Models of T cell anergy: is there a common molecular mechanism?

Cellular Components of the Tumor Environment in Gliomas-What Do We Know Today?

A generation ago, the molecular properties of tumor cells were the focus of scientific interest in oncology research. Since then, it has become increasingly apparent that the tumor environment (TEM), whose major components are non-neoplastic cell types, is also of utmost importance for our understanding of tumor growth, maintenance and resistance. In this review, we present the current knowledge concerning all cellular components within the TEM in gliomas, focusing on their molecular properties, expression patterns and influence on the biological behavior of gliomas. Insight into the TEM of gliomas has expanded considerably in recent years, including many aspects that previously received only marginal attention, such as the phenomenon of phagocytosis of glioma cells by macrophages and the role of the thyroid-stimulating hormone on glioma growth. We also discuss other topics such as the migration of lymphocytes into the tumor, phenotypic similarities between chemoresistant glioma cells and stem cells, and new clinical approaches with immunotherapies involving the cells of TEM.

The interplay of inflammation, exosomes and Ca2+ dynamics in diabetic cardiomyopathy

Diabetes mellitus is one of the prime risk factors for cardiovascular complications and is linked with high morbidity and mortality. Diabetic cardiomyopathy (DCM) often manifests as reduced cardiac contractility, myocardial fibrosis, diastolic dysfunction, and chronic heart failure. Inflammation, changes in calcium (Ca²⁺) handling and cardiomyocyte loss are often implicated in the development and progression of DCM. Although the existence of DCM was established nearly four decades ago, the exact mechanisms underlying this disease pathophysiology is constantly evolving. Furthermore, the complex pathophysiology of DCM is linked with exosomes, which has recently shown to facilitate intercellular (cell-to-cell) communication through biomolecules such as micro RNA (miRNA), proteins, enzymes, cell surface receptors, growth factors, cytokines, and lipids. Inflammatory response and Ca²⁺ signaling are interrelated and DCM  has been known to adversely affect many of these signaling molecules either qualitatively and/or quantitatively. In this literature review, we have demonstrated that Ca²⁺ regulators are tightly controlled at different molecular and cellular levels during various biological processes in the heart. Inflammatory mediators, miRNA and exosomes are shown to interact with these regulators, however how these mediators are linked to Ca²⁺ handling during DCM pathogenesis remains elusive. Thus, further investigations are needed to understand the mechanisms to restore cardiac Ca²⁺ homeostasis and function, and to serve as potential therapeutic targets in the treatment of DCM.

Mapping CAR T-Cell Design Space Using Agent-Based Models

Chimeric antigen receptor (CAR) T-cell therapy shows promise for treating liquid cancers and increasingly for solid tumors as well. While potential design strategies exist to address translational challenges, including the lack of unique tumor antigens and the presence of an immunosuppressive tumor microenvironment, testing all possible design choices in vitro and in vivo is prohibitively expensive, time consuming, and laborious. To address this gap, we extended the modeling framework ARCADE (Agent-based Representation of Cells And Dynamic Environments) to include CAR T-cell agents (CAR T-cell ARCADE, or CARCADE). We conducted in silico experiments to investigate how clinically relevant design choices and inherent tumor features—CAR T-cell dose, CD4⁺:CD8⁺ CAR T-cell ratio, CAR-antigen affinity, cancer and healthy cell antigen expression—individually and collectively impact treatment outcomes. Our analysis revealed that tuning CAR affinity modulates IL-2 production by balancing CAR T-cell proliferation and effector function. It also identified a novel multi-feature tuned treatment strategy for balancing selectivity and efficacy and provided insights into how spatial effects can impact relative treatment performance in different contexts. CARCADE facilitates deeper biological understanding of treatment design and could ultimately enable identification of promising treatment strategies to accelerate solid tumor CAR T-cell design-build-test cycles.

The optimized core peptide derived from CABIN1 efficiently inhibits calcineurin-mediated T-cell activation

The C-terminal fragment of CABIN1 interacts with calcineurin and represses the transcriptional activity of the nuclear factor of activated T cells (NFAT). However, the specific sequences and mechanisms through which it binds to calcineurin are unclear. This study determined that decameric peptide (CABIN1 residues 2146–2155) is minimally required for binding to calcineurin. This peptide contains a unique “PPTP” C-terminal sequence and a “PxIxIT” N-terminal motif. Furthermore, p38MAPK phosphorylated the threonine residue of the “PPTP” sequence under physiological conditions, dramatically enhancing the peptide’s binding affinity to calcineurin. Therefore, the CABIN1 peptide inhibited the calcineurin-NFAT pathway and the activation of T cells more efficiently than the VIVIT peptide without affecting calcineurin’s phosphatase activity. The CABIN1 peptide could thus be a more potent calcineurin inhibitor and provide therapeutic opportunities for various diseases caused by the calcineurin-NFAT pathway.

A peptide with therapeutic potential binds strongly to the cellular enzyme calcineurin and may prove valuable in anti-cancer and autoimmune disease treatments. Many cancers and autoimmune diseases are linked with overactivation of a key calcineurin-related pathway which is heavily involved in T cell activation. This pathway has long been a therapeutic target, but existing drugs show problems with stability and delivery, and can cause serious side effects. One known inhibitor of calcineurin is the protein CABIN1, but precisely how well it binds and how useful it may be is unclear. Now, Hong-Duk Youn at Seoul National University College of Medicine, South Korea, and co-workers have identified how one specific peptide from CABIN1 binds strongly to calcineurin. The CABIN1 peptide was stable and displayed greater efficiency at inhibiting calcineurin than another recently identified peptide candidate.

Effect of Cellular-Based Artificial Antigen Presenting Cells Expressing ICOSL, in T-cell Subtypes Differentiation and Activation

Purposes: Effective and selective T-cell activation and proliferation during the T-cell expansion phase of a cellular adoptive immunotherapy method, challenging because recent studies revealed the importance of each subtype of T-cells in different immunologic strategies against tumors, like CAR-T cell therapies. Artificial antigen presenting cells (aAPCs) regarded as a natural way to manipulate T-cell subtypes activation and specific proliferation. In the current study, we utilized K562 cells based aAPC method expressing the ICOSL molecule, to evaluate T-cell subtypes differentiation rate and functional status. Methods: CD3+T-cells isolated and, co-cultured with ICOSL expressing K562 cells. After 4, 6, and 10 days selective CD markers of T-cell subtypes and each subtype's activity-related genes levels evaluated by qPCR methods. Results: During the culture period, CD4+ Th related phenotype reduced continuously, and in day 10^th of culture CD4+ T-cell's population significantly reduced (P =0.029). In contrast, the CD8+ population ratio was ascending during the study period but was not statistically significant. FoxP3+CD25-, Treg population ratio was significantly increased during the time in comparison with the control group, as well as memory T-cell phenotypic marker, CD127+, expressing cells ratio. T-cell subpopulations activity-related genes expression levels evaluated too, and the Th1 related IL-2 and INF-γ reductions observed alongside regulatory T-cells gene (IL-10) and Cytotoxic T-cell's related gene (Geranzym-A) elevations. Conclusion: We concluded that the K562-ICOSL based aAPC system is working and effective in T-cell short to medium culture periods, and this approach preparing relatively selective milieu for CD8+ T-Cell differentiation and much less Treg differentiation.

T-Cell Molecular Modulation Responses in Atherosclerosis Anergy

Atherosclerosis continues to be a major cause of death in patients with cardiovascular diseases. The cooperative role of immunity has been recently considered in atherosclerotic plaque inflammation, especially adaptive immune response by T cells. In this review, we examine the possible role of T cells in atherosclerosis-mediated inflammation and conceivable therapeutic strategies that can ameliorate complications of atherosclerosis. The cytokines secreted by T-lymphocyte subsets, different pathophysiological profiles of microRNAs (miRs), and the growth factor/receptor axis have diverse effects on the inflammatory cycle of atherosclerosis. Manipulation of miRNA expression and prominent growth factor receptors involved in inflammatory cytokine secretion in atherosclerosis can be considered diagnostic biomarkers in the induction of anergy and blockade of atherosclerotic development. This manuscript reviews immunomodulation of T cells responses in atherosclerosis anergy.

[The ambiguous role of the inflammatory micromilieu in solid tumors]

BACKGROUND

Besides host defense against infections, the main function of the immune system is to eliminate tumor cells. Therefore, nearly, all solid tumors have a heterogeneous fibro-inflammatory microenvironment, which consists of myofibroblastic cells, extracellular matrix components, and infiltrates from various types of immune cell. In particular, pancreatic ductal adenocarcinoma is a prototype of a tumor with a pronounced inflammatory microenvironment, in which the majority of the tumor mass consists of nonneoplastic stromal and immune cells. Our own data and data from the literature indicate a protective role of tumor-infiltrating T cells for the host. On the other hand, we were able to show that a defined T cell subpopulation paradoxically promotes the progression of the tumor. Our investigations now focus on these cells, known as "Th17," in the tumor microenvironment.

OBJECTIVES

To elucidate the mechanisms of the infiltrated immune cells and their mediators in the tumor microenvironment.

MATERIALS AND METHODS

Human pancreatic cancer tissue was used for (immune) histological staining and morphometric analysis and the results were correlated with clinical parameters and with diffusion-weighted magnetic resonance imaging images. The molecular mechanisms were analyzed in cell culture approaches using human tumor cells and human immune cells. With molecular biological methods and functional assays cell growth, invasion and colony formation were assessed. The in vivo correlation of the results and functional interventions were tested in murine and avian (xenograft) models.

RESULTS AND CONCLUSION

Tumor-infiltrating immune cells of type Th17 and their mediators promoted the progression of the tumor depending on density, activation status, and cytokine profile. On molecular level, we identified a Th17-mediated increase of tumor cell migration and invasion, an increased neoangiogenesis, as well as a reorganization of the tumor stroma and microarchitecture. The data show that the progression of pancreatic cancer, depends on the status of activation and the cytokine profile of the infiltrated T cells.

Optimization of T-cell Receptor-Modified T Cells for Cancer Therapy

T-cell receptor (TCR)-modified T-cell gene therapy can target a variety of extracellular and intracellular tumor-associated antigens, yet has had little clinical success. A potential explanation for limited antitumor efficacy is a lack of T-cell activation in vivo We postulated that expression of proinflammatory cytokines in TCR-modified T cells would activate T cells and enhance antitumor efficacy. We demonstrate that expression of interleukin 18 (IL18) in tumor-directed TCR-modified T cells provides a superior proinflammatory signal than expression of interleukin 12 (IL12). Tumor-targeted T cells secreting IL18 promote persistent and functional effector T cells and a proinflammatory tumor microenvironment. Together, these effects augmented overall survival of mice in the pmel-1 syngeneic tumor model. When combined with sublethal irradiation, IL18-secreting pmel-1 T cells were able to eradicate tumors, whereas IL12-secreting pmel-1 T cells caused toxicity in mice through excessive cytokine secretion. In another xenograft tumor model, IL18 secretion enhanced the persistence and antitumor efficacy of NY-ESO-1-reactive TCR-modified human T cells as well as overall survival of tumor-bearing mice. These results demonstrate a rationale for optimizing the efficacy of TCR-modified T-cell cancer therapy through expression of IL18.See related commentary by Wijewarnasuriya et al., p. 732.

CaMKII Activity in the Inflammatory Response of Cardiac Diseases

Inflammation is a physiological process by which the body responds to external insults and stress conditions, and it is characterized by the production of pro-inflammatory mediators such as cytokines. The acute inflammatory response is solved by removing the threat. Conversely, a chronic inflammatory state is established due to a prolonged inflammatory response and may lead to tissue damage. Based on the evidence of a reciprocal regulation between inflammation process and calcium unbalance, here we described the involvement of a calcium sensor in cardiac diseases with inflammatory drift. Indeed, the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is activated in several diseases with an inflammatory component, such as myocardial infarction, ischemia/reperfusion injury, pressure overload/hypertrophy, and arrhythmic syndromes, in which it actively regulates pro-inflammatory signaling, among which includes nuclear factor kappa-B (NF-κB), thus contributing to pathological cardiac remodeling. Thus, CaMKII may represent a key target to modulate the severity of the inflammatory-driven degeneration.

Increased cystatin F levels correlate with decreased cytotoxicity of cytotoxic T cells

Background Cystatin F is a protein inhibitor of cysteine peptidases, expressed predominantly in immune cells and localised in endosomal/lysosomal compartments. In cytotoxic immune cells cystatin F inhibits both the major pro-granzyme convertases, cathepsins C and H that activate granzymes, and cathepsin L, that acts as perforin activator. Since perforin and granzymes are crucial molecules for target cell killing by cytotoxic lymphocytes, defects in the activation of either granzymes or perforin can affect their cytotoxic potential. Materials and methods Levels of cystatin F were assessed by western blot and interactions of cystatin F with cathepsins C, H and L were analysed by immunoprecipitation and confocal microscopy. In TALL-104 cells specific activities of the cathepsins and granzyme B were determined using peptide substrates. Results Two models of reduced T cell cytotoxicity of TALL-104 cell line were established, either by treatment by ionomycin or by immunosuppressive transforming growth factor beta. Reduced cytotoxicity correlated with increased levels of cystatin F and with attenuated activities of cathepsins C, H and L and of granzyme B. Co-localisation of cystatin F and cathepsins C, H and L and interactions between cystatin F and cathepsins C and H were demonstrated. Conclusions Cystatin F is designated as a possible regulator of T cell cytotoxicity, similar to its role in natural killer cells.

Multiplicity of Glucocorticoid Action in Inhibiting Allograft Rejection

Glucocorticoids (GCs) are used as immunosuppressive and antiinflammatory agents in organ transplantation and in treating autoimmune diseases and inflammatory disorders. GCs were shown to exert their antiproliferative effects directly through blockade of certain elements of an early membrane-associated signal transduction pathway, modulation of the expression of select adhesion molecules, and by suppression of cytokine synthesis and action. GCs may act indirectly by inducing lipocortin synthesis, which in turn, inhibits arachidonic acid release from membrane-bound stores, and also by inducing transforming growth factor (TGF)-β expression that subsequently blocks cytokine synthesis and T cell activation. Furthermore, by preferentially inhibiting the production of Th1 cytokines, GCs may enhance Th2 cell activity and, hence, precipitate a long-lasting state of tolerance through a preferential promotion of a Th2 cytokine-secreting profile. In exerting their antiproliferative effects, GCs influence both transcriptional and posttranscriptional events by binding their cytosolic receptor (GR), which subsequently binds the promoter region of cytokine genes on select DNA sites compatible with the GCs responsible elements (GRE) motif. In addition to direct DNA binding, GCs may also directly bind to, and hence antagonize, nuclear factors required for efficient gene expression, thereby markedly reducing transcriptional rate. The pleiotrophy of the GCs action, coupled with the diverse experimental conditions employed in assessing the GCs effects, indicate that GCs may utilize more than one mechanism in inhibiting T cell activation, and warrant careful scrutiny in assigning a mechanism by which GCs exert their antiproliferative effects. © 1998 Elsevier Science Inc.

Induction of tolerance against the arthritogenic antigen with type-II collagen peptide-linked soluble MHC class II molecules

In murine collagen-induced arthritis (CIA), self-reactive T cells can recognize peptide antigens derived from type-II collagen (CII). Activation of T cells is an important mediator of autoimmune diseases. Thus, T cells have become a focal point of study to treat autoimmune diseases. In this study, we evaluated the efficacy of recombinant MHC class II molecules in the regulation of antigen-specific T cells by using a self peptide derived from CII (CII260-274; IAGFKGEQGPKGEPG) linked to mouseI-A^q in a murine CIA model. We found that recombinant I-A^q/CII260-274 molecules could be recognized by CII-specific T cells and inhibit the same T cells in vitro. Furthermore, the development of CIA in mice was successfully prevented by in vivo injection of recombinant I-A^q/CII260-274 molecules. Thus, treatment with recombinant soluble MHC class II molecules in complex with an immunodominant self-peptide might offer a potential therapeutic for chronic inflammation in autoimmune disease such as rheumatoid arthritis. [BMB Reports 2016; 49(6): 331-336

Engagement of distinct epitopes on CD43 induces different co-stimulatory pathways in human T cells

Co‐receptors, being either co‐stimulatory or co‐inhibitory, play a pivotal role in T‐cell immunity. Several studies have indicated that CD43, one of the abundant T‐cell surface glycoproteins, acts not only as a potent co‐receptor but also as a negative regulator for T‐cell activation. Here we demonstrate that co‐stimulation of human peripheral blood (PB) T cells through two distinct CD43 epitopes recognized by monoclonal antibodies (mAb) CD43‐6E5 (T_6E5‐act) and CD43‐10G7 (T_10G7‐act) potently induced T‐cell proliferation. However, T‐cell co‐stimulation through two CD43 epitopes differentially regulated activation of nuclear factor of activated T cells (NFAT) and nuclear factor‐κB (NF‐κB) transcription factors, T‐cell cytokine production and effector function. T_6E5‐act produced high levels of interleukin‐22 (IL‐22) and interferon‐γ (IFN‐γ) similar to T cells activated via CD28 (T_CD28‐act), whereas T_10G7‐act produced low levels of inflammatory cytokines but higher levels of regulatory cytokines transforming growth factor‐β (TGF‐β) and interleukin‐35 (IL‐35). Compared with T_6E5‐act or to T_CD28‐act, T_10G7‐act performed poorly in response to re‐stimulation and further acquired a T‐cell suppressive function. T_10G7‐act did not directly inhibit proliferation of responder T cells, but formed stable heterotypic clusters with dendritic cells (DC) via CD2 to constrain activation of responder T cells. Together, our data demonstrate that CD43 is a unique and polarizing regulator of T‐cell function.

Immunoregulatory pathways following strong inflammatory processes markedly impair CD4+ T cell responses

As the research and use of immunotherapies is expanding, isolating ideal combinational strategies has become the next goal for many investigators. Vaccine therapies are also becoming one of the many combinational strategies being utilized in conjunction with immunostimulatory antibodies such as checkpoint blockade or adjuvants to stimulate immune responses. Here we review aspects of the immune responses that remain to be considered for designing future targeted therapies given the recent findings of the role of out of order T cell activation signaling. Specifically, we review some considerations in generating primary T cell responses under conditions of strong immunostimulatory signals based on recent studies completed by our group and others.

The role of CD40 ligand in systemic lupus erythematosus

CD40 ligand (CD40L, also known as CD154 or gp39) is a member of the tumor necrosis superfamily of transmembrane proteins. The interaction of CD40L on activated T cells with its receptor, CD40 on B cells, is necessary for normal immune function, including B cell differentiation, germinal center formation, and antibody isotype switching. Abnormal expressionof CD40L in patients with systemic lupus erythematosus (SLE) may contribute to autoantibody production and disease pathogenesis. Although murine models of monoclonal antibodies directed against CD40L initially showed promise, human trials either have failed to demonstrate efficacy or have been associated with adverse events. This review will summarize in vitro and murine model data and human clinical trials involving anti-CD40L monoclonal antibody.

Nanoscale Relationship Between CD4 and CD25 of T Cells Visualized with NSOM/QD-Based Dual-Color Imaging System

In this study, by using of near-field scanning optical microscopy (NSOM)/immune-labeling quantum dot (QD)-based dual-color imaging system, we achieved the direct visualization of nanoscale profiles for distribution and organization of CD4 and CD25 molecules in T cells. A novel and interesting finding was that though CD25 clustering as nanodomains were observed on the surface of CD4(+)CD25(high) regulatory T cells, these CD25 nanodomains were not co-localized with CD4 nanodomains. This result presented that the formation of these CD25 nanodomains on the surface of CD4(+)CD25(high) T cells were not associated with the response of T cell receptor (TCR)/CD3-dependent signal transduction. In contrast, on the surface of CD4(+)CD25(low) T cells, CD25 molecules distributed randomly without forming nanodomains while CD4 clustering as nanodomains can be observed; on the surface of CD8(+)CD25(+) T cells, CD25 clustering as nanodomains and co-localization with CD8 nanodomains were observed. Collectively, above these results exhibited that TCR/CD3-based microdomains were indeed required for TCR/CD3-mediated T cells activation and enhanced the immune activity of CD4(+)CD25(low) T cells or CD8(+)CD25(+) T cells. In particular, it was found that the formation of CD25 nanodomains and their segregation from TCR/CD3 microdomains were the intrinsic capability of CD4(+)CD25(high) T cells, suggesting this specific imaging feature of CD25 should be greatly associated with the regulatory activity of CD4(+)CD25(high) T cells. Importantly, this novel NSOM/QD-based dual-color imaging system will provide a useful tool for the research of distribution-function relationship of cell-surface molecules.

Therapeutic Potential of Hyporesponsive CD4(+) T Cells in Autoimmunity

The interaction between dendritic cells (DCs) and T cells is crucial on immunity or tolerance induction. In an immature or semi-mature state, DCs induce tolerance through T-cell deletion, generation of regulatory T cells, and/or induction of T-cell anergy. Anergy is defined as an unresponsive state that retains T cells in an “off” mode under conditions in which immune activation is undesirable. This mechanism is crucial for the control of T-cell responses against self-antigens, thereby preventing autoimmunity. Tolerogenic DCs (tDCs), generated in vitro from peripheral blood monocytes of healthy donors or patients with autoimmune pathologies, were shown to modulate immune responses by inducing T-cell hyporesponsiveness. Animal models of autoimmune diseases confirmed the impact of T-cell anergy on disease development and progression in vivo. Thus, the induction of T-cell hyporesponsiveness by tDCs has become a promising immunotherapeutic strategy for the treatment of T-cell-mediated autoimmune disorders. Here, we review recent findings in the area and discuss the potential of anergy induction for clinical purposes.

Expanding regulatory T cells alleviates chikungunya virus-induced pathology in mice

Chikungunya virus (CHIKV) infection is a reemerging pandemic human arboviral disease. CD4⁺ T cells were previously shown to contribute to joint inflammation in the course of CHIKV infection in mice. The JES6-1 anti-IL-2 antibody selectively expands mouse regulatory T cells (Tregs) by forming a complex with IL-2. In this study, we show that the IL-2 JES6-1-mediated expansion of Tregs ameliorates CHIKV-induced joint pathology. It does so by inhibiting the infiltration of CD4⁺ T cells due to the induction of anergy in CHIKV-specific CD4⁺ effector T cells. These findings suggest that activation of Tregs could also become an alternative approach to control CHIKV-mediated disease.

IMPORTANCE Chikungunya virus (CHIKV) has reemerged as a pathogen of global significance. Patients infected with CHIKV suffer from incapacitating joint pain that severely affects their daily functioning. Despite the best efforts, treatment is still inadequate. While T cell-mediated immunopathology in CHIKV infections has been reported, the role of regulatory T cells (Tregs) has not been explored. The JES6-1 anti-interleukin 2 (IL-2) antibody has been demonstrated to selectively expand mouse Tregs by forming a complex with IL-2. We reveal here that IL-2 JES6-1-mediated expansion of Tregs ameliorates CHIKV-induced joint pathology in mice by neutralizing virus-specific CD4⁺ effector T (Teff) cells. We show that this treatment abrogates the infiltration of pathogenic CD4⁺ T cells through induction of anergy in CHIKV-specific CD4⁺ Teff cells. This is the first evidence where the role of Tregs is demonstrated in CHIKV pathogenesis, and its expansion could control virus-mediated immunopathology.

TLR7 induces anergy in human CD4(+) T cells

The recognition of microbial patterns by Toll-like receptors (TLRs) is critical for activation of the innate immune system. Although TLRs are expressed by human CD4(+) T cells, their function is not well understood. Here we found that engagement of TLR7 in CD4(+) T cells induced intracellular calcium flux with activation of an anergic gene-expression program dependent on the transcription factor NFATc2, as well as unresponsiveness of T cells. As chronic infection with RNA viruses such as human immunodeficiency virus type 1 (HIV-1) induces profound dysfunction of CD4(+) T cells, we investigated the role of TLR7-induced anergy in HIV-1 infection. Silencing of TLR7 markedly decreased the frequency of HIV-1-infected CD4(+) T cells and restored the responsiveness of those HIV-1(+) CD4(+) T cells. Our results elucidate a previously unknown function for microbial pattern-recognition receptors in the downregulation of immune responses.

Interferon-gamma modification of mesenchymal stem cells: implications of autologous and allogeneic mesenchymal stem cell therapy in allotransplantation

Bone marrow-derived mesenchymal stem cells (MSC) have unique immunomodulatory and reparative properties beneficial for allotransplantation cellular therapy. The clinical administration of autologous or allogeneic MSC with immunosuppressive drugs is able to prevent and treat allograft rejection in kidney transplant recipients, thus supporting the immunomodulatory role of MSC. Interferon-gamma (IFN-γ) is known to enhance the immunosuppressive properties of MSC. IFN-γ preactivated MSC (MSC-γ) directly or indirectly modulates T cell responses by enhancing or inducing MSC inhibitory factors. These factors are known to downregulate T cell activation, enhance T cell negative signalling, alter T cells from a proinflammatory to an anti-inflammatory phenotype, interact with antigen-presenting cells and increase or induce regulatory cells. Highly immunosuppressive MSC-γ with increased migratory and reparative capacities may aid tissue repair, prolong allograft survival and induce allotransplant tolerance in experimental models. Nevertheless, there are contradictory in vivo observations related to allogeneic MSC-γ therapy. Many studies report that allogeneic MSC are immunogenic due to their inherent expression of major histocompatibility (MHC) molecules. Enhanced expression of MHC in allogeneic MSC-γ may increase their immunogenicity and this can negatively impact allograft survival. Therefore, strategies to reduce MSC-γ immunogenicity would facilitate "off-the-shelf" MSC therapy to efficiently inhibit alloimmune rejection and promote tissue repair in allotransplantation. In this review, we examine the potential benefits of MSC therapy in the context of allotransplantation. We also discuss the use of autologous and allogeneic MSC and the issues associated with their immunogenicity in vivo, with particular focus on the use of enhanced MSC-γ cellular therapy.

TCR stimulation without co-stimulatory signals induces expression of "tolerogenic" genes in memory CD4 T cells but does not compromise cell proliferation

Memory T cells resist co-stimulatory blockade and present a unique therapeutic challenge in transplantation and autoimmune diseases. Herein, we determined whether memory T cells express less "tolerogenic" genes than naïve T cells to reinforce a proliferative response under the deprivation of co-stimulatory signals. The expression of ∼40 tolerogenic genes in memory and naïve CD4(+) T cells was thus assessed during an in vitro TCR stimulation without co-stimulation. Briefly, upon TCR stimulation with an anti-CD3 mAb alone, memory CD4(+) T cells exhibited more proliferation than naïve CD4(+) T cells. To our surprise, at 24h upon anti-CD3 mAb stimulation, memory CD4(+) T cells expressed more than a 5-fold higher level of the transcription factor Egr2 and a 20-fold higher level of the transmembrane E3 ubiquitin ligase GRAIL than those in naïve T cells. Hence, the high-level expression of tolerogenic genes, Egr2 and GRAIL, in memory CD4(+) T cells does not prevent cell proliferation. Importantly, anti-CD3 mAb-stimulated memory CD4(+) T cells expressed high protein/gene levels of phosphorylated STAT5, Nedd4, Bcl-2, and Bcl-XL. Therefore, co-stimulation-independent proliferation of memory CD4(+) T cells may be due to elevated expression of molecules that support cell proliferation and survival, but not lack of tolerogenic molecules.

Integrating canonical and metabolic signalling programmes in the regulation of T cell responses

Over the past decade, our understanding of T cell activation, differentiation and function has markedly expanded, providing a greater appreciation of the signals and pathways that regulate these processes. It has become clear that evolutionarily conserved pathways that regulate stress responses, metabolism, autophagy and survival have crucial and specific roles in regulating T cell responses. Recent studies suggest that the metabolic pathways involving MYC, hypoxia-inducible factor 1α (HIF1α), AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) are activated upon antigen recognition and that they are required for directing the consequences of T cell receptor engagement. The purpose of this Review is to provide an integrated view of the role of these metabolic pathways and of canonical T cell signalling pathways in regulating the outcome of T cell responses.

Novel CD3-specific antibody induces immunosuppression via impaired phosphorylation of LAT and PLCγ1 following T-cell stimulation

The activation of T cells is known to be accompanied by the temporary downmodulation of the TCR/CD3 complex on the cell surface. Here, we established a novel monoclonal antibody, Dow2, that temporarily induces downmodulation of the TCR/CD3 complex in mouse CD4(+) T cells without activating T cells. Dow2 recognized the determinant on CD3ε; however, differences were observed in the binding mode between Dow2 and the agonistic anti-CD3ε Ab, 145-2C11. An injection of Dow2 in vivo resulted in T-cell anergy, and prolonged the survival of cardiac allografts without a marked increase in cytokine release. The phosphorylated forms of the signaling proteins PLC-γ1 and LAT in Dow2-induced anergic T cells were markedly decreased upon stimulation. However, the levels of phosphorylated LAT and PLCγ1 in Dow2-induced anergic T cells could be rescued in the presence of the proteasome inhibitor MG-132. These results suggest that proteasome-mediated degradation is involved in hypophosphorylated LAT and PLCγ1 in Dow2-induced anergic T cells. The novel CD3-specific Ab, Dow2, may provide us with a unique tool for inducing immunosuppression.

Modulation of the human T cell response by a novel non-mitogenic anti-CD3 antibody

The agonistic anti-human CD3ε antibody (Ab), OKT3, has been used to control acute transplant rejection. The in vivo administration of OKT3 was previously shown to induce the partial depletion of T cells and unresponsiveness (anergy) in the remaining CD4⁺ T cells. However, this therapy is also associated with the systemic release of several cytokines, which leads to a series of adverse side effects. We established a novel anti-human CD3ε Ab, 20-2b2, which recognized a close, but different determinant on the CD3ε molecule from that recognized by OKT3. 20-2b2 was non-mitogenic for human CD4⁺ T cells, could inhibit the activation of T cells in vitro, and induced T cell anergy in in vivo experiments using humanized mice. Cytokine release in humanized mice induced by the administration of 20-2b2 was significantly less than that induced by OKT3. Our results indicated that the CD3ε molecule is still an attractive, effective, and useful target for the modulation of T cell responses. The establishment of other Abs that recognize CD3ε, even though the determinant recognized by those Abs may be close to or different from that recognized by OKT3, may represent a novel approach for the development of safer Ab therapies using anti-CD3 Abs, in addition to the modification of OKT3 in terms of the induction of cytokine production.

Mechanisms Underlying CD4+ Treg Immune Regulation in the Adult: From Experiments to Models

To maintain immunological balance the organism has to be tolerant to self while remaining competent to mount an effective immune response against third-party antigens. An important mechanism of this immune regulation involves the action of regulatory T-cell (Tregs). In this mini-review, we discuss some of the known and proposed mechanisms by which Tregs exert their influence in the context of immune regulation, and the contribution of mathematical modeling for these mechanistic studies. These models explore the mechanisms of action of regulatory T cells, and include hypotheses of multiple signals, delivered through simultaneous antigen-presenting cell (APC) conjugation; interaction of feedback loops between APC, Tregs, and effector cells; or production of specific cytokines that act on effector cells. As the field matures, and competing models are winnowed out, it is likely that we will be able to quantify how tolerance-inducing strategies, such as CD4-blockade, affect T-cell dynamics and what mechanisms explain the observed behavior of T-cell based tolerance.

A breath of fresh aire

The origin and function of extrathymic Aire-expressing cells (eTACs) is incompletely defined. In this issue of Immunity, Gardner et al. (2013) show that eTACs are a distinct tolerogenic cell population that functionally inactivates CD4⁺ T cells to induce peripheral tolerance.

Casitas B lineage lymphoma b is a key regulator of peripheral tolerance in systemic lupus erythematosus

OBJECTIVE

To analyze whether the expression and modulation of T cell receptor (TCR) signaling is dependent on Casitas B lineage lymphoma b (Cbl-b) in T cells from patients with systemic lupus erythematosus (SLE) upon stimulation with a tolerogenic substance.

METHODS

Peripheral blood mononuclear cells were obtained from 20 patients with SLE (active disease or in remission) and 20 healthy controls. Levels of Cbl-b expression were measured using reverse transcription-polymerase chain reaction and Western blotting in peripheral CD4+ T cells from SLE patients and healthy controls upon anergy induction. Cell proliferation was measured using the carboxyfluorescein diacetate succinimidyl ester dilution method. Cytokine production was analyzed by luminometry, and surface expression of activation markers was assessed by flow cytometry. Transfection assays were performed to induce overexpression of Cbl-b, and phosphorylation of TCR-associated kinases was evaluated.

RESULTS

CD4+ T cells from SLE patients displayed resistance to anergy (as evidenced by increased cell proliferation, interleukin-2 production, and expression of activation and costimulatory markers), and this was associated with altered Cbl-b expression. Upon ionomycin treatment, primary T cells showed enhanced MAPK activity and decreased Akt phosphorylation, which was representative of the anergic state. In T cells from lupus patients, Cbl-b overexpression led to increased expression of phosphorylated MAPK, thus indicating the reversibility of anergy resistance.

CONCLUSION

These findings suggest that abnormal peripheral tolerance in SLE is caused by a deficiency in Cbl-b, and that this ubiquitin ligase plays a key role in regulating TCR signaling during the induction of peripheral tolerance.

Human iPS cell-derived hematopoietic progenitor cells induce T-cell anergy in in vitro-generated alloreactive CD8(+) T cells

Human induced pluripotent stem cells (iPSCs) have emerged as an alternative source of pluripotent stem cells that can be used for tissue regeneration in place of the controversial human embryonic stem cells. However, immunologic knowledge about iPSC derivatives remains enigmatic. Here, we characterized human iPS-derived CD34(+) hematopoietic progenitor cells (HPCs). These HPCs poorly express major histocompatibility complex (MHC) I antigens and are MHC-II negative. Interestingly, they moderately express nonclassical HLA-G and HLA-E molecules. Consequently, alloreactive HLA-A2-specific cytotoxic T cells failed to recognize HLA-A2-expressing HPCs but became anergic. Subsequent upregulation of MHC-I using interferon-γ stimulation and provision of CD28 cosignaling led to T-cell activation, confirming that poor delivery of signals 1 and 2 by the HPCs mediated T-cell anergy. These data indicate for the first time that HPCs induce T-cell anergy, a unique characteristic of iPSC-derived cells that confers immunologic advantage for allogenic transplantation. Although iPSCs are ideal for patient-tailored treatments with the anticipation that no immunosuppression will be required, in cases of gene defects, their derivatives could be used to treat diseases in nonhistocompatible recipients.

Phenolic-glycolipid-1 and lipoarabinomannan preferentially modulate TCR- and CD28-triggered proximal biochemical events, leading to T-cell unresponsiveness in mycobacterial diseases

BACKGROUND

Advanced stages of leprosy show T cell unresponsiveness and lipids of mycobacterial origin are speculated to modulate immune responses in these patients. Present study elucidates the role of phenolicglycolipid (PGL-1) and Mannose-capped lipoarabinomannan (Man-LAM) on TCR- and TCR/CD28- mediated signalling.

RESULTS

We observed that lipid antigens significantly inhibit proximal early signalling events like Zap-70 phosphorylation and calcium mobilization. Interestingly, these antigens preferentially curtailed TCR-triggered early downstream signalling events like p38 phosphorylation whereas potentiated that of Erk1/2. Further, at later stages inhibition of NFAT binding, IL-2 message, CD25 expression and T-cell blastogenesis by PGL-1 and Man-LAM was noted.

CONCLUSION

Altogether, we report that Man-LAM and PGL-1 preferentially interfere with TCR/CD28-triggered upstream cell signalling events, leading to reduced IL-2 secretion and T-cell blastogenesis which potentially could lead to immunosupression and thus, disease exacerbation, as noted in disease spectrum.

Subtle changes in TCRα CDR1 profoundly increase the sensitivity of CD4 T cells

Changes in the peptide and MHC molecules have been extensively examined for how they alter T cell activation, but many fewer studies have examined the TCR. Structural studies of how TCR differences alter T cell specificity have focused on broad variation in the CDR3 loops. However, changes in the CDR1 and 2 loops can also alter TCR recognition of pMHC. In this study we focus on two mutations in the CDR1α loop of the TCR that increased the affinity of a TCR for agonist Hb(64-76)/I-E(k) by increasing the on-rate of the reaction. These same mutations also conferred broader recognition of altered peptide ligands. TCR transgenic mice expressing the CDR1α mutations had altered thymic selection, as most of the T cells were negatively selected compared to T cells expressing the wildtype TCR. The few T cells that escaped negative selection and were found in the periphery were rendered anergic, thereby avoiding autoimmunity. T cells with the CDR1α mutations were completely deleted in the presence of Hb(64-76) as an endogenous peptide. Interestingly, the wildtype T cells were not eliminated, identifying a threshold affinity for negative selection where a 3-fold increase in affinity is the difference between incomplete and complete deletion. Overall, these studies highlight how small changes in the TCR can increase the affinity of TCR:pMHC but with the consequences of skewing selection and producing an unresponsive T cell.

Magnitude of stimulation dictates the cannabinoid-mediated differential T cell response to HIVgp120

Approximately 25% of immunocompromised HIV patients smoke marijuana for its putative therapeutic benefit. The goal of these studies was to test the hypothesis that marijuana-derived cannabinoids have immunomodulatory effects on HIV antigen-specific T cell effector function. A surrogate mouse model to induce polyclonal T cell responses against HIV(gp120) was established. THC, a marijuana-derived cannabinoid, suppressed or enhanced mouse CD8(+) T cell proliferation and the gp120-specific CTL response depending on the magnitude of the IFN-γ response. To determine the molecular mechanisms by which cannabinoids differentially modulate T cell responses, P/I or anti-CD3/CD28 antibodies were used for stimulation, and another marijuana-derived cannabinoid, CBD, was also investigated. THC or CBD suppressed or enhanced IFN-γ and IL-2 production by mouse splenocytes under optimal or suboptimal stimulation, respectively. Similar differential effects of cannabinoids on cytokine production were also observed on nuclear translocation of NFAT and with human PBMCs in response to P/I stimulation. However, THC and CBD elevated intracellular calcium, regardless of the stimulation level with P/I, suggesting that the cannabinoid-induced calcium increase provides an appropriate signal for activation in suboptimally stimulated T cells but an anergic-like signal as a result of excessive calcium in optimally stimulated T cells. Overall, these data demonstrate differential modulation by cannabinoids of a HIV antigen-specific response and identify a possible mechanism responsible for this effect.

Poxviral vectors for cancer immunotherapy

INTRODUCTION

Poxviral vaccines have been given to over 1 billion people in the successful global eradication of smallpox. Recombinant poxviruses have been investigated extensively as a novel immunotherapy for cancer, undergoing several iterations to optimize their immunogenicity and efficacy. The current platform expressing multiple costimulatory molecules plus a tumor-associated antigen such as PSA, that is, PSA-TRICOM (PROSTVAC-V/F), is promising and is currently in a Phase III randomized, placebo-controlled clinical trial in metastatic castration-resistant prostate cancer.

AREAS COVERED

This review discusses the clinical development of poxviral-based cancer vaccines, with a particular focus on the rationale for combining vaccines with other treatment modalities, including radiotherapy, chemotherapy, hormonal therapy, other immune-based therapies and molecularly targeted therapy. We also discuss the importance of appropriate patient selection in clinical trial design.

EXPERT OPINION

Preclinical and early clinical studies employing poxviral-vector vaccines have shown promising results with this novel immunologic approach, both alone and combined with other therapies. The challenges of translating the science of immunotherapy to clinical practice include clinical trial design that includes appropriate patient selection, appropriate end points and identification of meaningful surrogate biomarkers.

Differences in phosphorylation patterns of intracellular signaling proteins in T cells from kidney transplant patients with different outcomes

Transplant patients with long-term graft survival (LTS) may have developed mechanisms that prevent rejection and allow graft function under low or no immunosuppressive therapy. In murine models, T cell tolerance is associated with alterations in the expression/activation of proteins involved in T cell signaling. These alterations have not been reported in transplanted patients with different outcomes. This study aimed to evaluate calcium mobilization, the phosphorylation of different proteins involved in T cell signaling and the expression of molecules associated with anergy, in T cells from kidney transplant patients. No differences were observed in calcium mobilization, although transplanted patients had a tendency toward augmented calcium flux. Chronic rejection patients (ChrRx) displayed lower Lck basal phosphorylation levels compared with LTS patients, and the phosphorylation profile of proteins evaluated was different. Among the groups, phosphorylation of Zap-70 was higher in LTS patients compared with ChrRx, and LAT phosphorylation was lower in LTS and ChrRx patients compared with healthy controls. The expression of molecules related to the anergic phenotype was similar among the study groups. Results suggest that phosphorylation patterns, rather than phosphorylation levels, may correlate with transplant outcome and that anergy may not be the main mechanism mediating LTS.

T-cell activation and transplantation tolerance

Transplantation of allogeneic or "nonself" tissues stimulates a robust immune response leading to graft rejection, and therefore, most recipients of allogeneic organ transplants require the lifelong use of immune suppressive agents. Excellent outcomes notwithstanding, contemporary immunosuppressive medications are toxic, are often not taken by patients, and pose long-term risks of infection and malignancy. The ultimate goal in transplantation is to develop new treatments that will supplant the need for general immunosuppression. Here, we will describe the development and application of costimulation blockade to induce transplantation tolerance and discuss how the diverse array of signals that act on T cells will determine the balance between graft survival and rejection.

Antigen-specific versus antigen-nonspecific immunotherapeutic approaches for human melanoma: the need for integration for optimal efficacy?

Due to its immunogenecity and evidence of immune responses resulting in tumor regression, metastatic melanoma has been the target for numerous immunotherapeutic approaches. Unfortunately, based on the clinical outcomes, even the successful induction of tumor-specific responses does not correlate with efficacy. Immunotherapies can be divided into antigen-specific approaches, which seek to induce T cells specific to one or several known tumor associated antigens (TAA), or with antigen-nonspecific approaches, which generally activate T cells to become nonspecifically lytic effectors. Here the authors critically review the different immunotherapeutic approaches in melanoma.

MHC class II expression in pancreatic tumors: a link to intratumoral inflammation

Major histocompatibility complex class II antigens (MHC class II) are constitutively expressed by professional antigen presenting cells and present antigenic peptides to specific CD4+ T lymphocytes. MHC class II expression, however, can also be induced on epithelial cells and in a variety of solid tumors. We tested MHC class II expression on tissue samples derived from patients with pancreatic ductal adenocarcinoma (PDAC) and pancreatic endocrine tumors (PET). Immunohistochemistry revealed MHC class II expression in 86 of 112 (76.8%) PDAC samples and in 30 of 43 (70.0%) PET samples. In PDAC and PET, MHC class II expression correlated significantly with severity and activity of intratumoral inflammation, as well as with the infiltration of CD4+ T lymphocytes. High MHC class II expression significantly correlated with a better histological grade of differentiation in PDAC. In vitro MHC class II expression could be induced on PDAC tumor cell lines by interferon-γ. These cells were then able to present the staphylococci enterotoxin B superantigen to T lymphocytes, which resulted in T cell proliferation. Our findings suggest that MHC class II expression on pancreatic tumor cells is induced by the intratumoral inflammatory reaction in pancreatic tumors.

A perspective on non-catalytic Src homology (SH) adaptor signalling proteins

Intracellular adaptor signalling proteins are members of a large family of mediators crucial for signal transduction pathways. Structurally, these molecules contain one Src Homology 2 (SH2) domain and one or more Src Homology 3 (SH3) domain(s); with either a catalytic subunit, or with other non-catalytic modular subunits. Cells depend on these regulatory signalling molecules to transmit information to the nucleus from both external and internal cues including growth factors, cytokines and steroids. Although there is a vast library of adaptor signalling proteins expressed ubiquitously in cells, the vital role these SH containing proteins play in regulating cellular signalling lacks the recognition they deserve. Their target selection method via the SH domains is simple yet highly effective. The SH3 domain(s) interact with proteins that contain proline-rich motifs, whereas the SH2 domain only binds to proteins containing phosphotyrosine residues. This unique characteristic physically enables proteins from a diverse range of networks to assemble for amplification of a signalling event. The biological consequence generated from these adaptor signalling proteins in a constantly changing microenvironment have profound regulatory effect on cell fate decision particularly when this is involved in the progression of a diseased state.

Regulatory T cell therapy for the induction of clinical organ transplantation tolerance

The pursuit of transplantation tolerance is the holygrail in clinical organ transplantation. It has been established that regulatory T cells (Tregs) can confer donor-specific tolerance in mouse models of transplantation. However, this is crucially dependent on the strain combination, the organ transplanted and most importantly, the ratio of Tregs to alloreactive effector T cells. The ex vivo expansion of Tregs is one solution to increase the number of alloantigen specific cells capable of suppressing the alloresponse. Indeed, ex vivo expanded, alloantigen specific murine Tregs are shown to preferentially migrate to, and proliferate in, the graft and draining lymph node. In human transplantation it has been proposed that depletion of the majority of direct pathway alloreactive T cells will be required to tip the balance in favour of regulation. Ex vivo expansion of alloantigen specific, indirect pathway human Tregs, which can cross regulate the residual direct pathway has been established. Rapid expansion of these cells is possible, whilst they retain antigen specificity, suppressive properties and favourable homing markers. Furthermore, considerable progress has been made to define which immunosuppressive drugs favour the expansion and function of Tregs. Currently a series of clinical trials of adoptive Treg therapy in combination with depletion of alloreactive T cells and short term immunosuppression are underway for human transplantation with the aim of minimizing immunosuppressive drugs and completely withdrawal.

Impairment of immunological synapse formation in adaptively tolerant T cells

Adaptive tolerance is a hyporesponsive state in which lymphocyte Ag receptor signaling becomes desensitized after prolonged in vivo encounter with Ag. The molecular mechanisms underlying this hyporesponsive state in T cells are not fully understood, although a major signaling block has been shown to be present at the level of ZAP70 phosphorylation of linker for activation of T cells (LAT). In this study, we investigated the ability of adaptively tolerant mouse T cells to form conjugates with Ag-bearing APCs and to translocate signaling molecules into the interface between the T cells and APCs. Compared with naive or preactivated T cells, adaptively tolerant T cells showed no dramatic impairment in their formation of conjugates with APCs. In contrast, there was a large impairment in immunological synapse formation. Adaptively tolerant T cells were defective in their translocation of signaling molecules, such as ZAP70, LAT, and phospholipase C γ1, into the T cell-APC contact sites. Although Ag-induced activation of VAV1 was normal, VAV's recruitment into the synapse was also impaired. Interestingly, expressions of both IL-2-inducible T cell kinase and growth factor receptor-bound protein 2-related adaptor downstream of SHC were decreased by 60-80% in adaptively tolerant T cells. These decreases, in addition to the impairment in LAT phosphorylation by ZAP70, appear to be the major impediments to the phosphorylation of SLP76 (SRC homology 2 domain-containing leukocyte protein of 76 kDa) and the recruitment of VAV1, which are important for stable immunological synapse formation.

Invariant NKT cell anergy is induced by a strong TCR-mediated signal plus co-stimulation

Vα14 TCR expressing invariant NK T (iNKT) cells recognize α-galactosylceramide (αGC)/CD1d complex and produce large amounts of various cytokines before the onset of the adaptive immunity. After stimulation with a high dose (2-5 μg) of αGC in vivo, iNKT cells in the spleen and liver become anergic in terms of the proliferation and cytokine production to subsequent stimulation. In this study, we monitor how iNKT anergy is induced. Anergized iNKT cells dramatically reduced the expression of IL-2Rα, and exogenous IL-2 restored the ability to proliferate and produce IL-4 but not to produce IFN-γ. Anergized iNKT cells expressed high levels of programmed death-1 (PD-1). However, iNKT cells in PD-1-deficient mice became anergic as a result of αGC injection, as do normal mice. Furthermore, anti-PD-1 blocking mAb was unable to restore their responsiveness. When iNKT cells were stimulated with immobilized anti-CD3 in the presence or absence of anti-CD28, they produced cytokines in a dose-dependent manner. Unlike in naive CD4 T cells, the strong TCR-mediated signaling with co-stimulation renders them anergic to any subsequent stimulation with αGC and spleen dendritic cells (DCs). Moreover, iNKT cells also became anergic after stimulation with phorbol-12-myristate-13-acetate + ionophore. Finally, the injection of αGC-pulsed DCs was more potent in inducing anergy than B cells. These results indicate that strong TCR-mediated activation with co-stimulation provides signals that induce the anergic state in iNKT cells.

TCR-like antibodies distinguish conformational and functional differences in two- versus four-domain auto reactive MHC class II-peptide complexes

Antigen-presenting cell-associated four-domain MHC class II (MHC-II) molecules play a central role in activating autoreactive CD4(+) T cells involved in multiple sclerosis (MS) and type 1 diabetes (T1D). In contrast, two-domain MHC-II structures with the same covalently attached self-peptide (recombinant T-cell receptor ligands (RTLs)) can regulate pathogenic CD4(+) T cells and reverse clinical signs of experimental autoimmune diseases. RTL1000, which is composed of the β1α1 domains of human leukocyte antigen (HLA)-DR2 linked to the encephalitogenic human myelin oligodendrocyte glycoprotein (MOG)-35-55 peptide, was recently shown to be safe and well tolerated in a phase I clinical trial in MS. To evaluate the opposing biological effects of four- versus two-domain MHC-II structures, we screened phage Fab antibodies (Abs) for the neutralizing activity of RTL1000. Five different TCR-like Abs were identified that could distinguish between the two- versus four-domain MHC-peptide complexes while the cognate TCR was unable to make such a distinction. Moreover, Fab detection of native two-domain HLA-DR structures in human plasma implies that there are naturally occurring regulatory MHC-peptide complexes. These results demonstrate for the first time distinct conformational determinants characteristic of activating versus tolerogenic MHC-peptide complexes involved in human autoimmunity.

IL-35-mediated induction of a potent regulatory T cell population

Regulatory T cells (T(reg) cells) have a critical role in the maintenance of immunological self-tolerance. Here we show that treatment of naive human or mouse T cells with IL-35 induced a regulatory population, which we call 'iT(R)35 cells', that mediated suppression via IL-35 but not via the inhibitory cytokines IL-10 or transforming growth factor-β (TGF-β). We found that iT(R)35 cells did not express or require the transcription factor Foxp3, and were strongly suppressive and stable in vivo. T(reg) cells induced the generation of iT(R)35 cells in an IL-35- and IL-10-dependent manner in vitro and induced their generation in vivo under inflammatory conditions in intestines infected with Trichuris muris and within the tumor microenvironment (B16 melanoma and MC38 colorectal adenocarcinoma), where they contributed to the regulatory milieu. Thus, iT(R)35 cells constitute a key mediator of infectious tolerance and contribute to T(reg) cell-mediated tumor progression. Furthermore, iT(R)35 cells generated ex vivo might have therapeutic utility.

Interferon gamma licensing of human dendritic cells in T-helper-independent CD8+ alloimmunity

The high frequency of allogeneic reactive CD8(+) T cells in human and their resistance to immunosuppression might be one of the reasons why successful tolerance-inducing strategies in rodents have failed in primates. Studies on the requirement for T-helper cells in priming CD8(+) T-cell responses have led to disparate findings. Recent studies have reported CD8(+)-mediated allograft rejection independently of T-helper cells; however, the mechanisms that govern the activation of these T cells are far from being elucidated. In this study, we demonstrated that lipopolysaccharide-treated dendritic cells (DCs) were able to induce proliferation and cytotoxic activity of allogeneic CD8(+) T cells independently of CD4(+) T cells, while adding mycophenolic acid (MPA) to LPS abolished this capacity and resulted in anergic CD8(+) T cells that secreted high levels of interleukin-4 (IL-4), IL-5, IL-10, and transforming growth factor-β. Interestingly, we demonstrated that MPA inhibited the LPS-induced synthesis of tumor necrosis factor-α, IL-12, and interferon-γ (IFN-γ) in DCs. Importantly, we found that adding exogenous IFN-γ to MPA restored both the synthesis of cytokines and the ability to activate CD8(+) T cells. However, adding IL-12 or tumor necrosis factor-α had no effect. These results suggest that IFN-γ has an important role in licensing DCs to prime CD4-independent CD8 allogeneic T cells via an autocrine loop.

Grb2, a simple adapter with complex roles in lymphocyte development, function, and signaling

Lymphocyte development, activation, and tolerance depend on antigen receptor signaling transduced via multiple intracellular signalosomes. These signalosomes are assembled by different adapters. Given that signaling molecules can be either positive or negative regulators for a biochemical target, the complex of a target with different regulator may dictate the final signaling outcome. Grb2 is a simple adapter known to be involved in a variety of growth factor receptor signaling. However, its role in antigen receptor signaling as well as lymphocyte development and function has emerged only recently. Despite its simple molecular structure, recent experiments show that Grb2 may play a complex role in T and B-cell antigen receptor signaling. In this article, we review recent findings about the physiological role of Grb2 in T and B-cell development and activation and summarize the current mechanistic understanding of how Grb2 exerts its function following T and B-cell antigen receptor stimulation.

Allergen-specific subcutaneous immunotherapy in allergic asthma: immunologic mechanisms and improvement

Allergic asthma is a disease characterized by persistent allergen-driven airway inflammation, remodeling, and airway hyperresponsiveness. CD4(+) T-cells, especially T-helper type 2 cells, play a critical role in orchestrating the disease process through the release of the cytokines IL-4, IL-5, and IL-13. Allergen-specific immunotherapy (SIT) is currently the only treatment with a long-term effect via modifying the natural course of allergy by interfering with the underlying immunological mechanisms. However, although SIT is effective in allergic rhinitis and insect venom allergy, in allergic asthma it seldom results in complete alleviation of the symptoms. Improvement of SIT is needed to enhance its efficacy in asthmatic patients. Herein, the immunoregulatory mechanisms underlying the beneficial effects of SIT are discussed with the ultimate aim to improve its treatment efficacy.