The Good, the Bad and the Ugly of Testicular Immune Regulation: A Delicate Balance Between Immune Function and Immune Privilege

Unwrapping the immunological alterations in testicular germ cell tumors: From immune homeostasis to malignancy and emerging immunotherapies

BACKGROUND

Testicular germ cell tumors (TGCTs), derived from primordial germ cells, are rare malignancies with high curative potential. However, the emergence of new evidence indicating that 15% of patients experience tumor progression, leading to death, underscores the need for innovative therapeutics.

OBJECTIVES

This review aimed to explore the immune status in maintaining testicular health and the immune-related aspects of malignancy. Furthermore, it presents an overview of current data on the use of immunotherapy for TGCT patients.

RESULTS DISCUSSION

Recent advances in immunology have opened a promising avenue for studying diseases and highlighted its role in treating diseases. While the immunopathological facets of TGCTs are not fully understood, investigations suggest a complex interplay among testis-resident immune cells, testis-specific cells (i.e., Sertoli cells (SCs) and Leydig cells (LCs)), and immune-regulating mediators (e.g., sex hormones) in the normal testicle that foster the testicular immune privilege (TIP). Although TIP plays a crucial role in sperm production, it also makes testis vulnerable to tumor development. In the context of cancer-related inflammation, disruption of TIP leads to an imbalanced immune response, resulting in chronic inflammation that can contribute to testicular tissue dysfunction or loss, potentially aiding in cancer invasion and progression.

CONCLUSION

Comparing the immune profiles of normal and malignant testes is valuable and may provide insights into different aspects of testicular immunity and immune-based treatment approaches. For patients resistant to chemotherapy and with a poor prognosis, immunotherapy has shown promising results. However, its effectiveness in treating resistant TGCTs or preventing tumor recurrence is still uncertain.

Ebola Virus Disease Outbreaks: Lessons Learned From Past and Facing Future Challenges

INTRODUCTION

The purpose of this review is to examine African Ebola outbreaks from their first discovery to the present, to determine how the medical and public health response has changed and identify the causes for those changes. We sought to describe what is now known about the epidemiology and spread of Ebola virus disease (EVD) from the significant outbreaks that have occurred and outbreak control methods applied under often challenging circumstances. Given the substantial role that the U.S. Government and the U.S. DoD have played in the 2014 to 2016 West African Ebola outbreak, the role of the DoD and the U.S. Africa Command in controlling EVD is described.

MATERIALS AND METHODS

A descriptive method design was used to collect and analyze all available Ebola outbreak literature using the PubMed database. An initial literature search was conducted by searching for, obtaining, and reading original source articles on all major global Ebola outbreaks. To conduct a focused search, we used initial search terms "Ebola outbreak," "Ebola virus disease," "Ebola response," "Ebola countermeasures," and also included each country's name where Ebola cases are known to have occurred. From the 4,673 unique articles obtained from this search and subsequent article title review, 307 articles were identified for potential inclusion. Following abstract and article review, 45 original source articles were used to compile the history of significant Ebola outbreaks. From this compilation, articles focused on each respective subsection of this review to delineate and describe the history of EVD and response, identifying fundamental changes, were obtained and incorporated.

RESULTS

We present known Ebola virus and disease attributes, including a general description, seasonality and location, transmission capacity, clinical symptoms, surveillance, virology, historical EVD outbreaks and response, international support for Ebola outbreak response, U.S. DoD support, medical countermeasures supporting outbreak response, remaining gaps to include policy limitations, regional instability, climate change, migration, and urbanization, public health education and infrastructure, and virus persistence and public awareness.

CONCLUSIONS

The health and societal impacts of EVD on Africa has been far-reaching, with about 35,000 cases and over 15,000 deaths, with small numbers of cases spreading globally. However, the history of combatting EVD reveals that there is considerable hope for African nations to quickly and successfully respond to Ebola outbreaks, through use of endemic resources including Africa CDC and African Partner Outbreak Response Alliance and the U.S. Africa Command with greater DoD reachback. Although there remains much to be learned about the Ebola virus and EVD including whether the potential for novel strains to become deadly emerging infections, invaluable vaccines, antivirals, and public health measures are now part of the resources that can be used to combat this disease.

T cells in testicular germ cell tumors: new evidence of fundamental contributions by rare subsets

BACKGROUND

Immune cell infiltration is heterogeneous but common in testicular germ cell tumors (TGCT) and pre-invasive germ cell neoplasia in situ (GCNIS). Tumor-infiltrating T cells including regulatory T (Treg) and follicular helper T (Tfh) cells are found in other cancer entities, but their contributions to TGCT are unknown.

METHODS

Human testis specimens from independent patient cohorts were analyzed using immunohistochemistry, flow cytometry and single-cell RNA sequencing (scRNA-seq) with special emphasis on delineating T cell subtypes.

RESULTS

Profound changes in immune cell composition within TGCT, shifting from macrophages in normal testes to T cells plus B and dendritic cells in TGCT, were documented. In most samples (96%), the CD4+ T cell frequency exceeded that of CD8+ cells, with decreasing numbers from central to peripheral tumor areas, and to tumor-free, contralateral testes. T cells including Treg and Tfh were most abundant in seminoma compared to mixed tumors and embryonal carcinoma.

CONCLUSION

Despite considerable heterogeneity between patients, T cell subtypes form a key part of the TGCT microenvironment. The novel finding of rare Treg and Tfh cells in human testis suggests their involvement in TGCT pathobiology, with implications for understanding tumor progression, to assess patients' prognosis, and as putative targets for personalized immunotherapy.

Acute murine-betacoronavirus infection impairs testicular steroidogenesis and the quality of sperm production

Although several testicular alterations promoted by coronavirus infection have been demonstrated, the extent, causes, and players of testicular pathogenesis are not totally understood. The present study aimed to investigate the short-term effects on male fertility of intranasally administered murine hepatitis virus strain 3 (MHV-3), a member of the genus Betacoronavirus, which causes a severe systemic acute infection. This mouse model might be used as a in vivo prototype for investigating the impact of betacoronavirus on the endocrine and exocrine testicular functions with the advantage to be performed in a biosafety level 2 condition. Herein, we performed virological, histopathological, and molecular studies regarding the testicular spermatogenesis and the spermatic quality analyses in an MHV-3-infected C57BL/6 mice. The main outcomes showed that MHV-3 infects mouse testis and induces a testicular inflammatory state, impairing the steroidogenic pathway. The infection led to several alterations in the testicular parenchyma, such as: seminiferous epithelium sloughing, retention of residual bodies, germ cell apoptosis, alterations in intercellular junction proteins, and worse spermatogenic parameters. Moreover, the levels of plasmatic testosterone as well as the quality of sperm production reduced. Therefore, the present data suggest that the viral/inflammatory impairment of the steroidogenic pathway and the consequent imbalance of androgen levels is critical in testicular pathology, disturbing the SC barrier function and the germ cell differentiation. Our study is important for comprehending the effects of beta coronavirus infections on testis function in order to develop treatments that could prevent virus-mediated male infertility.

Morphology of the immune cells in the wall of the human uterine tube and their possible impact on reproduction-uterine tube as a possible immune privileged organ

The uterine tube, as well as other parts of the upper female reproductive system, is immunologically unique in its requirements for tolerance to allogenic sperm and semi-allogenic embryos, yet responds to an array of sexually transmitted pathogens. To understand this dichotomy, there is a need to understand the functional morphology of immune cells in the wall of the uterine tube. Thus, we reviewed scientific literature regarding immune cells and the human uterine tube by using the scientific databases. The human uterine tube has a diverse population of immunocompetent cells representing both the innate and adaptive immune systems. We describe in detail the possible roles of cells of the mononuclear phagocyte system (macrophages and dendritic cells), T and B lymphocytes, natural killer cells, neutrophils and mast cells in association with the reproductive functions of uterine tubes. We are also discussing about the possible "immune privilege" of the uterine tube, as another mechanism to tolerate sperm and embryo without eliciting an inflammatory immune response. In uterine tube is not present an anatomical blood-tissue barrier between antigens and circulation. However, the immune cells of the uterine tube probably represent a type of "immunological barrier," which probably includes the uterine tube among the immunologically privileged organs. Understanding how immune cells in the female reproductive tract play roles in reproduction is essential to understand not only the mechanisms of gamete transport and fertilization as well as embryo transport through the uterine tube, but also in improving results from assisted reproduction.

Testicular pathological alterations associated with SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the etiologic agent of the coronavirus disease 2019 (COVID-19), which caused one of the pandemics with the highest mortalities with millions of deaths and hundreds of millions of cases to date. Due to its potential for airborne transmission, many studies have focused on SARS-CoV-2 primarily as a respiratory disease. However, the spread of SARS-CoV-2 to non-respiratory organs has been experimentally demonstrated and clinically observed. During autopsy studies, histopathological lesions, and disruption of the blood-testes barrier (BTB) have been observed in the male reproductive tract. Here, we review findings from both autopsy cases and animal models that demonstrate testicular disease due to COVID-19 and present an overview of the pathological alterations that occur in the testes resulting from SARS-CoV-2 infection and explore its potential mechanisms.

The Sertoli Cell Complement Signature: A Suspected Mechanism in Xenograft Survival

The complement system is an important component of transplant rejection. Sertoli cells, an immune regulatory testicular cell, survive long-term when transplanted across immunological barriers; thus, understanding the mechanisms behind this unique survival would be of great benefit to the transplantation field. This study focused on Sertoli cell inhibition of complement as relevant in xenotransplantation. Neonatal pig Sertoli cells (NPSCs) survived activated human complement in vitro while neonatal pig islet (NPI) aggregates and pig aortic endothelial cell (PAEC) survival were diminished to about 65% and 12%, respectively. PAECs cultured in NPSC-conditioned media and human complement demonstrated a 200% increase in survival suggesting that NPSCs secrete complement-inhibiting substances that confer protection. Bioinformatic and molecular analyses identified 21 complement inhibitors expressed by NPSCs with several significantly increased in NPSCs compared to NPIs or PAECs. Lastly, RNA sequencing revealed that NPSCs express 25 other complement factors including cascade components and receptors. Overall, this study identified the most comprehensive Sertoli cell complement signature to date and indicates that the expression of a variety of complement inhibitors ensures a proper regulation of complement through redundant inhibition points. Understanding the regulation of the complement system should be further investigated for extending xenograft viability.

Transmigration of macrophages through primary adult rat Sertoli cells

The blood testis barrier (BTB) is often studied with isolated immature Sertoli cells (SCs), transepithelial resistance (TER) measurements and FITC dextran diffusion assays. Recently, it was found that even in the absence of SCs, only few immune cells enter the seminiferous tubules. Thus, in this study, we evaluated the testicular immunological barrier (TIB) in vitro by transmigration of macrophages through SCs with and without peritubular cells (PCs) and with or without matrigel (MG). Primary PCs were isolated from adult rat testis and kept in mono- or co-cultures with the conditionally reprogrammed primary adult Sertoli cell line (PASC1) from rat that has been recently generated by our group. Rat monocytes isolated from fresh blood were differentiated into M0 macrophages, and after polarization to M1 or M2 macrophages characterized by gene expression of CXCL11 and TNF-α for M1, or CCL17 and CCL22 for M2. Transmigration of LeukoTracker-labeled M0, M1, and M2 macrophages through mono- and co-cultures of PCs/SCs with and without MG demonstrated that SCs are the main constituent of the TIB in vitro with only a negligible contribution of PCs or MG. Moreover, M2 macrophages showed less migration activity compared to M0 or M1. Treatment of SCs with testosterone (T) showed positive effects on the barrier in contrast to negative effects by interleukin-6 (IL-6) or tumor necrosis factor-α (TNF-α). The new transmigration model is suitable to evaluate transmigration of macrophages through a barrier consisting of testicular cells and can be applied to study the integrity of testicular barriers with respect to immunological aspects.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

Why does viral RNA sometimes persist after recovery from acute infections?

DNA viruses often persist in the body of their host, becoming latent and recurring many months or years later. By contrast, most RNA viruses cause acute infections that are cleared from the host as they lack the mechanisms to persist. However, it is becoming clear that viral RNA can persist after clinical recovery and elimination of detectable infectious virus. This persistence can either be asymptomatic or associated with late progressive disease or nonspecific lingering symptoms, such as may be the case following infection with Ebola or Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Why does viral RNA sometimes persist after recovery from an acute infection? Where does the RNA come from? And what are the consequences?

Tissue-resident immunity in the female and male reproductive tract

The conception of how the immune system is organized has been significantly challenged over the last years. It became evident that not all lymphocytes are mobile and recirculate through secondary lymphoid organs. Instead, subsets of immune cells continuously reside in tissues until being reactivated, e.g., by a recurring pathogen or other stimuli. Consequently, the concept of tissue-resident immunity has emerged, and substantial evidence is now available to support its pivotal function in maintaining tissue homeostasis, sensing challenges and providing antimicrobial protection. Surprisingly, insights on tissue-resident immunity in the barrier tissues of the female reproductive tract are sparse and only slowly emerging. The need for protection from vaginal and amniotic infections, the uniqueness of periodic tissue shedding and renewal of the endometrial barrier tissue, and the demand for a tailored decidual immune adaptation during pregnancy highlight that tissue-resident immunity may play a crucial role in distinct compartments of the female reproductive tract. This review accentuates the characteristics of tissue-resident immune cells in the vagina, endometrium, and the decidua during pregnancy and discusses their functional role in modulating the risk for infertility, pregnancy complications, infections, or cancer. We here also review data published to date on tissue-resident immunity in the male reproductive organs, which is still a largely uncharted territory.

Therapeutic application of Sertoli cells for treatment of various diseases

Sertoli cells (SCs) are immune privileged cells found in the testis that function to immunologically protect maturing germ cells from immune destruction. This immune protection is due to the blood-testis-barrier, which prevents infiltration of cytotoxic immune cells and antibodies, and SC production of immunomodulatory factors, that favor a tolerogenic environment. The ability of SCs to create an immune privileged environment has led to the exploration of their potential use in the treatment of various diseases. SCs have been utilized to create a tolerogenic ectopic microenvironment, to protect co-grafted cells, and to deliver therapeutic proteins through gene therapy. To date, numerous studies have reported the potential use of SCs for the treatment of diabetes, neurodegenerative disorders, and restoration of spermatogenesis. Additionally, SCs have been investigated as a delivery vehicle for therapeutic products to treat other diseases like Laron syndrome, muscular dystrophy, and infections. This review will provide an overview of these therapeutic applications.