Simian immunodeficiency virus infection and immune responses in the pig-tailed macaque testis

The Role of Mononuclear Phagocytes in the Testes and Epididymis

The mononuclear phagocytic system (MPS) is the primary innate immune cell group in male reproductive tissues, maintaining the balance of pro-inflammatory and immune tolerance. This article aims to outline the role of mononuclear macrophages in the immune balance of the testes and epididymis, and to understand the inner immune regulation mechanism. A review of pertinent publications was performed using the PubMed and Google Scholar databases on all articles published prior to January 2021. Search terms were based on the following keywords: 'MPS', 'mononuclear phagocytes', 'testes', 'epididymis', 'macrophage', 'Mφ', 'dendritic cell', 'DC', 'TLR', 'immune', 'inflammation', and 'polarization'. Additionally, reference lists of primary and review articles were reviewed for other publications of relevance. This review concluded that MPS exhibits a precise balance in the male reproductive system. In the testes, MPS cells are mainly suppressed subtypes (M2 and cDC2) under physiological conditions, which maintain the local immune tolerance. Under pathological conditions, MPS cells will transform into M1 and cDC1, producing various cytokines, and will activate T cell specific immunity as defense to foreign pathogens or self-antigens. In the epididymis, MPS cells vary in the different segments, which express immune tolerance in the caput and pro-inflammatory condition in the cauda. Collectively, MPS is the control point for maintaining the immune tolerance of the testes and epididymis as well as for eliminating pathogens.

More than a Gender Issue: Testis as a Distinctive HIV Reservoir and Its Implication for Viral Eradication

Early establishment of HIV reservoir represents the main impediment to an HIV cure. Mainly composed of infected memory CD4 T-cells and macrophages, HIV reservoirs are found in several organs including lymph nodes, gut, and testes. In men, and as seen in brain and eyes, testes represent a distinctive organ characterized by an immune privilege, allowing the tolerance of spermatozoa which only develop after puberty, long after the establishment of systemic immunity. The immune privilege of testes relies on a strict testis-blood barrier, and a local immunosuppressive environment. Testes has been described as reservoir for several viruses including Ebola, Zika, and HIV. Indeed, HIV reservoirs were detected in tested viremic and virally suppressed donor taking antiretroviral therapy (ART). Herein, we discuss the distinctive environment found in human testes and describe a validated method allowing the characterization and quantification of HIV-infected CD4 T-cells in human testes. Using mechanical and enzymatic treatment, cells can be extracted from human testis samples. Characterization of those cells can be performed by flow cytometry and HIV reservoir quantification performed by nested qPCR after flow cytometry sorting.

Glucose Metabolism Disorder Induces Spermatogenic Dysfunction in Northern Pig-Tailed Macaques (Macaca leonina) With Long-Term SIVmac239 Infection

Although spermatogenic dysfunction is widely found in patients with human immunodeficiency virus (HIV), the underlying reasons remain unclear. Thus far, potential hypotheses involving viral reservoirs, testicular inflammation, hormone imbalance, and cachexia show inconsistent correlation with spermatogenic dysfunction. Here, northern pig-tailed macaques (NPMs) exhibited marked spermatogenic dysfunction after long-term infection with simian immunodeficiency virus (SIVmac239), with significant decreases in Johnsen scores, differentiated spermatogonial stem cells, and testicular proliferating cells. The above hypotheses were also evaluated. Results showed no differences between SIV- and SIV+ NPMs, except for an increase in follicle stimulating hormone (FSH) during SIV infection, which had no direct effect on the testes. However, long-term SIVmac239 infection undermined pancreatic islet β cell function, partly represented by significant reductions in cellular counts and autophagy levels. Pancreatic islet β cell dysfunction led to glucose metabolism disorder at the whole-body level, which inhibited lactate production by Sertoli cells in testicular tissue. As lactate is the main energy substrate for developing germ cells, its decrease was strongly correlated with spermatogenic dysfunction. Therefore, glucose metabolism disorder appears to be a primary cause of spermatogenic dysfunction in NPMs with long-term SIVmac239 infection.

T Lymphocytes and Testicular Immunity: A New Insight into Immune Regulation in Testes

The immune privilege of the testes is necessary to prevent immune attacks to gamete-specific antigens and paternal major histocompatibility complex (MHC) antigens, allowing for normal spermatogenesis. However, infection and inflammation of the male genital tract can break the immune tolerance and represent a significant cause of male infertility. Different T cell subsets have been identified in mammalian testes, which may be involved in the maintenance of immune tolerance and pathogenic immune responses in testicular infection and inflammation. We reviewed the evidence in the published literature on different T subtypes (regulatory T cells, helper T cells, cytotoxic T cells, γδ T cells, and natural killer T cells) in human and animal testes that support their regulatory roles in infertility and the orchitis pathology. While many in vitro studies have indicated the regulation potential of functional T cell subsets and their possible interaction with Sertoli cells, Leydig cells, and spermatogenesis, both under physiological and pathological processes, there have been no in situ studies to date. Nevertheless, the normal distribution and function of T cell subsets are essential for the immune privilege of the testes and intact spermatogenesis, and T cell-mediated immune response drives testicular inflammation. The distinct function of different T cell subsets in testicular homeostasis and the orchitis pathology suggests a considerable potential of targeting specific T cell subsets for therapies targeting chronic orchitis and immune infertility.

Pathways towards human immunodeficiency virus elimination

Antiretroviral therapy (ART) suppresses human immunodeficiency virus (HIV) infection. Research seeking to transform viral suppression into elimination has generated novel immune, chemical and molecular antiviral agents. However, none, to date, have excised latent integrated proviral DNA or removed infected cells from infected persons. These efforts included, but are not limited to, broadly neutralizing antibodies, "shock" and "kill" latency-reversing agents, innate immune regulators, and sequential long-acting antiretroviral nanoformulated prodrugs and CRISPR-Cas9 gene editing. While, the latter, enabled the complete excision of latent HIV-1 from the host genome success was so far limited. We contend that improvements in antiretroviral delivery, potency, agent specificity, or combinatorial therapies can provide a pathway towards complete HIV elimination.

From Ancient to Emerging Infections: The Odyssey of Viruses in the Male Genital Tract

The male genital tract (MGT) is the target of a number of viral infections that can have deleterious consequences at the individual, offspring, and population levels. These consequences include infertility, cancers of male organs, transmission to the embryo/fetal development abnormalities, and sexual dissemination of major viral pathogens such as human immunodeficiency virus (HIV) and hepatitis B virus. Lately, two emerging viruses, Zika and Ebola, have additionally revealed that the human MGT can constitute a reservoir for viruses cleared from peripheral circulation by the immune system, leading to their sexual transmission by cured men. This represents a concern for future epidemics and further underlines the need for a better understanding of the interplay between viruses and the MGT. We review here how viruses, from ancient viruses that integrated the germline during evolution through old viruses (e.g., papillomaviruses originating from Neanderthals) and more modern sexually transmitted infections (e.g., simian zoonotic HIV) to emerging viruses (e.g., Ebola and Zika) take advantage of genital tract colonization for horizontal dissemination, viral persistence, vertical transmission, and endogenization. The MGT immune responses to viruses and the impact of these infections are discussed. We summarize the latest data regarding the sources of viruses in semen and the complex role of this body fluid in sexual transmission. Finally, we introduce key animal findings that are relevant for our understanding of viral infection and persistence in the human MGT and suggest future research directions.

HIV Diversity and Genetic Compartmentalization in Blood and Testes during Suppressive Antiretroviral Therapy

HIV's ability to persist during suppressive antiretroviral therapy is the main barrier to cure. Immune-privileged tissues, such as the testes, may constitute distinctive sites of HIV persistence, but this has been challenging to study in humans. We analyzed the proviral burden and genetics in the blood and testes of 10 individuals on suppressive therapy who underwent elective gender-affirming surgery. HIV DNA levels in matched blood and testes were quantified by quantitative PCR, and subgenomic proviral sequences (nef region) were characterized from single templates. HIV diversity, compartmentalization, and immune escape burden were assessed using genetic and phylogenetic approaches. Diverse proviruses were recovered from the blood (396 sequences; 354 nef-intact sequences) and testes (326 sequences; 309 nef-intact sequences) of all participants. Notably, the frequency of identical HIV sequences varied markedly between and within individuals. Nevertheless, proviral loads, within-host unique HIV sequence diversity, and the immune escape burden correlated positively between blood and testes. When all intact nef sequences were evaluated, 60% of participants exhibited significant blood-testis genetic compartmentalization, but none did so when the evaluation was restricted to unique sequences per site, suggesting that compartmentalization, when present, is attributable to the clonal expansion of HIV-infected cells. Our observations confirm the testes as a site of HIV persistence and suggest that individuals with larger and more diverse blood reservoirs will have larger and more diverse testis reservoirs. Furthermore, while the testis microenvironment may not be sufficiently unique to facilitate the seeding of unique viral populations therein, differential clonal expansion dynamics may be at play, which may complicate HIV eradication.IMPORTANCE Two key questions in HIV reservoir biology are whether immune-privileged tissues, such as the testes, harbor distinctive proviral populations during suppressive therapy and, if so, by what mechanism. While our results indicated that blood-testis HIV genetic compartmentalization was reasonably common (60%), it was always attributable to differential frequencies of identical HIV sequences between sites. No blood-tissue data set retained evidence of compartmentalization when only unique HIV sequences per site were considered; moreover, HIV immune escape mutation burdens were highly concordant between sites. We conclude that the principal mechanism by which blood and testis reservoirs differ is not via seeding of divergent HIV sequences therein but, rather, via differential clonal expansion of latently infected cells. Thus, while viral diversity and escape-related barriers to HIV eradication are of a broadly similar magnitude across the blood and testes, clonal expansion represents a challenge. The results support individualized analysis of within-host reservoir diversity to inform curative approaches.

Infectious, inflammatory and 'autoimmune' male factor infertility: how do rodent models inform clinical practice?

BACKGROUND

Infection and inflammation of the reproductive tract are significant causes of male factor infertility. Ascending infections caused by sexually transmitted bacteria or urinary tract pathogens represent the most frequent aetiology of epididymo-orchitis, but viral, haematogenous dissemination is also a contributory factor. Limitations in adequate diagnosis and therapy reflect an obvious need for further understanding of human epididymal and testicular immunopathologies and their contribution to infertility. A major obstacle for advancing our knowledge is the limited access to suitable tissue samples. Similarly, the key events in the inflammatory or autoimmune pathologies affecting human male fertility are poorly amenable to close examination. Moreover, the disease processes generally have occurred long before the patient attends the clinic for fertility assessment. In this regard, data obtained from experimental animal models and respective comparative analyses have shown promise to overcome these restrictions in humans.

OBJECTIVE AND RATIONALE

This narrative review will focus on male fertility disturbances caused by infection and inflammation, and the usefulness of the most frequently applied animal models to study these conditions.

SEARCH METHODS

An extensive search in Medline database was performed without restrictions until January 2018 using the following search terms: 'infection' and/or 'inflammation' and 'testis' and/or 'epididymis', 'infection' and/or 'inflammation' and 'male genital tract', 'male infertility', 'orchitis', 'epididymitis', 'experimental autoimmune' and 'orchitis' or 'epididymitis' or 'epididymo-orchitis', antisperm antibodies', 'vasectomy'. In addition to that, reference lists of primary and review articles were reviewed for additional publications independently by each author. Selected articles were verified by each two separate authors and discrepancies discussed within the team.

OUTCOMES

There is clear evidence that models mimicking testicular and/or epididymal inflammation and infection have been instructive in a better understanding of the mechanisms of disease initiation and progression. In this regard, rodent models of acute bacterial epididymitis best reflect the clinical situation in terms of mimicking the infection pathway, pathogens selected and the damage, such as fibrotic transformation, observed. Similarly, animal models of acute testicular and epididymal inflammation using lipopolysaccharides show impairment of reproduction, endocrine function and histological tissue architecture, also seen in men. Autoimmune responses can be studied in models of experimental autoimmune orchitis (EAO) and vasectomy. In particular, the early stages of EAO development showing inflammatory responses in the form of peritubular lymphocytic infiltrates, thickening of the lamina propria of affected tubules, production of autoantibodies against testicular antigens or secretion of pro-inflammatory mediators, replicate observations in testicular sperm extraction samples of patients with 'mixed atrophy' of spermatogenesis. Vasectomy, in the form of sperm antibodies and chronic inflammation, can also be studied in animal models, providing valuable insights into the human response.

WIDER IMPLICATIONS

This is the first comprehensive review of rodent models of both infectious and autoimmune disease of testis/epididymis, and their clinical implications, i.e. their importance in understanding male infertility related to infectious and non-infectious/autoimmune disease of the reproductive organs.

Barriers to HIV Cure

Since the beginning of the epidemic, more than 70 million people have been infected with human immunodeficiency virus (HIV) and about 38 million have died from acquired immune deficiency syndrome (AIDS)-related illnesses. While the discovery of highly active antiretroviral therapy (HAART) in the mid 90's has saved millions of lives, a complete eradication of HIV is still not possible as HIV can persist for decades in a small reservoir of latently infected cells. Once reactivated, these latently infected cells can actively produce viral particles. Recent studies suggest that several sanctuaries exist within infected individuals where HIV can remain undetected by the immune system. These cellular, anatomical and microanatomical viral reservoirs represent a major obstacle for the eradication of HIV. Here we review recent findings on potential sanctuaries of HIV and address potential avenues to overcome these immunological barriers.

Tissue reservoirs of HIV

PURPOSE OF REVIEW

Tissue reservoirs of HIV may promote the persistent immunopathology responsible for non-AIDS morbidity and data support multifocal reactivation from tissues as the source of viral rebound during antiretroviral therapy (ART) interruption. The heterogeneity of tissue reservoirs and incomplete knowledge about their composition are obstacles to an HIV cure.

RECENT FINDINGS

In addition to the higher concentration of infected CD4 T cells found in both central lymphoid tissues and gut, specific subsets of CD4 T cells appear to play a disproportionate role in HIV persistence. Recently, a subset of central memory T cells enriched in lymph node germinal centers called T-follicular helper cells has been identified that expresses more viral RNA and occupies an anatomic niche inaccessible to cytotoxic T lymphocyte killing. Additional observations suggest that antiretroviral drug (ARV) concentrations may be lower in some tissues, raising the possibility for localized, low-level viral replication. Finally, some recent data implicate the persistence of infected, non-CD4 T-cell types in tissues during ART.

SUMMARY

The retention of infected cells in a wide variety of tissues, often with distinct viral and cellular characteristics, underscores the importance of studying tissue reservoirs in the development and assessment of cure strategies. Both inhibitory ARVs and latency-reversing drugs must reach these sites, and novel strategies may be needed to attack virus in cells as variable as T-follicular helper cells and macrophages.

Immune tolerance properties of the testicular tissue as a viral sanctuary site in ART-treated HIV-infected adults

OBJECTIVE

HIV persistence in long-lived infected cells and in anatomical sanctuary sites are major hurdles to HIV eradication. Testicular tissue may represent a significant viral sanctuary site as it constitutes an immunologically privileged compartment. We assessed immunotolerance properties of the testicular tissue in individuals receiving suppressive antiretroviral therapy (ART).

DESIGN AND METHODS

Testicular tissue and matched blood samples were collected from six virally suppressed adults and 10 HIV-uninfected controls prior to sex reassignment surgery. T cells were purified from freshly isolated testicular interstitial cell suspensions. T-cell subsets, expression of immune activation markers and HIV DNA were assessed in matched testicular cells and peripheral blood mononuclear cells (PBMCs).

RESULTS

When compared with PBMCs, testes were characterized by a lower CD4 T-cell proportion among total T cells, a decrease in the frequency of naive cells, an increase in the frequency of effector-memory T cells and an increase in CCR5 expression in both the HIV+ and HIV- groups. In HIV-infected individuals on ART, testes displayed higher T-cell immune activation (Coexpression of CD38 and Human Leukocyte Antigen - antigen D Related) than PBMCs. In both groups, testes were characterized by higher frequencies of immunosuppressive CD39 regulatory T cells and a massive increase in CD73 expression on CD8 T cells. In addition, a remarkable increase in indoleamine-pyrrole 2,3-dioxygenase immunosuppressive enzyme involved in tryptophan/kynurenine catabolism was observed in testes versus blood. Rare cells harboring HIV DNA were detected in testes from five out six participants.

CONCLUSION

These findings suggest that the adenosine and tryptophan/kynurenine immune-metabolic pathways contribute to immune tolerance in testicular tissue. Our results suggest that testes may represent a distinctive HIV sanctuary site during ART.

Antiretroviral drug transporters and metabolic enzymes in human testicular tissue: potential contribution to HIV-1 sanctuary site

OBJECTIVES

The testes are a potential viral sanctuary site for HIV-1 infection. Our study aims to provide insight into the expression and localization of key drug transporters and metabolic enzymes relevant to ART in this tissue compartment.

METHODS

We characterized gene and protein expression of 12 representative drug transporters and two metabolic enzymes in testicular tissue samples obtained from uninfected (n = 8) and virally suppressed HIV-1-infected subjects on ART (n = 5) and quantified antiretroviral drug concentrations in plasma and testicular tissues using LC/MS/MS from HIV-1-infected subjects.

RESULTS

Our data demonstrate that key ABC drug transporters (permeability glycoprotein, multidrug-resistance protein 1, 2 and 4, and breast cancer resistance protein), solute carrier transporters (organic anion transporting polypeptides 1B1 and 2B1, organic anion transporter 1, concentrative nucleoside transporter 1, equilibrative nucleoside transporter 2) and cytochrome P450 metabolic enzymes (CYP3A4 and CYP2D6) previously shown to interact with many commonly used antiretroviral drugs are expressed at the mRNA and protein level in the testes of both subject groups and localize primarily at the blood-testis barrier, with no significant differences between the two groups. Furthermore, we observed that PIs known to be substrates for ATP-binding cassette membrane transporters, displayed variable testicular tissue penetration, with darunavir concentrations falling below therapeutic values. In contrast, the NRTIs emtricitabine, lamivudine and tenofovir displayed favourable tissue penetration, reaching concentrations comparable to plasma levels. We also demonstrated that nuclear receptors, peroxisome proliferator-activated receptors α and γ exhibited higher gene expression in the testicular tissue compared with pregnane X receptor and constitutive androstane receptor, suggesting a potential regulatory pathway governing drug transporter and metabolic enzyme expression in this tissue compartment.

CONCLUSIONS

Our data suggest the testes are a complex pharmacological compartment that can restrict the distribution of certain antiretroviral drugs and potentially contribute to HIV-1 persistence.