed that RTT performed significantly better than SWE in differentiating OA from NOA in the TV overlap range. In conclusion, ultrasonographic RTT evaluation proved a promising diagnostic approach to differentiate OA from NOA, particularly in the TV overlap range.

Effects of therapeutic ultrasound and moderate heat on stallion testes

Transplantation of stem cells into dysfunctional testes is currently being investigated as a therapeutic option for men and stallions with advanced testicular degeneration. This series of "proof of concept" studies aimed to identify a safe and efficient method of inducing severe testicular degeneration to create an optimal equine recipient model for intratesticular stem cell transplantation (SCT). Two ex vivo and two in vivo experiments were conducted. At first, forty testes obtained from castrations were used to identify an effective therapeutic ultrasound (TUS) device and the protocol for increasing intratesticular temperature in stallions. Six min of treatment using the Vetrison Clinic Portable TUS machine raised the intratesticular temperature by 8°C-12.5 °C. This protocol was applied to treat three scrotal testes in three Miniature horse stallions, three times, every other day. Contralateral testes served as controls. There were signs of slight tubular degeneration in treated testes two and three weeks after TUS treatment. The number of seminiferous tubules (STs) with exfoliated germ cells (GCs) was increased in one testis only, three weeks after treatment. The degree of apoptosis of GCs was higher in each treated testis in comparison to the contralateral control testis. Next, the ability of various heating devices to increase intratesticular temperatures to at least 43 °C in stallion testes was tested, using twenty testes obtained from castrations. ThermaCare® Lower Back & Hip Pain Therapy Heatwrap (TC heat wrap) reliably increased intratesticular temperatures and kept them continuously between 43 °C and 48 °C for seven to 8 h. In the follow-up in vivo study, the left testes of three Miniature horse stallions were treated with TUS, after which both testes of each stallion were treated with moderate heat provided by the TC heat wrap (three times, every other day, for 5 h each time). There were signs of moderate tubular degeneration in the samples from all treated testes obtained three weeks after treatments (Heat only or Heat/TUS): areas with hypospermatogenesis, spermatogenic arrest, vacuolized Sertoli cells, numerous STs with exfoliated GCs, increased degree of GCs apoptosis, and changes in three histomorphometric numeric attributes of STs. We concluded that TUS or TC wraps increase intratesticular temperature of the isolated stallion testes. Further, treatment with TUS or moderate heat may induce mild to moderate degenerative changes in stallion testes. However, to achieve more robust result - severe testicular degeneration, our treatment protocol has to be modified.

Updates in Sertoli Cell-Mediated Signaling During Spermatogenesis and Advances in Restoring Sertoli Cell Function

Since their initial description by Enrico Sertoli in 1865, Sertoli cells have continued to enchant testis biologists. Testis size and germ cell carrying capacity are intimately tied to Sertoli cell number and function. One critical Sertoli cell function is signaling from Sertoli cells to germ cells as part of regulation of the spermatogenic cycle. Sertoli cell signals can be endocrine or paracrine in nature. Here we review recent advances in understanding the interplay of Sertoli cell endocrine and paracrine signals that regulate germ cell state. Although these findings have long-term implications for treating male infertility, recent breakthroughs in Sertoli cell transplantation have more immediate implications. We summarize the surge of advances in Sertoli cell ablation and transplantation, both of which are wedded to a growing understanding of the unique Sertoli cell niche in the transitional zone of the testis.

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.

Ex vivo human testes as a practical model to simulate ultrasound-guided testicular cell transplantation for human fertility restoration

OBJECTIVE

To develop an ex vivo model to practice ultrasound-guided injection of cellular material into human seminiferous tubules to simulate testicular cell transplantation (TCT).

DESIGN

Simulated TCT injections were performed in human testes removed during orchiectomy. The rete testis was the target site of injection. Successful retrograde infiltration of injected material into the lumen of the seminiferous tubules was detected using ultrasound and confirmed with histology.

SETTING

Single academic surgical center.

PATIENT(S)

Adult patients undergoing orchiectomy for nononcologic indications.

INTERVENTION(S)

The testes were injected with sonographic contrast (Optison), methylene blue, and fluorescent-labeled cells.

MAIN OUTCOME MEASURE(S)

A characteristic streaming pattern of sonographic contrast in the testis was used to define sonographic success, and the presence of methylene blue and fluorescent-labeled cells within the seminiferous tubules confirmed histologic success.

RESULT(S)

We performed simulated TCT injections in 30 testes obtained from 16 patients undergoing orchiectomy. We were able to achieve sonographic success in 57% of injections and confirmed that sonographic success is correlated with histologic success.

CONCLUSION(S)

Testicular cell transplantation injections can be practiced using human testes. As there appears to be a learning curve associated with this procedure, developing this infrastructure to practice these skills is critical before implementation in patients.

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.

Review of injection techniques for spermatogonial stem cell transplantation

BACKGROUND

Although the prognosis of childhood cancer survivors has increased dramatically during recent years, chemotherapy and radiation treatments for cancer and other conditions may lead to permanent infertility in prepubertal boys. Recent developments have shown that spermatogonial stem cell (SSC) transplantation may be a hope for restoring fertility in adult survivors of childhood cancers. For this reason, several centres around the world are collecting and cryopreserving testicular tissue or cells anticipating that, in the near future, some patients will return for SSC transplantation. This review summarizes the current knowledge and utility of SSC transplantation techniques.

OBJECTIVE AND RATIONALE

The aim of this narrative review is to provide an overview of the currently used experimental injection techniques for SSC transplantation in animal and human testes. This is crucial in understanding and determining the role of the different techniques necessary for successful transplantation.

SEARCH METHODS

A comprehensive review of peer-reviewed publications on this topic was performed using the PubMed and Google Scholar databases. The search was limited to English language work and studies between 1994 (from the first study on SSC transplantation) and April 2019. Key search terms included mouse, rat, boar, ram, dog, sheep, goat, cattle, monkey, human, cadaver, testes, SSC transplantation, injection and technique.

OUTCOMES

This review provides an extensive clinical overview of the current research in the field of human SSC transplantation. Rete testis injection with ultrasonography guidance currently seems the most promising injection technique thus far; however, the ability to draw clear conclusions is limited due to long ischemia time of cadaver testis, the relatively decreased volume of the testis, the diminishing size of seminiferous tubules, a lack of intratesticular pressure and leakage into the interstitium during the injection on human cadaver testis. Current evidence does not support improved outcomes from multiple infusions through the rete testes. Overall, further optimization is required to increase the efficiency and safety of the infusion method.

WIDER IMPLICATIONS

Identifying a favourable injection method for SSC transplantation will provide insight into the mechanisms of successful assisted human reproduction. Future research could focus on reducing leakage and establishing the optimal infusion cell concentrations and pressure.

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.

Cryostorage of testicular tissue and retransplantation of spermatogonial stem cells in the infertile male

Transplantation of own cryostored spermatogonial stem cells (SSCs) is a promising technique for fertility restoration when the SSC pool has been depleted. In this regard, cryopreservation of pre-pubertal testicular tissue or SSCs suspensions before gonadotoxic therapies is ethically accepted and increasingly proposed. SSC transplantation has also been considered to treat other causes of infertility relying on the possibility of propagating SSCs retrieved in the testes of infertile men before autologous re-transplantation. Although encouraging results were achieved in animals and in preclinical experiments, clinical perspectives are still limited by a number of unresolved technical and safety issues, such as the risk of cancer cell contamination of cells intended for transplantation and the genetic and epigenetic stability of SCCs when cultured before re-transplantation. Moreover, while genome editing techniques raise the hope of modifying the SSCs genome before re-transplantation, their application for reproductive purposes might be a step too far for the moment.

Experimental models of testicular development and function using human tissue and cells

The mammalian testis has two main roles, production of gametes for reproduction and synthesis of steroid- and peptide hormones for masculinization. These processes are tightly regulated and involve complex interactions between a number of germ and somatic cell-types that comprise a unique microenvironment known as the germ stem cell niche. In humans, failure of normal testicular development or function is associated with susceptibility to a variety of male reproductive disorders including disorders of sex development, infertility and testicular cancer. Whilst studies in rodent models have provided detailed insight into the signaling pathways and molecular mechanisms that regulate the testis, there are important species differences in testicular development, function and reproductive disorders that highlight the need for suitable experimental models utilising human testicular tissues or cells. In this review, we outline experimental approaches used to sustain cells and tissue from human testis at different developmental time-points and discuss relevant end-points. These include survival, proliferation and differentiation of cell lineages within the testis as well as autocrine, paracrine and endocrine function. We also highlight the utility of these experimental approaches for modelling the effects of environmental exposures on testicular development and function.

Tissue Engineering to Improve Immature Testicular Tissue and Cell Transplantation Outcomes: One Step Closer to Fertility Restoration for Prepubertal Boys Exposed to Gonadotoxic Treatments

Despite their important contribution to the cure of both oncological and benign diseases, gonadotoxic therapies present the risk of a severe impairment of fertility. Sperm cryopreservation is not an option to preserve prepubertal boys’ reproductive potential, as their seminiferous tubules only contain spermatogonial stem cells (as diploid precursors of spermatozoa). Cryobanking of human immature testicular tissue (ITT) prior to gonadotoxic therapies is an accepted practice. Evaluation of cryopreserved ITT using xenotransplantation in nude mice showed the survival of a limited proportion of spermatogonia and their ability to proliferate and initiate differentiation. However, complete spermatogenesis could not be achieved in the mouse model. Loss of germ cells after ITT grafting points to the need to optimize the transplantation technique. Tissue engineering, a new branch of science that aims at improving cellular environment using scaffolds and molecules administration, might be an approach for further progress. In this review, after summarizing the lessons learned from human prepubertal testicular germ cells or tissue xenotransplantation experiments, we will focus on the benefits that might be gathered using bioengineering techniques to enhance transplantation outcomes by optimizing early tissue graft revascularization, protecting cells from toxic insults linked to ischemic injury and exploring strategies to promote cellular differentiation.

Long-term health in recipients of transplanted in vitro propagated spermatogonial stem cells

STUDY QUESTION

Is testicular transplantation of in vitro propagated spermatogonial stem cells associated with increased cancer incidence and decreased survival rates in recipient mice?

SUMMARY ANSWER

Cancer incidence was not increased and long-term survival rate was not altered after transplantation of in vitro propagated murine spermatogonial stem cells (SSCs) in busulfan-treated recipients as compared to non-transplanted busulfan-treated controls.

WHAT IS KNOWN ALREADY

Spermatogonial stem cell autotransplantation (SSCT) is a promising experimental reproductive technique currently under development to restore fertility in male childhood cancer survivors. Most preclinical studies have focused on the proof-of-principle of the functionality and efficiency of this technique. The long-term health of recipients of SSCT has not been studied systematically.

STUDY DESIGN, SIZE, DURATION

This study was designed as a murine equivalent of a clinical prospective study design. Long-term follow-up was performed for mice who received a busulfan treatment followed by either an intratesticular transplantation of in vitro propagated enhanced green fluorescent protein (eGFP) positive SSCs (cases, n = 34) or no transplantation (control, n = 37). Using a power calculation, we estimated that 36 animals per group would be sufficient to provide an 80% power and with a 5% level of significance to demonstrate a 25% increase in cancer incidence in the transplanted group. The survival rate and cancer incidence was investigated until the age of 18 months.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Neonatal male B6D2F1 actin-eGFP transgenic mouse testis were used to initiate eGFP positive germline stem (GS) cell culture, which harbor SSCs. Six-week old male C57BL/6 J mice received a single dose busulfan treatment to deplete the testis from endogenous spermatogenesis. Half of these mice received a testicular transplantation of cultured eGFP positive GS cells, while the remainder of mice served as a control group. Mice were followed up until the age of 18 months (497-517 days post-busulfan) or sacrificed earlier due to severe discomfort or illness. Survival data were collected. To evaluate cancer incidence a necropsy was performed and tissues were collected. eGFP signal in transplanted testis and in benign and malignant lesions was assessed by standard PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

We found 9% (95% CI: 2-25%) malignancies in the transplanted busulfan-treated animals compared to 26% (95% CI: 14-45%) in the busulfan-treated control group, indicating no statistically significant difference in incidence of malignant lesions in transplanted and control mice (OR: 0.3, 95% CI: 0.1-1.1). Furthermore, none of the malignancies that arose in the transplanted animals contained eGFP signal, suggesting that they are not derived from the in vitro propagated transplanted SSCs. Mean survival time after busulfan treatment was found to be equal, with a mean survival time for transplanted animals of 478 days and 437 days for control animals (P = 0.076).

LARGE SCALE DATA

NA.

LIMITATIONS, REASONS FOR CAUTION

Although we attempted to mimic the future clinical application of SSCT in humans as close as possible, the mouse model that we used might not reflect all aspects of the future clinical setting.

WIDER IMPLICATIONS OF THE FINDINGS

The absence of an increase in cancer incidence and a decrease in survival of mice that received a testicular transplantation of in vitro propagated SSCs is reassuring in light of the future clinical application of SSCT in humans.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by KiKa (Kika86) and ZonMw (TAS 116003002). The authors report no financial or other conflict of interest relevant to the subject of this article.

Spermatogonial stem cell transplantation and male infertility: Current status and future directions

Objective

To summarise the current state of research into spermatogonial stem cell (SSC) therapies with a focus on future directions, as SSCs show promise as a source for preserving or initiating fertility in otherwise infertile men.

Materials and methods

We performed a search for publications addressing spermatogonial stem cell transplantation in the treatment of male infertility. The search engines PubMed and Google Scholar were used from 1990 to 2017. Search terms were relevant for spermatogonial stem cell therapies. Titles of publications were screened for relevance; abstracts were read, if related and full papers were reviewed for directly pertinent original research.

Results

In all, 58 papers were found to be relevant to this review, and were included in appropriate subheadings. This review discusses the various techniques that SSCs are being investigated to treat forms of male infertility.

Conclusions

Evidence does not yet support clinical application of SSCs in humans. However, significant progress in the in vitro and in vivo development of SSCs, including differentiation into functional germ cells, gives reason for cautious optimism for future research.

[Androprotect and prospects for fertility treatment]

BACKGROUND

Fertility protection is essential for men undergoing potentially gonadotoxic treatment. It is usually offered to adolescents and men in reproductive age by semen cryopreservation. In case of azoospermia, testicular sperm cryopreservation is an additional option. In prepubertal boys no sperm cryopreservation is possible. A purely experimental option is cryopreservation of spermatogonial stem cells in immature testis tissue.

METHOD

Transplantation of either immature testis tissue or testicular stem cells or spermatogonia generated in vitro from stem cells are possible options for fertility preservation in boys.

OBJECTIVES

In this article, the rationale for cryopreservation of gonadal stem cells and the experimental methods for refertilization are summarized. The current research, national and international clinical and research activities and possible perspectives of further development of fertility preservation are explained.

In search of an improved injection technique for the clinical application of spermatogonial stem cell transplantation

When fertility is impaired by anticancer treatment, spermatogonial stem cell transplantation (SSCT) could be used as a fertility restoration technique later on in life. Previously, we have demonstrated that a testicular cell suspension could be injected into a human cadaver testis, however, leakage to the interstitium was observed. In this study, injection of mouse testicular cells at an injection height of 50 cm (hydrostatic pressure) or via an automated injection pump (1400 µl, 2600 µl and 3000 µl) was evaluated. Significant difference in the filled radioactive volume was reached between the group in which 1400 µl was injected with an infusion pump and the groups in which 2600 µl (P = 0.019) or 3000 µl (P = 0.010) was injected. In all experimental groups green fluorescent protein positive (GFP⁺) cells were observed in the seminiferous tubules. In conclusion, a lower injection height did not resolve the leakage of the injected cells to the interstitium. Using the infusion pump resulted in more efficient filling of the seminiferous tubules with lower interexperimental variability. Although leakage to the interstitium was still observed, with further optimisation, the use of an infusion pump for clinical application is advantageous.

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.

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.

Fertility preservation in men with cancer

During the past decade, advances in cancer treatment have increased survival rates of both boys and men. However, cancer treatment itself can compromise fertility, especially exposure to alkylating agents and whole body irradiation, which cause substantial germ cell loss. Children and adolescents with testicular cancer, leukaemia, and Ewing sarcomas are at the highest risk of developing permanent sterility from cancer treatment. Consequently, various strategies to preserve fertility are necessary. Sperm cryopreservation is an effective but underused method to safeguard spermatozoa. In the past few years, large advances have been made in prepubertal germ cell storage aimed at subsequent transplantation of testicular tissue and associated stem cells. Although still experimental, these approaches offer hope to many men in whom germ cell loss is associated with sterility. The derivation of male gametes from stem cells also holds much promise; however, data are only available in animals, and the use of this method in human beings is probably many years away.

Testicular cell transplantation into the human testes

OBJECTIVE

To translate spermatogonial stem cell (SSC) transplantation towards a clinical application.

DESIGN

Mouse green fluorescent protein (GFP)-positive testicular cells were labeled with (99m)technetium and microbubbles. These labeled cells were injected into the rete testis of isolated human testes under ultrasound guidance. Three different conditions were tested: 1) 800 μL of a 20 million cells/mL suspension; 2) 800 μL of a 10 million cells/mL suspension; and 3) 1,400 μL of a 10 million cells/mL suspension. After injection, the human cadaver testes were analyzed with the use of single-photon-emission computerized tomography (SPECT) imaging and histology.

SETTING

Laboratory research environment.

PATIENT(S)

Cadaver testes, obtained from autopsies at the pathology department.

INTERVENTION(S)

Ultrasound-guided injection of mouse GFP-positive testicular cells.

MAIN OUTCOME MEASURE(S)

Presence of radioactive-labeled cells in the human cadaver testes and GFP-positive cells in the seminiferous tubules.

RESULT(S)

In all of the experimental groups, GFP-positive cells were observed in the seminiferous tubules, near and far from the rete testis, but also in the interstitium. On SPECT, significant difference was seen between the group injected with 800 μL of a 20 million cells/mL suspension (1,654.6 ± 907.6 mm³) and the group injected with 1,400 μL of a 10 million cells/mL suspension (3,614.9 ± 723.1 mm³). No significant difference was reached in the group injected with 800 μL of a 10 million cells/mL suspension.

CONCLUSION(S)

Injecting cells in the human cadaver testis is feasible, but further optimization is required.

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.

Restoring fertility in sterile childhood cancer survivors by autotransplanting spermatogonial stem cells: are we there yet?

Current cancer treatment regimens do not only target tumor cells, but can also have devastating effects on the spermatogonial stem cell pool, resulting in a lack of functional gametes and hence sterility. In adult men, fertility can be preserved prior to cancer treatment by cryopreservation of ejaculated or surgically retrieved spermatozoa, but this is not an option for prepubertal boys since spermatogenesis does not commence until puberty. Cryopreservation of a testicular biopsy taken before initiation of cancer treatment, followed by in vitro propagation of spermatogonial stem cells and subsequent autotransplantation of these stem cells after cancer treatment, has been suggested as a way to preserve and restore fertility in childhood cancer survivors. This strategy, known as spermatogonial stem cell transplantation, has been successful in mice and other model systems, but has not yet been applied in humans. Although recent progress has brought clinical application of spermatogonial stem cell autotransplantation in closer range, there are still a number of important issues to address. In this paper, we describe the state of the art of spermatogonial stem cell transplantation and outline the hurdles that need to be overcome before clinical implementation.