CD38+ CD45RB(low) CD4+ T cells: a population of T cells with immune regulatory activities in vitro

Tumour immune escape via P2X7 receptor signalling

While P2X7 receptor expression on tumour cells has been characterized as a promotor of cancer growth and metastasis, its expression by the host immune system is central for orchestration of both innate and adaptive immune responses against cancer. The role of P2X7R in anti-tumour immunity is complex and preclinical studies have described opposing roles of the P2X7R in regulating immune responses against tumours. Therefore, few P2X7R modulators have reached clinical testing in cancer patients. Here, we review the prognostic value of P2X7R in cancer, how P2X7R have been targeted to date in tumour models, and we discuss four aspects of how tumours skew immune responses to promote immune escape via the P2X7R; non-pore functional P2X7Rs, mono-ADP-ribosyltransferases, ectonucleotidases, and immunoregulatory cells. Lastly, we discuss alternative approaches to offset tumour immune escape via P2X7R to enhance immunotherapeutic strategies in cancer patients.

Lipid metabolic reprogramming of hepatic CD4+ T cells during SIV infection

While liver inflammation is associated with AIDS, little is known so far about hepatic CD4+ T cells. By using the simian immunodeficiency virus (SIV)-infected rhesus macaque (RM) model, we aimed to characterize CD4+ T cells. The phenotype of CD4+ T cells was assessed by flow cytometry from uninfected (n = 3) and infected RMs, with either SIVmac251 (n = 6) or SHIVSF162p3 (n = 6). After cell sorting of hepatic CD4+ T cells, viral DNA quantification and RNA sequencing were performed.Thus, we demonstrated that liver CD4+ T cells strongly expressed the SIV coreceptor, CCR5. We showed that viremia was negatively correlated with the percentage of hepatic effector memory CD4+ T cells. Consistent with viral sensing, inflammatory and interferon gene transcripts were increased. We also highlighted the presence of harmful CD4+ T cells expressing GZMA and members of TGFB that could contribute to fuel inflammation and fibrosis. Whereas RNA sequencing demonstrated activated CD4+ T cells displaying higher levels of mitoribosome and membrane lipid synthesis transcripts, few genes were related to glycolysis and oxidative phosphorylation, which are essential to sustain activated T cells. Furthermore, we observed lower levels of mitochondrial DNA and higher levels of genes associated with damaged organelles (reticulophagy and mitophagy). Altogether, our data revealed that activated hepatic CD4+ T cells are reprogrammed to lipid metabolism. Thus, strategies aiming to reprogram T cell metabolism with effector function could be of interest for controlling viral infection and preventing liver disorders.IMPORTANCEHuman immunodeficiency virus (HIV) infection may cause liver diseases, associated with inflammation and tissue injury, contributing to comorbidity in people living with HIV. Paradoxically, the contribution of hepatic CD4+ T cells remains largely underestimated. Herein, we used the model of simian immunodeficiency virus (SIV)-infected rhesus macaques to access liver tissue. Our work demonstrates that hepatic CD4+ T cells express CCR5, the main viral coreceptor, and are infected. Viral infection is associated with the presence of inflamed and activated hepatic CD4+ T cells expressing cytotoxic molecules. Furthermore, hepatic CD4+ T cells are reprogrammed toward lipid metabolism after SIV infection. Altogether, our findings shed new light on hepatic CD4+ T cell profile that could contribute to liver injury following viral infection.

BMP-6 promotes type 2 immune response during enhancement of rat mandibular bone defect healing

Introduction

Bone morphogenetic proteins (BMPs) are used as key therapeutic agents for the treatment of difficult fractures. While their effects on osteoprogenitors are known, little is known about their effects on the immune system.

Methods

We used permutations of BMP-6 (B), vascular endothelial growth factor (V), and Hedgehog signaling pathway activator smoothened agonist (S), to treat a rat mandibular defect and investigated healing outcomes at week 8, in correlation with the cellular landscape of the immune cells in the fracture callus at week 2.

Results

Maximum recruitment of immune cells to the fracture callus is known to occur at week 2. While the control, S, V, and VS groups remained as nonunions at week 8; all BMP-6 containing groups - B, BV, BS and BVS, showed near-complete to complete healing. This healing pattern was strongly associated with significantly higher ratios of CD4 T (CD45⁺CD3⁺CD4⁺) to putative CD8 T cells (CD45⁺CD3⁺CD4^-), in groups treated with any permutation of BMP-6. Although, the numbers of putative M1 macrophages (CD45⁺CD3^-CD11b/c⁺CD38^high) were significantly lower in BMP-6 containing groups in comparison with S and VS groups, percentages of putative - Th1 cells or M1 macrophages (CD45⁺CD4⁺IFN-γ⁺) and putative - NK, NKT or cytotoxic CD8T cells (CD45⁺CD4^-IFN-γ⁺) were similar in control and all treatment groups. Further interrogation revealed that the BMP-6 treatment promoted type 2 immune response by significantly increasing the numbers of CD45⁺CD3^-CD11b/c⁺CD38^low putative M2 macrophages, putative - Th2 cells or M2 macrophages (CD45⁺CD4⁺IL-4⁺) cells and putative - mast cells, eosinophils or basophils (CD45⁺CD4^-IL-4⁺ cells). CD45^- non-haematopoietic fractions of cells which encompass all known osteoprogenitor stem cells populations, were similar in control and treatment groups.

Discussion

This study uncovers previously unidentified regulatory functions of BMP-6 and shows that BMP-6 enhances fracture healing by not only acting on osteoprogenitor stem cells but also by promoting type 2 immune response.

The adaptor protein TRAF3 is an immune checkpoint that inhibits myeloid-derived suppressor cell expansion

Myeloid-derived suppressor cells (MDSCs) are aberrantly expanded in cancer patients and under other pathological conditions. These cells orchestrate the immunosuppressive and inflammatory network to facilitate cancer metastasis and mediate patient resistance to therapies, and thus are recognized as a prime therapeutic target of human cancers. Here we report the identification of the adaptor protein TRAF3 as a novel immune checkpoint that critically restrains MDSC expansion. We found that myeloid cell-specific Traf3-deficient (M-Traf3 ^-/-) mice exhibited MDSC hyperexpansion during chronic inflammation. Interestingly, MDSC hyperexpansion in M-Traf3 ^-/- mice led to accelerated growth and metastasis of transplanted tumors associated with an altered phenotype of T cells and NK cells. Using mixed bone marrow chimeras, we demonstrated that TRAF3 inhibited MDSC expansion via both cell-intrinsic and cell-extrinsic mechanisms. Furthermore, we elucidated a GM-CSF-STAT3-TRAF3-PTP1B signaling axis in MDSCs and a novel TLR4-TRAF3-CCL22-CCR4-G-CSF axis acting in inflammatory macrophages and monocytes that coordinately control MDSC expansion during chronic inflammation. Taken together, our findings provide novel insights into the complex regulatory mechanisms of MDSC expansion and open up unique perspectives for the design of new therapeutic strategies that aim to target MDSCs in cancer patients.

CD38 Correlates with an Immunosuppressive Treg Phenotype in Lupus-Prone Mice

CD38 is a transmembrane glycoprotein expressed by T-cells. It has been reported that patients with systemic lupus erythematosus (SLE) showed increased CD38⁺CD25⁺ T-cells correlating with immune activation and clinical signs. Contrariwise, CD38 deficiency in murine models has shown enhanced autoimmunity development. Recent studies have suggested that CD38⁺ regulatory T-cells are more suppressive than CD38⁻ regulatory T-cells. Thus, we have suggested that CD38 overexpression in SLE patients could play a role in regulating immune activation cells instead of enhancing it. This study found a correlation between CD38 with FoxP3 expression and immunosuppressive molecules (CD69, IL-10, CTLA-4, and PD-1) in T-cells from lupus-prone mice (B6.MRL-Fas^lpr/J). Additionally, B6.MRL-Fas^lpr/J mice showed a decreased proportion of CD38⁺ Treg cells regarding wild-type mice (WT). Furthermore, Regulatory T-Cells (Treg cells) from CD38-/- mice showed impairment in expressing immunosuppressive molecules and proliferation after stimulation through the T-cell receptor (TCR). Finally, we demonstrated an increased ratio of IFN-γ/IL-10 secretion in CD38-/- splenocytes stimulated with anti-CD3 compared with the WT. Altogether, our data suggest that CD38 represents an element in maintaining activated and proliferative Treg cells. Consequently, CD38 could have a crucial role in immune tolerance, preventing SLE development through Treg cells.

Expression of CD38 in Mast Cells: Cytological and Histotopographic Features

The biological significance of the CD38 molecule goes beyond metabolic, enzymatic, and proliferative functions. CD38 possesses the functions of an exoenzyme and receptor, and is actively involved in the mechanisms of adhesion, migration, intercellular signaling, formation of immune synapses, and modulation of the activity of a wide range of immune and non-immune cells. The aim of this study was the immunohistochemical assessment of the cytological and histotopographic characteristics of CD38 expression in mast cells. CD38 expression was found in a minority of the mast cell population. It is characterized by wide variability from low to high levels. The intensity of CD38 expression in mast cells has organ-specific features and depends on the development of pathological processes in a specific tissue microenvironment. The mechanisms of intercellular interaction between mast cells and CD38+ cells foster new understanding of the protumorigenic or antitumor potential of tryptase.

A population of CD4hiCD38hi T cells correlates with disease severity in patients with acute malaria

OBJECTIVE

CD4⁺ T cells are critical mediators of immunity to Plasmodium spp. infection, but their characteristics during malarial episodes and immunopathology in naturally infected adults are poorly defined. Flow cytometric analysis of PBMCs from patients with either P. falciparum or P. knowlesi malaria revealed a pronounced population of CD4⁺ T cells co-expressing very high levels of CD4 and CD38 we have termed CD4^hiCD38^hi T cells. We set out to gain insight into the function of these novel cells.

METHODS

CD4⁺ T cells from 18 patients with P. falciparum or P. knowlesi malaria were assessed by flow cytometry and sorted into populations of CD4^hiCD38^hi or CD4^norm T cells. Gene expression in the sorted populations was assessed by qPCR and NanoString.

RESULTS

CD4^hiCD38^hi T cells expressed high levels of CD4 mRNA and canonical type 1 regulatory T-cell (TR1) genes including IL10, IFNG, LAG3 and HAVCR2 (TIM3), and other genes with relevance to cell migration and immunomodulation. These cells increased in proportion to malaria disease severity and were absent after parasite clearance with antimalarials.

CONCLUSION

In naturally infected adults with acute malaria, a prominent population of type 1 regulatory T cells arises that can be defined by high co-expression of CD4 and CD38 (CD4^hiCD38^hi) and that correlates with disease severity in patients with falciparum malaria. This study provides fundamental insights into T-cell biology, including the first evidence that CD4 expression is modulated at the mRNA level. These findings have important implications for understanding the balance between immunity and immunopathology during malaria.

P2X7 Receptor at the Crossroads of T Cell Fate

The P2X7 receptor is a ligand-gated, cation-selective channel whose main physiological ligand is ATP. P2X7 receptor activation may also be triggered by ARTC2.2-dependent ADP ribosylation in the presence of extracellular NAD. Upon activation, this receptor induces several responses, including the influx of calcium and sodium ions, phosphatidylserine externalization, the formation of a non-selective membrane pore, and ultimately cell death. P2X7 receptor activation depends on the availability of extracellular nucleotides, whose concentrations are regulated by the action of extracellular nucleotidases such as CD39 and CD38. The P2X7 receptor has been extensively studied in the context of the immune response, and it has been reported to be involved in inflammasome activation, cytokine production, and the migration of different innate immune cells in response to ATP. In adaptive immune responses, the P2X7 receptor has been linked to T cell activation, differentiation, and apoptosis induction. In this review, we will discuss the evidence of the role of the P2X7 receptor on T cell differentiation and in the control of T cell responses in inflammatory conditions.

CD38, a Receptor with Multifunctional Activities: From Modulatory Functions on Regulatory Cell Subsets and Extracellular Vesicles, to a Target for Therapeutic Strategies

CD38 is a multifunctional cell surface protein endowed with receptor/enzymatic functions. The protein is generally expressed at low/intermediate levels on hematological tissues and some solid tumors, scoring the highest levels on plasma cells (PC) and PC-derived neoplasia. CD38 was originally described as a receptor expressed by activated cells, mainly T lymphocytes, wherein it also regulates cell adhesion and cooperates in signal transduction mediated by major receptor complexes. Furthermore, CD38 metabolizes extracellular NAD+, generating ADPR and cyclic ADPR. This ecto-enzyme controls extra-cellular nucleotide homeostasis and intra-cellular calcium fluxes, stressing its relevance in multiple physiopathological conditions (infection, tumorigenesis and aging). In clinics, CD38 was adopted as a cell activation marker and in the diagnostic/staging of leukemias. Quantitative surface CD38 expression by multiple myeloma (MM) cells was the basic criterion used for therapeutic application of anti-CD38 monoclonal antibodies (mAbs). Anti-CD38 mAbs-mediated PC depletion in autoimmunity and organ transplants is currently under investigation. This review analyzes different aspects of CD38's role in regulatory cell populations and how these effects are obtained. Characterizing CD38 functional properties may widen the extension of therapeutic applications for anti-CD38 mAbs. The availability of therapeutic mAbs with different effects on CD38 enzymatic functions may be rapidly translated to immunotherapeutic strategies of cell immune defense.

The absolute counts of peripheral T lymphocyte subsets in patient with ankylosing spondylitis and the effect of low-dose interleukin-2

The aim of this analysis is to investigate the level of T cell subsets in ankylosing spondylitis (AS) and the effect of low-dose interleukin 2 (IL-2).This is a retrospective cohort study, we collected basic information, inflammatory markers, BASDAI scores, and T lymphocyte subsets of peripheral blood in patients with AS, baseline analysis, correlation analysis and comparative analysis before and after treatment were performed.Data from 73 patients (of these, 36 patients were treated with IL-2) and 85 the health were included. The absolute numbers of peripheral CD4 Treg and CD8 Treg cells were lower, while the Th17 cell number and the ratio of Th17/CD4 Treg and CD4/CD8 Treg were higher. The CD4 Treg levels and the ratio of Th17/CD4 Tregs were correlated with BASDAI. The CD4 Treg, CD8 Treg, and Th17 cells were increased after treatment with IL-2 and the ratio of Th17/CD4 Treg was decreased.Increase in ratio of Th17/CD4 Treg involved in the occurrence of AS. At the same time, low-dose IL-2 could decrease the ratio of Th17/CD4 Treg in short time, low-dose IL-2 can be used to treat autoimmune diseases to avoid adverse reactions caused by immunosuppressants. Further clinical study is needed on the efficacy of IL-2.

A single administration of human adipose tissue-derived mesenchymal stromal cells (MSC) induces durable and sustained long-term regulation of inflammatory response in experimental colitis

Current therapies for inflammatory bowel diseases (IBD) are aimed at controlling the exacerbated response in the gut, but no treatment is fully effective for many refractory patients. Mesenchymal stromal cells (MSC) are multi-potent cells with regulatory immunosuppressive activity that may control inflammatory diseases. In this study, we investigated the short- and especially the long-term protective effects of MSC on experimental colitis. We show that MSC elicited protection to acute intestinal inflammation with gain of weight, improvement in the clinical disease score and expressive reduction in the mortality rate of treated mice. MSC changed the population of neutrophils, eosinophils and augmented the frequency of CD4 T lymphocytes in the gut-draining lymph nodes, together with reduced accumulation of these cells in the colon intraepithelial compartment. Interestingly, there were increased levels of programmed death 1 (PD-1) and glucocorticoid-induced tumour necrosis factor receptor family-related receptor (GITR) in the spleen regulatory T cells of mice that received MSC treatment, which also presented a reversal in the pattern of immune response in the gut, with diminished inflammatory, T helper type 1 (Th1) and Th17 profile, in contrast to augmented Th2 responses. Most strikingly, this balanced response elicited by a single administration of MSC during the acute colitis persisted long-term, with restored goblet cells, eosinophils and maintenance of elevated gut interleukin (IL)-4, besides increased CD4⁺ CD25⁺ PD-1⁺ cells in the spleen and reduced Th17 response in mesenteric lymph nodes (MLN) of treated mice on day 60. Taken together, our findings provided a significant contribution to translational immunology by pointing human adipose tissue-derived MSC as a novel therapeutic approach with long-term beneficial regulatory effects in experimental colitis.

Differential expression pattern of co-inhibitory molecules on CD4+ T cells in uncomplicated versus complicated malaria

The immune response of malaria patients is a main factor influencing the clinical severity of malaria. A tight regulation of the CD4+ T cell response or the induction of tolerance have been proposed to contribute to protection from severe or clinical disease. We therefore compared the CD4+ T cell phenotypes of Ghanaian children with complicated malaria, uncomplicated malaria, asymptomatic Plasmodium falciparum (Pf) infection or no infection. Using flow cytometric analysis and automated multivariate clustering, we characterized the expression of the co-inhibitory molecules CTLA-4, PD-1, Tim-3, and LAG-3 and other molecules implicated in regulatory function on CD4+ T cells. Children with complicated malaria had higher frequencies of CTLA-4+ or PD-1+ CD4+ T cells than children with uncomplicated malaria. Conversely, children with uncomplicated malaria showed a higher proportion of CD4+ T cells expressing CD39 and Granzyme B, compared to children with complicated malaria. In contrast, asymptomatically infected children expressed only low levels of co-inhibitory molecules. Thus, different CD4+ T cell phenotypes are associated with complicated versus uncomplicated malaria, suggesting a two-sided role of CD4+ T cells in malaria pathogenesis and protection. Deciphering the signals that shape the CD4+ T cell phenotype in malaria will be important for new treatment and immunization strategies.

Spectrum of T-lymphocyte activities regulating allergic lung inflammation

Despite advances in the treatment of asthma, optimization of symptom control remains an unmet need in many patients. These patients, labeled severe asthma, are responsible for a substantial fraction of the disease burden. In these patients, research is needed to define the cellular and molecular pathways contributing to disease which in large part are refractory to corticosteroid treatment. The causes of steroid-resistant asthma are multifactorial and result from complex interactions of genetics, environmental factors, and innate and adaptive immunity. Adaptive immunity, addressed here, integrates the activities of distinct T-cell subsets and by definition is dynamic and responsive to an ever-changing environment and the influences of epigenetic modifications. These T-cell subsets exhibit different susceptibilities to the actions of corticosteroids and, in some, corticosteroids enhance their functional activation. Moreover, these subsets are not fixed in lineage differentiation but can undergo transcriptional reprogramming in a bidirectional manner between protective and pathogenic effector states. Together, these factors contribute to asthma heterogeneity between patients but also in the same patient at different stages of their disease. Only by carefully defining mechanistic pathways, delineating their sensitivity to corticosteroids, and determining the balance between regulatory and effector pathways will precision medicine become a reality with selective and effective application of targeted therapies.

Reduced Plasmodium Parasite Burden Associates with CD38+ CD4+ T Cells Displaying Cytolytic Potential and Impaired IFN-γ Production

Using a unique resource of samples from a controlled human malaria infection (CHMI) study, we identified a novel population of CD4+ T cells whose frequency in the peripheral blood was inversely correlated with parasite burden following P. falciparum infection. These CD4+ T cells expressed the multifunctional ectoenzyme CD38 and had unique features that distinguished them from other CD4+ T cells. Specifically, their phenotype was associated with proliferation, activation and cytotoxic potential as well as significantly impaired production of IFN-γ and other cytokines and reduced basal levels of activated STAT1. A CD38+ CD4+ T cell population with similar features was identified in healthy uninfected individuals, at lower frequency. CD38+ CD4+ T cells could be generated in vitro from CD38- CD4+ T cells after antigenic or mitogenic stimulation. This is the first report of a population of CD38+ CD4+ T cells with a cytotoxic phenotype and markedly impaired IFN-γ capacity in humans. The expansion of this CD38+ CD4+ T population following infection and its significant association with reduced blood-stage parasite burden is consistent with an important functional role for these cells in protective immunity to malaria in humans. Their ubiquitous presence in humans suggests that they may have a broad role in host-pathogen defense.

TRIAL REGISTRATION

ClinicalTrials.gov clinical trial numbers ACTRN12612000814875, ACTRN12613000565741 and ACTRN12613001040752.

Higher Sensitivity of Foxp3+ Treg Compared to Foxp3- Conventional T Cells to TCR-Independent Signals for CD69 Induction

T lymphocytes elicit specific responses after recognizing cognate antigen. However, antigen-experienced T cells can also respond to non-cognate stimuli, such as cytokines. CD4⁺ Foxp3⁺ regulatory T cells (Treg) exhibit an antigen-experienced-like phenotype. Treg can regulate T cell responses in an antigen-specific or bystander way, and it is still unclear as to which extent they rely on T cell receptor (TCR) signals. The study of the antigen response of Treg has been hampered by the lack of downstream readouts for TCR stimuli. Here we assess the effects of TCR signals on the expression of a classical marker of early T cell activation, CD69. Although it can be induced following cytokine exposure, CD69 is commonly used as a readout for antigen response on T cells. We established that upon in vitro TCR stimulation CD69 induction on Foxp3⁺ Treg cells was more dependent on signaling via soluble factors than on TCR activation. By contrast, expression of the activation marker Nur77 was only induced after TCR stimulation. Our data suggest that Treg are more sensitive to TCR-independent signals than Foxp3^- cells, which could contribute to their bystander activity.

Treg and CTLA-4: two intertwining pathways to immune tolerance

Both the CTLA-4 pathway and regulatory T cells (Treg) are essential for the control of immune homeostasis. Their therapeutic relevance is highlighted by the increasing use of anti-CTLA-4 antibody in tumor therapy and the development of Treg cell transfer strategies for use in autoimmunity and transplantation settings. The CTLA-4 pathway first came to the attention of the immunological community in 1995 with the discovery that mice deficient in Ctla-4 suffered a fatal lymphoproliferative syndrome. Eight years later, mice lacking the critical Treg transcription factor Foxp3 were shown to exhibit a remarkably similar phenotype. Much of the debate since has centered on the question of whether Treg suppressive function requires CTLA-4. The finding that it does in some settings but not in others has provoked controversy and inevitable polarization of opinion. In this article, I suggest that CTLA-4 and Treg represent complementary and largely overlapping mechanisms of immune tolerance. I argue that Treg commonly use CTLA-4 to effect suppression, however CTLA-4 can also function in the non-Treg compartment while Treg can invoke CTLA-4-independent mechanisms of suppression. The notion that Foxp3 and CTLA-4 direct independent programs of immune regulation, which in practice overlap to a significant extent, will hopefully help move us towards a better appreciation of the underlying biology and therapeutic significance of these pathways.

Low-dose gemcitabine depletes regulatory T cells and improves survival in the orthotopic Panc02 model of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive human neoplasms with extremely poor prognosis and a low survival rate. Immunosuppressive cell populations, e.g. regulatory T cells (Treg), appear to be important in PDAC, contributing to patient's poor prognosis. Therefore, we investigated the PDAC microenvironment with a focus on conventional and regulatory T cells in view of their potential therapeutic importance. We found that tumors from the murine Panc02 orthotopic model of PDAC were infiltrated with high numbers of Treg. Remarkably, these cells exhibited the effector/memory phenotype, suggesting their enhanced suppressive activity and higher proliferation capacity. Although we observed a steady increase in transforming growth factor-β (TGF-β) levels in the tumors, treatment with a specific inhibitor of TGF-β receptor I kinase failed to abrogate Treg accumulation. A CCR4 antagonist did not affect Treg percentage in the tumor either. However, intense Treg cell division in the tumor microenvironment was demonstrated, suggesting local proliferation as a major mechanism of Treg accumulation in PDAC. Notably, this accumulation was reduced by low-dose gemcitabine administration, resulting in a modestly increased survival of PDAC mice. Our results provide an insight into mechanisms of immunosuppression in PDAC, suggesting an important role for proliferative expansion of effector/memory Treg. Low-dose gemcitabine therapy selectively depletes Treg, providing a basis for new modalities of PDAC therapy.

Ectonucleotidase CD38 demarcates regulatory, memory-like CD8+ T cells with IFN-γ-mediated suppressor activities

Regulatory CD8(+) T cells are critical for self-tolerance and restricting excessive immune responses. The variety of immune functions they fulfill, the heterogeneity of their phenotype, and the mechanism of action are still poorly understood. Here we describe that regulatory CD8(+) T cells exhibiting immunosuppressive actions in vitro and in vivo are recognized as CD38(high) T cells and present in naive mice. CD38 is a glycosylated membrane protein with ectonucleotidase properties. CD8(+)CD38(high) (CD44(+)CD122(+)CD62L(high)) lymphocytes suppress CD4(+) effector T-cell proliferation in an antigen-non specific manner via IFN-γ. While direct cell-to-cell contact is needed for this suppressor activity, it is independent of membrane-bound TGF-β and granzyme B release. IL-15 potentiates the suppressive activity of CD8(+)CD38(high) T cells and controls their survival and expansion. In humans CD8(+)CD38(high) T cells inhibit CD4(+) effector T cell proliferation. In vivo, CD8(+)CD38(high), but not CD8(+)CD38(-) T cells mitigate murine experimental autoimmune encephalomyelitis (EAE) by reducing the clinical score and delaying disease occurrence. EAE suppression is enhanced by pre-treatment of CD8(+)CD38(high) T cells with IL-15. These findings add evidence that the expression of ectoenzyme receptor family members positively correlates with suppressor functions and identifies CD8(+)CD38(high) T cells as potential inhibitors of excessive immune responses.

CD4+ T cells disarm or delete cytotoxic T lymphocytes under IL-17-polarizing conditions

Previous studies have shown that TGF-β acts cooperatively with IL-6 to elicit a high frequency of IL-17-secreting CD4(+) T cells (termed Th17) and an elevated CD8(+)IL-17(+) T cell population (termed Tc17). These CD8(+) cells fail to behave like most cytotoxic T lymphocytes that express IFN-γ and granzyme B, but they exhibit a noncytotoxic phenotype. Although a significant increase in the number of these Tc17 cells was found in tumors, their role and interaction with other cell types remain unclear. In this study, we demonstrate that the presence of CD4(+)CD25(-) T cells, but not the CD4(+)CD25(+) (regulatory T [Treg]) cell population, significantly reduced the elicitation of Tc17 cells, possibly as a result of the induction of apoptotic signals. Importantly, these signals may be derived from soluble mediators, and the addition of anti-IL-2 restored the reduction of Tc17 cells in the presence of CD4(+)CD25(-) T cells. Finally, the elicited Tc17 and Treg cells exhibited a close association in patients with head and neck cancer, indicating that the surrounding Treg cells might maintain the survival of the Tc17 cells. Taken together, these results reveal an intriguing mechanism in which Tc17 cells are controlled by a finely tuned collaboration between the different types of CD4(+) T cells in distinct tumor microenvironments.

Thirty Years with HIV Infection-Nonprogression Is Still Puzzling: Lessons to Be Learned from Controllers and Long-Term Nonprogressors

In the early days of the HIV epidemic, it was observed that a minority of the infected patients did not progress to AIDS or death and maintained stable CD4+ cell counts. As the technique for measuring viral load became available it was evident that some of these nonprogressors in addition to preserved CD4+ cell counts had very low or even undetectable viral replication. They were therefore termed controllers, while those with viral replication were termed long-term nonprogressors (LTNPs). Genetics and virology play a role in nonprogression, but does not provide a full explanation. Therefore, host differences in the immunological response have been proposed. Moreover, the immunological response can be divided into an immune homeostasis resistant to HIV and an immune response leading to viral control. Thus, non-progression in LTNP and controllers may be due to different immunological mechanisms. Understanding the lack of disease progression and the different interactions between HIV and the immune system could ideally teach us how to develop a functional cure for HIV infection. Here we review immunological features of controllers and LTNP, highlighting differences and clinical implications.

Incomplete immune recovery in HIV infection: mechanisms, relevance for clinical care, and possible solutions

Treatment of HIV-infected patients with highly active antiretroviral therapy (HAART) usually results in diminished viral replication, increasing CD4+ cell counts, a reversal of most immunological disturbances, and a reduction in risk of morbidity and mortality. However, approximately 20% of all HIV-infected patients do not achieve optimal immune reconstitution despite suppression of viral replication. These patients are referred to as immunological nonresponders (INRs). INRs present with severely altered immunological functions, including malfunction and diminished production of cells within lymphopoetic tissue, perturbed frequencies of immune regulators such as regulatory T cells and Th17 cells, and increased immune activation, immunosenescence, and apoptosis. Importantly, INRs have an increased risk of morbidity and mortality compared to HIV-infected patients with an optimal immune reconstitution. Additional treatment to HAART that may improve immune reconstitution has been investigated, but results thus far have proved disappointing. The reason for immunological nonresponse is incompletely understood. This paper summarizes the known and unknown factors regarding the incomplete immune reconstitution in HIV infection, including mechanisms, relevance for clinical care, and possible solutions.

CD62L(neg)CD38⁺ expression on circulating CD4⁺ T cells identifies mucosally differentiated cells in protein fed mice and in human celiac disease patients and controls

OBJECTIVES

The aim of this study was to identify new markers of mucosal T cells to monitor ongoing intestinal immune responses in peripheral blood.

METHODS

Expression of cell-surface markers was studied in mice on ovalbumin (OVA)-specific T cells in the gut-draining mesenteric lymph nodes (MLN) after OVA feed. The effect of the local mucosal mediators retinoic acid (RA) and transforming growth factor-β (TGF-β) on the induction of a mucosal phenotype was determined in in vitro T-cell differentiation assays with murine and human T cells. Tetramer stainings were performed to study gluten-specific T cells in the circulation of patients with celiac disease, a chronic small-intestinal inflammation.

RESULTS

In mice, proliferating T cells in MLN were CD62L(neg)CD38(+) during both tolerance induction and abrogation of intestinal homeostasis. This mucosal CD62L(neg)CD38(+) T-cell phenotype was efficiently induced by RA and TGF-β in mice, whereas for human CD4(+) T cells RA alone was sufficient. The CD4(+)CD62L(neg)CD38(+) T-cell phenotype could be used to identify T cells with mucosal origin in human peripheral blood, as expression of the gut-homing chemokine receptor CCR9 and β(7) integrin were highly enriched in this subset whereas expression of cutaneous leukocyte-associated antigen was almost absent. Tetramer staining revealed that gluten-specific T cells appearing in blood of treated celiac disease patients after oral gluten challenge were predominantly CD4(+)CD62L(neg)CD38(+). The total percentage of circulating CD62L(neg)CD38(+) of CD4 T cells was not an indicator of intestinal inflammation as percentages did not differ between pediatric celiac disease patients, inflammatory bowel disease patients and respective controls. However, the phenotypic selection of mucosal T cells allowed cytokine profiling as upon restimulation of CD62L(neg)CD38(+) cells interleukin-10 (IL-10) and interferon-γ (IFN-γ) transcripts were readily detected in circulating mucosal T cells.

CONCLUSIONS

By selecting for CD62L(neg)CD38(+) expression that comprises 5-10% of the cells within the total CD4(+) T-cell pool we are able to highly enrich for effector T cells with specificity for mucosal antigens. This is of pivotal importance for functional studies as this purification enhances the sensitivity of cytokine detection and cellular activation.

The PI3K p110δ regulates expression of CD38 on regulatory T cells

The PI3K pathway has emerged as a key regulator of regulatory T cell (Treg) development and homeostasis and is required for full Treg-mediated suppression. To identify new genes involved in PI3K-dependent suppression, we compared the transcriptome of WT and p110δ^D910A Tregs. Among the genes that were differentially expressed was the gene for the transmembrane cyclic ADP ribose hydrolase CD38. Here we show that CD38 is expressed mainly by a subset of Foxp3⁺CD25⁺CD4⁺ T cells originating in the thymus and on Tregs in the spleen. CD38^high WT Tregs showed superior suppressive activity to CD38^low Tregs, which failed to upregulate CD73, a surface protein which is important for suppression. However, Tregs from heterozygous CD38^+/− mice were unimpaired despite lower levels of CD38 expression. Therefore, CD38 can be used as a marker for Tregs with high suppressive activity and the impaired Treg function in p110δ^D910A mice can in part be explained by the failure of CD38^high cells to develop.

Allogeneic apoptotic thymocyte-stimulated dendritic cells expand functional regulatory T cells

Dendritic cells (DCs) play an important role in the clearance of apoptotic cells. The removal of apoptotic cells leads to peripheral tolerance, although their role is still not clear. We show that the uptake of apoptotic thymocytes by DCs converts these cells into tolerogenic DCs resistant to maturation by lipopolysaccharide, modulating the production of interleukin-12 and up-regulating the expression of transforming growth factor-β(1) latency associated peptide. We also observed that DCs pulsed with apoptotic cells in the allogeneic context were more efficient in the expansion of regulatory T cells (Tregs), and that this expansion requires contact between DCs and the T cell. The Tregs sorted from in vitro culture suppressed the proliferation of splenocytes in vitro in a specific and non-specific manner. In the in vivo model, the transfer of CD4(+) CD25(-) cells to Nude mice induced autoimmunity, with cell infiltrate found in the stomach, colon, liver and kidneys. The co-transfer of CD4(+) CD25(-) and CD4(+) CD25(+) prevented the presence of cell infiltrates in several organs and increased the total cell count in lymph nodes. Our data indicate that apoptotic cells have an important role in peripheral tolerance via induction of tolerogenic DCs and CD4(+) CD25(+) Foxp3(+) cells that present regulatory functions.

Role of 4-1BB receptor in the control played by CD8(+) T cells on IFN-gamma production by Mycobacterium tuberculosis antigen-specific CD4(+) T Cells

Background

Antigen-specific IFN-γ producing CD4⁺ T cells are the main mediators of protection against Mycobacterium tuberculosis infection both under natural conditions and following vaccination. However these cells are responsible for lung damage and poor vaccine efficacy when not tightly controlled. Discovering new tools to control nonprotective antigen-specific IFN-γ production without affecting protective IFN-γ is a challenge in tuberculosis research.

Methods and Findings

Immunization with DNA encoding Ag85B, a candidate vaccine antigen of Mycobacterium tuberculosis, elicited in mice a low but protective CD4⁺ T cell-mediated IFN-γ response, while in mice primed with DNA and boosted with Ag85B protein a massive increase in IFN-γ response was associated with loss of protection. Both protective and non-protective Ag85B-immunization generated antigen-specific CD8⁺ T cells which suppressed IFN-γ-secreting CD4⁺ T cells. However, ex vivo ligation of 4-1BB, a member of TNF-receptor super-family, reduced the massive, non-protective IFN-γ responses by CD4⁺ T cells in protein-boosted mice without affecting the low protective IFN-γ-secretion in mice immunized with DNA. This selective inhibition was due to the induction of 4-1BB exclusively on CD8⁺ T cells of DNA-primed and protein-boosted mice following Ag85B protein stimulation. The 4-1BB-mediated IFN-γ inhibition did not require soluble IL-10, TGF-β, XCL-1 and MIP-1β. In vivo Ag85B stimulation induced 4-1BB expression on CD8⁺ T cells and in vivo 4-1BB ligation reduced the activation, IFN-γ production and expansion of Ag85B-specific CD4⁺ T cells of DNA-primed and protein-boosted mice.

Conclusion/Significance

Antigen-specific suppressor CD8⁺ T cells are elicited through immunization with the mycobacterial antigen Ag85B. Ligation of 4-1BB receptor further enhanced their suppressive activity on IFN-γ-secreting CD4⁺ T cells. The selective expression of 4-1BB only on CD8⁺ T cells in mice developing a massive, non-protective IFN-γ response opens novel strategies for intervention in tuberculosis pathology and vaccination through T-cell co-stimulatory-based molecular targeting.

Modeling the role of IL-2 in the interplay between CD4+ helper and regulatory T cells: assessing general dynamical properties

Mathematical models accounting for well-known evidences relating to the dynamics of interleukin 2, helper and regulatory T cells are presented. These models extend an existent model (the so-called cross-regulation model of immunity), by assuming IL-2 as the growth factor produced by helper cells, but used by both helper and regulatory cells to proliferate and survive. Two model variants, motivated by current literature, are explored. The first variant assumes that regulatory cells suppress helper cells by limiting IL-2 production and consuming the available IL-2; i.e. they just trigger competition for IL-2. The second model variant adds to the latter competitive mechanism the direct inhibition of helper cells activation by regulatory cells. The extended models retain key dynamical features of the cross-regulation model. But such reasonable behavior depends on parameter constraints, which happen to be realistic and lead to interesting biological discussions. Furthermore, the introduction of IL-2 in these models breaks the local/specific character of interactions, providing new properties to them. In the extended models, but not in the cross-regulation model, the response triggered by an antigen affects the response to other antigens in the same lymph node. The first model variant predicts an unrealistic coupling of the immune reactions to all the antigens in the lymph node. In contrast, the second model variant allows the coexistent of concomitant tolerant and immune responses to different antigens. The IL-2 derived from an ongoing immune reaction reinforces tolerance to other antigens in the same lymph node. Overall the models introduced here are useful extensions of the cross-regulation formalism. In particular, they might allow future studies of the effect of different IL-2 modulation therapies on CD4+ T cell dynamics.

An imbalance of esophageal effector and regulatory T cell subsets in experimental eosinophilic esophagitis in mice

We recently reported a critical role for T cells in the induction of eosinophilic esophagitis (EE) in mice; however, the role of specific T cell subsets in disease pathogenesis is not yet understood. In the current study, we tested the hypothesis that allergen-induced EE develops in response to the disproportion of functionally different effector and regulatory T cells in the esophagus. Fluorescence-activated cell sorter analysis was performed to examine activated T cell subsets using the cell surface activation markers CD25 and CD69. A significant increase in activated CD4(+) and CD4(-) T cells was observed in the total esophageal cells isolated from the mouse model of EE. Furthermore, an imbalance in the effector and regulatory T cells was observed in the esophagus. The esophageal CD4(+)CD45RB(high) effector T cells in allergen-challenged mice increased compared with saline-challenged mice (65.4 +/- 3.6 x 10(3) to 44.8 +/- 4.2 x 10(3)), whereas CD4(+)CD45RB(low) mostly regulatory T cells decreased in allergen-challenged mice compared with saline-challenged mice (5.8 +/- 0.9 x 10(3) from 10.2 +/- 1.7 x 10(3)). The functional characteristics were examined by analysis of the pro- and anti-inflammatory cytokine profile of purified low and high CD4(+)CD45RB subsets from the spleen. Additionally, a significantly reduced interleukin (IL)-2 production by CD4(+)CD45RB(low) cells in allergen-challenged mice compared with saline-challenged mice was observed. The reduced IL-2 in the CD4(+)CD45RB(low) subset may be associated with reduction of CD4(+)CD45RB(low) subset. In conclusion, our results suggest that local regulatory interaction of CD45RB(high) and CD45RB(low) CD4(+) T cells may be required for protective and pathogenic immunity in EE.

Role of regulatory T-cells in autoimmunity

There has been considerable historical interest in the concept of a specialist T-cell subset which suppresses over-zealous or inappropriate T-cell responses. However, it was not until the discovery that CD4(+)CD25(+) T-cells had suppressive capabilities both in vitro and in vivo that this concept regained credibility and developed into one of the most active research areas in immunology today. The notion that in healthy individuals there is a subset of T(reg)-cells (regulatory T-cells) involved in 'policing' the immune system has led to the intensive exploration of the role of this subset in disease resulting in a number of studies concluding that a quantitative or qualitative decline in T(reg)-cells is an important part of the breakdown in self-tolerance leading to the development of autoimmune diseases. Although T(reg)-cells have subsequently been widely postulated to represent a potential immunotherapy option for patients with autoimmune disease, several studies of autoimmune disorders have demonstrated high numbers of T(reg)-cells in inflamed tissue. The present review highlights the need to consider a range of other factors which may be impairing T(reg)-cell function when considering the mechanisms involved in the breakdown of self-tolerance rather than focussing on intrinsic T(reg)-cell factors.

CD25+ T(reg) specifically suppress auto-Ab generation against pancreatic tissue autoantigens

To study B-cell tolerance against non-lymphoid tissue autoantigens, we generated transgenic rat insulin promoter (RIP)-OVA/hen egg lysozyme (HEL) mice expressing the model antigens, OVA and HEL, in pancreatic islets. Their vaccination with OVA or HEL induced far less auto-Ab titers compared with non-transgenic controls. Depletion of CD25(+) cells during immunization completely restored auto-Ab production, but did not affect antibodies against a foreign control antigen. Depletion at later time-points was not effective. OVA-specific CD25(+) FoxP3(+) T(reg) were more frequent in the autoantigen-draining pancreatic LN than in other secondary lymphatics of RIP-OVA/HEL mice. Consistently, B cells were suppressed in that LN and also in the spleen, which is known to concentrate circulating antigen, such as the antigens used for vaccination. Suppression involved preventing expansion of autoreactive B cells in response to autoantigen, reducing antibody production per B-cell and isotype changes. These findings demonstrate that CD25(+) T(reg) suppress auto-Ab production against non-lymphoid tissue antigens in an antigen-specific manner.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

Abnormal regulatory and effector T cell function predispose to autoimmunity following xenogeneic thymic transplantation

Porcine thymus grafts support robust murine and human thymopoiesis, generating a diverse T cell repertoire that is deleted of donor and host-reactive cells, achieving specific xenograft tolerance. Positive selection is mediated exclusively by the xenogeneic thymic MHC. Although thymectomized, T cell-depleted normal mice usually remain healthy following xenogeneic thymic transplantation, thymus-grafted congenitally athymic mice frequently develop multiorgan autoimmunity. We investigated the etiology of this syndrome by adoptively transferring lymphocyte populations from fetal pig thymus-grafted BALB/c nude mice to secondary BALB/c nude recipients. Fetal pig thymus-grafted nude mice generated normal numbers of CD25(+)Foxp3(+)CD4 T cells, but these cells lacked the capacity to block autoimmunity. Moreover, thymocytes and peripheral CD4(+)CD25(-) cells from fetal pig thymus-grafted nude mice, but not those from normal mice, induced autoimmunity in nude recipients. Injection of thymic epithelial cells from normal BALB/c mice into fetal pig thymus grafts reduced autoimmunity and enhanced regulatory function of splenocytes. Our data implicate abnormalities in postthymic maturation, expansion, and/or survival of T cells positively selected by a xenogeneic MHC, as well as incomplete intrathymic deletion of thymocytes recognizing host tissue-specific Ags, in autoimmune pathogenesis. Regulatory cell function is enhanced and negative selection of host-specific thymocytes may potentially also be improved by coimplantation of recipient thymic epithelial cells in the thymus xenograft.

Regulatory T cells in human immunodeficiency virus-infected patients are elevated and independent of immunological and virological status, as well as initiation of highly active anti-retroviral therapy

Infection with human immunodeficiency virus (HIV) causes a dysregulation of the immune system. This is caused by HIV-specific as well as non-specific mechanisms and has not been explained fully. In particular, knowledge is lacking about the potential role of host-mediated immunosuppressive mechanisms. During recent years it has become evident that a subpopulation of T cells [T regulatory (T(regs))] play a major role in sustaining tolerance to self-antigens. To investigate the influence of initiation of highly active anti-retroviral therapy (HAART) on the T(reg) level in HIV-infected patients we have conducted a prospective study enrolling treatment-naive HIV-infected patients just prior to starting treatment with HAART, measuring levels of T(regs) by flow cytometry and mRNA expression of forkhead box P3 (FoxP3) at weeks 0, 4, 12 and 24 of treatment. In this prospective study neither the percentage of CD4(+)CD25(high+) nor the expression of FoxP3 changed significantly during 24 weeks of HAART. Furthermore, HIV patients have higher T(regs) measured as percentages of CD4(+)CD25(high+) cells paralleled by higher levels of FoxP3 compared with healthy controls. The elevated level of T(regs) was found to be independent of both immunological and virological status, indicating that initiation of HAART has minor effects on the T(reg) level in HIV-infected patients.

Development of regulatory T cells requires IL-7Ralpha stimulation by IL-7 or TSLP

Interleukin-7 (IL-7), a cytokine produced by stromal cells, is required for thymic development and peripheral homeostasis of most major subsets of T cells. We examined whether regulatory T (Treg) cells also required the IL-7 pathway by analyzing IL-7Ralpha(-/-) mice. We observed a striking reduction in cells with the Treg surface phenotype (CD4, CD25, GITR (glucocorticoid-induced tumor necrosis factor [TNF]-like receptor), CD45RB, CD62L, CD103) or intracellular markers (cytotoxic T-lymphocyte-associated antigen-4, CTLA-4, and forkhead box transcription factor 3, Foxp3). Foxp3 transcripts were virtually absent in IL-7Ralpha(-/-) lymphoid tissues, and no Treg cell suppressive activity could be detected. There are 2 known ligands for IL-7Ralpha: IL-7 itself and thymic stromal lymphopoietin (TSLP). Surprisingly, mice deficient in IL-7 or the other chain of the TSLP receptor (TSLPR) developed relatively normal numbers of Treg cells. Combined deletion of IL-7 and TSLP receptor greatly reduced Treg cell development in the thymus but was not required for survival of mature peripheral Treg cells. We conclude that Treg cells, like other T cells, require signals from the IL-7 receptor, but unlike other T cells, do not require IL-7 itself because of at least partially overlapping actions of IL-7 and TSLP for development of Treg cells.

Evolution and function of the ADP ribosyl cyclase/CD38 gene family in physiology and pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

Suppression of HIV-specific and allogeneic T cell activation by human regulatory T cells is dependent on the strength of signals

Regulatory T cells (Tregs) suppress immune responses against both self and non-self antigens. Tregs require activation through the T cell receptor (TCR) and IL-2 to exert their suppressive functions. However, how strength of TCR signals modulate the potency of Treg-mediated suppression of antigen-specific T cell activation remain unclear. We found that both strength of TCR signals and ratios of Tregs to target cells, either through superantigen, allogeneic antigens or HIV-specific peptides, modified the suppressive ability of Tregs. While human Tregs were able to mediate suppression in the presence of only autologous antigen-presenting cells, this was much less efficient as compared to when Tregs were activated by allogeneic dendritic cells. In another physiologically relevant system, we show that the strength of peptide stimulation, high frequency of responder CD8+ T cells or presence of high IL-2 can override the suppression of HIV-specific CD8+ T cells by Tregs. These findings suggest that ratios and TCR activation of human Tregs, are important parameters to overcome robust immune responses to pathogens or allogeneic antigens. Modulating the strength of T cell signals and selective enhancement or depletion of antigen-specific Tregs thus may have implications for designing potent vaccines and regulating immune responses during allogeneic transplantation and chronic infections.

Decreased CD4+CD25+bright T cells in peripheral blood of patients with primary Sjogren's syndrome

CD4+CD25+bright T cells played a crucial role in the suppression of immune response. Recently, decreased levels of CD4+CD25+bright T cells in the peripheral blood of patients with systemic lupus erythematosus were reported, suggesting the potential role of CD4+CD25+bright T cells in human autoimmune diseases. Primary Sjögren's syndrome (pSS) is another common human systemic autoimmune disease. The present study aimed to investigate the levels of CD4+CD25+bright T cells in pSS and to correlate their levels with some biomarkers of inflammation and immune activation. Thirty-three patients with pSS and 35 age- and sex-matched normal individuals were enrolled in the study. The flowcytometric method was applied in the measurement of CD4+CD25+bright T cells. The results showed that patients with pSS had statistically lower levels of CD4+CD25+bright T cells than normal controls, expressed either as absolute cell numbers (mean+/-SD: 47.07+/-25.53 cells/mm3 versus 79.55+/-34.56 cells/mm3, P<0.001) or as percentages of peripheral blood mononuclear cells (mean+/-SD: 2.79+/-1.06% versus 3.84+/-1.42%, P<0.001) or as percentages of CD4+ T cells (mean+/-SD: 7.85+/-2.62% versus 11.68+/-3.78%, P<0.005). Moreover, there were statistically significant inverse correlations between the levels of CD4+CD25+bright T cells and some parameters of inflammation or immune activation including erythrocyte sedimentation rate, C-reactive protein, IgG and rheumatoid factors. The result suggested that CD4+CD25+bright T cells were likely to play anti-inflammatory and immunosuppressive roles in the pathogenesis of pSS. However, the exact functions of decreased circulating CD4+CD25+bright T cells in pSS need further elucidated.

Characterization of mouse CD4 T cell subsets defined by expression of KLRG1

The mouse killer cell lectin-like receptor G1 (KLRG1) is an inhibitory receptor known to be expressed on a subset of NK cells and antigen-experienced CD8 T cells. Here, we have characterized expression of KLRG1 on CD4+ T cells from normal mice. While a polyclonal TCR repertoire suggests thymic origin of KLRG1+ CD4+ cells, KLRG1 expression was found to be restricted to peripheral CD4+ T cells. Based on phenotypic analyses, a minority of KLRG1+ CD4+ cells are effector/memory cells with a proliferative history. The majority of KLRG1+ CD4+ cells are, however, bona fide Treg cells that depend on IL-2 and/or CD28 and express both FoxP3 and high levels of intracellular CD152. KLRG1-expressing Treg are contained within the CD38+ subset but are only partially overlapping with the CD25+ CD4+ Treg subset. In functional assays, KLRG1+ CD4+ cells were anergic to TCR stimulation with respect to proliferation, and sorted KLRG1+ CD25+ CD4+ cells were equal or superior to KLRG1+ CD25- CD4+ cells, which were more potent than KLRG1- CD25+ CD4+ cells in suppressing responder cell proliferation. Together, our results demonstrate that KLRG1 expression defines novel and distinctive subsets of senescent effector/memory and potent regulatory CD4+ T cells.

Antigen, in the Presence of TGF-β, Induces Up-Regulation of FoxP3gfp+ in CD4+ TCR Transgenic T Cells That Mediate Linked Suppression of CD8+ T Cell Responses

CD4(+)CD25(+) regulatory T cells (Tregs) inhibit immune responses to a variety of Ags, but their specificity and mechanism of suppression are controversial. This controversy is largely because many studies focused on natural Tregs with undefined specificities and suppression has frequently been measured on polyclonal T cell responses. To address the issue of specificity further, we have bred K(d)-specific, CD4(+) TCR (TCR75) transgenic mice to Foxp3(gfp) knockin reporter mice to permit sorting of Tregs with a known specificity. Foxp3(gfp).TCR75 mice did not express significant numbers of natural FoxP3(+) Tregs expressing the TCR75 transgenes, but FoxP3 expression was induced by stimulating with K(d) plus TGF-beta. The resulting GFP(+) TCR75 cells were anergic, whereas the GFP(-) TCR75 cells proliferated upon restimulation with K(d) peptide. Yet both exhibited severely reduced expression of intracellular IFN-gamma and TNF-alpha upon restimulation. GFP(+), but not GFP(-), TCR75 T cells suppressed responses by naive TCR75 T cells and by nontransgenic spleen cells stimulated with anti-CD3. GFP(+) TCR75 cells also inhibited polyclonal C57BL/6 anti-K(d) CTL responses if the APC expressed K(d) and both MHC class I and class II, and responses by OT1 T cells to B6.K(d).OVA but not B6.K(d) plus OVA expressing APC, demonstrating linked-suppression of CD8 responses. Thus, Tregs exhibit a greater degree of specificity in vitro than previously appreciated. The observation that Tregs and responder T cells must recognize the same APC provides a mechanistic explanation for the observation that Tregs must be in direct contact with effector T cells to suppress their responses.

Role of NKT cells in allogeneic islet graft survival

Although NKT cells expressing CD1d-reactive TCR exerted protective role in autoimmune diseases, the regulatory function of CD1d-dependent NKT cells in alloimmune responses has not been investigated thoroughly. Here, we demonstrated the regulatory effects of NKT cells using a pancreas islet transplantation model. CD40/CD154 blocking induced long-term graft survival in most B6 recipients, but B6.CD1d(-/-) recipients showed co-stimulation blockade-resistant rejection. Adoptive transfer of NKT cells into B6.CD1d(-/-) restored tolerizing capacity of co-stimulatory blockade. Activation of NKT cells was effective for the prolongation of graft survival and up-regulated membrane-bound TGF-beta expression transiently on their cell surface. The activated CD1d-dependent NKT cells inhibited alloantigen-driven cell proliferation through cell contacts and the beneficial effect of CD154 blocking for allograft survival was related to TGF-beta pathway. Thus, we can conclude that NKT cells are essential for the stable allograft survival and the regulatory function is dependent on, at least in part, TGF-beta engagement.

Antibody blocking of MHC II on human activated regulatory T cells abrogates their suppressive potential

Natural regulatory CD4(+)CD25(+)Foxp3(+) T cells control peripheral immune responses. Freshly isolated regulatory T-cell populations are regarded as being unable to suppress the proliferation of strongly stimulated effector T cells. We now provide evidence that it is not the strength of the proliferative signal to effector T cells but activation and accessibility of regulatory T cells that determine whether suppression may occur. Human regulatory T cells were initially cocultured with allogeneic monocyte-derived dendritic cells for a short time and were then rendered accessible for effector T cells by removal of the dendritic cells. That way activated regulatory T cells effectively suppressed the proliferation of autologous effector T cells which was strongly driven by cell-sized Dynabeads coated with CD3/CD28 antibodies. Although regulatory T cells are known to display MHC II molecules and to upregulate their expression along with activation, a role of MHC II molecules in forming the contact to effector T cells was not yet envisaged. However, blocking of MHC II on activated regulatory T cells abrogated their suppressive potential. It should not be excluded that self-MHC molecules on physically accessible activated regulatory T cells arrange the contact to effector T cells.

Regulation of type 1 diabetes by NKT cells

Type 1 diabetes is an autoimmune disease due to the destruction of insulin-producing pancreatic beta cells. Natural Killer T (NKT) cells are a T-cell subset that links the innate and adaptive immune systems. NKT cells play a key regulatory role in type 1 diabetes. The absence of NKT cells correlates with exacerbation of type 1 diabetes, whereas an increased frequency and/or activation of NKT cells prevents beta-cell autoimmunity. Various mechanisms are involved in the protective effect of NKT cells. The goal is now to translate knowledge gained from mouse models into human therapeutics.

A Potential Side Effect of Cyclosporin A: Inhibition of CD4+CD25+ Regulatory T Cells in Mice

BACKGROUND

CD4CD25 regulatory T (Treg) cells are essential for the induction and maintenance of immunologic self-tolerance as well as transplant tolerance. The effects of cyclosporin A (CsA), a widely used immunosuppressive agent, on CD4CD25Treg cells in mice were investigated.

METHODS

Balb/c mice were injected with CsA or control solution for one month. The levels, phenotype, and function of CD4CD25Treg cells in these mice were then assayed.

RESULTS

The percentages and total cell numbers of CD4CD25Treg cells in the peripheral blood and spleen were significantly reduced after the treatment with CsA. The total numbers of CD4CD25Treg cells in the thymus of CsA-treated mice were markedly reduced as compared to the control mice. However, the percentage of CD4CD25Treg cells in the thymus of CsA-treated mice was markedly enhanced. More CD4CD25Treg cells expressing high levels of CD44 and CD45RB, and less CD4CD25Treg cells expressing CD62L were observed in CsA-treated mice, compared with the control mice. CD4CD25Treg cells expressed slightly lower levels of Foxp3 in CsA-treated mice. Furthermore, CsA markedly impaired the immunosuppressive function of CD4CD25Treg cells.

CONCLUSIONS

CsA significantly impaired the development and function of CD4CD25Treg cells. The present studies suggest that CsA may block the potential induction of immune tolerance and increase the susceptibility to develop autoimmune diseases while preventing graft rejection.

Differential roles of the co-stimulatory molecules GITR and CTLA-4 in the immune response to Trichinella spiralis

We investigated the roles of the regulatory molecules glucocorticoid-induced TNF receptor family-related protein (GITR) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) in murine infection with the nematode parasite Trichinella spiralis. Expression of GITR and CTLA-4 was rapidly upregulated on cells in the mesenteric lymph nodes and spleen, with approximately 80% of CD4+ lymphocytes expressing GITR by day 7 post-infection, coinciding with release and dissemination of newborn larvae. As the infection progressed to the chronic muscle phase, expression of GITR returned to normal, whereas CTLA-4 was sustained as late as day 60. Mice treated with anti-GITR antibodies rapidly developed higher titres of parasite-specific IgG1, IgG2a, IgG2b and IgM than controls. This was accompanied by elevated background lymphocyte proliferation, but parasite establishment in the intestine or the muscle was unaffected. In contrast, treatment with anti-CTLA-4 antibody resulted in elevated serum IgE, enhanced production of interleukin-4 and interleukin-10, and lower numbers of parasites recovered from skeletal muscle. These results reveal different temporal and regulatory roles for CTLA-4 and GITR in immune responses to helminth infection.

Mechanisms of allergen-specific immunotherapy: T-regulatory cells and more

Activation-induced cell death, anergy, or immune response modulation by regulatory T cells (Treg cells) are essential mechanisms of peripheral T-cell tolerance. Genetic predisposition and environmental instructions tune thresholds for the activation of T cells, other inflammatory cells, and resident tissue cells in allergic diseases. Skewing allergen-specific effector T cells to a Treg-cell phenotype seems to be crucial in maintaining a healthy immune response to allergens and successful allergen-specific immunotherapy. The Treg-cell response is characterized by an abolished allergen-specific T-cell proliferation and the suppressed secretion of T-helper 1- and T-helper 2-type cytokines. Suppressed proliferative and cytokine responses against allergens are induced by multiple suppressor factors, including cytokines such as interleukin-10 (IL-10) and transforming growth factor beta (TGF-beta), and cell surface molecules such as cytotoxic T-lymphocyte antigen-4, programmed death-1, and histamine receptor 2. The increased levels of IL-10 and TGF-beta produced by Treg cells potently suppress IgE production while simultaneously increasing the production of noninflammatory isotypes IgG4 and IgA, respectively. In addition, Treg cells directly or indirectly suppress the activity of effector cells of allergic inflammation, such as mast cells, basophils, and eosinophils. In conclusion, peripheral tolerance to allergens is controlled by multiple active suppression mechanisms on T cells, regulation of antibody isotypes, and suppression of effector cells. The application of current knowledge of Treg cells and related mechanisms of peripheral tolerance may soon lead to more rational and safer approaches to the prevention and cure of allergic disease.

Dimorphic Plasmodium falciparum merozoite surface protein-1 epitopes turn off memory T cells and interfere with T cell priming

The leading blood-stage malaria vaccine candidate antigen, Plasmodium falciparum merozoite surface protein-1 (MSP-1) occurs in two major allelic types worldwide. The molecular basis promoting this stable dimorphism is unknown. In this study, we have shown that allelic altered peptide ligand (APL) T cell epitopes of MSP-1 mutually inhibited IFN-gamma secretion as well as proliferation of CD4+ T cells in 27/34 malaria exposed Gambian volunteers. Besides this inhibition of malaria-specific immunity, the same variant epitopes were also able to impair the priming of human T cells in malaria naive individuals. Epitope variants capable of interfering with T cell priming as well as inhibiting memory T cell effector functions offer a uniquely potent combination for immune evasion. Indeed, enhanced co-habitation of parasites bearing such antagonistic allelic epitope regions was observed in a study of 321 West African children, indicating a survival advantage for parasites able to engage this inhibitory immune interference mechanism.

Mucosal but not peripheral FOXP3+ regulatory T cells are highly increased in untreated HIV infection and normalize after suppressive HAART

Recent evidence indicates that regulatory T cells (T(regs)) play an important role in HIV infection. However, although the gastrointestinal mucosa is a key compartment in HIV disease, no data on mucosal T(regs) in HIV infection are available. In this study, we compared the frequency of T(regs) in duodenal mucosa and peripheral blood (PB) of 13 treatment-naive and 13 suppressively treated HIV-infected patients with that of 6 patients with norovirus infection and 12 healthy controls. T(regs) were quantified by immunohistochemistry (CD3/FOXP3) and further characterized (CD25, CTLA-4, GITR) by immunohistochemistry, immunofluorescence, and fluorescence-activated cell sorting (FACS). Both the frequency and the absolute count of mucosal T(regs) were highly increased in untreated HIV patients but were normal in treated HIV patients. In contrast, in peripheral blood of HIV patients, the absolute number of T(regs) was not increased, and their frequency was only slightly elevated. In norovirus infection, frequency of mucosal T(regs) in the CD4+ T-cell subset was not elevated. The high increase in count and frequency of mucosal T(regs) seems to be a characteristic feature of untreated HIV infection, suggesting a significant contribution of T(regs) to the pathogenesis of HIV disease. Their role may be 2-edged: attenuating HIV-induced immune hyperactivation while suppressing the immune response to HIV and mucosal pathogens.

Functional and Molecular Comparison of Anergic and Regulatory T Lymphocytes

Tolerance in vivo is maintained by multiple mechanisms that function to prevent autoimmunity. An encounter of CD4+ T cells with a circulating self-Ag leads to partial thymic deletion, the development of CD25+ regulatory T cells (Tregs), and functional anergy in the surviving CD25- population. We have compared anergic and regulatory T cells of the same Ag specificity generated in vivo by the systemic self-Ag. Anergic cells are unresponsive to the self-Ag that induces tolerance, but upon transfer into a new host and immunization, anergic cells can induce a pathologic autoimmune reaction against tissue expressing the same Ag. Tregs, in contrast, are incapable of mediating harmful reactions. To define the basis of this functional difference, we have compared gene expression profiles of anergic and regulatory T cells. These analyses show that Tregs express a distinct molecular signature, but anergic cells largely lack such a profile. Anergic cells express transcripts that are associated with effector differentiation, e.g., the effector cytokines IL-4 and IFN-gamma. Anergic cells do not produce these cytokines in response to self-Ag, because the cells exhibit a proximal signaling block in response to TCR engagement. Thus, anergy reflects an aborted activation pathway that can readily be reversed, resulting in pathologic effector cell responses, whereas Treg development follows a distinct developmental pathway that extinguishes effector functions.