Progressive CD127 down‐regulation correlates with increased apoptosis of CD8 T cells during chronic HIV‐1 infection

Chronic HIV‐1 infection can induce a significant decrease in CD127 expression on CD8 T cells, but the underlying mechanisms and immunological consequences are unclear. In this study, we investigated CD127 expression on CD8 T cells from a total of 51 HIV‐1‐infected subjects and 16 healthy individuals and analyzed the association between CD127 expression and CD8 T‐cell apoptosis in these HIV‐1‐infected subjects. We found that CD127 expression on total CD8 T cells was significantly down‐regulated, which was correlated with the increased CD8 T‐cell apoptosis and disease progression of chronic HIV‐1 infection. The in vitro addition of IL‐7 efficiently rescued the spontaneous apoptosis of CD8 T cells from HIV‐1‐infected individuals. IL‐7 stimulation also transiently down‐regulated CD127 expression, whereas some of the CD127^? CD8 T cells regained CD127 expression soon after IL‐7 was retracted from the incubation medium. Thus, IL‐7 stimulation reduced apoptosis of both CD127⁺ and CD127^?CD8 T cells to some degree. These data indicate that CD127 loss might impair IL‐7 signaling and increase CD8 T‐cell apoptosis during HIV‐1 infection. This study, therefore, will extend the notion that IL‐7 could be a good candidate for immunotherapy in HIV‐1‐infected patients.     

IL-7Ralpha expression on CD4+ T lymphocytes decreases with HIV disease progression and inversely correlates with immune activation

Many factors can influence the rate of HIV disease progression, including those that maintain T cell homeostasis. One key homeostatic regulator is the IL‐7 receptor (IL‐7R). Previous studies have shown IL‐7R expression levels decrease in HIV infection, but effects on memory subtypes, CD4⁺ T cells, and cell function have not been explored. The present study examined the expression of the IL‐7Rα chain on naïve and memory T lymphocyte subsets of both HIV‐positive and HIV‐negative individuals from Nairobi, Kenya to assess the role of IL‐7Rα in HIV disease. Expression of IL‐7Rα was significantly reduced in all CD4⁺ and CD8⁺ T cell subsets in HIV‐positive individuals. This reduction was further enhanced in those with advanced HIV progression. Expression of IL‐7Rα was inversely correlated to immune activation, and apoptosis, and was positively correlated with CD4 count in both bivariate and multivariate analysis. Expression of IL‐7Rα did not correlate with HIV viral loads, indicating the elevated immune activation seen in HIV‐infected individuals may be impacting expression of IL‐7Rα, independent of viral loads. Signaling via the IL‐7R is essential for T cell homeostasis and maintenance of T cell memory. Reduction of this receptor may contribute to the homeostatic disruption seen in HIV.     

Human rhinoviruses induce IL‐35‐producing Treg via induction of B7‐H1 (CD274) and sialoadhesin (CD169) on DC

IL‐35 is a heterodimer of EBV‐induced gene 3 and of the p35 subunit of IL‐12, and recently identified as an inhibitory cytokine produced by natural Treg in mice, but not in humans. Here we demonstrate that DC activated by human rhinoviruses (R‐DC) induce IL‐35 production and release, as well as a suppressor function in CD4⁺ and CD8⁺ T cells derived from human peripheral blood but not in naïve T cells from cord blood. The induction of IL‐35‐producing T cells by R‐DC was FOXP3‐independent, but blocking of B7‐H1 (CD274) and sialoadhesin (CD169) on R‐DC with mAb against both receptors prevented the induction of IL‐35. Thus, the combinatorial signal delivered by R‐DC to T cells via B7‐H1 and sialoadhesin is crucial for the induction of human IL‐35⁺ Treg. These results demonstrate a novel pathway and its components for the induction of immune‐inhibitory T cells.     

CD161++CD8+ T cells,including the MAIT cell subset,are specifically activated by IL‐12+IL‐18 in a TCR‐independent manner

CD161⁺⁺CD8⁺ T cells represent a novel subset that is dominated in adult peripheral blood by mucosal‐associated invariant T (MAIT) cells, as defined by the expression of a variable‐α chain 7.2 (Vα7.2)‐Jα33 TCR, and IL‐18Rα. Stimulation with IL‐18+IL‐12 is known to induce IFN‐γ by both NK cells and, to a more limited extent, T cells. Here, we show the CD161⁺⁺ CD8⁺ T‐cell population is the primary T‐cell population triggered by this mechanism. Both CD161⁺⁺Vα7.2⁺ and CD161⁺⁺Vα7.2^? T‐cell subsets responded to IL‐12+IL‐18 stimulation, demonstrating this response was not restricted to the MAIT cells, but to the CD161⁺⁺ phenotype. Bacteria and TLR agonists also indirectly triggered IFN‐γ expression via IL‐12 and IL‐18. These data show that CD161⁺⁺ T cells are the predominant T‐cell population that responds directly to IL‐12+IL‐18 stimulation. Furthermore, our findings broaden the potential role of MAIT cells beyond bacterial responsiveness to potentially include viral infections and other inflammatory stimuli.     

Control of Schistosoma mansoni egg‐induced inflammation by IL‐4‐responsive CD4+CD25−CD103+Foxp3− cells is IL‐10‐dependent

Host protection to helminth infection requires IL‐4 receptor α chain (IL‐4Rα) signalling and the establishment of finely regulated Th2 responses. In the current study, the role of IL‐4Rα‐responsive T cells in Schistosoma mansoni egg‐induced inflammation was investigated. Egg‐induced inflammation in IL‐4Rα‐responsive BALB/c mice was accompanied with Th2‐biased responses, whereas T‐cell‐specific IL‐4Rα‐deficient BALB/c mice (iLck^creIl4ra^?/lox) developed Th1‐biased responses with heightened inflammation. The proportion of Foxp3⁺ Treg in the draining LN of control mice did not correlate with the control of inflammation and was reduced in comparison to T‐cell‐specific IL‐4Rα‐deficient mice. This was due to IL‐4‐mediated inhibition of CD4⁺Foxp3⁺ Treg conversion, demonstrated in adoptively transferred Rag2^?/? mice. Interestingly, reduced footpad swelling in Il4ra^?/lox mice was associated with the induction of IL‐4 and IL‐10‐secreting CD4⁺CD25^?CD103⁺Foxp3^? cells, confirmed in S. mansoni infection studies. Transfer of IL‐4Rα‐responsive CD4⁺CD25^?CD103⁺ cells, but not CD4⁺CD25^high or CD4⁺CD25^?CD103^? cells, controlled inflammation in iLck^creIl4ra^?/lox mice. The control of inflammation depended on IL‐10, as transferred CD4⁺CD25^?CD103⁺ cells from IL‐10‐deficient mice were not able to effectively downregulate inflammation. Together, these results demonstrate that IL‐4 signalling in T cells inhibits Foxp3⁺ Treg in vivo and promotes CD4⁺CD25^?CD103⁺Foxp3^? cells that control S. mansoni egg‐induced inflammation via IL‐10.     

With(out) a little help from my friends: An IL‐12/CD40L‐mediated feed‐forward loop between CD8+ T cells and DCs

CD40–CD40L interactions are important for both antigen‐dependent B‐cell differentiation and effector and memory T‐cell formation. The prevailing view is that CD40L is expressed on activated CD4⁺ T cells, which enables them to provide help to high‐affinity B cells in GCs and to license DCs for efficient induction of CD8⁺ T‐cell responses. Interestingly, CD8⁺ T cells themselves can also express CD40L and, in this issue of the European Journal of Immunology, Thiel and colleagues [Eur. J. Immunol. 2013. 43: 1511‐1517] show that CD40L expression on these cells can be part of a self‐sustaining feed‐forward loop, in which expression of CD40L is induced by IL‐12 and TCR signaling. This provides a paradigm shift in our thinking about the requirements of effector CD8⁺ T‐cell development and the role herein of CD4⁺ T cells to provide help in this process.     

Expression of IL‐15RA or an IL‐15/IL‐15RA fusion on CD8+ T cells modifies adoptively transferred T‐cell function in cis

IL‐15 and IL‐15 receptor alpha (IL‐15RA) play a significant role in multiple aspects of T‐cell biology. However, given the evidence that IL‐15RA can present IL‐15 in trans, the functional capacity of IL‐15RA expressed on CD8⁺ T cells to modify IL‐15 functions in cis is currently unclear. In the current study, we explore the functional consequences of IL‐15RA, expression on T cells using a novel method to transfect naive CD8⁺ T cells. We observed that RNA nucleofection led to highly efficient, non‐toxic, and rapid manipulation of protein expression levels in unstimulated CD8⁺ T cells. We found that transfection of unstimulated CD8⁺ T cells with IL‐15RA RNA led to enhanced viability of CD8⁺ T cells in response to IL‐15. Transfection with IL‐15RA enhanced IL‐15‐mediated phosphorylation of STAT5 and also promoted IL‐15‐mediated proliferation in vivo of adoptively transferred naïve CD8⁺ T cells. We demonstrated that IL‐15RA can present IL‐15 via cis‐presentation on CD8⁺ T cells. Finally, we showed that transfection with a chimeric construct linking IL‐15 to IL‐15RA cell autonomously enhances the viability and proliferation of primary CD8⁺ T cells and cytotoxic potential of antigen‐specific CD8⁺ T cells. The clinical implications of the current study are discussed.     

Emergence of a distinct HIV‐specific IL‐10‐producing CD8+ T‐cell subset with immunomodulatory functions during chronic HIV‐1 infection

Interleukin‐10 (IL‐10) plays a key role in regulating proinflammatory immune responses to infection but can interfere with pathogen clearance. Although IL‐10 is upregulated throughout HIV‐1 infection in multiple cell subsets, whether this is a viral immune evasion strategy or an appropriate response to immune activation is unresolved. Analysis of IL‐10 production at the single cell level in 51 chronically infected subjects (31 antiretroviral (ART) naïve and 20 ART treated) showed that a subset of CD8⁺ T cells with a CD25^neg FoxP3^neg phenotype contributes substantially to IL‐10 production in response to HIV‐1 gag stimulation. The frequencies of gag‐specific IL‐10‐ and IFN‐γ‐producing T cells in ART‐naïve subjects were strongly correlated and the majority of these IL‐10⁺ CD8⁺ T cells co‐produced IFN‐γ; however, patients with a predominant IL‐10⁺/IFN‐γ^neg profile showed better control of viraemia. Depletion of HIV‐specific CD8⁺ IL‐10⁺ cells from PBMCs led to upregulation of CD38 on CD14⁺ monocytes together with increased IL‐6 production, in response to gag stimulation. Increased CD38 expression was positively correlated with the frequency of the IL‐10⁺ population and was also induced by exposure of monocytes to HIV‐1 in vitro. Production of IL‐10 by HIV‐specific CD8⁺ T cells may represent an adaptive regulatory response to monocyte activation during chronic infection.     

Bystander activation of CD4+ T cells

Bystander activation of T cells, i.e. the stimulation of unrelated (heterologous) T cells by cytokines during an Ag‐specific T‐cell response, has been best described for CD8⁺ T cells. In the CD8⁺ compartment, the release of IFN and IFN‐inducers leads to the production of IL‐15, which mediates the proliferation of CD8⁺ T cells, notably memory‐phenotype CD8⁺ T cells. CD4⁺ T cells also undergo bystander activation, however, the signals inducing this Ag‐nonspecific stimulation of CD4⁺ T cells are less well known. A study in this issue of the European Journal of Immunology sheds light on this aspect, suggesting that common γ‐chain cytokines including IL‐2 might be involved in bystander activation of CD4⁺ T cells.     

Chronic myelogenous leukemia maintains specific CD8+ T cells through IL‐7 signaling

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease of hematopoietic stem cells. The disease progresses after several years from an initial chronic phase to a blast phase. Leukemia‐specific T cells are regularly detected in CML patients and may be involved in the immunological control of the disease. Here, we analyzed the role of leukemia‐specific CD8⁺ T cells in CML disease control and the mechanism that maintains CD8⁺ T‐cell immunosurveillance in a retroviral‐induced murine CML model. To study antigen‐specific immune responses, the glycoprotein of the lymphocytic choriomeningitis virus was used as model leukemia antigen. Leukemia‐specific CTL activity was detectable in vivo in CML mice and depletion of CD8⁺ T cells rapidly led to disease progression. CML‐specific CTL were characterized by the expression of the IL‐7 receptor α‐chain. In addition, leukemia cells produced IL‐7 that was crucial for the maintenance of leukemia‐specific CTL and for disease control. Therefore, CML cells maintain the specific CD8⁺ T‐cell‐mediated immune control by IL‐7 secretion. This results in prolonged control of disease and probably contributes to the characteristic chronic phase of the disease.     

Human bone marrow contains a subset of quiescent early memory CD8+ T cells characterized by high CD127 expression and efflux capacity

Even today it is still not completely understood how CD8⁺ T‐cell memory is maintained long term. Since bone marrow (BM) is a niche for immunological memory, we sought to identify long‐lasting early memory CD8⁺ T cells in this compartment. To achieve this, we looked for CD8⁺ T cells that are able to efflux Rhodamine 123, a typical property of stem cells. Indeed, we identified a distinct subset of CD8⁺ T cells in BM, with the capacity to efflux and high CD127 expression. These CD127^hi effluxers are conventional CD8⁺ T cells exhibiting a broad TCR‐Vβ repertoire and are generated in response to viral peptides in vitro. CD127^hi effluxer CD8⁺ T cells have an early memory phenotype defined by preferential TNF‐α production and a Bcl‐2^hi, KLRG‐1^low profile. This population has long telomeres and shows constitutively low frequencies of Ki‐67 expression ex vivo, but has a high proliferative and differentiation capacity in vitro. However, IL‐15 downmodulates CD127 in CD127^hi effluxer CD8⁺ T cells in vitro. Consequently, the CD127^low effluxer subset may comprise cells recently exposed to IL‐15. Taken together, CD127^hi effluxer CD8⁺ T cells represent a novel population of early memory T cells resident in BM with properties required for long‐lived memory.     

Phosphorylated STAT3 and PD‐1 regulate IL‐17 production and IL‐23 receptor expression in Mycobacterium tuberculosis infection

We studied the factors that regulate IL‐23 receptor expression and IL‐17 production in human tuberculosis infection. Mycobacterium tuberculosis (M. tb)‐stimulated CD4⁺ T cells from tuberculosis patients secreted less IL‐17 than did CD4⁺ T cells from healthy tuberculin reactors (PPD⁺). M. tb‐cultured monocytes from tuberculosis patients and PPD⁺ donors expressed equal amounts of IL‐23p19 mRNA and protein, suggesting that reduced IL‐23 production is not responsible for decreased IL‐17 production by tuberculosis patients. Freshly isolated and M. tb‐stimulated CD4⁺ T cells from tuberculosis patients had reduced IL‐23 receptor and phosphorylated STAT3 (pSTAT3) expression, compared with cells from PPD⁺ donors. STAT3 siRNA reduced IL‐23 receptor expression and IL‐17 production by CD4⁺ T cells from PPD⁺ donors. Tuberculosis patients had increased numbers of PD‐1⁺ T cells compared with healthy PPD⁺ individuals. Anti‐PD‐1 antibody enhanced pSTAT3 and IL‐23R expression and IL‐17 production by M. tb‐cultured CD4⁺ T cells of tuberculosis patients. Anti‐tuberculosis therapy decreased PD‐1 expression, increased IL‐17 and IFN‐γ production and pSTAT3 and IL‐23R expression. These findings demonstrate that increased PD‐1 expression and decreased pSTAT3 expression reduce IL‐23 receptor expression and IL‐17 production by CD4⁺ T cells of tuberculosis patients.     

The microRNA‐9/B‐lymphocyte‐induced maturation protein‐1/IL‐2 axis is differentially regulated in progressive HIV infection

The fine control of T‐cell differentiation and its impact on HIV disease states is poorly understood. In this study, we demonstrate that B‐lymphocyte‐induced maturation protein‐1 (Blimp‐1/Prdm1) is highly expressed in CD4⁺ T cells from chronically HIV‐infected (CHI) patients compared to cells from long‐term nonprogressors or healthy controls. Stimulation through the T‐cell receptor in the presence ofIL‐2 induces Blimp‐1 protein expression. We show here that Blimp‐1 levels are translationally regulated by microRNA‐9 (miR‐9). Overexpression of miR‐9 induces Blimp‐1 repression, restoring IL‐2 secretion in CD4⁺ T cells via reduction in the binding of Blimp‐1 to the il‐2 promoter. In CHI patients where IL‐2 expression is reduced and there is generalized T‐cell dysfunction, we show differential expression of both miR‐9 and Blimp‐1 in CD4⁺ cells compared with levels in long‐term nonprogressors. These data identify a novel miR‐9/Blimp‐1/IL‐2 axis that is dysregulated in progressive HIV infection.     

CD8+ MAIT cells infiltrate into the CNS and alterations in their blood frequencies correlate with IL‐18 serum levels in multiple sclerosis

Recent findings indicate a pathogenic involvement of IL‐17‐producing CD8⁺ T cells in multiple sclerosis (MS). IL‐17 production has been attributed to a subset of CD8⁺ T cells that belong to the mucosal‐associated invariant T (MAIT) cell population. Here, we report a reduction of CD8⁺ MAIT cells in the blood of MS patients compared with healthy individuals, which significantly correlated with IL‐18 serum levels in MS patients. In vitro stimulation of peripheral blood mononuclear cells from healthy individuals and MS patients with IL‐18 specifically activated CD8⁺ MAIT cells. Moreover, IL‐18 together with T‐cell receptor stimulation induced, specifically on CD8⁺ MAIT cells, an upregulation of the integrin very late antigen‐4 that is essential for the infiltration of CD8⁺ T cells into the CNS. Notably, we were able to identify CD8⁺ MAIT cells in MS brain lesions by immunohistochemistry while they were almost absent in the cerebrospinal fluid (CSF). In summary, our findings indicate that an IL‐18–driven activation of CD8⁺ MAIT cells contributes to their CNS infiltration in MS, in turn leading to reduced CD8⁺ MAIT‐cell frequencies in the blood. Therefore, CD8⁺ MAIT cells seem to play a role in the innate arm of immunopathology in MS.