Inflammation Perturbs the IL-7 Axis, Promoting Senescence and Exhaustion that Broadly Characterize Immune Failure in Treated HIV Infection

Altered IL-7 signaling in CD4+ T cells from patients with visceral leishmaniasis

BACKGROUND

CD4+ T cells play a central role in control of L. donovani infection, through IFN-γ production required for activation of macrophages and killing of intracellular parasites. Impaired control of parasites can in part be explained by hampered CD4+ T cells effector functions in visceral leishmaniasis (VL) patients. In a recent studies that defined transcriptional signatures for CD4+ T cells from active VL patients, we found that expression of the IL-7 receptor alpha chain (IL-7Rα; CD127) was downregulated, compared to CD4+ T cells from endemic controls (ECs). Since IL-7 signaling is critical for the survival and homeostatic maintenance of CD4+ T cells, we investigated this signaling pathway in VL patients, relative to ECs.

METHODS

CD4+ T cells were enriched from peripheral blood collected from VL patients and EC subjects and expression of IL7 and IL7RA mRNA was measured by real time qPCR. IL-7 signaling potential and surface expression of CD127 and CD132 on CD4+ T cell was analyzed by multicolor flow cytometry. Plasma levels of soluble IL-7 and sIL-7Rα were measured by ELISA.

RESULT

Transcriptional profiling data sets generated previously from our group showed lower IL7RA mRNA expression in VL CD4+ T cells as compared to EC. A significant reduction was, however not seen when assessing IL7RA mRNA by RT-qPCR. Yet, the levels of soluble IL-7Rα (sIL-7Rα) were reduced in plasma of VL patients compared to ECs. Furthermore, the levels of soluble IL-7 were higher in plasma from VL patients compared to ECs. Interestingly, expression of the IL-7Rα protein was higher on VL patient CD4+ T cells as compared to EC, with activated CD38+ CD4+ T cells showing higher surface expression of IL-7Rα compared to CD38- CD4+ T cells in VL patients. CD4+ T cells from VL patients had higher signaling potential baseline and after stimulation with recombinant human IL-7 (rhIL-7) compared to EC, as measured by phosphorylation of STAT5 (pSTAT5). Interestingly, it was the CD38 negative cells that had the highest level of pSTAT5 in VL patient CD4+ T cells after IL-7 stimulation. Thus, despite unaltered or potentially lowered IL7RA mRNA expression by CD4+ T cells from VL patients, the surface expression of the IL-7Rα was higher compared to EC and increased pSTAT5 was seen following exposure to rhIL-7. Accordingly, IL-7 signaling appears to be functional and even enhanced in VL CD4+ T cells and cannot explain the impaired effector function of VL CD4+ T cells. The enhanced plasma IL-7 may serve as part of homeostatic feedback mechanism regulating IL7RA expression in CD4+ T cells.

Immune checkpoint inhibitors as potential therapy for reverting T-cell exhaustion and reverting HIV latency in people living with HIV

The immune system of people living with HIV (PLWH) is persistently exposed to antigens leading to systemic inflammation despite combination antiretroviral treatment (cART). This inflammatory milieu promotes T-cell activation and exhaustion. Furthermore, it produces diminished effector functions including loss of cytokine production, cytotoxicity, and proliferation, leading to disease progression. Exhausted T cells show overexpression of immune checkpoint molecules (ICs) on the cell surface, including programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT), and lymphocyte activation gene-3 (LAG-3). The ICs also play a crucial role in T-cell exhaustion by reducing the immune response to cancer antigens. Immunotherapy based on immune checkpoint inhibitors (ICIs) has changed the management of a diversity of cancers. Additionally, the interest in exploring this approach in the setting of HIV infection has increased, including AIDS-defining cancers and non-AIDS-defining cancers in PLWH. To date, research on this topic suggests that ICI-based therapies in PLWH could be a safe and effective approach. In this review, we provide an overview of the current literature on the potential role of ICI-based immunotherapy not only in cancer remission in PLWH but also as a therapeutic intervention to restore immune response against HIV, revert HIV latency, and attain a functional cure for HIV infection.

Endotoxemia Associated with Liver Disease Correlates with Systemic Inflammation and T Cell Exhaustion in Hepatitis C Virus Infection

Both acute and chronic hepatitis C virus (HCV) infections are characterized by inflammation. HCV and reduced liver blood filtration contribute to inflammation; however, the mechanisms of systemic immune activation and dysfunction as a result of HCV infection are not clear. We measured circulating inflammatory mediators (IL-6, IP10, sCD163, sCD14), indices of endotoxemia (EndoCab, LBP, FABP), and T cell markers of exhaustion and senescence (PD-1, TIGIT, CD57, KLRG-1) in HCV-infected participants, and followed a small cohort after direct-acting anti-viral therapy. IL-6, IP10, Endocab, LBP, and FABP were elevated in HCV participants, as were T cell co-expression of exhaustion and senescence markers. We found positive associations between IL-6, IP10, EndoCab, LBP, and co-expression of T cell markers of exhaustion and senescence. We also found numerous associations between reduced liver function, as measured by plasma albumin levels, and T cell exhaustion/senescence, inflammation, and endotoxemia. We found positive associations between liver stiffness (TE score) and plasma levels of IL-6, IP10, and LBP. Lastly, plasma IP10 and the proportion of CD8 T cells co-expressing PD-1 and CD57 decreased after initiation of direct-acting anti-viral therapy. Although associations do not prove causality, our results support the model that translocation of microbial products, resulting from decreased liver blood filtration, during HCV infection drives chronic inflammation that results in T cell exhaustion/senescence and contributes to systemic immune dysfunction.

The Therapeutic Values of IL-7/IL-7R and the Recombinant Derivatives in Glioma: A Narrative Review

Interleukin-7 (IL-7) is essential for maintaining the immune system's defense functions by regulating the development and homeostasis of lymphocytes. Findings have shown the high efficacy of IL-7/IL-7 receptor (IL-7R)-based immunotherapy on various malignancies, with confirmation in both animal models and humans. In recent years, the progression-free survival and overall survival of patients suffering from gliomas significantly increased by introducing C7R-expressing chimeric antigen receptor (CAR)-T cells and long-acting IL-7 agonists such as NT-I7 (rhIL-7-hyFc, Efineptakin alfa). However, the effect of IL-7-based immunotherapies on the resistance of tumor cells to chemotherapy (when used simultaneously with chemotherapy agents) is still ambiguous and requires further studies. This article first reviews the pathophysiological roles of IL-7/IL-7R in tumors, focusing on gliomas. Subsequently, it discusses the therapeutic values of IL-7/IL-7R and the recombinant derivatives in gliomas.

Interleukin 6 Blockade With Tocilizumab Diminishes Indices of Inflammation That Are Linked to Mortality in Treated Human Immunodeficiency Virus Infection

BACKGROUND

People with human immunodeficiency virus (PWH) are at increased risk for comorbidities, and plasma interleukin 6 (IL-6) levels are among the most robust predictors of these outcomes. Tocilizumab (TCZ) blocks the receptor for IL-6, inhibiting functions of this cytokine.

METHODS

This was a 40-week, placebo-controlled, crossover trial (NCT02049437) where PWH on stable antiretroviral therapy (ART) were randomized to receive 3 monthly doses of TCZ or matching placebo intravenously. Following a 10-week treatment period and a 12-week washout, participants were switched to the opposite treatment. The primary endpoints were safety and posttreatment levels of C-reactive protein (CRP) and CD4+ T-cell cycling. Secondary endpoints included changes in inflammatory indices and lipid levels.

RESULTS

There were 9 treatment-related toxicities of grade 2 or greater during TCZ administration (mostly neutropenia) and 2 during placebo administration. Thirty-one of 34 participants completed the study and were included in a modified intent-to-treat analysis. TCZ reduced levels of CRP (median decrease, 1819.9 ng/mL, P < .0001; effect size, 0.87) and reduced inflammatory markers in PWH, including D-dimer, soluble CD14, and tumor necrosis factor receptors. T-cell cycling tended to decrease in all maturation subsets after TCZ administration, but was only significant among naive CD4 T cells. Lipid levels, including lipid classes that have been related to cardiovascular disease risk, increased during TCZ treatment.

CONCLUSIONS

TCZ is safe and decreases inflammation in PWH; IL-6 is a key driver of the inflammatory environment that predicts morbidity and mortality in ART-treated PWH. The clinical significance of lipid elevations during TCZ treatment requires further study. Clinical Trials Registration. NCT02049437.

Gestational Viral Infections: Role of Host Immune System

Viral infections in pregnancy are major causes of maternal and fetal morbidity and mortality. Infections can develop in the neonate transplacentally, perinatally, or postnatally (from breast milk or other sources) and lead to different clinical manifestations, depending on the viral agent and the gestational age at exposure. Viewing the peculiar tolerogenic status which characterizes pregnancy, viruses could exploit this peculiar immunological status to spread or affect the maternal immune system, adopting several evasion strategies. In fact, both DNA and RNA virus might have a deep impact on both innate and acquired immune systems. For this reason, investigating the interaction with these pathogens and the host's immune system during pregnancy is crucial not only for the development of most effective therapies and diagnosis but mostly for prevention. In this review, we will analyze some of the most important DNA and RNA viruses related to gestational infections.

Recent Developments in Protein Lactylation in PTSD and CVD: Novel Strategies and Targets

In 1938, Corneille Heymans received the Nobel Prize in physiology for discovering that oxygen sensing in the aortic arch and carotid sinus was mediated by the nervous system. The genetics of this process remained unclear until 1991 when Gregg Semenza while studying erythropoietin, came upon hypoxia-inducible factor 1, for which he obtained the Nobel Prize in 2019. The same year, Yingming Zhao found protein lactylation, a posttranslational modification that can alter the function of hypoxia-inducible factor 1, the master regulator of cellular senescence, a pathology implicated in both post-traumatic stress disorder (PTSD) and cardiovascular disease (CVD). The genetic correlation between PTSD and CVD has been demonstrated by many studies, of which the most recent one utilizes large-scale genetics to estimate the risk factors for these conditions. This study focuses on the role of hypertension and dysfunctional interleukin 7 in PTSD and CVD, the former caused by stress-induced sympathetic arousal and elevated angiotensin II, while the latter links stress to premature endothelial cell senescence and early vascular aging. This review summarizes the recent developments and highlights several novel PTSD and CVD pharmacological targets. They include lactylation of histone and non-histone proteins, along with the related biomolecular actors such as hypoxia-inducible factor 1α, erythropoietin, acid-sensing ion channels, basigin, and Interleukin 7, as well as strategies to delay premature cellular senescence by telomere lengthening and resetting the epigenetic clock.

IL7 genetic variation and toxicity to immune checkpoint blockade in patients with melanoma

Treatment with immune checkpoint blockade (ICB) frequently triggers immune-related adverse events (irAEs), causing considerable morbidity. In 214 patients receiving ICB for melanoma, we observed increased severe irAE risk in minor allele carriers of rs16906115, intronic to IL7. We found that rs16906115 forms a B cell-specific expression quantitative trait locus (eQTL) to IL7 in patients. Patients carrying the risk allele demonstrate increased pre-treatment B cell IL7 expression, which independently associates with irAE risk, divergent immunoglobulin expression and more B cell receptor mutations. Consistent with the role of IL-7 in T cell development, risk allele carriers have distinct ICB-induced CD8+ T cell subset responses, skewing of T cell clonality and greater proportional repertoire occupancy by large clones. Finally, analysis of TCGA data suggests that risk allele carriers independently have improved melanoma survival. These observations highlight key roles for B cells and IL-7 in both ICB response and toxicity and clinical outcomes in melanoma.

Inflammation, Immune Senescence, and Dysregulated Immune Regulation in the Elderly

An optimal immune response requires the appropriate interaction between the innate and the adaptive arms of the immune system as well as a proper balance of activation and regulation. After decades of life, the aging immune system is continuously exposed to immune stressors and inflammatory assaults that lead to immune senescence. In this review, we will discuss inflammaging in the elderly, specifically concentrating on IL-6 and IL-1b in the context of T lymphocytes, and how inflammation is related to mortality and morbidities, specifically cardiovascular disease and cancer. Although a number of studies suggests that the anti-inflammatory cytokine TGF-b is elevated in the elderly, heightened inflammation persists. Thus, the regulation of the immune response and the ability to return the immune system to homeostasis is also important. Therefore, we will discuss cellular alterations in aging, concentrating on senescent T cells and CD4+ CD25+ FOXP3+ regulatory T cells (Tregs) in aging

Gut-derived bacterial toxins impair memory CD4+ T cell mitochondrial function in HIV-1 infection

People living with HIV (PLWH) who are immune nonresponders (INRs) are at greater risk of comorbidity and mortality than are immune responders (IRs) who restore their CD4+ T cell count after antiretroviral therapy (ART). INRs have low CD4+ T cell counts (<350 c/μL), heightened systemic inflammation, and increased CD4+ T cell cycling (Ki67+). Here, we report the findings that memory CD4+ T cells and plasma samples of INRs from several cohorts are enriched in gut-derived bacterial solutes p-cresol sulfate (PCS) and indoxyl sulfate (IS) that both negatively correlated with CD4+ T cell counts. In vitro PCS or IS blocked CD4+ T cell proliferation, induced apoptosis, and diminished the expression of mitochondrial proteins. Electron microscopy imaging revealed perturbations of mitochondrial networks similar to those found in INRs following incubation of healthy memory CD4+ T cells with PCS. Using bacterial 16S rDNA, INR stool samples were found enriched in proteolytic bacterial genera that metabolize tyrosine and phenylalanine to produce PCS. We propose that toxic solutes from the gut bacterial flora may impair CD4+ T cell recovery during ART and may contribute to CD4+ T cell lymphopenia characteristic of INRs.

Association between inflammation and coagulation biomarkers and carotid atherosclerosis among treated people with HIV

Background

Atherosclerotic cardiovascular disease (CVD) is a common cause of morbidity among people with human immunodeficiency virus (PWH) who initiate antiretroviral therapy (ART). Little is known about the roles of inflammation in atherosclerotic CVD among PWH.

Methods

This cross-sectional evaluation included 178 PWH between 40 and 70 years on stable (>3 months) ART who were derived from the ongoing, prospective cohort for Comparative HIV and Aging Research in Taizhou (CHART), China, from February 2017 to August 2018. Carotid intima-media thickness (cIMT) ≥1 mm was considered as cIMT thickening indicative of atherosclerotic CVD. Plasma inflammation and coagulation biomarkers were quantified by a multiplex bead cytokine assay for 27 cytokines and enzyme-linked immunosorbent assay (ELISA) for soluble CD14 and D-dimer, respectively. We performed a series of multiparametric analyses of biomarkers and developed a composite score for atherosclerotic CVD assessment among PWH.

Results

Of 178 PWH, 53 (30.9%) had cIMT thickening. In multivariable logistic analysis adjusting for CVD and human immunodeficiency virus-specific risk factors, interleukin (IL)-4 (odds ratio [OR] = 19.0; 95% confidence interval [CI], 1.6–226.5), IL-7 (OR = 16.7; 95% CI, 1.8–151.7), IL-10 (OR = 11.9; 95% CI, 2.0–72.1), and D-dimer (OR = 3.1; 95% CI, 1.0–10.1) were significantly associated with cIMT thickening. We also developed a composite score incorporating markers (IL-7, IL-10, D-dimer, and hypertension) that accurately evaluated atherosclerotic CVD.

Conclusions

The associations of IL-4, IL-7, IL-10, and D-dimer with atherosclerosis underscores research needs to further understand the inflammatory mechanisms in the pathogenesis of atherosclerosis CVD among treated PWH. The composite score for atherosclerotic CVD assessment could be useful for risk stratification in PWH.

Soluble Immune Checkpoints Are Dysregulated in COVID-19 and Heavy Alcohol Users With HIV Infection

Immune checkpoints (ICPs) consist of paired receptor-ligand molecules that exert inhibitory or stimulatory effects on immune defense, surveillance, regulation, and self-tolerance. ICPs exist in both membrane and soluble forms in vivo and in vitro. Imbalances between inhibitory and stimulatory membrane-bound ICPs (mICPs) in malignant cells and immune cells in the tumor immune microenvironment (TIME) have been well documented. Blockades of inhibitory mICPs have emerged as an immense breakthrough in cancer therapeutics. However, the origin, structure, production regulation, and biological significance of soluble ICPs (sICPs) in health and disease largely remains elusive. Soluble ICPs can be generated through either alternative mRNA splicing and secretion or protease-mediated shedding from mICPs. Since sICPs are found in the bloodstream, they likely form a circulating immune regulatory system. In fact, there is increasing evidence that sICPs exhibit biological functions including (1) regulation of antibacterial immunity, (2) interaction with their mICP compartments to positively or negatively regulate immune responses, and (3) competition with their mICP compartments for binding to the ICP blocking antibodies, thereby reducing the efficacy of ICP blockade therapies. Here, we summarize current data of sICPs in cancer and infectious diseases. We particularly focus on sICPs in COVID-19 and HIV infection as they are the two ongoing global pandemics and have created the world's most serious public health challenges. A "storm" of sICPs occurs in the peripheral circulation of COVID-19 patients and is associated with the severity of COVID-19. Similarly, sICPs are highly dysregulated in people living with HIV (PLHIV) and some sICPs remain dysregulated in PLHIV on antiretroviral therapy (ART), indicating these sICPs may serve as biomarkers of incomplete immune reconstitution in PLHIV on ART. We reveal that HIV infection in the setting of alcohol misuse exacerbates sICP dysregulation as PLHIV with heavy alcohol consumption have significantly elevated plasma levels of many sICPs. Thus, both stimulatory and inhibitory sICPs are present in the bloodstream of healthy people and their balance can be disrupted under pathophysiological conditions such as cancer, COVID-19, HIV infection, and alcohol misuse. There is an urgent need to study the role of sICPs in immune regulation in health and disease.

Interleukin-7 aggravates myocardial ischaemia/reperfusion injury by regulating macrophage infiltration and polarization

Interleukin (IL)‐7 is known to enhance the macrophages cytotoxic activity and that macrophages play a pivotal role in the development and progression of myocardial ischaemia/reperfusion (I/R) injury. However, the effects of IL‐7 on macrophages infiltration and polarization in myocardial I/R injury are currently unclear. This study aimed to evaluate the effects of the IL‐7 expression on myocardial I/R injury and their relationship with macrophages. The data showed that IL‐7 expression in mouse heart tissue increases following I/R injury and that IL‐7 knockout or anti‐IL‐7 antibody treatment significantly improve I/R injury, including reduction in myocardial infarction area, a serum troponin T level decreases and an improvement in cardiac function. On the other hand, recombinant IL‐7 (rIL‐7) supplementation induces opposite effects and the anti‐IL‐7 antibody significantly reduces the cardiomyocyte apoptosis and macrophage infiltration. rIL‐7 cannot directly cause apoptosis, but it can induce cardiomyocyte apoptosis through macrophages, in addition to increase the macrophages migration in vitro. Anti‐IL‐7 antibody affects the cytokine production in T helper (Th) 1 and Th2 cells and also promotes the macrophages differentiation to M2 macrophages. However, anti‐IL‐7 antibody does not reduce the M1 macrophage number, and it only increases the ratio of M2/M1 macrophages in mice heart tissues after I/R injury. Taking together, these data reveal that IL‐7 plays an intensifying role in myocardial I/R injury by promoting cardiomyocyte apoptosis through the regulation of macrophage infiltration and polarization.

Compromised long-lived memory CD8+ T cells are associated with reduced IL-7 responsiveness in HIV-infected immunological nonresponders

Immune deficiency is one of the hallmarks of HIV infection and a major cause of adverse outcomes in people living with HIV (PLWH). Long-lived memory CD8⁺ T cells (LLMCs) are essential executors of long-term protective immunity; however, the generation and maintenance of LLMCs during chronic HIV infection are not well understood. In the present study, we analyzed circulating LLMCs in healthy controls (HCs) and PLWH with different disease statuses, including treatment naïve patients (TNs), complete responders (CRs), and immunological nonresponders (INRs). We found that both TNs and INRs showed severely compromised LLMCs compared with HCs and CRs, respectively. The decrease of LLMCs in TNs correlated positively with the reduction of their precursors, namely memory precursor effector T cells (MPECs), which might be associated with elevated pro-inflammatory cytokines. Strikingly, INRs showed an accumulation of MPECs, which exhibited diminished responsiveness to interleukin 7 (IL-7), thereby indicating abrogated differentiation into LLMCs. Moreover, in vitro studies showed that treatment with dexamethasone could improve the IL7-phosphorylated (p)-signal transducer and activator of transcription (STAT5) response by upregulating the expression of the interleukin 7 receptor (IL-7Rα) on MPECs in INRs. These findings provide insights that will encourage the development of novel therapeutics to improve immune function in PLWH.

Lymphopenia in primary Sjögren's syndrome is associated with premature aging of naïve CD4+ T cells

OBJECTIVE

To investigate peripheral lymphopenia, a frequent finding in primary Sjögren's syndrome (pSS) associated with higher disease activity and increased mortality.

METHODS

Prospective, cross-sectional study of consecutive patients with pSS (n = 66) and healthy controls (n = 181). Lymphocyte subsets were analysed by flow cytometry, naïve (CD45RA+) and memory (CD45RO+) CD4+ T cells were purified by MACS technology. In vitro proliferation and senescence-associated β-galactosidase (SABG) were assessed by flow cytometry. Telomere length and TCR excision circles (TREC) were measured by real-time PCR. Telomerase activity was analysed according to the telomeric repeat amplification protocols (TRAP).

RESULTS

In pSS, lymphopenia mainly affected naïve CD4+ T cells. We noted a lower frequency of proliferating naïve CD4+ T cells ex vivo and decreased homeostatic proliferation in response to IL-7 stimulation in vitro. Furthermore, naïve CD4+ T cells exhibited signs of immune cell aging including shortened telomeres, a reduction in IL-7R expression and accumulation of SABG. The senescent phenotype could be explained by telomerase insufficiency and drastically reduced levels of T-cell receptor excision circles (TRECs), indicating a history of extensive post-thymic cell division. TRECs correlated with the number of naïve CD4+ T cells linking the extend of earlier proliferation to the inability to sustain normal cell numbers.

CONCLUSION

In pSS, evidence for increased proliferation of naïve CD4+ T cells earlier in life is associated with a senescent phenotype unable to sustain homeostasis. The lack of naïve CD4+ T cells forms the basis of lymphopenia frequently observed in pSS.

Markers of T Cell Exhaustion and Senescence and Their Relationship to Plasma TGF-β Levels in Treated HIV+ Immune Non-responders

Background: Immune non-responders (INR) are HIV+, ART-controlled (>2 yrs) people who fail to reconstitute their CD4 T cell numbers. Systemic inflammation and markers of T cell senescence and exhaustion are observed in INR. This study aims to investigate T cell senescence and exhaustion and their possible association with soluble immune mediators and to understand the immune profile of HIV-infected INR. Selected participants were <50 years old to control for the confounder of older age. Methods: Plasma levels of IL-6, IP10, sCD14, sCD163, and TGF-β and markers of T cell exhaustion (PD-1, TIGIT) and senescence (CD57, KLRG-1) were measured in ART-treated, HIV+ participants grouped by CD4 T cell counts (n = 63). Immune parameters were also measured in HIV-uninfected, age distribution-matched controls (HC; n = 30). Associations between T cell markers of exhaustion and senescence and plasma levels of immune mediators were examined by Spearman rank order statistics. Results: Proportions of CD4 T cell subsets expressing markers of exhaustion (PD-1, TIGIT) and senescence (CD57, KLRG-1) were elevated in HIV+ participants. When comparing proportions between INR and IR, INR had higher proportions of CD4 memory PD-1+, EM CD57+, TEM TIGIT+ and CD8 EM and TEM TIGIT+ cells. Plasma levels of IL-6, IP10, and sCD14 were elevated during HIV infection. IP10 was higher in INR. Plasma TGF-β levels and CD4 cycling proportions of T regulatory cells were lower in INR. Proportions of CD4 T cells expressing TIGIT, PD-1, and CD57 positively correlated with plasma levels of IL-6. Plasma levels of TGF-β negatively correlated with proportions of TIGIT+ and PD-1+ T cell subsets. Conclusions: INR have lower levels of TGF-β and decreased proportions of cycling CD4 T regulatory cells and may have difficulty controlling inflammation. IP10 is elevated in INR and is linked to higher proportions of T cell exhaustion and senescence seen in INR.

Definition of Immunological Nonresponse to Antiretroviral Therapy: A Systematic Review

BACKGROUND

Terms and criteria to classify people living with HIV on antiretroviral therapy who fail to achieve satisfactory CD4 T-cell counts are heterogeneous, and need revision and summarization.

METHODS

We performed a systematic review of PubMed original research articles containing a set of predefined terms, published in English between January 2009 and September 2018. The search retrieved initially 1360 studies, of which 103 were eligible. The representative terminology and criteria were extracted and analyzed.

RESULTS

Twenty-two terms and 73 criteria to define the condition were identified. The most frequent term was "immunological nonresponders" and the most frequent criterion was "CD4 T-cell count <350 cells/µL after ≥24 months of virologic suppression." Most criteria use CD4+ T-cell counts as a surrogate, either as an absolute value or as a change after a defined period of time [corrected]. Distinct values and time points were used. Only 9 of the 73 criteria were used by more than one independent research team. Herein we propose 2 criteria that could help to reach a consensus.

CONCLUSIONS

The high disparity in terms and criteria here reported precludes data aggregation and progression of the knowledge on this condition, because it renders impossible to compare data from different studies. This review will foster the discussion of terms and criteria to achieve a consensual definition.

Soluble PD-L1: a potential immune marker for HIV-1 infection and virological failure

Despite viral control, basal chronic inflammation and its related comorbidities remain unsolved problems among HIV-infected individuals. Soluble factors derived from myeloid cells have emerged as potent markers associated with HIV-related comorbidities and mortality. In the present report, we explored the relationship between soluble programmed death-ligand 1 (sPD-L1) and HIV-1 infection, antiretroviral therapy (ART), CD4/CD8 ratio, viral load (VL), and sexually transmitted coinfections.A prospective observational study on 49 HIV-1 infected adults.We found sPD-L1 levels were significantly higher in 49 HIV infected subjects than in 30 uninfected adults (1.05 ng/ml vs 0.52 ng/ml; P < .001). In this line, sPD-L1 levels were found to be elevated in 16 HIV infected subjects with undetectable VL compared with the uninfected subjects (0.75 ng/ml vs 0.52 ng/ml; P = .02). Thirteen ART-treated individuals with virological failure exhibited the highest sPDL1 levels, which were significantly higher than both 20 ART naïve infected individuals (1.68 ng/ml vs 0.87 ng/ml; P = .003) and the 16 ART-treated individuals with suppressed viremia (1.68 ng/ml vs 0.79 ng/ml; P = 002). Entire cohort data showed a statistically significant positive correlation between VL and sPD-L1 levels in plasma (r = 0.3; P = 036).Our findings reveal sPDL-1 as a potential biomarker for HIV infection especially interesting in those individuals with virological failure.

Toll-like receptor distribution in colonic epithelium and lamina propria is disrupted in HIV viremic, immune success, and failure

DESIGN

Since intestinal immunity and the microbiome are disrupted in HIV disease, we studied the abundance of innate immune sensors, Toll-like receptors (TLRs), in the mucosa of participants with viremia, prior to antiretroviral therapy (ART), immune success (>500 CD4 T cells/μl after 2 years of ART; suppressed viremia), and immune failure (<350 CD4 T cells/μl after 2 years of ART; suppressed viremia). We hypothesized that disruption of intestinal TLR abundance and location provides a mechanism behind persistent inflammation.

METHODS

Immunofluorescence for TLR3, TLR4, and TLR9 on paraffin embedded biopsies from uninfected, viremic, immune success, and immune failure colons was imaged by deconvolution microscopy and quantified with MetaMorph software. Plasma levels of C-reactive protein, IL-6, and intestinal fatty-acid binding protein (I-FABP) were correlated with TLR expression.

RESULTS

Viremic participants have significantly higher levels of TLR3 and TLR9 on surface epithelium and in crypts when compared with uninfected controls. TLR3 is further elevated in immune failure and immune success. TLR9 abundance remains elevated in immune failure and is normalized in immune success. TLR9 expression in the crypt and lamina propria positively associates with C-reactive protein and IL-6 and negatively with I-FABP. TLR4 is significantly lower on surface epithelium and higher in crypts in viremic. Its expression in the lamina propria positively correlates with IL-6 and negatively correlates with I-FABP.

CONCLUSION

Mucosal TLR imbalance and deregulation, and the resulting mucosal TLR desensitization and hypervigilance, remain after suppressive ART, in the presence or absence of T-cell recovery, likely contributing to chronic systemic inflammation.

Incomplete immune reconstitution in HIV/AIDS patients on antiretroviral therapy: Challenges of immunological non-responders

The morbidity and mortality of HIV type-1 (HIV-1)-related diseases were dramatically diminished by the grounds of the introduction of potent antiretroviral therapy, which induces persistent suppression of HIV-1 replication and gradual recovery of CD4⁺ T-cell counts. However, ∼10-40% of HIV-1-infected individuals fail to achieve normalization of CD4⁺ T-cell counts despite persistent virological suppression. These patients are referred to as "inadequate immunological responders," "immunodiscordant responders," or "immunological non-responders (INRs)" who show severe immunological dysfunction. Indeed, INRs are at an increased risk of clinical progression to AIDS and non-AIDS events and present higher rates of mortality than HIV-1-infected individuals with adequate immune reconstitution. To date, the underlying mechanism of incomplete immune reconstitution in HIV-1-infected patients has not been fully elucidated. In light of this limitation, it is of substantial practical significance to deeply understand the mechanism of immune reconstitution and design effective individualized treatment strategies. Therefore, in this review, we aim to highlight the mechanism and risk factors of incomplete immune reconstitution and strategies to intervene.

Naïve/Effector CD4 T cell ratio as a useful predictive marker of immune reconstitution in late presenter HIV patients: A multicenter study

A significant proportion of HIV-infected patients experiencing a late diagnosis highlights the need to define immunological protocols able to help the clinicians in identifying patients at higher risk for immunological failure. The aim of the study was to evaluate the feasibility of easy cytometric tests in defining the effect of antiretroviral treatment (cART) on immunological homeostasis and in identifying predictive markers of early immune recovery. Chronic HIV infected patients (n = 202) were enrolled in a prospective multicentric study, and their immunological profile was studied before (w0) and after 24 weeks (w24) of antiretroviral treatment (cART) using a standardized flow cytometric panel. Based on CD4 T cell count before treatment, patients were divided in late (LP: CD4 <350/mmc), intermediate (IP: 350/mmc<CD4<500/mmc) and early (EP: CD4 >500/mmc) presenters. In all groups, cART introduction increased CD4 and CD4/CD8 T cell ratio, naïve T cell (CD4 and CD8) and CD127-expressing CD4 T cells. In parallel, cART significantly reduced effector memory T cells (CD4 and CD8) and T cell activation (CD38+CD8 and CD95+CD4 T cells). Moreover, the frequency of Naïve and Effector CD4 T cells before treatment correlated with several immune parameters key associated with the pathogenesis of HIV, thus mirroring the health of immune system. Interestingly, we identified the Naïve/Effector CD4 T cell ratio (N/EM) at w0 as a marker able to predict early immune recovery. Specifically, in LP, N/EM ratio was significantly higher in immunological responder patients (CD4>500/mmc at w24) when compared to immunological non responder (CD4 T cells <500/mmc at w24). Finally, a multivariate analysis indicates that after 24w patients with N/EM ratio higher than 1.86 at w0 recovered 96 CD4 T cells more than those with N/EM ratio lower than 0.46. Altogether, our data define an easy protocol able to define reliable immunological markers useful for the characterization of immune profile in viremic HIV patients and identify the naïve/effector CD4 T cell ratio as a new tool able to predict an early immune reconstitution potential.

Elevated Autotaxin and LPA Levels During Chronic Viral Hepatitis and Hepatocellular Carcinoma Associate with Systemic Immune Activation

Circulating autotaxin (ATX) is elevated in persons with liver disease, particularly in the setting of chronic hepatitis C virus (HCV) and HCV/HIV infection. It is thought that plasma ATX levels are, in part, attributable to impaired liver clearance that is secondary to fibrotic liver disease. In a discovery data set, we identified plasma ATX to be associated with parameters of systemic immune activation during chronic HCV and HCV/HIV infection. We and others have observed a partial normalization of ATX levels within months of starting interferon-free direct-acting antiviral (DAA) HCV therapy, consistent with a non-fibrotic liver disease contribution to elevated ATX levels, or HCV-mediated hepatocyte activation. Relationships between ATX, lysophosphatidic acid (LPA) and parameters of systemic immune activation will be discussed in the context of HCV infection, age, immune health, liver health, and hepatocellular carcinoma (HCC).

The Role of the BCL-2 Family of Proteins in HIV-1 Pathogenesis and Persistence

Advances in HIV-1 therapy have transformed the once fatal infection into a manageable, chronic condition, yet the search for a widely applicable approach to cure remains elusive. The ineffectiveness of antiretroviral therapy (ART) in reducing the size of the HIV-1 latent reservoir has prompted investigation into the mechanisms of HIV-1 latency and immune escape. One of the major regulators of apoptosis, the BCL-2 protein, alongside its homologous family members, is a major target of HIV-1-induced change. Recent studies have now demonstrated the association of this protein with cells that support proviral forms in the setting of latency and have helped identify BCL-2 as a novel and promising therapeutic target for HIV-1 therapy directed at possible cure. This review aims to systematically review the interactions of HIV-1 with BCL-2 and its homologs and to examine the possibility of using BCL-2 inhibitors in the study and elimination of the latent reservoir.

The Diverse Function of PD-1/PD-L Pathway Beyond Cancer

The recent success of PD-1 and PD-L1 blockade in cancer therapy illustrates the important role of the PD-1/PD-L1 pathway in the regulation of antitumor immune responses. However, signaling regulated by the PD-1/PD-L pathway is also associated with substantial inflammatory effects that can resemble those in autoimmune responses, chronic infection, and sepsis, consistent with the role of this pathway in balancing protective immunity and immunopathology, as well as in homeostasis and tolerance. Targeting PD-1/PD-L1 to treat cancer has shown benefits in many patients, suggesting a promising opportunity to target this pathway in autoimmune and inflammatory disorders. Here, we systematically evaluate the diverse biological functions of the PD-1/PD-L pathway in immune-mediated diseases and the relevant mechanisms that control these immune reactions.

Blocking Formation of the Stable HIV Reservoir: A New Perspective for HIV-1 Cure

Recent studies demonstrate that the stable HIV-1 reservoir in resting CD4+ T cells is mostly formed from viruses circulating when combination antiretroviral therapy (ART) is initiated. Here we explore the immunological basis for these observations. Untreated HIV-1 infection is characterized by a progressive depletion of memory CD4+ T cells which mostly express CD127, the α chain of the IL-7 receptor (IL-7R). Depletion results from both direct infection and bystander loss of memory CD4+ T cells in part attributed to dysregulated IL-7/IL-7R signaling. While IL-7/IL7R signaling is not essential for the generation of effector CD4+ T cells from naïve cells, it is essential for the further transition of effectors to memory CD4+ T cells and their subsequent homeostatic maintenance. HIV-1 infection therefore limits the transition of CD4+ T cells from an effector to long-lived memory state. With the onset of ART, virus load (VL) levels rapidly decrease and the frequency of CD127+ CD4+ memory T cells increases, indicating restoration of effector to memory transition in CD4+ T cells. Collectively these data suggest that following ART initiation, HIV-1 infected effector CD4+ T cells transition to long-lived, CD127+ CD4+ T cells forming the majority of the stable HIV-1 reservoir. We propose that combining ART initiation with inhibition of IL-7/IL-7R signaling to block CD4+ T cell memory formation will limit the generation of long-lived HIV-infected CD4+ T cells and reduce the overall size of the stable HIV-1 reservoir.

Type I interferon signaling, regulation and gene stimulation in chronic virus infection

Type I Interferons (IFN-I) mediate numerous immune interactions during viral infections, from the establishment of an antiviral state to invoking and regulating innate and adaptive immune cells that eliminate infection. While continuous IFN-I signaling plays critical roles in limiting virus replication during both acute and chronic infections, sustained IFN-I signaling also leads to chronic immune activation, inflammation and, consequently, immune exhaustion and dysfunction. Thus, an understanding of the balance between the desirable and deleterious effects of chronic IFN-I signaling will inform our quest for IFN-based therapies for chronic viral infections as well as other chronic diseases, including cancer. As such the factors involved in induction, propagation and regulation of IFN-I signaling, from the initial sensing of viral nucleotides within the cell to regulatory downstream signaling factors and resulting IFN-stimulated genes (ISGs) have received significant research attention. This review summarizes recent work on IFN-I signaling in chronic infections, and provides an update on therapeutic approaches being considered to counter such infections.

Increased Regulatory T-Cell Activity and Enhanced T-Cell Homeostatic Signaling in Slow Progressing HIV-infected Children

Pediatric slow progressors (PSP) are rare ART-naïve, HIV-infected children who maintain high CD4 T-cell counts and low immune activation despite persistently high viral loads. Using a well-defined cohort of PSP, we investigated the role of regulatory T-cells (TREG) and of IL-7 homeostatic signaling in maintaining normal-for-age CD4 counts in these individuals. Compared to children with progressive disease, PSP had greater absolute numbers of TREG, skewed toward functionally suppressive phenotypes. As with immune activation, overall T-cell proliferation was lower in PSP, but was uniquely higher in central memory TREG (CM TREG), indicating active engagement of this subset. Furthermore, PSP secreted higher levels of the immunosuppressive cytokine IL-10 than children who progressed. The frequency of suppressive TREG, CM TREG proliferation, and IL-10 production were all lower in PSP who go on to progress at a later time-point, supporting the importance of an active TREG response in preventing disease progression. In addition, we find that IL-7 homeostatic signaling is enhanced in PSP, both through preserved surface IL-7receptor (CD127) expression on central memory T-cells and increased plasma levels of soluble IL-7receptor, which enhances the bioactivity of IL-7. Combined analysis, using a LASSO modeling approach, indicates that both TREG activity and homeostatic T-cell signaling make independent contributions to the preservation of CD4 T-cells in HIV-infected children. Together, these data demonstrate that maintenance of normal-for-age CD4 counts in PSP is an active process, which requires both suppression of immune activation through functional TREG, and enhanced T-cell homeostatic signaling.

Trypanosoma cruzi-specific IFN-γ-producing cells in chronic Chagas disease associate with a functional IL-7/IL-7R axis

Background

The severity of cardiac disease in chronic Chagas disease patients is associated with different features of T-cell exhaustion. Here, we assessed whether the ability of T cells to secrete IFN-γ in response to T. cruzi was linked to disruption in immune homeostasis and inflammation in patients with chronic Chagas disease.

Methodology/Principal findings

PBMCs from chronic Chagas disease patients and uninfected controls were examined for frequencies of T. cruzi-responsive IFN-γ-producing cells by ELISPOT and cellular expression and function of IL-7R using flow cytometry. Serum levels of IL-7, IL-21, IL-27, soluble IL-7R, and inflammatory cytokines were also evaluated by ELISA or CBA techniques. Patients possessing T. cruzi-specific IFN-γ-producing cells (i.e. IFN-γ producers) had higher levels of memory T cells capable of modulating the alpha chain of IL-7R and an efficient response to IL-7 compared to that in patients lacking (i.e. IFN-γ nonproducers) parasite-specific T-cell responses. IFN-γ producers also showed low levels of soluble IL-7R, high basal expression of Bcl-2 in T cells and low basal frequencies of activated CD25⁺ T cells. Modulation of IL-7R was inversely associated with serum IL-6 levels and positively associated with serum IL-8 levels. Circulating IL-21 and IL-27 levels were not associated with the frequency of IFN-γ producing cells but were reduced in less severe clinical forms of the disease. In vitro stimulation of PBMCs with IL-7 or IL-27 enhanced IFN-γ production in IFN-γ producers but not in IFN-γ nonproducers.

Conclusions/Significance

Alterations of the IL-7/IL-7R axis and in the levels of inflammatory cytokines were linked to impaired T. cruzi-specific IFN-γ production. These alterations might be responsible of the process of immune exhaustion observed in chronic Chagas disease.

Mechanisms of acquired immune response against Trypanosoma cruzi antigens include both humoral and cellular components that might be critical in a chronic infection. Through a vast number of studies, several groups have postulated that, similar to other chronic infections, T-cell responses in chronic Trypanosoma cruzi infection are driven to exhaustion. Alterations in T-cell signaling pathways have emerged as one of the mechanisms of immune exhaustion. Here, we investigated whether the ability of T cells to secrete IFN-γ in response to T. cruzi was linked to the expression and function of the IL-7 receptor and the cytokines involved in regulating this axis in patients with different clinical forms of chronic Chagas disease. This study showed that the ability of T cells to secrete IFN-γ in response to T. cruzi is linked to an efficient modulation and function of IL-7R and low levels of inflammatory cytokines. Low IFN-γ-ELISPOT responses could not be reverted by in vitro treatment with IL-7. These findings contribute to our understanding of the long-term consequences of T. cruzi-infection and might be useful to delineate novel therapeutic strategies.

Higher Interleukin-7 serum concentrations in patients with cystic fibrosis correlate with impaired lung function

BACKGROUND

Patients with cystic fibrosis (CF) are highly susceptible to infection and colonization of pulmonary epithelia. Repeated and chronic infections may affect disease course and efficacy of host immune protection. Higher Interleukin (IL)-7 serum levels, indicating impaired T-cell response to IL-7, have been described for chronic viral and mycobacterial infections.

METHODS

Time course measures of IL-7 serum concentrations in patients with CF (n = 164; n = 78 for the second time point) and healthy controls (n = 60) were done. CF patients were characterized for disease severity parameters as well as infection status and association with IL-7 serum levels was determined.

RESULTS

CF patients had significantly higher IL-7 serum concentrations as compared to healthy controls (9.79 pg/ml, IQR 6.76-13.6 versus 4.55 pg/ml, IQR 2.76-9.51, p < .001). IL-7 serum levels were negatively correlated with individual CF patient's BMI (r = -0.19, p = .021) and a tendency of increased IL-7 levels in Staphylococcus aureus infected CF patients was found. Linear regression of multiple parameters revealed significant negative correlation of FEV1_%pred with IL-7 serum concentrations in patients with CF (ß-coefficient: -0.04, 95% confidence interval [-0.08; -0.003], p = .034). Time course analyses after 1 year +/- 6 months showed increased IL-7 serum levels (time point 1:9.26 pg/ml, IQR 6.94-13.12 time point 2:10.86 pg/ml, IQR 9.14-14.76, p = .016) that correlated negatively with decreased FEV1_%pred during CF disease course.

CONCLUSIONS

High IL-7 serum levels were found in CF patients and correlated with impaired lung function during CF disease course. As a candidate biomarker of T-cell dysfunction, higher IL-7 serum level may also indicate worsened immune competence of patients with CF.

Cycling CD4+ T cells in HIV-infected immune nonresponders have mitochondrial dysfunction

Immune nonresponder (INR) HIV-1-infected subjects are characterized by their inability to reconstitute the CD4+ T cell pool after antiretroviral therapy. This is linked to poor clinical outcome. Mechanisms underlying immune reconstitution failure are poorly understood, although, counterintuitively, INRs often have increased frequencies of circulating CD4+ T cells in the cell cycle. While cycling CD4+ T cells from healthy controls and HIV+ patients with restored CD4+ T cell numbers complete cell division in vitro, cycling CD4+ T cells from INRs do not. Here, we show that cells with the phenotype and transcriptional profile of Tregs were enriched among cycling cells in health and in HIV infection. Yet there were diminished frequencies and numbers of Tregs among cycling CD4+ T cells in INRs, and cycling CD4+ T cells from INR subjects displayed transcriptional profiles associated with the impaired development and maintenance of functional Tregs. Flow cytometric assessment of TGF-β activity confirmed the dysfunction of Tregs in INR subjects. Transcriptional profiling and flow cytometry revealed diminished mitochondrial fitness in Tregs among INRs, and cycling Tregs from INRs had low expression of the mitochondrial biogenesis regulators peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1α) and transcription factor A for mitochondria (TFAM). In vitro exposure to IL-15 allowed cells to complete division, restored the expression of PGC1α and TFAM, and regenerated mitochondrial fitness in the cycling Tregs of INRs. Our data suggest that rescuing mitochondrial function could correct the immune dysfunction characteristic of Tregs in HIV-1-infected subjects who fail to restore CD4+ T cells during antiretroviral therapy.

Distinct Treatment Outcomes of Antiparasitic Therapy in Trypanosoma cruzi-Infected Children Is Associated With Early Changes in Cytokines, Chemokines, and T-Cell Phenotypes

Background: In contrast to adults, Trypanosoma cruzi-infected children have more broadly functional Trypanosoma cruzi-specific T cells, and the total T-cell compartment exhibits fewer signs of immune exhaustion. However, not much is known about the link between immunocompetence and the treatment efficacy for human Chagas disease.

Methods: Using cytokine enzyme-linked immunosorbent spot (ELISPOT) polychromatic flow cytometry, cytometric bead assay, multiplex serological assays and quantitative PCR, we evaluated T. cruzi-specific T-cell and antibody immune responses, T-cell phenotypes and parasitemia in children in the early chronic phase of Chagas disease undergoing anti-Trypanosoma cruzi treatment.

Results: Treatment with benznidazole or nifurtimox induced a decline in T. cruzi-specific IFN-γ- and IL-2-producing cells and proinflammatory cytokines and chemokines. T-cell responses became detectable after therapy in children bearing T-cell responses under background levels prior to treatment. The total frequencies of effector, activated and antigen-experienced T cells also decreased following anti-T. cruzi therapy, along with an increase in T cells expressing the receptor of the homeostatic cytokine IL-7. Posttreatment changes in several of these markers distinguished children with a declining serologic response suggestive of successful treatment from those with sustained serological responses in a 5-year follow-up study. A multivariate analysis demonstrated that lower frequency of CD4⁺CD45RA⁻CCR7⁻CD62L⁻ T cells prior to drug therapy was an independent indicator of successful treatment.

Conclusions: These findings further validate the usefulness of alternative metrics to monitor treatment outcomes. Distinct qualitative and quantitative characteristics of T cells prior to drug therapy may be linked to treatment efficacy.

Effects of Fish Oil on HIV-Related Inflammation and Markers of Immunosenescence: A Randomized Clinical Trial

Objective: To explore the safety and efficacy of fish oil to modulate parameters of inflammation and immunosenescence in HIV-infected older adults.

Design: This study uses a randomized, controlled, double-blind clinical trial.

Setting: The study was conducted in an outpatient HIV/AIDS clinic in a large urban Midwestern city in the United States.

Subjects: A total of 37 clinically stable HIV-infected adults between the ages of 40 and 70 years of age participated.

Interventions: Fish oil 1.6 g/day was administered for 12 weeks or placebo.

Outcome measures: Inflammatory cytokine production, surface markers of immunosenescence, and adverse events were measured.

Results: After 12 weeks of supplementation, there were no significant differences between the treatment and control groups on any measures of inflammation or immunosenescence in both CD4⁺ and CD8⁺ T lymphocytes. More participants in the treatment group reported adverse gastrointestinal events compared with the control group.

Conclusions: A 12-week supplementation regimen of 1.6 g/day of fish oil did not favorably modulate parameters of inflammation or immune senescence in HIV-infected adults. Future studies should test agents that directly target mechanisms that underlie HIV-related inflammation to determine whether reducing inflammation can reverse immunosenescence.

Expression of PD-1 and Tim-3 markers of T-cell exhaustion is associated with CD4 dynamics during the course of untreated and treated HIV infection

Introduction

T-cell exhaustion has been involved in the pathogenesis of HIV infection. We have longitudinally analyzed PD1 and Tim3 surrogate markers of T-cells exhaustion, in parallel with other markers of HIV progression, and its potential association with CD4 changes in treated and untreated infection.

Patients and methods

96 HIV patients, 49 of them followed in the absence of cART (cART-naïve group) and 47 after initiation of cART (cART group) were included and followed for a median of 43 [IQR: 31–60] months. PD1 and Tim3 expression, CD8 T-cells activation, recent thymic emigrants, activation/apoptosis and turnover of CD4 cells were assessed at baseline and during follow up. Univariate and multivariate associations with CD4 evolution were explored.

Results

Parameters significantly associated with CD4 depletion in cART-naïve group were: baseline level (p = 0.02) and variation (p = 0.002) of PD1 and Tim3 co-expression on CD8, and variation of CD95 expression on CD4 (p = 0.007). Parameters significantly associated with CD4 restoration in cART group were: baseline level of CD38+HLADR- subset of CD8 (p = 0.01), variation of PD1 expression on CD8 (p = 0.036), variation of Tim3 expression on CD4 (p = 0.039) and variation of CD95 expression on CD4 (p = 0.035).

Conclusions

Our results suggest that PD1 and Tim3 markers of exhaustion have a pivotal role in CD4 dynamics in HIV patients and its down-regulation would be a desirable effect of immunotherapies aimed to restore CD4 T-cell pool during progression of HIV infection.

Immune checkpoint blockade in infectious diseases

The upregulation of immune checkpoint molecules, such as programmed cell death protein 1 (PD1) and cytotoxic T lymphocyte antigen 4 (CTLA4), on immune cells occurs during acute infections, such as malaria, as well as during chronic persistent viral infections, including HIV and hepatitis B virus. These pathways are important for preventing immune-driven pathology but can also limit immune-mediated clearance of the infection. The recent success of immune checkpoint blockade in cancer therapy suggests that targeting these pathways would also be effective for preventing and treating a range of infectious diseases. Here, we review our current understanding of immune checkpoint pathways in the pathogenesis of infectious diseases and discuss the potential for therapeutically targeting these pathways in this setting.

Is weak CD4+ gain in the course of suppressive combination antiretroviral therapy for HIV infection a current clinical challenge? A case report and brief review of the literature

Background

Individuals lacking immune recovery during suppressive cART will still represent a clinical issue in the years to come, given the high proportion of HIV-infected subjects introducing therapy late in the course of disease. Understanding the mechanisms underlying poor CD4+ T-cell gain is crucial for the correct clinical management of individuals in this context.

Case presentation

An HIV-infected subject with poor CD4+ T-cell gain in the course of suppressive antiretroviral therapy was extensively investigated to identify the mechanisms behind inadequate CD4+ reconstitution. In particular, we studied the phenotype of circulating T-cells, interleukin-7 signaling in peripheral blood and bone marrow, gut function and microbial translocation markers as well as the composition of the faecal microbiota. Numerous therapeutic interventions ranging from antiretroviral therapy intensification to immunotherapy and anti-hepatitis C virus treatment were also employed in order to target the possible causes of poor immune-recovery.

Conclusions

Poor CD4+ T-cell gain on suppressive antiretroviral therapy is multifactorial and thus represents a clinical challenge. Clinicians should investigate subjects’ immune profile as well as possible causes of chronic antigenic stimulation for the administration of the most appropriate therapeutic strategies in this setting.

Increased CD127+ and decreased CD57+ T cell expression levels in HIV-infected patients on NRTI-sparing regimens

BACKGROUND

NRTIs-sparing regimens exert favourable profiles on T-cell homeostasis associated parameters. Our aim was to analyze the effect of NRTIs sparing regimen (NRTI-sparing-cART) vs NRTIs-containing regimen (NRTI-cART), on T-cell homeostasis associated parameters in naive HIV-infected patients.

METHODS

Biomarkers of cell survival (CD127) and replicative senescence (CD57), were measured by multiparametric flow cytometry for T-cell phenotyping on peripheral blood mononuclear cells (PBMCs) samples just before (baseline) and after 48 weeks of undetectable viral load in patients on NRTI-sparing-cART (N = 13) and NRTI-cART (N = 14). After 48 weeks a subgroup of patients (n = 5) on NRTI-cART switched to NRTI-sparing-cART for another additional 48 weeks. In vitro assays were performed on PBMCs from HIV-uninfected healthy donors exposed or not to HIV. To analyze the independent factors associated with type of cART bivariate and stepwise multivariate analysis were performed after adjusting for basal CD4+, CD8+ and nadir CD4+ T-cell counts.

RESULTS

After 48 weeks of a NRTI-sparing-cART vs NRTI-cART patients have higher effector memory (EM) CD4+ CD127+ T-cell levels, lower EM CD4+ CD57+ T-cell levels, higher CD8+ CD127+ T-cell levels, lower CD8+ CD57+ T-cell levels and higher memory CD8+ T-cell levels. This effect was confirmed in the subgroup of patients who switched to NRTI-sparing-cART. In vitro assays confirmed that the deleterious effect of a NRTIs-containing regimen was due to NRTIs.

CONCLUSIONS

The implementation of NRTI-sparing regimens, with a favourable profile in CD127 and CD57 T-cell expression, could benefit cART-patients. These results could have potential implications in a decrease in the number of Non-AIDS events.

Pre-vaccine plasma levels of soluble inflammatory indices negatively predict responses to HAV, HBV, and tetanus vaccines in HCV and HIV infection

BACKGROUND

Chronic hepatitis C virus (HCV) and HIV infections are associated with impaired responses to neo-antigens contained in hepatitis A virus (HAV)/hepatitis B virus (HBV) vaccines, yet responsible mechanisms are unclear.

METHODS

ACTG 5232 and CFAR0910 were clinical trials where pre-vaccine levels of plasma IP10, IL-6, sCD163 and sCD14 were measured in viremic HCV- (n = 15) or HIV-infected participants (n = 24) and uninfected controls (n = 10). Accelerated dosing HAV/HBV vaccine and tetanus booster were administered and antibody response was measured at 0, 1, 3, 8, and 24 weeks.

RESULTS

Pre-vaccine plasma IP10, IL-6, and sCD14 levels were elevated in both HCV and HIV-infected participants, while sCD163 was also elevated in HCV-infected participants. Pre-immunization tetanus antibody levels were lower in HIV-infected than in uninfected participants, while vaccine induced antibody responses were intact in HCV and HIV-infected participants. After HAV/HBV vaccination, HCV and HIV-infected participants had lower and less durable HAV and HBV antibody responses than uninfected controls. Among HCV-infected participants, pre-vaccine plasma IP10, IL-6, sCD14, and sCD163 levels inversely correlated with HAV, HBV and tetanus antibody responses after vaccine. Low HAV/HBV vaccine responses in HIV-infected participants prohibited assessment of immune correlates.

CONCLUSIONS

During HCV and HIV infection markers of systemic inflammation reflect immune dysfunction as demonstrated by poor response to HAV/HBV neo-antigen vaccine.

Barriers to HIV remission research in low- and middle-income countries

INTRODUCTION

HIV eradication and remission research has largely taken place in high-income countries. In low- and middle-income countries (LMIC), there may be factors that have a substantial impact on the size of the latent HIV reservoir and the immunological response to infection. If a curative strategy is to be available to all HIV-infected individuals, these factors must be understood.

METHODS

We use a scoping review to examine the literature on biological factors that may have an impact on HIV persistence in LMIC. Three databases were searched without date restrictions.

RESULTS

Uncontrolled viral replication and higher coinfection prevalence may alter the immunological milieu of individuals in LMIC and increase the size of the HIV reservoir. Differences in HIV subtype could also influence the measurement and size of the HIV reservoir. Immune activation may differ due to late presentation to care, presence of chronic infections, increased gut translocation of bacterial products and poor nutrition.

CONCLUSIONS

Research on HIV remission is urgently needed in LMIC. Research into chronic immune activation in resource poor environments, the immune response to infection, the mechanisms of HIV persistence and latency in different viral clades and the effect of the microbiological milieu must be performed. Geographic differences, which may be substantial and may delay access to curative strategies, should be identified.

CD161 Expression on Mucosa-Associated Invariant T Cells is Reduced in HIV-Infected Subjects Undergoing Antiretroviral Therapy Who Do Not Recover CD4+ T Cells

Background:

Mucosa-associated invariant T (MAIT) cells are a recently identified class of innate-like T cells that are involved in the mucosal immune response. MAIT cells are characterized by expression of TCR Vα7.2 and CD161. In HIV infection, there is a profound early loss of MAIT cells from the circulation that never fully recovers, even after prolonged viral control with antiretroviral therapy (ART).

Methods:

We analyzed PBMCs from fresh whole blood from HIV-negative or ART-treated HIV-positive donors with full (Immune Success) or impaired (Immune Failure) CD4⁺ T- cell recovery by flow cytometry for T-cell markers, TCR Vα7.2, and CD161. The PBMCs were cultured with or without TCR-mediated stimulation, and CD161 expression was assessed on Vα7.2⁺ T cells. Interferon-γ (IFNγ) production was assessed by intracellular cytokine staining.

Results:

We found a decrease in the percentage of CD3⁺ T cells that expressed CD161 and the percentage of Vα7.2⁺ T cells that expressed CD161, in HIV-infected individuals. We also found a significant increase in the percentage of T cells that were Vα7.2⁺CD161- in immune failure compared to controls, accompanied by an increase in the percentage of Vα7.2⁺CD161- T cells that express CD8⁺ in donors with immune failure, but not immune success. After TCR stimulation in vitro, Vα7.2⁺ T cells reduced expression of CD161, yet Vα7.2⁺ CD161- cells from immune failure donors retained the ability to express IFNγ on stimulation.

Conclusions:

Our findings suggest that in immune failure patients, the reduction in peripheral MAIT cells is due, at least in part, to a loss in CD161 expression, and is not merely the result of trafficking into mucosal tissues or cell death. These CD161- cells retain their function.

Aberrant plasma IL-7 and soluble IL-7 receptor levels indicate impaired T-cell response to IL-7 in human tuberculosis

T-cell proliferation and generation of protective memory during chronic infections depend on Interleukin-7 (IL-7) availability and receptivity. Regulation of IL-7 receptor (IL-7R) expression and signalling are key for IL-7-modulated T-cell functions. Aberrant expression of soluble (s) and membrane-associated (m) IL-7R molecules is associated with development of autoimmunity and immune failure in acquired immune deficiency syndrome (AIDS) patients. Here we investigated the role of IL-7/IL-7R on T-cell immunity in human tuberculosis. We performed two independent case-control studies comparing tuberculosis patients and healthy contacts. This was combined with follow-up examinations for a subgroup of tuberculosis patients under therapy and recovery. Blood plasma and T cells were characterised for IL-7/sIL-7R and mIL-7R expression, respectively. IL-7-dependent T-cell functions were determined by analysing STAT5 phosphorylation, antigen-specific cytokine release and by analysing markers of T-cell exhaustion and inflammation. Tuberculosis patients had lower soluble IL-7R (p < 0.001) and higher IL-7 (p < 0.001) plasma concentrations as compared to healthy contacts. Both markers were largely independent and aberrant expression normalised during therapy and recovery. Furthermore, tuberculosis patients had lower levels of mIL-7R in T cells caused by post-transcriptional mechanisms. Functional in vitro tests indicated diminished IL-7-induced STAT5 phosphorylation and impaired IL-7-promoted cytokine release of Mycobacterium tuberculosis-specific CD4⁺ T cells from tuberculosis patients. Finally, we determined T-cell exhaustion markers PD-1 and SOCS3 and detected increased SOCS3 expression during therapy. Only moderate correlation of PD-1 and SOCS3 with IL-7 expression was observed. We conclude that diminished soluble IL-7R and increased IL-7 plasma concentrations, as well as decreased membrane-associated IL-7R expression in T cells, reflect impaired T-cell sensitivity to IL-7 in tuberculosis patients. These findings show similarities to pathognomonic features of impaired T-cell functions and immune failure described in AIDS patients.

IL-7 is important for the development and homeostasis of T cells and promotes antigen-specific T-cell responses. Aberrant expression of plasma IL-7 and soluble IL-7R are found in autoimmune diseases and chronic viral infections. In AIDS patients—especially those who fail to reconstitute T-cell numbers during therapy—impaired IL-7-promoted T-cell functions indicated T-cell exhaustion/senescence. In order to evaluate the potential impact of IL-7 on tuberculosis, we characterised various parameters involved in the IL-7-response of tuberculosis patients and healthy contacts. Despite IL-7 being available at higher plasma levels among tuberculosis patients, the T-cell response to IL-7 was impaired when compared to healthy contacts. Soluble IL-7R levels were aberrantly low in plasma during acute tuberculosis but did not account for impaired IL-7 usage. Chronic inflammation in tuberculosis patients—reflected by increased IL-6 plasma levels—did not account for dysfunctional T-cell responses and analysed T-cell exhaustion markers were only moderately correlated. Our findings demonstrate that availability of IL-7 alone is not sufficient to promote protective T-cell immunity against tuberculosis. We describe aberrant IL-7/soluble IL-7R expression and impaired IL-7-mediated T-cell functions in tuberculosis patients with similarities and differences to described IL-7 dysregulation seen in patients with AIDS.

Cytokines and T-Cell Homeostasis in HIV Infection

Untreated human immunodeficiency virus (HIV) infection is characterized by progressive CD4(+) T-cell depletion and CD8(+) T-cell expansion, and CD4(+) T-cell depletion is linked directly to the risk for opportunistic infections and infection-associated mortality. With suppression of HIV replication by antiretroviral therapy, circulating CD4(+) Tcell numbers typically improve while CD8(+) T-cell expansion persists, and both CD4(+) T-cell cytopenia and CD8(+) T-cell expansion are associated with morbidity and mortality. In this brief review, we report on the role that selected homeostatic and inflammatory cytokines may play both in the failure of CD4(+) T-cell restoration and the CD8(+) T-cell expansion that characterize HIV infection.

Responsiveness to IL-7 but not to IFN-α is diminished in CD4+ T cells from treated HIV infected patients who experience poor CD4+ T-cell recovery

OBJECTIVE

To assess CD4 T-cell responsiveness to IL-7 and IFN-α in HIV-infected patients who experience poor recovery of CD4 T-cell counts during therapy (immune failure patients).

DESIGN

Responses to IL-7 and IFN-α were compared between HIV-infected immune failure (CD4 cell counts <379 cells/μl) patients and immune success (CD4 cell counts >500 cells/μl) as well as healthy control patients.

METHODS

Flow cytometry was used to assess peripheral blood mononuclear cells for IL-7-induced proliferation, CD25 expression, and signaling (signal transducer and activator of transcription 5 phosphorylation and Akt phosphorylation) in CD4 T cells. Freshly isolated cells were characterized by expression of IL-7Rα (CD127) among CD4 T-cell maturation subsets by flow cytometry and sorted CD3 T cells were assessed for expression of IFN-α and interferon stimulated genes (2'-5'-oligoadenylate synthetase-1 and myxovirus resistance A protein) by quantitative real-time PCR. Responses to IFN-α were assessed by induction of signal transducer and activator of transcription 1 phosphorylation and inhibition of IL-7-induced CD4 T-cell proliferation.

RESULTS

IL-7-induced proliferation and CD25 expression were decreased in CD4 T cells from immune failure patients. CD127 expressing CD4 T cells were decreased, whereas expression of 2'-5'-oligoadenylate synthetase-1, myxovirus resistance A protein, and IFN-α mRNA were increased in total CD3 T cells from immune failure patients. CD127 expression correlated with CD25 induction but not proliferation, whereas T-cell IFN-α mRNA was associated with reduced proliferation in CD4 T cells from immune failure patients. IFN-α-mediated induction of signal transducer and activator of transcription 1 phosphorylation and inhibition of proliferation were not diminished in CD4 T cells from immune failure patients.

CONCLUSION

IL-7 responsiveness is impaired in immune failure patients and may be related to expression of CD127 and IFN-α.

Partial recovery of senescence and differentiation disturbances in CD8+ T cell effector-memory cells in HIV-1 infection after initiation of anti-retroviral treatment

Immune senescence as well as disturbed CD8⁺ T cell differentiation are a hallmark of chronic HIV infection. Here, we investigated to what extent immune senescence is reversible after initiation of anti-retroviral treatment (ART). Peripheral blood mononuclear cells (PBMCs) from a cohort of HIV patients with different disease courses, including untreated viral controllers (n = 10), viral non-controllers (n = 16) and patients on ART (n = 20), were analysed and compared to uninfected controls (n = 25) by flow cytometry on bulk and HIV-specific major histocompatibility complex (MHC) class I tetramer⁺ CD8⁺ T cells for expression of the memory markers CCR7 and CD45RO, as well as the senescence marker CD57 and the differentiation and survival marker CD127. Furthermore, a subset of patients was analysed longitudinally before and after initiation of ART. Frequencies of CD57⁺ CD8⁺ T cells decreased after initiation of ART in central memory (Tcm) but not in effector memory T cell populations (TemRO and TemRA). The frequency of CD127⁺ CD8⁺ cells increased in Tcm and TemRO. We observed a reduction of CD127^- T cells in Tcm, TemRO and partially in TemRA subsets after initiation of ART. Importantly, HIV-specific CD8⁺ TemRO cells predominantly displayed a CD127^- CD57⁺ phenotype in untreated HIV-patients, whereas the CD127⁺ CD57^- phenotype was under-represented in these patients. The frequency of the CD127⁺ CD57^- CD8⁺ T cell subpopulation correlated strongly with absolute CD4⁺ counts in HIV-infected patients before and after initiation of ART. These findings can be interpreted as a phenotypical correlate of CD8⁺ memory T cell differentiation and the premature 'ageing' of the immune system, which was even observed in successfully virally suppressed HIV patients.

Impact of HIV-1 infection on the feto-maternal crosstalk and consequences for pregnancy outcome and infant health

Adaptation of the maternal immune system to establish maternal/fetal equilibrium is required for a successful pregnancy. Viral infections, including HIV-1 infection, can alter this maternal/fetal equilibrium, with significant consequences for pregnancy outcome, including miscarriages, impaired fetal growth, and premature delivery. Furthermore, maternal HIV-1 infection has been shown to have a long-term impact on the developing fetal immune system also when the infant is not infected with the virus. In this review, we discuss the consequences of maternal HIV-1 infection and antiretroviral therapy on pregnancy outcome and the health of the uninfected HIV-1-exposed infant.

IL-15 promotes activation and expansion of CD8+ T cells in HIV-1 infection

In HIV-1-infected patients, increased numbers of circulating CD8+ T cells are linked to increased risk of morbidity and mortality. Here, we identified a bystander mechanism that promotes CD8 T cell activation and expansion in untreated HIV-1-infected patients. Compared with healthy controls, untreated HIV-1-infected patients have an increased population of proliferating, granzyme B+, CD8+ T cells in circulation. Vβ expression and deep sequencing of CDR3 revealed that in untreated HIV-1 infection, cycling memory CD8 T cells possess a broad T cell repertoire that reflects the repertoire of the resting population. This suggests that cycling is driven by bystander activation, rather than specific antigen exposure. Treatment of peripheral blood mononuclear cells with IL-15 induced a cycling, granzyme B+ phenotype in CD8+ T cells. Moreover, elevated IL-15 expression in the lymph nodes of untreated HIV-1-infected patients correlated with circulating CD8+ T cell counts and was normalized in these patients following antiretroviral therapy. Together, these results suggest that IL-15 drives bystander activation of CD8+ T cells, which predicts disease progression in untreated HIV-1-infected patients and suggests that elevated IL-15 may also drive CD8+ T cell expansion that is linked to increased morbidity and mortality in treated patients.