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

Circulating GDF-15: a biomarker for metabolic dysregulation and aging in people living with HIV

Despite effective control of HIV replication by antiretroviral therapy (ART), a significant number of people living with HIV (PLWH) fail to achieve complete immune reconstitution and thus are deemed immune non-responders (INRs). Compared with immune responders (IRs) who have restored their CD4 T cell numbers and functions, CD4 T cells from these INRs exhibit prominent mitochondrial dysfunction and premature aging, which play a major role in increasing the incidence of non-AIDS, non-communicable diseases (NCDs). To date, there are no reliable biomarkers that can be used to typify and manage PLWH, especially INRs with non-AIDS NCDs. Growth differential factor-15 (GDF-15) is a transforming growth factor-β (TGF-β) family member known to regulate several biological processes involved in cell aging and stress responses. Since PLWH exhibit premature aging and metabolic dysregulation, here we measured the plasma levels of GDF-15 by ELISA and metabolic proteins by proteomic array and correlated the results with clinical parameters in ART-controlled PLWH (including INRs and IRs) and healthy subjects (HS). We found that GDF-15 levels were significantly elevated in PLWH compared to HS. GDF-15 levels were positively correlated with age and negatively associated with body mass and LDL cholesterol levels in the study subjects. Also, elevated GDF-15 levels were correlated with differential dysregulation of multiple metabolic proteins in PLWH. These results suggest that GDF-15 protein may serve as a biomarker of metabolic dysregulation and aging, and this biomarker will be useful in clinical trials targeting aging and metabolic disorders in ART-treated PLWH.

Advances in Mechanism of HIV-1 Immune Reconstitution Failure: Understanding Lymphocyte Subpopulations and Interventions for Immunological Nonresponders

In individuals diagnosed with AIDS, the primary method of sustained suppression of HIV-1 replication is antiretroviral therapy, which systematically increases CD4+ T cell levels and restores immune function. However, there is still a subset of 10-40% of people living with HIV who not only fail to reach normal CD4+ T cell counts but also experience severe immune dysfunction. These individuals are referred to as immunological nonresponders (INRs). INRs have a higher susceptibility to opportunistic infections and non-AIDS-related illnesses, resulting in increased morbidity and mortality rates. Therefore, it is crucial to gain new insights into the primary mechanisms of immune reconstitution failure to enable early and effective treatment for individuals at risk. This review provides an overview of the dynamics of key lymphocyte subpopulations, the main molecular mechanisms of INRs, clinical diagnosis, and intervention strategies during immune reconstitution failure, primarily from a multiomics perspective.

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.

Dominant CD4+ T cell receptors remain stable throughout antiretroviral therapy-mediated immune restoration in people with HIV

In people with HIV (PWH), the post-antiretroviral therapy (ART) window is critical for immune restoration and HIV reservoir stabilization. We employ deep immune profiling and T cell receptor (TCR) sequencing and examine proliferation to assess how ART impacts T cell homeostasis. In PWH on long-term ART, lymphocyte frequencies and phenotypes are mostly stable. By contrast, broad phenotypic changes in natural killer (NK) cells, γδ T cells, B cells, and CD4+ and CD8+ T cells are observed in the post-ART window. Whereas CD8+ T cells mostly restore, memory CD4+ T subsets and cytolytic NK cells show incomplete restoration 1.4 years post ART. Surprisingly, the hierarchies and frequencies of dominant CD4 TCR clonotypes (0.1%-11% of all CD4+ T cells) remain stable post ART, suggesting that clonal homeostasis can be independent of homeostatic processes regulating CD4+ T cell absolute number, phenotypes, and function. The slow restoration of host immunity post ART also has implications for the design of ART interruption studies.

The role of pyroptosis in incomplete immune reconstitution among people living with HIV：Potential therapeutic targets

Globally, HIV infection causes significant morbidity and mortality, and is a major public health problem. Despite the fact that widespread use of antiretroviral therapy (ART) has substantially altered the natural history of HIV infection from originally being a universally lethal disease to now being a chronic medical condition for those taking appropriate treatment, approximately 10-40% of people living with HIV (PLWH) who take effective ART and maintain long-term viral suppression fail to achieve normalization of CD4 + T-cell counts. This phenomenon is referred to as incomplete immune reconstitution or immunological non-response. Although the precise mechanisms underlying this outcome have not been elucidated, recent evidence indicates that excessive pyroptosis may play a crucial role in the development of incomplete immune reconstitution. Pyroptosis is characterized by the formation of pores in the cell membrane, cell rupture, and secretion of intracellular contents and pro-inflammatory cytokines, including IL-1β and IL-18. This excessive inflammation-induced programmed cell death leads to a massive loss of CD4 + T-cells, and inflammatory consequences that may promote and sustain incomplete immune reconstitution. Herein, we review the possible pathways activated in HIV infection by inflammasomes that act as switches of pyroptosis, and the role of pyroptosis in HIV, as well as the relevance of CD4 + T-cells in incomplete immune reconstitution. We also highlight the possible mechanisms of pyroptosis involved in incomplete immune reconstitution, thus paving the way for the development of potential targets for the treatment of incomplete immune reconstitution.

Cellular and molecular insights into incomplete immune recovery in HIV/AIDS patients

Highly active antiretroviral therapy (ART) can effectively inhibit virus replication and restore immune function in most people living with human immunodeficiency virus (HIV). However, an important proportion of patients fail to achieve a satisfactory increase in CD4⁺ T cell counts. This state is called incomplete immune reconstitution or immunological nonresponse (INR). Patients with INR have an increased risk of clinical progression and higher rates of mortality. Despite widespread attention to INR, the precise mechanisms remain unclear. In this review, we will discuss the alterations in the quantity and quality of CD4⁺ T as well as multiple immunocytes, changes in soluble molecules and cytokines, and their relationship with INR, aimed to provide cellular and molecular insights into incomplete immune reconstitution.

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.

Decreased CD73+ Double-Negative T Cells and Elevated Level of Soluble CD73 Correlated With and Predicted Poor Immune Reconstitution in HIV-Infected Patients After Antiretroviral Therapy

Although extensive use of antiretroviral therapy (ART) has made great progress in controlling HIV replication and improving CD4+ T cell recovery, the immune reconstitution remained insufficient in some patients, who were defined as poor immunological responders (PIRs). These PIRs were at a high risk of AIDS-related and non-AIDS complications, resulting in higher morbidity and mortality rate. Thus, it is a major challenge and urgently needed to distinguish PIRs early and improve their immune function in time. Immune activation is a key factor that leads to impaired immune reconstitution in people living with HIV (PLWH) who are receiving effective ART. Double negative T cells (DNT) were reported to associate with the control of immune activation during HIV infection. However, the precise mechanisms by which DNT cells exerted their suppressive capacity during HIV infection remained puzzled. CD73, both a soluble and a membrane-bound form, display immunosuppressive effects through producing adenosine (ADO). Thus, whether DNT cells expressed CD73 and mediated immune suppression through CD73-ADO pathway needs to be investigated. Here, we found a significant downregulation of CD73 expression on DNT cells in treatment-naïve PLWH (TNs) compared to healthy controls, accompanied with increased concentration of sCD73 in plasma. Both the frequency of CD73+ DNT cells and the level of plasma sCD73 recovered after ART treatment. However, PIRs showed decreased percentage of CD73+ DNT cells compared to immunological responders (IRs). The frequency of CD73+ DNT cells was positively correlated with CD4+ T cell count and CD4/CD8 ratio, and negatively correlated with immune activation in PLWH. The level of sCD73 also showed a negative correlation to CD4+ T cell count and CD4/CD8 ratio. More importantly, in the present cohort, a higher level of sCD73 at the time of initiating ART could predict poor immune reconstitution in PLWH after long-term ART. Our findings highlighted the importance of CD73+ DNT cells and sCD73 in the disease progression and immune reconstitution of PLWH, and provided evidences for sCD73 as a potential biomarker of predicting immune recovery.

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.

Mitochondrial Functions Are Compromised in CD4 T Cells From ART-Controlled PLHIV

The hallmark of HIV/AIDS is a gradual depletion of CD4 T cells. Despite effective control by antiretroviral therapy (ART), a significant subgroup of people living with HIV (PLHIV) fails to achieve complete immune reconstitution, deemed as immune non-responders (INRs). The mechanisms underlying incomplete CD4 T cell recovery in PLHIV remain unclear. In this study, CD4 T cells from PLHIV were phenotyped and functionally characterized, focusing on their mitochondrial functions. The results show that while total CD4 T cells are diminished, cycling cells are expanded in PLHIV, especially in INRs. HIV-INR CD4 T cells are more activated, displaying exhausted and senescent phenotypes with compromised mitochondrial functions. Transcriptional profiling and flow cytometry analysis showed remarkable repression of mitochondrial transcription factor A (mtTFA) in CD4 T cells from PLHIV, leading to abnormal mitochondrial and T cell homeostasis. These results demonstrate a sequential cellular paradigm of T cell over-activation, proliferation, exhaustion, senescence, apoptosis, and depletion, which correlates with compromised mitochondrial functions. Therefore, reconstituting the mtTFA pathway may provide an adjunctive immunological approach to revitalizing CD4 T cells in ART-treated PLHIV, especially in INRs.

People with HIV-1 demonstrate type 1 interferon refractoriness associated with upregulated USP18

HIV-1 infection persists in humans despite expression of antiviral type 1 interferons (IFN). Even exogenous administration of IFNα only marginally reduces HIV-1 abundance, raising the hypothesis that people living with HIV-1 (PLWH) are refractory to type 1 IFN. We demonstrated type 1 IFN refractoriness in CD4+ and CD8+ T cells isolated from HIV-1 infected persons by detecting diminished STAT1 phosphorylation (pSTAT1) and interferon-stimulated gene (ISG) induction upon type 1 IFN stimulation compared to healthy controls. Importantly, HIV-1 infected people who were virologically suppressed with antiretrovirals also showed type 1 IFN refractoriness. We found that USP18 levels were elevated in people with refractory pSTAT1 and ISG induction and confirmed this finding ex vivo in CD4+ T cells from another cohort of HIV-HCV coinfected persons who received exogenous pegylated interferon-α2b in a clinical trial. We used a cell culture model to recapitulate type 1 IFN refractoriness in uninfected CD4+ T cells that were conditioned with media from HIV-1 inoculated PBMCs, inhibiting de novo infection with antiretroviral agents. In this model, RNA interference against USP18 partly restored type 1 IFN responses in CD4+ T cells. We found evidence of type 1 IFN refractoriness in PLWH irrespective of virologic suppression that was associated with upregulated USP18, a process that might be therapeutically targeted to improve endogenous control of infection.ImportancePeople living with HIV-1 (PLWH) have elevated constitutive expression of type 1 interferons (IFN). However, it is unclear whether this impacts downstream innate immune responses. We identified refractory responses to type 1 IFN stimulation in T cells from PLWH, independent of antiretroviral treatment. Type 1 IFN refractoriness was linked to elevated USP18 levels in the same cells. Moreover, we found that USP18 levels predicted the anti-HIV-1 effect of type 1 IFN-based therapy on PLWH. In vitro, we demonstrated that refractory type 1 IFN responses were transferrable to HIV-1 uninfected target CD4+ T cells, and this phenomenon was mediated by type 1 IFN from HIV-1 infected cells. Type 1 IFN responses were partially restored by USP18 knockdown. Our findings illuminate a new mechanism by which HIV-1 contributes to innate immune dysfunction in PLWH, through the continuous production of type 1 IFN that induces a refractory state of responsiveness.

SAMHD1 expression is associated with low immune activation but not correlated with HIV‑1 DNA levels in CD4+ T cells of patients with HIV‑1

Sterile α motif and histidine/aspartic acid domain‑containing protein 1 (SAMHD1) can inhibit reverse transcription of human immunodeficiency virus‑1 (HIV‑1) by hydrolyzing intracellular deoxy‑ribonucleoside triphosphate. However, its role in HIV‑1 disease progression has not been extensively studied. To study the impacts of SAMHD1 on HIV‑1 disease progression, especially on DNA levels, we investigated SAMHD1 levels in the peripheral blood of HIV‑1 elite controllers (ECs), antiretroviral therapy (ART) naive viremic progressors (VPs) and patients with HIV‑1 receiving ART (HIV‑ARTs) compared with healthy controls. In addition, the present study analyzed the relationship between SAMHD1 and interferon‑α, immune activation and HIV‑1 DNA levels. The results of the present study demonstrated elevated SAMHD1 expression in the peripheral blood mononuclear cells of all patients withHIV‑1, but higher SAMHD1 expression in the CD4+ T cells of only ECs compared with healthy controls. Immune activation was increased in the VPs and decreased in the ECs compared with healthy controls. Substantially lower HIV‑1 DNA levels were identified in ECs compared with those in VPs and HIV‑ARTs. SAMHD1 expression was associated with low levels of immune activation. No significant correlation was observed between SAMHD1 and HIV‑1 DNA levels. Overall, the findings of the present study indicated that SAMHD1 was highly expressed in ECs, which may be associated with low immune activation levels, but was not directly related to HIV‑1 DNA levels.

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.

IL7RA genetic variants differentially affect IL-7Rα expression and alternative splicing: a role in autoimmune and infectious diseases?

Interleukin-7 receptor α chain (IL-7Rα) single nucleotide polymorphisms (SNPs) are associated with susceptibility to immunopathologies like autoimmune and inflammatory diseases. The current hypothesis about underlying mechanisms is based on the regulation of IL-7 availability for self-reactive T cells by influencing the generation of a soluble (s)IL-7Rα variant. This assumption was mainly predicated on the well-defined IL7RA SNP rs6897932, which affects alternative splicing and causes aberrant generation of the sIL-7Rα variant with potential effects on the IL-7 serum reservoir. However, more recent studies shed light on novel functions of autoimmunity risk-associated IL7RA SNPs and characterized the largely neglected effect of rs6897932 on membrane (m)IL-7Rα expression. These findings as well as a described role of impaired mIL-7Rα expression and IL7RA SNP influence on chronic infectious diseases necessitates the reevaluation of previous findings on the role of IL7RA SNPs in immunopathology.

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.

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.

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.

Interferon-α-Mediated Activation of T Cells from Healthy and HIV-Infected Individuals Is Suppressed by Δ9-Tetrahydrocannabinol

Patients with HIV routinely use medicinal cannabinoids to treat neuropathic pain, anxiety, and human immunodeficiency virus (HIV)-associated wasting. However, Δ⁹-tetrahydrocannabinol (THC), the primary psychoactive cannabinoid in cannabis, suppresses T-cell function and secretion of interferons, both critically important in the antiviral immune response. Interferon-α (IFNα), a key cytokine in T-cell activation and peripheral control of HIV infection, can potentiate responsiveness to interleukin-7 (IL-7), a crucial homeostatic cytokine for peripheral T-cell maintenance. The objective of this investigation was to compare the response of T cells to stimulation by IFNα and IL-7 in T cells from healthy and HIV⁺ donors in the absence and presence of THC. To compare T-cell responses between healthy and HIV⁺ donors signaling through IFNα receptor, IFNα-induced expression of IL-7α receptor (IL-7Rα), cognate signaling through IL-7R, and on IL-7-mediated T-cell proliferation were measured by flow cytometry and real-time quantitative polymerase chain reaction. CD8⁺ T cells from HIV⁺ donors showed a diminished response to IFNα-induced phosphorylated signal transducer and activator of transcription-1 activation compared with CD8⁺ T cells from healthy donors, whereas CD4⁺ T cells from HIV⁺ donors and healthy donors were comparable. Treatment with IFNα promoted IL-7R expression and potentiated IL-7-induced STAT5 phosphorylation to augment IL-7-mediated proliferation by T cells from healthy and HIV⁺ donors. Finally, HIV⁺ donors exhibited reduced sensitivity to THC-mediated suppression by IFNα- and IL-7-mediated stimulation compared with healthy donors. These results further support THC as being immune suppressive while identifying putatively beneficial aspects of cannabinoid-based therapies in HIV⁺ patients.

Interleukin-7 Regulates T Follicular Helper Cell Function in Patients with Chronic Hepatitis C

Signaling through interleukin (IL)-7 is essential and required for development, differentiation, proliferation, and homeostasis of T cells. However, the role of IL-7 in regulation of CD4⁺ T cells in chronic viral infections was not fully elucidated. Thus, the aim of the current study was to investigate the immunomodulatory activity of IL-7 to T follicular helper (Tfh) cells and its contribution to pathogenesis of chronic HCV, hepatitis C virus (HCV) infection. A total of 47 patients with chronic hepatitis C and 19 normal controls were enrolled. Serum IL-7 and proportion of Tfh cells was measured. The regulatory function of IL-7 to Tfh cells was also investigated in CD4⁺ T cells and CD4⁺ T/HCVcc-infected Huh7.5 cell cocultured system. Serum IL-7 concentration was significantly downregulated in patients with chronic hepatitis C, and was negatively correlated with HCV RNA level. Tfh frequency and Tfh-associated cytokines (IL-21 and IL-6) were also reduced in chronic HCV-infected patients. Moreover, recombinant IL-7 stimulation elevated proportion of Tfh cells and IL-21/IL-6 secretion in both HCV-specific and nonspecific manners. Furthermore, IL-7-treated CD4⁺ T cells exhibited elevated antiviral activities without killing infected hepatocytes, which presented as inhibition of HCV RNA, induction of antiviral proteins, and promotion of cytokine production (especially IL-21) in cocultured system. This process might be dependent on IL-6 secretion. The current data revealed that IL-7 regulated HCV-specific and nonspecific activated Tfh cells, which might contribute to viral clearance. IL-7 could be a potential therapeutic agent for the treatment of chronic hepatitis C.

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.