CD4+ CD25+ regulatory T cells impair HIV-1-specific CD4 T cell responses by upregulating interleukin-10 production in monocytes

IL-27 expression regulation and its effects on adaptive immunity against viruses

IL-27, a member of the IL-6/IL-12 cytokine superfamily, is primarily secreted by antigen presenting cells, specifically by dendric cells, macrophages and B cells. IL-27 has antiviral activities and modulates both innate and adaptive immune responses against viruses. The role of IL-27 in the setting of viral infections is not well defined and both pro-inflammatory and anti-inflammatory functions have been described. Here, we discuss the latest advancements in the role of IL-27 in several viral infection models of human disease. We highlight important aspects of IL-27 expression regulation, the critical cell sources at different stages of the infection and their impact in cell mediated immunity. Lastly, we discuss the need to better define the antiviral and modulatory (pro-inflammatory vs anti-inflammatory) properties of IL-27 in the context of human chronic viral infections.

Immune-checkpoint expression in antigen-presenting cells (APCs) of cytomegaloviruses infection after transplantation: as a diagnostic biomarker

Cytomegalovirus (CMV), a member of the Herpesviridae family, mostly causes only slight feverish symptoms or can be asymptomatic in immunocompetent individuals. However, it is known to be particularly a significant cause of morbidity in immunocompromised patients, including transplant recipients, whose immune system has been weakened due to the consumption of immunosuppressor drugs. Therefore, the diagnosis of CMV infection after transplantation is crucial. New diagnostic methods for the quick detection of CMV have been developed as a result of understanding the clinical importance of invasive CMV. Antigen-presenting cells (APCs) and T cells are important components of the immune system and it may be possible to diagnose viral infections using immunological markers, such as lymphocytosis, cytotoxic T lymphocytes (CTL), and serum cytokine levels. Moreover, PD-1, CTLA 4, and TIGIT, which are expressed on certain T cells and antigen-presenting cells, are over-expressed during the infection. The assessment of CMV infection based on T cell and APC activity, and the expression of immunological checkpoints, can be helpful for the diagnosis of transplant patients at risk for CMV infection. In this review, we will investigate how immune checkpoints affect immune cells and how they impair organ transplantation after CMV infection.

Interleukin-10 contributes to reservoir establishment and persistence in SIV-infected macaques treated with antiretroviral therapy

Interleukin-10 (IL-10) is an immunosuppressive cytokine that signals through STAT3 to regulate T follicular helper (Tfh) cell differentiation and germinal center formation. In SIV-infected macaques, levels of IL-10 in plasma and lymph nodes (LNs) were induced by infection and not normalized with antiretroviral therapy (ART). During chronic infection, plasma IL-10 and transcriptomic signatures of IL-10 signaling were correlated with the cell-associated SIV-DNA content within LN CD4+ memory subsets, including Tfh cells, and predicted the frequency of CD4+ Tfh cells and their cell-associated SIV-DNA content during ART, respectively. In ART-treated rhesus macaques, cells harboring SIV-DNA by DNAscope were preferentially found in the LN B cell follicle in proximity to IL-10. Finally, we demonstrated that the in vivo neutralization of soluble IL-10 in ART-treated, SIV-infected macaques reduced B cell follicle maintenance and, by extension, LN memory CD4+ T cells, including Tfh cells and those expressing PD-1 and CTLA-4. Thus, these data support a role for IL-10 in maintaining a pool of target cells in lymphoid tissue that serve as a niche for viral persistence. Targeting IL-10 signaling to impair CD4+ T cell survival and improve antiviral immune responses may represent a novel approach to limit viral persistence in ART-suppressed people living with HIV.

Understanding the mechanism of action of cytomegalovirus-induced regulatory T cells

We previously showed that CMV-induced CD4⁺CD27^-CD28^- T cells have regulatory (Treg) function. Here we sought to identify the target/s and the mechanistic underpinning/s of this effect. CMV-induced CD4⁺CD27^-CD28^-were sorted from CMV-stimulated PBMC and added to CMV-stimulated autologous PBMC cultures. Transwell experiments showed that the CMV-induced Treg mechanism of action required cell-to-cell contact. CMV-Treg significantly decreased proliferation of autologous CMV-stimulated CD8⁺ and, to a lesser extent, CD4⁺ T cells; reduced activation and increased apoptosis of CD4⁺ and CD8⁺ T cells; and increased apoptosis and expression of CTLA-4, T cell-inhibitory ligand, on dendritic cells. There was no effect on monocytes. Anti-PD-1, but not anti-CTLA-4, mAb-treatment increased proliferation of CD8⁺ T cells and decreased apoptosis of CD4⁺ and CD8⁺ T cells. Our data indicated that CD8⁺ T cells were the main target of CMV-specific Treg, which induced apoptosis of their targets using the PD-1 pathway.

7-oxo-DHEA enhances impaired M. tuberculosis-specific T cell responses during HIV-TB coinfection

BACKGROUND

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB), affecting approximately one third of the world's population. Development of an adequate immune response will determine disease progression or progress to chronic infection. Risk of developing TB among human immunodeficiency virus (HIV)-coinfected patients (HIV-TB) is 20-30 times higher than those without HIV infection, and a synergistic interplay between these two pathogens accelerates the decline in immunological functions. TB treatment in HIV-TB coinfected persons is challenging and it has a prolonged duration, mainly due to the immune system failure to provide an adequate support for the therapy. Therefore, we aimed to study the role of the hormone 7-oxo-dehydroepiandrosterone (7-OD) as a modulator of anti-tuberculosis immune responses in the context of HIV-TB coinfection.

METHODS

A cross-sectional study was conducted among HIV-TB patients and healthy donors (HD). We characterized the ex vivo phenotype of CD4 + T cells and also evaluated in vitro antigen-specific responses by Mtb stimulation of peripheral blood mononuclear cells (PBMCs) in the presence or absence of 7-OD. We assessed lymphoproliferative activity, cytokine production and master transcription factor profiles.

RESULTS

Our results show that HIV-TB patients were not able to generate successful anti-tubercular responses in vitro compared to HD, as reduced IFN-γ/IL-10 and IFN-γ/IL-17A ratios were observed. Interestingly, treatment with 7-OD enhanced Th1 responses by increasing Mtb-induced proliferation and the production of IFN-γ and TNF-α over IL-10 levels. Additionally, in vitro Mtb stimulation augmented the frequency of cells with a regulatory phenotype, while 7-OD reduced the proportion of these subsets and induced an increase in CD4 + T-bet+ (Th1) subpopulation, which is associated with clinical data linked to an improved disease outcome.

CONCLUSIONS

We conclude that 7-OD modifies the cytokine balance and the phenotype of CD4 + T cells towards a more favorable profile for mycobacteria control. These results provide new data to delineate novel treatment approaches as co-adjuvant for the treatment of TB.

Monocyte Based Correlates of Immune Activation and Viremia in HIV-Infected Long-Term Non-Progressors

Background: Disease progression monitoring through CD4 counts alone can be inadequate in HIV infection as ongoing immune activation may result in Serious non-AIDS events (SNAEs). SNAEs involve monocyte activation driven chronic inflammation with significant sequelae observed even during HAART. Here, we attempted to delineate functional monocyte based signatures across stages of HIV disease progression. Methods: Participants spanning four cohorts were recruited-pre-ART (PA; <7 years of infection; n = 20), long-term non-progressors (LTNP; >7 years of infection, CD4 > 350 cells/μL, n = 20), individuals on therapy (ART; n = 18) and seronegative controls (SN; n = 15). Immunophenotyping of monocyte subsets and evaluation of expression of HIV-binding receptors-CD4 and CCR5, marker of immune activation- HLA-DR and M2 phenotype-mannose receptor (CD206) was followed by association of monocyte-specific parameters with conventional markers of disease progression such as absolute CD4 count, CD4/CD8 ratio, viral load, and T cell activation. Results: A significant expansion of intermediate monocytes (CD14++CD16+) with a concomitant decline in classical subset (CD14++CD16-) was observed in all infected cohorts compared to seronegative controls. In addition, an expansion of the non-classical subset (CD14+CD16++) was observed in long-term non-progressors. Dysregulation in monocyte subsets associated with CD4 count and CD4/CD8 ratio in PAs but not in LTNPs. We report for the first time that expression of CD206 is most prominent on intermediate monocytes which also have the highest expression of CD4, CCR5, and HLA-DR. Despite preserved CD4 counts, LTNPs had similar immune activation profiles to PAs, as evidenced by elevated HLA-DR expression across monocyte subsets. HLA-DR expression, similar to that in SNs, observed in the ART group indicated partial immune restoration within the monocyte compartment. Increased CD206 expression on monocytes together with frequency of activated CD4+ T lymphocytes (HLA-DR+CD38+) showed significant and positive association with viral load in LTNPs, but not PAs. Conclusion: Our results describe for the first time the presence of monocyte dysregulation involving increased activation in LTNPs, who, in spite of preserved CD4 counts, may remain susceptible to prolonged effects of systemic inflammation and highlight CD206, as a unique non-T correlate of viremia, in viremic non-progression.

Occurrence of hypocortisolism in HIV patients: Is the picture changing?

Background

The occurrence of endocrine diseases in people who are infected with HIV is traditionally thought to occur in the setting of AIDS with opportunistic infections and malignancies. However, recent studies find the correlation between hypocortisolism and stage of HIV (CD4 count and WHO clinical stage) inconsistent.

Methods

This descriptive cross-sectional study included three hundred and fifty (350) consecutive patients with HIV infection. They were interviewed, and subsequently underwent laboratory evaluation for the detection of hypocortisolism. Blood samples for serum cortisol estimation were taken at baseline and at 30 minutes following the administration of 1µg of tetracosactrin (Synacthen). In addition, the patients had blood samples taken at 0 minutes (baseline) for CD4+ lymphocyte cell counts.

Results

At baseline, 108 (30.9%) participants had serum cortisol levels below 100 µg/L with a median value of 55.48 µg/L (11.36-99.96 µg/L), but only 57 (16.3%) study participants had stimulated serum cortisol levels below 180 µg/L with median of 118 µg/L (19.43-179.62). There was no significant difference in the occurrence of clinical features between participants with low and normal serum cortisol, nor WHO clinical stage, CD4 count and ART regimen. The occurrence of hypocortisolism was higher among participants who had been on ART for a longer period of time.

Conclusion

There is a high prevalence of hypocortisolism among HIV patients by biochemical testing, especially those who have been on ARVs for a longer duration. Hypocortisolism cannot be predicted based on the participants' WHO clinical stage of disease, CD4 cell count, or the treatment regimen.

Funding

Personal Funds.

P2X Antagonists Inhibit HIV-1 Productive Infection and Inflammatory Cytokines Interleukin-10 (IL-10) and IL-1β in a Human Tonsil Explant Model

HIV-1 causes a persistent infection of the immune system that is associated with chronic comorbidities. The mechanisms that underlie this inflammation are poorly understood. Emerging literature has implicated proinflammatory purinergic receptors and downstream signaling mediators in HIV-1 infection. This study probed whether inhibitors of purinergic receptors would reduce HIV-1 infection and HIV-1-stimulated inflammation. An ex vivo human tonsil histoculture infection model was developed to support HIV-1 productive infection and stimulated the inflammatory cytokine interleukin-1 beta (IL-1β) and the immunosuppressive cytokine interleukin-10 (IL-10). This study tests whether inhibitors of purinergic receptors would reduce HIV-1 infection and HIV-1-stimulated inflammation. The purinergic P2X1 receptor antagonist NF449, the purinergic P2X7 receptor antagonist A438079, and azidothymidine (AZT) were tested in HIV-1-infected human tonsil explants to compare levels of inhibition of HIV-1 infection and HIV-stimulated inflammatory cytokine production. All drugs limited HIV-1 productive infection, but P2X-selective antagonists (NF449 and A438079) significantly lowered HIV-stimulated IL-10 and IL-1β. We further observed that P2X1- and P2X7-selective antagonists can act differentially as inhibitors of both HIV-1 infection and HIV-1-stimulated inflammation. Our findings highlight the differential effects of HIV-1 on inflammation in peripheral blood compared to those in lymphoid tissue. For the first time, we demonstrate that P2X-selective antagonists act differentially as inhibitors of both HIV-1 infection and HIV-1-stimulated inflammation. Drugs that block these pathways can have independent inhibitory activities against HIV-1 infection and HIV-induced inflammation.IMPORTANCE Patients who are chronically infected with HIV-1 experience sequelae related to chronic inflammation. The mechanisms of this inflammation have not been elucidated. Here, we describe a class of drugs that target the P2X proinflammatory signaling receptors in a human tonsil explant model. This model highlights differences in HIV-1 stimulation of lymphoid tissue inflammation and peripheral blood. These drugs serve to block both HIV-1 infection and production of IL-10 and IL-1β in lymphoid tissue, suggesting a novel approach to HIV-1 therapeutics in which both HIV-1 replication and inflammatory signaling are simultaneously targeted.

Cytokine-Mediated Tissue Injury in Non-human Primate Models of Viral Infections

Viral infections trigger robust secretion of interferons and other antiviral cytokines by infected and bystander cells, which in turn can tune the immune response and may lead to viral clearance or immune suppression. However, aberrant or unrestricted cytokine responses can damage host tissues, leading to organ dysfunction, and even death. To understand the cytokine milieu and immune responses in infected host tissues, non-human primate (NHP) models have emerged as important tools. NHP have been used for decades to study human infections and have played significant roles in the development of vaccines, drug therapies and other immune treatment modalities, aided by an ability to control disease parameters, and unrestricted tissue access. In addition to the genetic and physiological similarities with humans, NHP have conserved immunologic properties with over 90% amino acid similarity for most cytokines. For example, human-like symptomology and acute respiratory syndrome is found in cynomolgus macaques infected with highly pathogenic avian influenza virus, antibody enhanced dengue disease is common in neotropical primates, and in NHP models of viral hepatitis cytokine-induced inflammation induces severe liver damage, fibrosis, and hepatocellular carcinoma recapitulates human disease. To regulate inflammation, anti-cytokine therapy studies in NHP are underway and will provide important insights for future human interventions. This review will provide a comprehensive outline of the cytokine-mediated exacerbation of disease and tissue damage in NHP models of viral infections and therapeutic strategies that can aid in prevention/treatment of the disease syndromes.

Immune Checkpoint Blockade Restores HIV-Specific CD4 T Cell Help for NK Cells

Immune exhaustion is an important feature of chronic infections, such as HIV, and a barrier to effective immunity against cancer. This dysfunction is in part controlled by inhibitory immune checkpoints. Blockade of the PD-1 or IL-10 pathways can reinvigorate HIV-specific CD4 T cell function in vitro, as measured by cytokine secretion and proliferative responses upon Ag stimulation. However, whether this restoration of HIV-specific CD4 T cells can improve help to other cell subsets impaired in HIV infection remains to be determined. In this study, we examine a cohort of chronically infected subjects prior to initiation of antiretroviral therapy (ART) and individuals with suppressed viral load on ART. We show that IFN-γ induction in NK cells upon PBMC stimulation by HIV Ag varies inversely with viremia and depends on HIV-specific CD4 T cell help. We demonstrate in both untreated and ART-suppressed individuals that dual PD-1 and IL-10 blockade enhances cytokine secretion of NK cells via restored HIV-specific CD4 T cell function, that soluble factors contribute to these immunotherapeutic effects, and that they depend on IL-2 and IL-12 signaling. Importantly, we show that inhibition of the PD-1 and IL-10 pathways also increases NK degranulation and killing of target cells. This study demonstrates a previously underappreciated relationship between CD4 T cell impairment and NK cell exhaustion in HIV infection, provides a proof of principle that reversal of adaptive immunity exhaustion can improve the innate immune response, and suggests that immune checkpoint modulation that improves CD4/NK cell cooperation can be used as adjuvant therapy in HIV infection.

Role of T. cruzi exposure in the pattern of T cell cytokines among chronically infected HIV and Chagas disease patients

OBJECTIVES

The impact of Chagas disease (CD) in HIV-infected patients is relevant throughout the world. In fact, the characterization of the adaptive immune response in the context of co-infection is important for predicting the need for interventions in areas in which HIV and Chagas disease co-exist.

METHODS

We described and compared the frequency of cytokine-producing T cells stimulated with soluble antigen of Trypanosoma cruzi (T. cruzi) using a cytometric assay for the following groups: individuals with chronic Chagas disease (CHR, n=10), those with Chagas disease and HIV infection (CO, n=11), those with only HIV (HIV, n=14) and healthy individuals (C, n=15).

RESULTS

We found 1) a constitutively lower frequency of IL-2+ and IFN-γ+ T cells in the CHR group compared with the HIV, CO and healthy groups; 2) a suppressive activity of soluble T. cruzi antigen, which down-regulated IL-2+CD4+ and IFN-γ+CD4+ phenotypes, notably in the healthy group; 3) a down-regulation of inflammatory cytokines on CD8+ T cells in the indeterminate form of Chagas disease; and 4) a significant increase in IL-10+CD8+ cells distinguishing the indeterminate form from the cardiac/digestive form of Chagas disease, even in the presence of HIV infection.

CONCLUSIONS

Taken together, our data suggest the presence of an immunoregulatory response in chronic Chagas disease, which seems to be driven by T. cruzi antigens. Our findings provide new insights into immunotherapeutic strategies for people living with HIV/AIDS and Chagas disease.

Therapeutic vaccines for allergic disease

Allergic diseases are highly prevalent worldwide and affect all age groups, contributing to a high personal and socioeconomic burden. Treatment with an “allergy vaccine” or allergen immunotherapy aims to provide long-lasting benefits by inducing unresponsiveness to the relevant antigen. The consequences of the therapy are considered disease modifying and range from dampening of the immediate immune responses to the reduction of secondary tissue remodeling. Furthermore, allergen immunotherapy interventions have a potential to slow or cease the development of additional allergic manifestations with a long-term overall effect on morbidity and quality of life. Here, we review proposed mechanisms underlying the therapeutic effects of immunotherapy for allergic diseases. Further, we discuss both standard and novel approaches and possible future directions in the development of allergen immunotherapy.

Divergent Annexin A1 expression in periphery and gut is associated with systemic immune activation and impaired gut immune response during SIV infection

HIV-1 disease progression is paradoxically characterized by systemic chronic immune activation and gut mucosal immune dysfunction, which is not fully defined. Annexin A1 (ANXA1), an inflammation modulator, is a potential link between systemic inflammation and gut immune dysfunction during the simian immunodeficiency virus (SIV) infection. Gene expression of ANXA1 and cytokines were assessed in therapy-naïve rhesus macaques during early and chronic stages of SIV infection and compared with SIV-negative controls. ANXA1 expression was suppressed in the gut but systemically increased during early infection. Conversely, ANXA1 expression increased in both compartments during chronic infection. ANXA1 expression in peripheral blood was positively correlated with HLA-DR+CD4+ and CD8+ T-cell frequencies, and negatively associated with the expression of pro-inflammatory cytokines and CCR5. In contrast, the gut mucosa presented an anergic cytokine profile in relation to ANXA1 expression. In vitro stimulations with ANXA1 peptide resulted in decreased inflammatory response in PBMC but increased activation of gut lymphocytes. Our findings suggest that ANXA1 signaling is dysfunctional in SIV infection, and may contribute to chronic inflammation in periphery and with immune dysfunction in the gut mucosa. Thus, ANXA1 signaling may be a novel therapeutic target for the resolution of immune dysfunction in HIV infection.

T-Cell Activation Independently Associates With Immune Senescence in HIV-Infected Recipients of Long-term Antiretroviral Treatment

Background.  Aging-associated noncommunicable comorbidities are more prevalent among human immunodeficiency virus type 1 (HIV)–infected individuals than among HIV-uninfected individuals. Residual HIV-related chronic immune activation and senescence may increase the risk of developing comorbidities.

Methods.  Immune phenotyping, thymic output, and telomere length were assessed in 94 HIV-infected individuals who were aged >45 years and receiving antiretroviral therapy (ART; cases) and 95 age-matched uninfected controls.

Results.  Cases had lower CD4+ T-cell counts, higher CD8+ T-cell counts, and increased levels of immune activation (ie, increased soluble CD14 [sCD14] level and increased percentages of CD38+HLA-DR+ cells among both CD4+ and CD8+ T cells), regulatory T cells, and percentage of programmed cell death 1 (PD-1)–expressing cells among CD4+ T cells. Immune senescence levels (ie, percentages of CD27−CD28− cells or CD57+ cells) were comparable between cases and controls. Peripheral blood mononuclear cells from cases had shorter telomeres but increased single-joint T-cell receptor excision circle content and CD31+ naive CD4+ T cells. Although cytomegalovirus (CMV) antibody titers were higher in cases, CMV-specific T-cell responses were comparable between cases and controls. T-cell senescence in cases was independently associated with T-cell activation but not with CMV-specific immune responses.

Conclusions.  Despite long-term receipt of ART, HIV-infected adults had higher levels of immune activation, regulatory T cells, and PD-1–expressing CD4+ cells and shorter telomeres. The increased soluble CD14 levels and percentage of CD38+HLA-DR+ cells among CD4+ T cells correlated with shorter telomeres and increased regulatory T-cell levels. This suggests that HIV influences immune function irreversibly, with several pathways that are persistently abnormal during effective ART. Therapies aimed at improving immune health during ART are needed.

Increased Frequency of CD49b/LAG-3(+) Type 1 Regulatory T Cells in HIV-Infected Individuals

In HIV-1 infection elevated serum levels of interferon-α (IFN-α) and interleukin-10 (IL-10) are associated with immune hyperactivation and disease progression. Recently, coexpression of CD49b and LAG-3 was shown to identify Type 1 regulatory T (Tr1) cells, which secrete large amounts of the immunosuppressive cytokine IL-10. We analyzed the frequency of CD49b/LAG-3(+) Tr1 cells in the peripheral blood of HIV-infected individuals at different stages of the disease. We found increased levels of CD49b/LAG-3(+) Tr1 cells as well as IL-10 in HIV patients. With disease progression, Tr1 cells negatively correlate with frequency of plasmacytoid dendritic cells (pDCs), the main producers of IFN-α. However, elevated IL-10 levels could not be ascribed to the CD49b/LAG-3(+)Tr1 cell population. Moreover, we showed in vitro that IFN-α leads to an upregulation of IL-10 as well as CD49b/LAG-3(+) Tr1 cell counts in healthy controls, recapitulating effects observed in vivo during HIV infection. Our results suggest that overexpression of IFN-α during HIV infection drives the generation of CD49b/LAG-3(+) Tr1 cells and the immunosuppressive cytokine IL-10. Furthermore, it remains unclear whether elevated IL-10 levels are beneficial or detrimental in regard to disease progression.

Role of Regulatory T Cells and Inhibitory Molecules in the Development of Immune Exhaustion During Human Immunodeficiency Virus Type 1 Infection

One of the key hallmarks of chronic human immunodeficiency virus type 1 (HIV-1) infection is the persistent immune activation triggered since early stages of the infection, followed by the development of an exhaustion phenomena, which leads to the inability of immune cells to respond appropriately to the virus and other pathogens, constituting the acquired immunodeficiency syndrome (AIDS); this exhausting state is characterized by a loss of effector functions of immune cells such as proliferation, production of cytokine, as well as cytotoxic potential and it has been attributable to an increased response of regulatory T cells and recently also to the expression in different cell populations of inhibitory molecules, such as programmed death receptor-1 (PD-1), cytotoxic T lymphocyte antigen-4 (CTLA-4), T cell immunoglobulin-3 (Tim-3), and lymphocyte activation gene-3 (LAG-3). The importance of these molecules relies on the possibility to restore the immune response once these molecules are blocked, constituting a potential therapeutic target for treatment during HIV infection. In this regard, we explored the available data evaluating the functional role of Treg cells and inhibitory molecules during the infection in both blood and gut-associated lymphoid tissue (GALT) and their contribution to the development of immune exhaustion and progression to AIDS, as well as their therapeutic potential.

Understanding HIV latency: the road to an HIV cure

Treatment with antiretroviral therapy dramatically increases the survival of HIV-infected individuals. However, treatment has to be continued for life because it does not lead to the full eradication of infection. HIV persists in resting CD4(+) T cells, and possibly other cell types, and can reemerge from these cells when therapy is interrupted. Here, we review molecular mechanisms that have been proposed to contribute to HIV latency, as well as the relative roles of cis- and trans-acting mechanisms. We also discuss existing and future therapeutic opportunities regarding HIV latency that might lead to a future cure for HIV infection.

Animal models for viral infection and cell exhaustion

PURPOSE OF REVIEW

Despite eliciting an early antiviral T cell response, HIV-specific T cells are unable to prevent disease progression, partly because of their loss of effector functions, known as T cell exhaustion. Restoring this T cell functionality represents a critical step for regaining immunological control of HIV-1 replication, and may be fundamental for the development of a functional cure for HIV. In this context, the use of animal models is invaluable for evaluating the efficacy and mechanisms of novel therapeutics aimed at reinvigorating T cell functions.

RECENT FINDINGS

Although nonhuman primates continue to be a mainstay for studying HIV pathogenesis and therapies, recent advances in humanized mouse models have improved their ability to recapitulate the features of cell exhaustion during HIV infection. Targeting coinhibitory receptors in HIV-infected and simian immunodeficiency virus (SIV)-infected animals has resulted in viral load reductions, presumably by reinvigorating the effector functions of T cells. Additionally, studies combining programmed death-1 (PD-1) blockade with suppressive antiretroviral therapy provide further support to the use of coinhibitory receptor blockades in restoring T cell function by delaying viral load rebound upon antiretroviral therapy interruption. Future in-vivo studies should build on recent in-vitro data, supporting the simultaneous targeting of multiple regulators of cell exhaustion.

SUMMARY

In this review, we describe the most recent advances in the use of animal models for the study of cell exhaustion following HIV/SIV infection. These findings suggest that the use of animal models is increasingly critical in translating immunotherapeutics into clinical practice.

Tuberculosis distorts the inhibitory impact of interleukin-10 in HIV infection

OBJECTIVES

This study aimed to assess how Mycobacterium tuberculosis (MTB) coinfection alters the impact of interleukin-10 in chronic HIV infection.

DESIGN

We assessed plasma cytokine levels (interleukin-10, interferon-γ, tumor necrosis factor-α, interleukin-2, interleukin-6 and interleukin-13) in 82 individuals presenting with HIV monoinfection, HIV-LTBI (latent MTB infection) coinfection or HIV-TB (active tuberculosis) coinfection. We also assessed the influence of MTB on the functional impact of interleukin-10 receptor alpha (interleukin-10Rα) blockade on HIV and MTB-specific CD4(+) T cells.

METHODS

Plasma cytokine levels were measured by high sensitivity Luminex. We used an ex-vivo interleukin-10Rα blockade assay to assess if functional enhancement of HIV and MTB-specific CD4(+) T cells was possible following a 48-h stimulation with HIV gag or pooled ESAT-6 (6 kDa early secretory antigenic target) and CFP-10 (10-kDa culture filtrate protein) peptides. Cell supernatant was collected 48 h after stimulation and the cytokine profile was measured by Luminex.

RESULTS

Plasma interleukin-10 levels were elevated in HIV-TB as compared with HIV monoinfection (P < 0.05) and HIV-LTBI (P < 0.05). Plasma interleukin-10 levels correlated to HIV viral load in HIV monoinfection (P = 0.016) and HIV-LTBI (P = 0.042), but not HIV-TB. Ex-vivo blockade of interleukin-10Rα significantly enhanced MTB and HIV-specific CD4(+) T-cell function in HIV-LTBI individuals but not in HIV-TB individuals.

CONCLUSION

Tuberculosis disrupts the correlation between interleukin-10 and markers of HIV disease progression. In addition, HIV-TB is associated with a more inflammatory cytokine milieu compared with HIV monoinfection. Interestingly, interleukin-10Rα blockade can enhance both HIV and MTB-specific T-cell function in HIV-LTBI, but not in HIV-TB coinfection.

Immunogenetics of small ruminant lentiviral infections

The small ruminant lentiviruses (SRLV) include the caprine arthritis encephalitis virus (CAEV) and the Maedi-Visna virus (MVV). Both of these viruses limit production and can be a major source of economic loss to producers. Little is known about how the immune system recognizes and responds to SRLVs, but due to similarities with the human immunodeficiency virus (HIV), HIV research can shed light on the possible immune mechanisms that control or lead to disease progression. This review will focus on the host immune response to HIV-1 and SRLV, and will discuss the possibility of breeding for enhanced SRLV disease resistance.

Regulatory T cells and the risk of CMV end-organ disease in patients with AIDS

OBJECTIVES

Cytomegalovirus (CMV)-specific T-cell effectors (CMV-Teff) protect against CMV end-organ disease (EOD). In HIV-infected individuals, their numbers and function vary with CD4 cell numbers and HIV load. The role of regulatory T cells (Treg) in CMV-EOD has not been extensively studied. We investigated the contribution of Treg and Teff toward CMV-EOD in HIV-infected individuals independently of CD4 cell numbers and HIV load and controlling for CMV reactivations.

DESIGN

We matched 43 CMV-EOD cases to 93 controls without CMV-EOD, but with similar CD4 cell numbers and HIV plasma RNA. CMV reactivation was investigated by blood DNA polymerase chain reaction over 32 weeks preceding the CMV-EOD in cases and preceding the matching point in controls.

METHODS

CMV-Teff and Treg were characterized by the expression of interferon-γ (IFN-γ), interleukin 2, tumor necrosis factor α (TNFα), MIP1β, granzyme B (GrB), CD107a, TNFα, FOXP3, and CD25.

RESULTS

Sixty-five percent cases and 20% controls had CMV reactivations. In multivariate analyses that controlled for CMV reactivations, none of the CMV-Teff subsets correlated with protection, but high CMV-GrB enzyme-linked immunosorbent spot responses and CMV-specific CD4FOXP3+%, CD4TNFα+%, and CD8CD107a% were significant predictors of CMV-EOD.

CONCLUSIONS

Because both FOXP3 and GrB have been previously associated with Treg activity, we conclude that CMV-Treg may play an important role in the development of CMV-EOD in advanced HIV disease. We were not able to identify a CMV-Teff subset that could be used as a surrogate of protection against CMV-EOD in this highly immunocompromised population.

Fallen angels or risen apes? A tale of the intricate complexities of imbalanced immune responses in the pathogenesis and progression of immune-mediated and viral cancers

Excessive immune responses directed against foreign pathogens, self-antigens, or commensal microflora can cause cancer establishment and progression if the execution of tight immuno-regulatory mechanisms fails. On the other hand, induction of potent tumor antigen-specific immune responses together with stimulation of the innate immune system is a pre-requisite for effective anti-tumor immunity, and if suppressed by the strong immuno-regulatory mechanisms can lead to cancer progression. Therefore, it is crucial that the inevitable co-existence of these fundamental, yet conflicting roles of immune-regulatory cells is carefully streamlined as imbalances can be detrimental to the host. Infection with chronic persistent viruses is characterized by severe immune dysfunction resulting in T cell exhaustion and sometimes deletion of antigen-specific T cells. More often, this is due to increased immuno-regulatory processes, which are triggered to down-regulate immune responses and limit immunopathology. However, such heightened levels of immune disruption cause a concomitant loss of tumor immune-surveillance and create a permissive microenvironment for cancer establishment and progression, as demonstrated by increased incidences of cancer in immunosuppressed hosts. Paradoxically, while some cancers arise as a consequence of increased immuno-regulatory mechanisms that inhibit protective immune responses and impinge on tumor surveillance, other cancers arise due to impaired immuno-regulatory mechanisms and failure to limit pathogenic inflammatory responses. This intricate complexity, where immuno-regulatory cells can be beneficial in certain immune settings but detrimental in other settings underscores the need for carefully formulated interventions to equilibrate the balance between immuno-stimulatory and immuno-regulatory processes.

Impact of HIV co-infection on plasma level of cytokines and chemokines of pulmonary tuberculosis patients

BACKGROUND

The immunologic environment during HIV/M. tuberculosis co-infection is characterized by cytokine and chemokine irregularities that have been shown to increase immune activation, viral replication, and T cell dysfunction.

METHODS

We analysed ex vivo plasma samples from 17 HIV negative and 16 HIV pulmonary tuberculosis co infected cases using Luminex assay to see impact of HIV co-infection on plasma level of cytokines and chemokines of pulmonary tuberculosis patients before and after anti Tuberculosis treatment.

RESULTS

The median plasma level of IFN-γ, IL-4, MCP-3, MIP-1β and IP-10 was significantly different (P < 0.05) before and after treatment in HIV negative TB patients but not in HIV positive TB patients. There was no significant difference between HIV positive and HIV negative TB patients (P > 0.05) in the plasma level of any of the cytokines or chemokines before treatment and anti TB treatment did not change the level of any of the measured cytokines in HIV positive tuberculosis patients. The ratio of IFN-γ/IL-10 and IFN-γ/IL-4 showed a significant increase after treatment in HIV negative TB cases but not in HIV positive TB cases which might indicate prolonged impairment of immune response to TB in HIV positive TB patients as compared to HIV negative tuberculosis patients.

CONCLUSIONS

HIV positive and HIV negative Tuberculosis patients display similar plasma cytokine and chemokine pattern. However, anti TB treatment significantly improves the Th1 cytokines and level of chemokines but does not restore the immune response in HIV positive individuals.

Differential impact of PD-1 and/or interleukin-10 blockade on HIV-1-specific CD4 T cell and antigen-presenting cell functions

Antigen persistence in chronic infections and cancer upregulates inhibitory networks, such as the PD-1 and interleukin-10 (IL-10) pathways, that impair immunity and lead to disease progression. These pathways are attractive targets for immunotherapy, as demonstrated by recent clinical trials of PD-1/PD-L1 blockade in cancer patients. However, in HIV-1 infection not all subjects respond to inhibition of either pathway and the mechanistic interactions between these two networks remain to be better defined. Here we demonstrate that in vitro blockade of PD-L1 and/or IL-10Rα results in markedly different profiles of HIV-1-specific CD4 T cell restoration. Whereas PD-L1 blockade leads to balanced increase in gamma interferon (IFN-γ), IL-2, and IL-13 secretion, IL-10Rα blockade preferentially restores IFN-γ production. In viremic subjects, combined PD-L1/IL-10Rα blockade results in a striking 10-fold increase in IFN-γ secretion by HIV-1-specific CD4 T cells that is not observed in subjects with spontaneous (elite controllers) or therapy-induced control of viral replication. In contrast to the dramatic increase in IFN-γ production, concurrent blockade has a marginal additive effect on IL-2 production, IL-13 secretion, and HIV-1-specific CD4 T cell proliferation. IFN-γ produced by Thelper cells upregulates PD-L1, HLA I/II, and IL-12 expression by monocytes. The effect of combined blockade on IFN-γ was dependent on reciprocal reinforcement through IL-12. These studies provide crucial information on the different immunoregulatory qualities of PD-1 and IL-10 in progressive disease and link exhausted virus-specific CD4 T cells and monocytes in the regulation of IFN-γ and IL-12 secretion.

IMPORTANCE

Infection with HIV results in most people in uncontrolled viral replication and progressive weakening of the body defenses. In the absence of antiviral therapy, this process results in clinical disease, or AIDS. An important reason why HIV continues to multiply is that a population of white blood cells called CD4 T cells that targets the virus fails to work properly. At least part of this impairment is under the control of inhibitory mechanisms that can be blocked to improve the function of these CD4 T cells. In this report, we show that blocking one or two of the molecules involved, called PD-1 and IL-10, has different effects on the individual functions of these cells and that one is strongly improved. We investigate how these effects are caused by interactions between CD4 T cells and antigen-presenting cells. These observations can have implications for new therapeutic approaches in HIV infection.

Evaluating the potential of IL-27 as a novel therapeutic agent in HIV-1 infection

Interleukin 27 (IL-27) is an immunomodulatory cytokine with important roles in both the innate and adaptive immune systems. In the last five years, the addition of exogenous IL-27 to primary cell cultures has been demonstrated to decrease HIV-1 replication in a number of cell types including peripheral blood mononuclear cells (PBMCs), CD4+ T cells, macrophages and dendritic cells. These in vitro findings suggest that IL-27 may have therapeutic value in the setting of HIV-1 infection. In this review, we describe the current knowledge of the biology of IL-27, its effects primarily on HIV-1 replication but also in other viral infections and explore its potential role as a therapeutic cytokine for the treatment of patients with HIV-1 infection.

In vitro assay to evaluate the impact of immunoregulatory pathways on HIV-specific CD4 T cell effector function

T cell exhaustion is a major factor in failed pathogen clearance during chronic viral infections. Immunoregulatory pathways, such as PD-1 and IL-10, are upregulated upon this ongoing antigen exposure and contribute to loss of proliferation, reduced cytolytic function, and impaired cytokine production by CD4 and CD8 T cells. In the murine model of LCMV infection, administration of blocking antibodies against these two pathways augmented T cell responses. However, there is currently no in vitro assay to measure the impact of such blockade on cytokine secretion in cells from human samples. Our protocol and experimental approach enable us to accurately and efficiently quantify the restoration of cytokine production by HIV-specific CD4 T cells from HIV infected subjects. Here, we depict an in vitro experimental design that enables measurements of cytokine secretion by HIV-specific CD4 T cells and their impact on other cell subsets. CD8 T cells were depleted from whole blood and remaining PBMCs were isolated via Ficoll separation method. CD8-depleted PBMCs were then incubated with blocking antibodies against PD-L1 and/or IL-10Rα and, after stimulation with an HIV-1 Gag peptide pool, cells were incubated at 37 °C, 5% CO2. After 48 hr, supernatant was collected for cytokine analysis by beads arrays and cell pellets were collected for either phenotypic analysis using flow cytometry or transcriptional analysis using qRT-PCR. For more detailed analysis, different cell populations were obtained by selective subset depletion from PBMCs or by sorting using flow cytometry before being assessed in the same assays. These methods provide a highly sensitive and specific approach to determine the modulation of cytokine production by antigen-specific T-helper cells and to determine functional interactions between different populations of immune cells.

HIV type 1 gp120-induced expansion of myeloid derived suppressor cells is dependent on interleukin 6 and suppresses immunity

BACKGROUND

Factors responsible for myeloid-derived suppressor cell (MDSC) expansion and T-cell dysfunction during human immunodeficiency virus type 1 (HIV) infection are unknown. This study investigated the role of MDSCs during HIV infection.

METHODS

Peripheral blood mononuclear cells (PBMCs) were cultured with gp120 and infectious or inactivated HIV, with or without anti-interleukin 6 (IL-6) antibody. CD33(+), CD4(+), and CD8(+) cells were isolated from PBMCs and cocultured in the presence or absence of inducible nitric oxide synthase (iNOS), reactive oxygen species (ROS), and arginase 1 inhibitors. CD11b(+)CD33(+)CD14(+)HLA-DR(-/lo) MDSCs, phosphorylated STAT3 (pSTAT3), and CD4(+)CD25(+)FoxP3(+) cells were evaluated by flow cytometry. IL-6, interferon γ (IFN-γ), interleukin 10 (IL-10), and gp120 levels were quantified by an enzyme-linked immunosorbent assay.

RESULTS

MDSCs expanded when PBMCs were exposed to infectious or inactivated HIV. Exposure to gp120 led to MDSC expansion, with increases in IL-6 levels and pSTAT3 expression. Anti-IL-6 abrogated MDSC expansion and pSTAT3 expression. gp120-expanded CD33(+) MDSCs inhibited IFN-γ release from autologous T cells, which was restored upon ROS and iNOS inhibition. gp120-expanded CD33(+) MDSCs increased IL-10 and CD4(+)CD25(+)FoxP3(+) regulatory T-cell levels in CD4(+) T-cell cocultures. Finally, high frequencies of MDSCs were present in HIV-infected persons, compared with healthy controls.

CONCLUSIONS

These findings demonstrate that HIV gp120 induces IL-6 and MDSC expansion, which contributes to immune suppression by modulating cytokine and cellular responses.

The split personality of regulatory T cells in HIV infection

Natural regulatory T cells (Tregs) participate in responses to various chronic infections including HIV. HIV infection is associated with a progressive CD4 lymphopenia and defective HIV-specific CD8 responses known to play a key role in the control of viral replication. Persistent immune activation is a hallmark of HIV infection and is involved in disease progression independent of viral load. The consequences of Treg expansion, observed in HIV infection, could be either beneficial, by suppressing generalized T-cell activation, or detrimental, by weakening HIV-specific responses and thus contributing to viral persistence. The resulting balance between Tregs contrasting outcomes might have critical implications in pathogenesis. Topics covered in this review include HIV-induced alterations of Tregs, Treg cell dynamics in blood and tissues, Treg-suppressive function, and the relationship between Tregs and immune activation. This review also provides a focus on the role of CD39(+) Tregs and other regulatory cell subsets. All these issues will be explored in different situations including acute and chronic infection, antiretroviral treatment-mediated viral control, and spontaneous viral control. Results must be interpreted with regard to both the Treg definition used in context and to the setting of the disease in an attempt to draw clearer conclusions from the apparently conflicting results.

Cytokine production and dysregulation in HIV pathogenesis: lessons for development of therapeutics and vaccines

Numerous studies have characterized the cytokine modulation observed in human immunodeficiency virus (HIV) infected individuals, from initial infection through chronic disease. Progressive and non-progressive HIV infection models show the cytokine milieu differs in terms of production and responsiveness in these two groups, suggesting an understanding of the role cytokines play during infection is necessary for directing the immune response toward viral control. This review will cover cytokine induction and dysfunction during HIV pathogenesis, with a focus on the interplay between cytokines and transcription factors, T cell activation, and exhaustion. We highlight cytokines that have either vaccine adjuvant or therapeutic potential and discuss the need to identify key factors required for prevention of progression, clearance of infection, or protection from acquisition.