CD28, Ox-40, LFA-1, and CD4 modulation of Th1/Th2 differentiation is directly dependent on the dose of antigen

The Role of OX40-OX40L Axis in the Pathogenesis of Atopic Dermatitis

OX40 is a co-stimulatory immune checkpoint molecule that promotes the activation and the effector function of T lymphocytes through interaction with its ligand (OX40L) on antigen-presenting cells. OX40-OX40L axis plays a crucial role in Th1 and Th2 cell expansion, particularly during the late phases or long-lasting response. Atopic dermatitis is characterized by an immune dysregulation of Th2 activity and by an overproduction of proinflammatory cytokines such as interleukin (IL)-4 and IL-13. Other molecules involved in its pathogenesis include thymic stromal lymphopoietin, IL-33, and IL-25, which contribute to the promotion of OX40L expression on dendritic cells. Lesional skin in atopic dermatitis exhibits a higher level of OX40L+-presenting cells compared with other dermatologic diseases or normal skin. Recent clinical trials using antagonizing anti-OX40 or anti-OX40L antibodies have shown symptom improvement and cutaneous manifestation alleviation in patients with atopic dermatitis. These findings suggest the relevance of the OX40-OX40L axis in atopic dermatitis pathogenesis.

IgE-mediated regulation of IL-10 and type I IFN enhances rhinovirus-induced Th2 differentiation by primary human monocytes

Rhinovirus (RV) infections are linked to the development and exacerbation of allergic diseases including allergic asthma. IgE, another contributor to atopic disease pathogenesis, has been shown to regulate DC antiviral functions and influence T cell priming by monocytes. We previously demonstrated that IgE-mediated stimulation of monocytes alters multiple cellular functions including cytokine secretion, phagocytosis, and influenza-induced Th1 development. In this study, we investigate the effects of IgE-mediated stimulation on monocyte-driven, RV-induced T cell development utilizing primary human monocyte-T cell co-cultures. We demonstrate that IgE crosslinking of RV-exposed monocytes enhances monocyte-driven Th2 differentiation. This increase in RV-induced Th2 development was regulated by IgE-mediated inhibition of virus-induced type I IFN and induction of IL-10. These findings suggest an additional mechanism by which two clinically significant risk factors for allergic disease exacerbations-IgE-mediated stimulation and rhinovirus infection-may synergistically promote Th2 differentiation and allergic inflammation.

Combination of PD-1 Inhibitor and OX40 Agonist Induces Tumor Rejection and Immune Memory in Mouse Models of Pancreatic Cancer

BACKGROUND & AIMS

Advanced pancreatic ductal adenocarcinoma (PDAC) is resistant to therapy, including immune checkpoint inhibitors. We evaluated the effects of a neutralizing antibody against programmed cell death 1 (PD-1) and an agonist of OX40 (provides a survival signal to activated T cells) in mice with pancreatic tumors.

METHODS

We performed studies in C57BL/6 mice (controls), Kras^G12D/+;Trp53^R172H/+;Pdx-1-Cre (KPC) mice, and mice with orthotopic tumors grown from Panc02 cells, Kras^G12D;P53^flox/flox;PDX-1-Cre;Luciferase (KPC-Luc) cells, or mT4 cells. After tumors developed, mice were given injections of control antibody or anti-OX40 and/or anti-PD-1 antibody. Some mice were then given injections of antibodies against CD8, CD4, or NK1.1 to deplete immune cells, and IL4 or IL7RA to block cytokine signaling. Bioluminescence imaging was used to monitor tumor growth. Tumor tissues collected and single-cell suspensions were analyzed by time of flight mass spectrometry analysis. Mice that were tumor-free 100 days after implantation of orthotopic tumors were rechallenged with PDAC cells (KPC-Luc or mT4) and survival was measured. Median levels of PD-1 and OX40 mRNAs in PDACs were determined from The Cancer Genome Atlas and compared with patient survival times.

RESULTS

In mice with orthotopic tumors, all those given control antibody or anti-PD-1 died within 50 days, whereas 43% of mice given anti-OX40 survived for 225 days; almost 100% of mice given the combination of anti-PD-1 and anti-OX40 survived for 225 days, and tumors were no longer detected. KPC mice given control antibody, anti-PD-1, or anti-OX40 had median survival times of 50 days or less, whereas mice given the combination of anti-PD-1 and anti-OX40 survived for a median 88 days. Mice with orthotopic tumors that were given the combination of anti-PD-1 and anti-OX40 and survived 100 days were rechallenged with a second tumor; those rechallenged with mT4 cells survived an additional median 70 days and those rechallenged with KPC-Luc cells survived long term, tumor free. The combination of anti-PD-1 and anti-OX40 did not slow tumor growth in mice with antibody-mediated depletion of CD4+ T cells. Mice with orthotopic tumors given the combination of anti-PD-1 and anti-OX40 that survived after complete tumor rejection were rechallenged with KPC-Luc cells; those with depletion of CD4+ T cells before the rechallenge had uncontrolled tumor growth. Furthermore, KPC orthotopic tumors from mice given the combination contained an increased number of CD4+ T cells that expressed CD127 compared with mice given control antibody. The combination of agents reduced the proportion of T-regulatory and exhausted T cells and decreased T-cell expression of GATA3; tumor size was negatively associated with numbers of infiltrating CD4+ T cells, CD4+CD127+ T cells, and CD8+CD127+ T cells, and positively associated with numbers of CD4+PD-1+ T cells, CD4+CD25+ T cells, and CD8+PD-1+ T cells. PDACs with high levels of OX40 and low levels of PD-1 were associated with longer survival times of patients.

CONCLUSIONS

Pancreatic tumors appear to evade the immune response by inducing development of immune-suppressive T cells. In mice, the combination of anti-PD-1 inhibitory and anti-OX40 agonist antibodies reduces the proportion of T-regulatory and exhausted T cells in pancreatic tumors and increases numbers of memory CD4+ and CD8+ T cells, eradicating all detectable tumor. This information can be used in development of immune-based combination therapies for PDAC.

Role of Co-stimulatory Molecules in T Helper Cell Differentiation

CD4⁺ T cells play a central role in orchestrating the immune response to a variety of pathogens but also regulate autoimmune responses, asthma, allergic responses, as well as tumor immunity. To cover this broad spectrum of responses, naïve CD4⁺ T cells differentiate into one of several lineages of T helper cells, including Th1, Th2, Th17, and T_FH, as defined by their cytokine pattern and function. The fate decision of T helper cell differentiation integrates signals delivered through the T cell receptor, cytokine receptors, and the pattern of co-stimulatory signals received. In this review, we summarize the contribution of co-stimulatory and co-inhibitory receptors to the differentiation and maintenance of T helper cell responses.

OX40 and OX40L protein expression of tumor infiltrating lymphocytes in non-small cell lung cancer and its role in clinical outcome and relationships with other immune biomarkers

Background

Anti-tumoral immunotherapy of anti-program death-1/program death-ligand 1 (PD-1/PD-L1) immune checkpoint therapy demonstrated promising efficacy and tolerability in patients with lung cancer. Apart from inhibitory checkpoints, OX40, the co-stimulatory receptor related to T cell priming and proliferation, was valued identically. In this study, the relationship between OX40/OX40L expressed on tumor infiltrating lymphocytes (TILs), PD-1/PD-L1 and other immunological factors, as well as its role serving as the potential prognostic biomarker, were analyzed in NSCLC.

Methods

We investigated the relationship between OX40/OX40L, PD-1/PD-L1 and TILs in surgical samples from 139 patients with NSCLC by immunohistochemistry (IHC). Factors related to OX40/OX40L expression were analyzed by logistic regression and multi-linear regression. Cox analysis was also performed to find the influencing factors. Survival analysis was conducted in order to testify its role in predicting patients' prognosis.

Results

The TILs OX40, OX40L expression were negatively correlated with the PD-1/PD-L1 expression, respectively. PD-1 expression was negatively correlated with the TILs OX40 expression [R=0.250, (P=0.003)], it was also negatively correlated with the TILs OX40L expression [R=0.386, (P=0.0001)]. PD-1 expression was positively correlated with TILs grades and negatively correlated with the TILs OX40L expression in multiple linear model [R=0.531, (X1, 95% CI: 3.552-8.176, P=0.0001; X2, 95% CI: 0.216-0.683), (P=0.0001)]. The expression of TILs OX40 varied significantly among tumor OX40 and OX40L, PD-1, PD-L1, TILs and pathology types. Tumor OX40L expression, TILs OX40L expression, PD-1 expression, PD-L1 expression and TILs were considered as risk factors for TILs OX40 expression. The staging and TILs OX40L were considered as risk factors for overall survival (OS) while stage and gender were risk factors for recurrence-free survival (RFS). The low-expression of OX40 was related to longer RFS, OS and better prognosis.

Conclusions

OX40 plays a pivotal role in NSCLC, which was closely correlated with immunological factors, RFS and prognosis.

Resiquimod-Mediated Activation of Plasmacytoid Dendritic Cells Is Amplified in Multiple Sclerosis

Background: Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system. The cause of multiple sclerosis is unknown but there are several evidences that associate the genetic basis of the disease with environmental causes. An important association between viral infection and development of MS is clearly demonstrated. Viruses have a strong impact on innate immune cells. In particular, myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs), are able to respond to viruses and to activate the adaptive immune response. Methods: In this study we mimic viral infection using synthetic single-strand RNA, Resiquimod, and we compared the response of both DC subsets derived from healthy donors and MS patients by characterizing the expression of costimulatory molecules on the DC surface. Results: We found that pDCs from MS patients express higher levels of OX40-L, HLA-DR, and CD86 than healthy donors. Moreover, we found that blood cells from MS patients and healthy donors upon Resiquimod-stimulation are enriched in a subpopulation of pDCs, characterized by a high amount of costimulatory molecules. Conclusion: Overall, these results indicate that activation of pDCs is enhanced in MS, likely due to a latent viral infection, and that costimulatory molecules expressed on pDCs could mediate a protective response against the viral trigger of autoimmunity.

Long Chain Polyunsaturated Fatty Acids (LCPUFAs) in the Prevention of Food Allergy

N-3 long chain polyunsaturated fatty acids (LCPUFAs) are considered to possess protective properties for human health by impacting on immunological reactions. An “inflammation-suppressive” effect appears to be the common denominator of the beneficial effects of most of these dietary components which may protect against the development of chronic immune disorders such as (food) allergy. LCPUFAs, especially n-3 LCPUFAs, have been shown to interact with both the sensitization as well as the effector phase in food allergy in pre-clinical models. In this review, we explore the anti-allergic properties of LCPUFAs by providing an overview of clinical, in vivo and in vitro studies. Furthermore, we discuss the susceptibility of LCPUFAs to lipid oxidation and possible strategies to support the efficacy of LCPUFAs in reducing the allergy risk by using additional components with anti-oxidative and anti-inflammatory capacities such as the flavonoid quercetin. Finally, we propose new strategies to prevent (food) allergy using combinations of LCPUFAs and additional nutrients in diets or supplements, and postulate to investigate the use of LCPUFAs in allergic symptom relief.

Cell Adhesion Molecules and Their Roles and Regulation in the Immune and Tumor Microenvironment

The immune system and cancer have a complex relationship with the immune system playing a dual role in tumor development. The effector cells of the immune system can recognize and kill malignant cells while immune system-mediated inflammation can also promote tumor growth and regulatory cells suppress the anti-tumor responses. In the center of all anti-tumor responses is the ability of the immune cells to migrate to the tumor site and to interact with each other and with the malignant cells. Cell adhesion molecules including receptors of the immunoglobulin superfamily and integrins are of crucial importance in mediating these processes. Particularly integrins play a vital role in regulating all aspects of immune cell function including immune cell trafficking into tissues, effector cell activation and proliferation and the formation of the immunological synapse between immune cells or between immune cell and the target cell both during homeostasis and during inflammation and cancer. In this review we discuss the molecular mechanisms regulating integrin function and the role of integrins and other cell adhesion molecules in immune responses and in the tumor microenvironment. We also describe how malignant cells can utilize cell adhesion molecules to promote tumor growth and metastases and how these molecules could be targeted in cancer immunotherapy.

The effect of antigen dose on T cell-targeting vaccine outcome

During the past 3-4 decades, an increasing amount of evidence has pointed to the complex role of the antigen dose or T cell receptor (TCR) stimulation strength on the subsequent type, duration and "flavor" or quality of the response. Antigen dose was initially shown to impact Th1/Th2 bias, and later also shown to differentially affect development and induction of Tregs, Th17, T-follicular helper (Tfh), cells, and others. In recent years the quality of both CD4/8 T cells during infections, cancer and/or autoimmunity has turned out to be critical for subsequent disease outcome. Importantly, different vaccination strategies also lead to different types of T cell responses, and the role of the antigen dose is emerging as an important factor as well as a tool for investigators to utilize in fine-tuning vaccine efficacy. This commentary will highlight essential background of how antigen dose can impact and affect the quality of T cell responses, and discuss how this translates in different vaccine settings.

Differential T-cell receptor signals for T helper cell programming

Upon encounter with their cognate antigen, naive CD4 T cells become activated and are induced to differentiate into several possible T helper (Th) cell subsets. This differentiation depends on a number of factors including antigen-presenting cells, cytokines and co-stimulatory molecules. The strength of the T-cell receptor (TCR) signal, related to the affinity of TCR for antigen and antigen dose, has emerged as a dominant factor in determining Th cell fate. Recent studies have revealed that TCR signals of high or low strength do not simply induce quantitatively different signals in the T cells, but rather qualitatively distinct pathways can be induced based on TCR signal strength. This review examines the recent literature in this area and highlights important new developments in our understanding of Th cell differentiation and TCR signal strength.

Characterisation of chicken OX40 and OX40L

The Tumour Necrosis Factor superfamilies of receptors and ligands play a crucial role in the regulation of effective immune responses against pathogens and malignant cells. In chickens, only few members have been identified. Here, we characterise the chicken homologues for mammalian costimulatory molecules OX40 and OX40L, which are involved in sustaining T cell responses. Both genes were identified by virtue of their genomic localisation close to highly conserved genes and their structural relationship to their mammalian homologues. Following cloning and expression of soluble and cell-associated chicken OX40 and OX40L, we confirmed their mutual interaction via ELISA and flow cytometric analyses. In addition, we showed the application of soluble OX40-Fc in staining of chicken cells. Whereas non-activated cells did not express OX40L, activation by IL-2 and IL-12 resulted in upregulation of OX40L on αβ and γδ T cell populations. Our results demonstrate the existence of the costimulatory OX40-OX40L system in the chicken and provide the basis for further investigations of chicken T cell responses.

Role of Polyamines in Immune Cell Functions

The immune system is remarkably responsive to a myriad of invading microorganisms and provides continuous surveillance against tissue damage and developing tumor cells. To achieve these diverse functions, multiple soluble and cellular components must react in an orchestrated cascade of events to control the specificity, magnitude and persistence of the immune response. Numerous catabolic and anabolic processes are involved in this process, and prominent roles for l-arginine and l-glutamine catabolism have been described, as these amino acids serve as precursors of nitric oxide, creatine, agmatine, tricarboxylic acid cycle intermediates, nucleotides and other amino acids, as well as for ornithine, which is used to synthesize putrescine and the polyamines spermidine and spermine. Polyamines have several purported roles and high levels of polyamines are manifest in tumor cells as well in autoreactive B- and T-cells in autoimmune diseases. In the tumor microenvironment, l-arginine catabolism by both tumor cells and suppressive myeloid cells is known to dampen cytotoxic T-cell functions suggesting there might be links between polyamines and T-cell suppression. Here, we review studies suggesting roles of polyamines in normal immune cell function and highlight their connections to autoimmunity and anti-tumor immune cell function.

Influence of Inflammation in the Process of T Lymphocyte Differentiation: Proliferative, Metabolic, and Oxidative Changes

T lymphocytes, from their first encounter with their specific antigen as naïve cell until the last stages of their differentiation, in a replicative state of senescence, go through a series of phases. In several of these stages, T lymphocytes are subjected to exponential growth in successive encounters with the same antigen. This entire process occurs throughout the life of a human individual and, earlier, in patients with chronic infections/pathologies through inflammatory mediators, first acutely and later in a chronic form. This process plays a fundamental role in amplifying the activating signals on T lymphocytes and directing their clonal proliferation. The mechanisms that control cell growth are high levels of telomerase activity and maintenance of telomeric length that are far superior to other cell types, as well as metabolic adaptation and redox control. Large numbers of highly differentiated memory cells are accumulated in the immunological niches where they will contribute in a significant way to increase the levels of inflammatory mediators that will perpetuate the new state at the systemic level. These levels of inflammation greatly influence the process of T lymphocyte differentiation from naïve T lymphocyte, even before, until the arrival of exhaustion or cell death. The changes observed during lymphocyte differentiation are correlated with changes in cellular metabolism and these in turn are influenced by the inflammatory state of the environment where the cell is located. Reactive oxygen species (ROS) exert a dual action in the population of T lymphocytes. Exposure to high levels of ROS decreases the capacity of activation and T lymphocyte proliferation; however, intermediate levels of oxidation are necessary for the lymphocyte activation, differentiation, and effector functions. In conclusion, we can affirm that the inflammatory levels in the environment greatly influence the differentiation and activity of T lymphocyte populations. However, little is known about the mechanisms involved in these processes. The elucidation of these mechanisms would be of great help in the advance of improvements in pathologies with a large inflammatory base such as rheumatoid arthritis, intestinal inflammatory diseases, several infectious diseases and even, cancerous processes.

Effector/memory CD4 T cells making either Th1 or Th2 cytokines commonly co-express T-bet and GATA-3

Naïve CD4 T (NCD4T) cells post-activation undergo programming for inducible production of cytokines leading to generation of memory cells with various functions. Based on cytokine based polarization of NCD4T cells in vitro, programming for either ‘Th1’ (interferon-gamma [IFNg]) or ‘Th2’ (interleukin [IL]-4/5/13) cytokines is thought to occur via mutually exclusive expression and functioning of T-bet or GATA-3 transcription factors (TFs). However, we show that a high proportion of mouse and human memory-phenotype CD4 T (MCD4T) cells generated in vivo which expressed either Th1 or Th2 cytokines commonly co-expressed T-bet and GATA-3. While T-bet levels did not differ between IFNg-expressing and IL-4/5/13-expressing MCD4T cells, GATA-3 levels were higher in the latter. These observations were also confirmed in MCD4T cells from FVB/NJ or aged C57BL/6 or IFNg-deficient mice. While MCD4T cells from these strains showed greater Th2 commitment than those from young C57BL/6 mice, pattern of co-expression of TF was similar. Effector T cells generated in vivo following immunization also showed TF co-expression in Th1 or Th2 cytokine producing cells. We speculated that the difference in TF expression pattern of MCD4T cells generated in vivo and those generated in cytokine polarized cultures in vitro could be due to relative absence of polarizing conditions during activation in vivo. We tested this by NCD4T cell activation in non-polarizing conditions in vitro. Anti-CD3 and anti-CD28-mediated priming of polyclonal NCD4T cells in vitro without polarizing milieu generated cells that expressed either IFNg or IL-4/5/13 but not both, yet both IFNg- and IL-4/5/13-expressing cells showed upregulation of both TFs. We also tested monoclonal T cell populations activated in non-polarizing conditions. TCR-transgenic NCD4T cells primed in vitro by cognate peptide in non-polarizing conditions which expressed either IFNg or IL-4/5/13 also showed a high proportion of cells co-expressing TFs, and their cytokine commitment varied depending on genetic background or priming conditions, without altering pattern of TF co-expression. Thus, the model of mutually antagonistic differentiation programs driven by mutually exclusively expressed T-bet or GATA-3 does not completely explain natural CD4 T cell priming outcomes.

OX40: Structure and function - What questions remain?

OX40 is a type 1 transmembrane glycoprotein, reported nearly 30 years ago as a cell surface antigen expressed on activated T cells. Since its discovery, it has been validated as a bone fide costimulatory molecule for T cells and member of the TNF receptor family. However, many questions still remain relating to its function on different T cell sub-sets and with recent interest in its utility as a target for antibody-mediated immunotherapy, there is a growing need to gain a better understanding of its biology. Here, we review the expression pattern of OX40 and its ligand, discuss the structure of the receptor:ligand interaction, the downstream signalling it can elicit, its function on different T cell subsets and how antibodies might engage with it to provide effective immunotherapy.

Aberrantly methylated DNA regions lead to low activation of CD4+ T-cells in IgA nephropathy

IgAN (IgA nephropathy) is the most common form of primary glomerulonephritis worldwide and has a strong genetic component. In this setting, DNA methylation could also be an important factor influencing this disease. We performed a genome-wide screening for DNA methylation in CD4(+) T-cells from IgAN patients and found three regions aberrantly methylated influencing genes involved in the response and proliferation of CD4(+) T-cells. Two hypomethylated regions codified genes involved in TCR (T-cell receptor) signalling, TRIM27 (tripartite motif-containing 27) and DUSP3 (dual-specificity phosphatase 3), and an hypermethylated region included the VTRNA2-1 (vault RNA 2-1) non-coding RNA, also known as miR-886 precursor. We showed that the aberrant methylation influences the expression of these genes in IgAN patients. Moreover, we demonstrated that the hypermethylation of the miR-886 precursor led to a decreased CD4(+) T-cell proliferation following TCR stimulation and to the overexpression of TGFβ (transforming growth factor β). Finally, we found a Th1/Th2 imbalance in IgAN patients. The IL (interleukin)-2/IL-5 ratio was notably higher in IgAN patients and clearly indicated a Th1 shift. In conclusion, we identified for the first time some specific DNA regions abnormally methylated in IgAN patients that led to the reduced TCR signal strength of the CD4(+) T-cells and to their anomalous response and activation that could explain the T-helper cell imbalance. The present study reveals new molecular mechanisms underlying the abnormal CD4(+) T-cell response in IgAN patients.

Presentation of high antigen-dose by splenic B220(lo) B cells fosters a feedback loop between T helper type 2 memory and antibody isotype switching

Effective humoral immunity ensues when antigen presentation by B cells culminates in productive cooperation with T lymphocytes. This collaboration, however, remains ill-defined because naive antigen-specific B cells are rare and difficult to track in vivo. Herein, we used a defined transfer model to examine how B lymphocytes, as antigen-presenting cells, shape the development of T-cell memory suitable for generation of relevant antibody responses. Specifically, we examined how B cells presenting different doses of antigen during the initial priming phase shape the development of CD4 T-cell memory and its influence on humoral immunity. The findings indicate that B cells presenting low dose of antigen favour the development of T helper type 1 (Th1) type memory, while those presenting a high antigen dose yielded better Th2 memory cells. The memory Th2 cells supported the production of antibodies by effector B cells and promoted isotype switching to IgG1. Moreover, among the B-cell subsets tested for induction of Th2 memory, the splenic but not peritoneal B220(lo) cells were most effective in sustaining Th2 memory development as well as immunoglobulin isotype switching, and this function involved a tight control by programmed death 1-programmed death ligand 2 interactions.

PKC-Theta is a Novel SC35 Splicing Factor Regulator in Response to T Cell Activation

Alternative splicing of nuclear pre-mRNA is essential for generating protein diversity and regulating gene expression. While many immunologically relevant genes undergo alternative splicing, the role of regulated splicing in T cell immune responses is largely unexplored, and the signaling pathways and splicing factors that regulate alternative splicing in T cells are poorly defined. Here, we show using a combination of Jurkat T cells, human primary T cells, and ex vivo naïve and effector virus-specific T cells isolated after influenza A virus infection that SC35 phosphorylation is induced in response to stimulatory signals. We show that SC35 colocalizes with RNA polymerase II in activated T cells and spatially overlaps with H3K27ac and H3K4me3, which mark transcriptionally active genes. Interestingly, SC35 remains coupled to the active histone marks in the absence of continuing stimulatory signals. We show for the first time that nuclear PKC-θ co-exists with SC35 in the context of the chromatin template and is a key regulator of SC35 in T cells, directly phosphorylating SC35 peptide residues at RNA recognition motif and RS domains. Collectively, our findings suggest that nuclear PKC-θ is a novel regulator of the key splicing factor SC35 in T cells.

Development and Function of Protective and Pathologic Memory CD4 T Cells

Immunological memory is one of the defining features of the adaptive immune system. As key orchestrators and mediators of immunity, CD4 T cells are central to the vast majority of adaptive immune responses. Generated following an immune response, memory CD4 T cells retain pertinent information about their activation environment enabling them to make rapid effector responses upon reactivation. These responses can either benefit the host by hastening the control of pathogens or cause damaging immunopathology. Here, we will discuss the diversity of the memory CD4 T cell pool, the signals that influence the transition of activated T cells into that pool, and highlight how activation requirements differ between naïve and memory CD4 T cells. A greater understanding of these factors has the potential to aid the design of more effective vaccines and to improve regulation of pathologic CD4 T cells, such as in the context of autoimmunity and allergy.

Responses to LPS boost effector CD8 T-cell accumulation outside of signals 1 and 2

Immunization with adjuvant plus antigen induces durable T-cell immunity and is a mainstay of vaccines. Here, the consequence of separating antigen stimulation of T cells from the adjuvant response was studied in a re-transfer model. Effector CD8 T cells in recipient mice were exposed to lipopolysaccharide (LPS), the Toll-like receptor 4 (TLR4) ligand, which significantly increased persistence. While accumulation in lymphoid and non-lymphoid organs was evident, this result depended upon the timing of LPS administration and the presence of the TLR4 adaptor TRIF in the recipient mice. Interestingly, there was very little impact of the LPS response on subset differentiation, which rather appeared to be programmed by antigen and costimulation. To discern factors that limit accumulation, interleukin 10 (IL-10) was targeted since it is a product of TLR4 triggering and mitigates inflammation. Blockade of IL-10 increased accumulation even though the effector CD8 T cells were well past the priming phase, but upon recall interferon-γ secretion was not affected as would be expected when IL-10 is present during priming. Thus, the adjuvant-altered microenvironment is effective not only in the presence of antigen but also during a window of effector CD8 T-cell stasis, suggesting that pathogen-associated molecular pattern molecules released during co-infection, or by vaccines, could alter the survival fate of specific effector T cells.Cellular & Molecular Immunology advance online publication, 20 July 2015; doi:10.1038/cmi.2015.69.

Optimal T Cell Activation and B Cell Antibody Responses In Vivo Require the Interaction between Leukocyte Function-Associated Antigen-1 and Kindlin-3

Kindlin-3 is an important integrin regulator that is mutated in the rare genetic disorder, leukocyte adhesion deficiency type III, a disorder characterized by defective neutrophil trafficking and platelet function, leading to recurrent bacterial infections and bleeding. Kindlin-3 is also known to regulate T cell adhesion in vitro and trafficking in vivo, but whether the integrin/kindlin interaction regulates T or B cell activation in vivo is unclear. In this study, we used TTT/AAA β2-integrin knock-in (KI) mice and TCR-transgenic (OT-II) KI mice, in which the integrin/kindlin connection is disrupted, to investigate the role of the integrin/kindlin interaction in T cell activation. We show that basal T cell activation status in these animals in vivo is normal, but they display reduced T cell activation by wild-type Ag-loaded dendritic cells in vitro. In addition, T cell activation in vivo is reduced. We also show that basal Ab levels are normal in TTT/AAA β2-integrin KI mice, but B cell numbers in lymph nodes and IgG and IgM production after immunization are reduced. In conclusion, we show that the integrin/kindlin interaction is required for trafficking of immune cells, as well as for T cell activation and B cell Ab responses in vivo. These results imply that the immunodeficiency found in leukocyte adhesion deficiency type III patients, in addition to being caused by defects in neutrophil function, may be due, in part, to defects in lymphocyte trafficking and activation.

Human blood CD1c dendritic cells stimulate IL-12-independent IFN-γ responses and have a strikingly low inflammatory profile

Adaptive immune responses are initiated by resident myeloid tissue DC. A major fraction of tissue DC express CD1c⁺ and is thought to be derived from blood CD1c DC, an idea supported here by the observation that they express tissue-homing molecules and rapidly differentiate into cells with a tissue DC phenotype. Responses are thought to be augmented/modulated further by inflammatory moDC. Although much accepted human myeloid DC cell biology is based on moDC studies, we find these 2 DC populations to be functionally distinct. Stimulated moDC produce high levels of IL-10 and the Th1-promoting cytokine IL-12. Under identical conditions, CD1c DC synthesized no IL-10 and no or low levels of IL-12. Despite this, CD1c DC stimulated a strong Th1 response, demonstrated by IL-12 neutralization to be IL-12 independent, whereas the response induced by moDC was IL-12 dependent. This finding was supported by studies on a patient with a highly reduced ability to synthesize IL-12, whose CD1c DC induced a good Th1 response contrasting with the failure of his moDC, which were impaired in IL-12 production, to induce IFN-γ-secreting T cells. The IL-10 and IL-12 data were confirmed by microarray analysis, which also showed that stimulated moDC produced inflammatory-associated chemokines and cytokines, whereas stimulated CD1c DC showed minimal up-regulation of these genes. Thus, moDC, widely used as a human myeloid DC model, do not faithfully reflect the properties of CD1c tissue DC, making the initial response to a pathogen or vaccine.

PLGA-nanoparticle mediated delivery of anti-OX40 monoclonal antibody enhances anti-tumor cytotoxic T cell responses

OX40 (CD134) is a tumor necrosis factor (TNF) receptor expressed mainly on activated T cells and transmits a potent costimulatory signal once engaged. Agonistic anti-OX40 monoclonal antibody (mAb) enhances tumor immune response leading to therapeutic effects in mouse tumor models. However, when tested in phase I clinical trials it did not show objective clinical activity in cancer patients. In this study, we examined the feasibility of nanoparticle (NP)-mediated delivery of anti-OX40 mAb to efficiently induce cytotoxic T lymphocyte (CTL) responses. The biodegradable poly(DL-lactide-co-glycolide) nanoparticle (PLGA-NP) carrying anti-OX40 mAb, anti-OX40-PLGA-NP, was prepared by double emulsion method and showed an average diameter of 86 nm with a loading efficiency of 25%. We found that anti-OX40-PLGA-NP induced CTL proliferation and tumor antigen-specific cytotoxicity as well as cytokine production more strongly than free anti-OX40 mAb. These results suggest that PLGA-based nanoparticle formulation may provide efficient delivery system of anti-OX40 mAb for cancer immunotherapy.

T cell-activation in neuromyelitis optica lesions plays a role in their formation

Background

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system (CNS), which is characterized by the presence of pathogenic serum autoantibodies against aquaporin 4 (AQP4) in the vast majority of patients. The contribution of T cells to the formation of astrocyte destructive lesions is currently unclear. However, active human NMO lesions contain CD4⁺ T-lymphocytes expressing the activation marker Ox40, and the expression is more profound compared to that seen in MS lesions of comparable activity. Therefore, we analyzed the role of T-cell activation within the CNS in the initiation of NMO lesions in an experimental model of co-transfer of different encephalitogenic T-cells and human AQP4 antibody containing NMO immunoglobulin (NMO IgG). We further studied the expression of the T-cell activation marker Ox40 in NMO and multiple sclerosis lesions in different stages of activity.

Results

All encephalitogenic T-cell lines used in our experiments induced brain inflammation with a comparable extent of blood brain barrier damage, allowing human NMO IgG to penetrate into the brain and spinal cord tissue. However, astrocyte destructive NMO lesions were only seen with T-cells, which showed signs of activation in the lesions. T-cell activation was reflected by the expression of the activation marker Ox40 and pronounced production of γ-IFN, which was able to increase the production of complement proteins and of the Fc gamma III receptor (Fcgr3) and decreased production of complement inhibitory protein Factor H in microglia.

Conclusions

Our data indicate that local activation of T-cells provide an inflammatory environment in the CNS, which allows AQP4 auto-antibodies to induce astrocyte destructive NMO-like lesions.

Targeting CD28 to prevent transplant rejection

INTRODUCTION

The pivotal role of costimulatory pathways in regulating T-cell activation versus tolerance has stimulated tremendous interest in their manipulation for therapeutic purposes. Of these, the CD28-B7 pathway is arguably the most important and best studied. Therapeutic targets of CD28 are currently used in the treatment of melanoma, autoimmune diseases and in transplantation.

AREAS COVERED

In this review, we summarize our current knowledge of CD28 and cytotoxic T-lymphocyte antigen-4 (CTLA-4) signaling, and review the current state and challenges of harnessing them to promote transplant tolerance.

EXPERT OPINION

Despite the success of belatacept, a first-in-class CTLA-4 fusion protein now clinically used in transplantation, it is apparent that we have only scratched the surface in understanding the complexities of how costimulatory pathways modulate the immune system. Our initial assumption that positive costimulators activate effector T cells and prevent tolerance, while negative costimulators inhibit effector T cells and promote tolerance, is clearly an oversimplified view. Indeed, belatacept is not only capable of blocking deleterious CD28-B7 interactions that promote effector T-cell responses but can also have undesired effects on tolerogenic regulatory T-cell populations.

Combined targeting of costimulatory (OX40) and coinhibitory (CTLA-4) pathways elicits potent effector T cells capable of driving robust antitumor immunity

Ligation of the TNF receptor family costimulatory molecule OX40 (CD134) with an agonist anti-OX40 monoclonal antibody (mAb) enhances antitumor immunity by augmenting T-cell differentiation as well as turning off the suppressive activity of the FoxP3(+)CD4(+) regulatory T cells (Treg). In addition, antibody-mediated blockade of the checkpoint inhibitor CTLA-4 releases the "brakes" on T cells to augment tumor immunotherapy. However, monotherapy with these agents has limited therapeutic benefit particularly against poorly immunogenic murine tumors. Therefore, we examined whether the administration of agonist anti-OX40 therapy in the presence of CTLA-4 blockade would enhance tumor immunotherapy. Combined anti-OX40/anti-CTLA-4 immunotherapy significantly enhanced tumor regression and the survival of tumor-bearing hosts in a CD4 and CD8 T cell-dependent manner. Mechanistic studies revealed that the combination immunotherapy directed the expansion of effector T-bet(high)/Eomes(high) granzyme B(+) CD8 T cells. Dual immunotherapy also induced distinct populations of Th1 [interleukin (IL)-2, IFN-γ], and, surprisingly, Th2 (IL-4, IL-5, and IL-13) CD4 T cells exhibiting increased T-bet and Gata-3 expression. Furthermore, IL-4 blockade inhibited the Th2 response, while maintaining the Th1 CD4 and effector CD8 T cells that enhanced tumor-free survival. These data demonstrate that refining the global T-cell response during combination immunotherapy can further enhance the therapeutic efficacy of these agents.

CD3Z genetic polymorphism in immune response to hepatitis B vaccination in two independent Chinese populations

Vaccination against hepatitis B virus is an effective and routine practice that can prevent infection. However, vaccine-induced immunity to hepatitis B varies among individuals. CD4⁺ T helper cells, which play an important role in both cellular and humoral immunity, are involved in the immune response elicited by vaccination. Polymorphisms in the genes involved in stimulating the activation and proliferation of CD4⁺ T helper cells may influence the immune response to hepatitis B vaccination. In the first stage of the present study, a total of 111 single nucleotide polymorphisms (SNPs) in 17 genes were analyzed, using the iPLEX MassARRAY system, among 214 high responders and 107 low responders to hepatitis B vaccination. Three SNPs (rs12133337 and rs10918706 in CD3Z, rs10912564 in OX40L) were associated significantly with the immune response to hepatitis B vaccination (P = 0.008, 0.041, and 0.019, respectively). The three SNPs were analyzed further with the TaqMan-MGB or TaqMan-BHQ probe-based real-time polymerase chain reaction in another independent population, which included 1090 high responders and 636 low responders. The minor allele ‘C’ of rs12133337 continued to show an association with a lower response to hepatitis B vaccination (P = 0.033, odds radio = 1.28, 95% confidence interval = 1.01–1.61). Furthermore, in the stratified analysis for both the first and second populations, the association of the minor allele ‘C’ of rs12133337 with a lower response to hepatitis B vaccination was more prominent after individuals who were overweight or obese (body mass index ≥25 kg/m²) were excluded (1^st stage: P = 0.003, 2^nd stage: P = 0.002, P-combined = 9.47e-5). These findings suggest that the rs12133337 polymorphism in the CD3Z gene might affect the immune response to hepatitis B vaccination, and that a lower BMI might increase the contribution of the polymorphism to immunity to hepatitis B vaccination.

Rv2468c, a novel Mycobacterium tuberculosis protein that costimulates human CD4+ T cells through VLA-5

Mtb regulates many aspects of the host immune response, including CD4+ T lymphocyte responses that are essential for protective immunity to Mtb, and Mtb effects on the immune system are paradoxical, having the capacity to inhibit (immune evasion) and to activate (adjuvant effect) immune cells. Mtb regulates CD4+ T cells indirectly (e.g., by manipulation of APC function) and directly, via integrins and TLRs expressed on T cells. We now report that previously uncharacterized Mtb protein Rv2468c/MT2543 can directly regulate human CD4+ T cell activation by delivering costimulatory signals. When combined with TCR stimulation (e.g., anti-CD3), Rv2468c functioned as a direct costimulator for CD4+ T cells, inducing IFN-γ secretion and T cell proliferation. Studies with blocking antibodies and soluble RGD motifs demonstrated that Rv2468c engaged integrin VLA-5 (α5β1) on CD4+ T cells through its FN-like RGD motif. Costimulation by Rv2468c induced phosphorylation of FAKs and Pyk2. These results reveal that by expressing molecules that mimic host protein motifs, Mtb can directly engage receptors on CD4+ T cells and regulate their function. Rv2468c-induced costimulation of CD4+ T cells could have implications for TB immune pathogenesis and Mtb adjuvant effect.

Preferential replication of vaccinia virus in the ovaries is independent of immune regulation through IL-10 and TGF-β

Vaccinia virus (VACV) exhibits a strong tropism for ovarian tissue and can cause ovary pathology and sterility. Why VACV preferentially accumulates in this organ is not known. Here we show that multiple immune cell populations infiltrated the ovaries following VACV infection, including virus-specific CD8 T cells making both IFN-γ and TNF. This was also accompanied by the induction of interleukin (IL)-10 and TGF-β, suggesting that VACV may exploit the ovarian environment for immune evasion via induction of these suppressive cytokines. To test this we used several strategies, including neutralizing these cytokines, and exogenous targeting of the T-cell response, to determine if this inhibited virus replication in the ovaries. We found that the VACV-specific CD8 T-cell immunity and the clearance of virus were not enhanced in the ovaries of infected mice in which IL-10 receptor (IL-10R) was blocked with antagonist antibody. VACV replication was also only moderately affected in the ovaries of infected IL-10 knockout mice. Similarly, blockade of TGF-β with antagonist antibody demonstrated no effect on CD8 T-cell immunity or VACV replication. Lastly, an agonist antibody targeting the tumor necrosis factor receptor superfamily member OX40 (TNFRSF4) enhanced the number of VACV-specific CD8 T cells producing IFN-γ in lymphoid tissue, but had no effect on CD8 T-cell infiltration of the ovaries or on the viral load. Collectively, the results indicate that preferential replication of VACV in the ovaries may not be dependent on immune suppressive mechanisms in this tissue.

Interleukin 12 and CD86 Regulate Th1 and Th2 Development Induced by a Range of Antigen Doses Presented by Peyer's Patch and Spleen Cells

In this study, we demonstrate the role of interleukin 12 (IL-12), CD80 and CD86 in T helper type 1 (Th1) and Th2 differentiation induced through antigen presentation by Peyer's patch (PP) and spleen (SPL) cells with various doses of antigen. IL-12 was found to be critical for the induction of Th1-type cytokine producing cells, while antigen-dose dependent patterns of differentiation into Th2-type cytokine producing cells were not altered by the blockade of IL-12. Further, the difference in the pattern of Th2-type cytokine producing cell differentiation induced by PP and SPL cells depending on the antigen dosage were preserved in the absence of IL-12. When the function of CD86 was blocked by specific antibody, the induction of Th1-type cytokine producing cells was kept at high levels through every antigen dose, and the difference between PP and SPL cells was abrogated. With regard to Th2 induction, CD86 enhanced the differentiation of Th2-type cytokine producing cells but it was not essential in the case of antigen presentation by SPL cells. These results suggest that antigen-dose dependent changes in Th2 cell induction are regulated by additional factors which cannot induce antigen-dose dependent changes in Th1 cell differentiation by themselves.

Dendritic Cells from Spleen, Mesenteric Lymph Node and Peyer's Patch Can Induce the Production of Both IL-4 and IFN-gamma from Primary Cultures of Naive CD4(+) T Cells in a Dose-Dependent Manner

Dendritic cells (DCs) as antigen presenting cells can stimulate naive CD4(+) T cells and initiate the primary immune response which controls Th1/Th2 development. It has been suggested that DCs derived from different tissues have distinct properties. We investigated whether DCs from mesenteric lymph nodes (MLN), Peyer's patches (PP) and spleen (SPL) could induce different responses of naive CD4(+) T cells to varying doses of antigen by using a co-culture system of DCs and T cells. DCs from each tissue induced IL-4 secretion from naive CD4(+)T cells in the presence of low dose antigenic peptide, and induced IFN-gamma production at high doses of antigen. When purified CD11c(+)/B220(-) DCs were used, MLN-derived DCs induced a higher amount of IFN-gamma secretion from naive CD4(+) T cells, compared with SPL-derived DCs. We could not detect large differences in the expressions of costimulatory molecules on the surface of these two populations of DCs. On the other hand, we found that large amounts of IL-12 were secreted from MLN DCs in an antigen dose-dependent fashion. In conclusion, DCs from SPL, MLN and PP can induce the production of both IL-4 and IFN-gamma from naive CD4(+) T cells, depending on antigen dose. MLN-derived CD11c(+)/B220(-) DCs induce higher IFN-gamma production from naive CD4(+) T cells than SPL-derived DCs, through efficient IL-12 secretion.

T helper cell differentiation more than just cytokines

CD4(+) T helper (T(H)) cells play a critical role in orchestrating a pleiotropy of immune activities against a large variety of pathogens. It is generally thought that this is achieved through the acquisition of highly specialized functions after activation followed by the differentiation into various functional subsets. The differentiation process of naive precursor T(H) cells into defined effector subsets is controlled by cells of the innate immune system and their complex array of effector molecules such as secreted cytokines and membrane bound costimulatory molecules. These provide a unique quantitative or qualitative signal initiating T(H) development, which is subsequently reinforced via T cell-mediated feedback signals and selective survival and proliferative cues, ultimately resulting in the predominance of a particular T cell subset. In recent years, the number of defined T(H)cell subsets has expanded and the once rigid division of labor among them has been blurred with reports of plasticity among the subsets. In this chapter, we summarize and speculate on the current knowledge of the differentiation requirements of T(H) cell lineages, with particular focus on the T(H)17 subset.

Mechanisms by which chronic ethanol feeding limits the ability of dendritic cells to stimulate T-cell proliferation

BACKGROUND

As initiators of immune responses, dendritic cells (DCs) are required for antigen (Ag)-specific activation of naïve T cells in the defense against infectious agents. The increased susceptibility to and severity of infection seen in chronic alcoholics could be because of impaired DCs initiation of naïve T-cell responses. Specifically, these DCs may not provide adequate Signals 1 (Ag presentation), 2 (costimulation), or 3 (cytokine production) to these T cells.

METHODS

Using the Meadows-Cook murine model of chronic alcohol abuse, the ability of ethanol (EtOH)-exposed DCs to stimulate T-cell proliferation, acquire and process Ag, express costimulatory molecules, and produce inflammatory cytokines was assessed.

RESULTS

Normal naïve T cells primed by EtOH-exposed DCs showed decreased proliferation in vitro and in vivo, compared to water-fed control mice. These EtOH-exposed DCs, after activation by CpG or tumor necrosis factor alpha (TNFα), were less able to upregulate costimulatory molecules CD40, CD80, or CD86, and produced less IL-12 p40, TNFα, and IFNα than DCs from water-fed mice. TLR9 and TNF receptor expression were also reduced in/on EtOH-exposed DCs. No evidence of defective Ag acquisition or processing as a result of EtOH feeding was identified.

CONCLUSIONS

Inadequate proliferation of normal T cells following stimulation by EtOH-exposed DCs is likely a result of diminished Signal 2 and Signal 3. Lack of adequate inflammatory stimulation of EtOH-exposed DCs because of diminished receptors for inflammatory mediators appears to be at least partially responsible for their dysfunction. These findings provide a mechanism to explain increased morbidity and mortality from infectious diseases in alcoholics and suggest targets for therapeutic intervention.

Signaling through OX40 enhances antitumor immunity

The existence of tumor-specific T cells, as well as their ability to be primed in cancer patients, confirms that the immune response can be deployed to combat cancer. However, there are obstacles that must be overcome to convert the ineffective immune response commonly found in the tumor environment to one that leads to sustained destruction of tumor. Members of the tumor necrosis factor (TNF) superfamily direct diverse immune functions. OX40 and its ligand, OX40L, are key TNF members that augment T-cell expansion, cytokine production, and survival. OX40 signaling also controls regulatory T-cell differentiation and suppressive function. Studies over the past decade have demonstrated that OX40 agonists enhance antitumor immunity in preclinical models using immunogenic tumors; however, treatment of poorly immunogenic tumors has been less successful. Combining strategies that prime tumor-specific T cells together with OX40 signaling could generate and maintain a therapeutic antitumor immune response.

Control of immunity by the TNFR-related molecule OX40 (CD134)

TNFR/TNF superfamily members can control diverse aspects of immune function. Research over the past 10 years has shown that one of the most important and prominent interactions in this family is that between OX40 (CD134) and its partner OX40L (CD252). These molecules strongly regulate conventional CD4 and CD8 T cells, and more recent data are highlighting their ability to modulate NKT cell and NK cell function as well as to mediate cross-talk with professional antigen-presenting cells and diverse cell types such as mast cells, smooth muscle cells, and endothelial cells. Additionally, OX40-OX40L interactions alter the differentiation and activity of regulatory T cells. Blocking OX40L has produced strong therapeutic effects in multiple animal models of autoimmune and inflammatory disease, and, in line with a prospective clinical future, reagents that stimulate OX40 signaling are showing promise as adjuvants for vaccination as well as for treatment of cancer.

IL-4 directs both CD4 and CD8 T cells to produce Th2 cytokines in vitro, but only CD4 T cells produce these cytokines in response to alum-precipitated protein in vivo

While IL-4 directs CD4 T cells to produce Th2 cytokines (including IL-4, IL-13, IL-5) in vitro it has been shown that production of these cytokines can be induced in vivo in the absence of IL-4/IL-13/STAT-6 signaling. The present report shows that CD8 as well as CD4 T cells activated through their TCR, in vitro upregulate the Th2-features - IL-4, IL-13, IL-5, and GATA-3. However, in vivo while alum-precipitated antigen strongly and selectively induces these Th2-features in CD4 T cells, CD8 T cells mount a markedly different response to this antigen. This CD8 response is associated with strong proliferation and production of IFN-gamma, but no Th2-features are induced. Alum-protein formulations are widely used in human vaccines and typically induce strong antibody responses characterized by the differentiation of IL-4-producing CD4 T cells and immunoglobulin class switching to IgG1. Nevertheless, the mechanism responsible for CD4 Th2 and follicular helper T cell commitment triggered by these alum-protein vaccines is still poorly understood. Analysis of the in vivo response to alum-precipitated protein shows that while subsets of CD4 T cells strongly upregulate Th2 and follicular helper T cell features including the surface markers OX40, CXCR5, PD-1, IL-17RB and the transcription factor c-Maf, CD8 T cells do not. These discrete differences between responding CD4 and CD8 T cells provide further insight into the differences between Th2 polarization of CD4 T cells directed by IL-4 in vitro and the induction of IL-4 production by CD4 T cells in vivo in response to alum-precipitated protein.

OX40-OX40 ligand interaction in T-cell-mediated immunity and immunopathology

T-cell activation is mediated not only by antigen stimulation through T-cell receptors but also by costimulatory signals through costimulatory molecules. Among several costimulatory molecules, the tumor necrosis factor (TNF) receptor family member OX40 plays a key role in the survival and homeostasis of effector and memory T cells. According to the conventional understanding of OX40 costimulation, an interaction between OX40 and OX40 ligand (OX40L) occurs when activated T cells bind to professional antigen-presenting cells (APCs). The T-cell functions, including cytokine production, expansion, and survival, are then enhanced by the OX40 costimulatory signals. Over the last half-decade, evidence has accumulated that OX40 signals are critical for controlling the function and differentiation of Foxp3(+) regulatory T cells, indicating a new aspect of OX40-mediated autoimmunity. Furthermore, the expression of OX40L by mast cells was shown to be important for controlling inflammation through regulatory T-cell function. Besides the essential role played by OX40 signaling in generating memory CD4 T cells, recent reports show that it also has a unique role in generating memory CD8 T cells. In addition, recent genome-wide association studies have identified single-nucleotide polymorphisms of the OX40L and OX40 genes that are related to cardiovascular diseases and SLE, providing direct evidence for the involvement of the OX40-OX40L interaction in human diseases. Here, we review recent progress on how the OX40-OX40L interaction regulates T-cell tolerance, peripheral T-cell homeostasis, and T-cell-mediated inflammatory diseases.

The role of OX40-mediated co-stimulation in T-cell activation and survival

The extent of T-cell activation, proliferation, and survival that follows T-cell receptor (TCR) ligation is controlled by several factors, including the strength of TCR stimulation, the availability of prosurvival cytokines, and the presence or absence of co-stimulatory signals. In addition to engagement of the CD28 co-stimulatory receptor by its natural ligands, B7.1 (CD80) and B7.2 (CD86), recent work has begun to elucidate the mechanisms by which signaling through the OX40 (CD134) co-stimulatory receptor, a member of the tumor necrosis factor receptor (TNFR) superfamily, affects T-cell responses. Importantly, OX40 ligation has been shown to augment CD4 and CD8 T-cell clonal expansion, effector differentiation, survival, and in some cases, abrogate the suppressive activity of regulatory FoxP3+CD25+CD4+ T cells. In this review, we focus on the mechanisms regulating OX40 expression on activated T cells as well as the role of OX40-mediated co-stimulation in boosting T-cell clonal expansion, effector differentiation, and survival.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.

The significance of OX40 and OX40L to T-cell biology and immune disease

SUMMARY

OX40 (CD134) and its binding partner, OX40L (CD252), are members of the tumor necrosis factor receptor/tumor necrosis factor superfamily and are expressed on activated CD4(+) and CD8(+) T cells as well as on a number of other lymphoid and non-lymphoid cells. Costimulatory signals from OX40 to a conventional T cell promote division and survival, augmenting the clonal expansion of effector and memory populations as they are being generated to antigen. OX40 additionally suppresses the differentiation and activity of T-regulatory cells, further amplifying this process. OX40 and OX40L also regulate cytokine production from T cells, antigen-presenting cells, natural killer cells, and natural killer T cells, and modulate cytokine receptor signaling. In line with these important modulatory functions, OX40-OX40L interactions have been found to play a central role in the development of multiple inflammatory and autoimmune diseases, making them attractive candidates for intervention in the clinic. Conversely, stimulating OX40 has shown it to be a candidate for therapeutic immunization strategies for cancer and infectious disease. This review provides a broad overview of the biology of OX40 including the intracellular signals from OX40 that impact many aspects of immune function and have promoted OX40 as one of the most prominent costimulatory molecules known to control T cells.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Dendritic cells--why can they help and hurt us

Dendritic cells (DCs) show a Janus-like functional behavior. They help us by their orchestration of numerous immune responses to defend our body against invading pathogenic micro-organisms and also induce regulatory T cells to inhibit immune reactions against autoantigens as well as diverse harmless environmental antigens. However, DCs can also be of harm to us when misguided by their microenvironment as in allergic and autoimmune diseases or when DCs are targeted and exploited by microbes and cancer cells to evade the immune defense. This huge and diverse functional repertoire of DCs requires complex decision-making processes and the integration of multiple stimulatory and inhibitory signals. Although a given DC type has an extensive functionally plasticity, DCs are heterogeneous and individual DC subtypes are differentially distributed in tissues, express distinct sets of pattern recognition receptors and differ in their capacity to program naive T cells. With the help of transgenic mouse models and selective ablation of individual DC subtypes, we are just at the beginning of understanding the DC system in its complexity. Obtaining a more detailed knowledge of the DC system in mice and men holds strong promise for the successful induction of immunity and tolerance in therapeutic trials. This review presents the recent advances in the understanding of DC biology and discusses why and how DC can help and hurt us.

OX40 (CD134) and OX40L

The interaction between OX40 and OX40L plays an important role in antigen-specific T-cell expansion and survival. While OX40 is expressed predominantly on T-lymphocytes early after antigen activation, OX40L is expressed on activated antigen presenting cells and endothelial cells within acute inflammatory environments. We discuss here how ligation of OX40 by OX40L leads to enhanced T-cell survival, along with local inflammatory responses that appear critical for both effective T-cell mediated responses and chronic immune pathologies. We describe how interventions that block or mimic the OX40-OX40L interaction can be applied to treat autoimmune diseases or enhance anti-tumor immune responses. The clinically relevant properties of these agents emphasize the importance of this particular TNFSF-TNFSF in health and disease.

Immune responses of mice with different genetic backgrounds to improved multiepitope, multitarget malaria vaccine candidate antigen FALVAC-1A

FALVAC-1A is a second-generation multitarget, multiepitope synthetic candidate vaccine against Plasmodium falciparum, incorporating elements designed to yield a stable and immunogenic molecule. Characteristics of the immunogenicity of FALVAC-1A were evaluated in congenic (H-2(b), H-2(k), and H-2(d)) and outbred strains of mice. The influences of four adjuvants (aluminum phosphate, QS-21, Montanide ISA-720, and copolymer CRL-1005) on different aspects of the immune response were also assessed. FALVAC-1A generated strong antibody responses in all mouse strains. The highest mean enzyme-linked immunosorbent assay (ELISA) antibody concentrations against FALVAC-1A were observed in the outbred ICR mice, followed by B10.BR, B10.D2, and C57BL/6 mice, though this order varied for the different adjuvants, with no statistical differences between mouse strains. In all mouse strains, the highest anti-FALVAC-1A antibody titers in ELISAs were induced by FALVAC-1A in copolymer and ISA-720 formulations, followed by QS-21 and AlPO4. These antibodies were of all four subclasses, though immunoglobulin G1 (IgG1) predominated, with the exception of FALVAC-1A with the QS-21 adjuvant, which induced predominantly IgG2c responses. Both sporozoites and blood stages of P. falciparum were recognized by anti-FALVAC-1A sera in the immunofluorescence assay. In addition to antibody, cellular immune responses were detected; these responses were studied by examining spleen cells producing gamma interferon and interleukin-4 in enzyme-linked immunospot assays. In summary, FALVAC-1A was found to be highly immunogenic and elicited functionally relevant antibodies that can recognize sporozoites and blood-stage parasites in diverse genetic backgrounds.

The modulatory effects of lipopolysaccharide-stimulated B cells on differential T-cell polarization

Lipopolysaccharide (LPS) is a major component of environmental microbial products. Studies have defined the LPS dose as a critical determining factor in driving differential T-cell polarization but the direct effects of LPS on individual antigen-presenting cells is unknown. Here, we investigated the effects of LPS doses on naive B cells and the subsequent modulatory effects of these LPS-activated B cells on T-cell polarization. The LPS was able to induce a proliferative response starting at a dose of 100 ng/ml and was capable of enhancing antigen internalization at a dose of 1 microg/ml in naive B cells. Following LPS stimulation, up-regulation of the surface markers CD40, CD86, I-Ad, immunoglobulin M, CD54 and interleukin-10 production, accompanied by down-regulation of CD5 and CD184 (CXCR4) were observed in a LPS dose-dependent manner. Low doses (<10 ng/ml) of LPS-activated B cells drove T helper type 2 polarization whereas high doses (>0.1 microg/ml) of LPS-activated B cells resulted in T regulatory type 1 cell polarization. In conclusion, LPS-activated B cells acquire differential modulatory effects on T-cell polarization. Such modulatory effects of B cells are dependent on the stimulation with LPS in a dose-dependent manner. These observations may provide one of the mechanistic explanations for the influence of environmental microbes on the development of allergic diseases.

Dendritic cell expression of OX40 ligand acts as a costimulatory, not polarizing, signal for optimal Th2 priming and memory induction in vivo

Costimulatory cross-talk can occur at multiple cellular levels to potentiate expansion and polarization of Th responses. Although OX40L ligand (OX40L) is thought to play a key role in Th2 development, the critical cellular source of this molecule has yet to be identified. In this study, we demonstrate that OX40L expression by the initiating dendritic cell (DC) is a fundamental requirement for optimal induction of primary and memory Th2 responses in vivo. Analysis of the kinetics of the residual Th2 response primed by OX40L-deficient DC suggested a failure to stimulate appropriate expansion and/or survival of T cells, rather than an inability to polarize per se. The dependence upon OX40L was predominantly due to the provision of signaling through OX40 rather than retrograde signaling to the DC. Mechanistically, impaired Th2 priming in the absence of OX40L was not due to exaggerated regulation because there was no evidence of increased expansion or function of regulatory cell populations, suppression through IL-10 production, or hyporesponsiveness to secondary challenge. These data define a critical role for DC-derived OX40L in the induction and development of Th2 responses in vivo.

IRX-2, a novel in vivo immunotherapeutic, induces maturation and activation of human dendritic cells in vitro

IRX-2 is a uniform, well-defined set of natural cytokines currently in Phase II clinical trials for squamous cell carcinoma of the head and neck (HNSCC). In preliminary clinical studies of HNSCC patients, IRX-2 therapy has shown promising results, increasing overall survival of patients from 32% to 61% at 48 months. Although it is known that specific cytokines in IRX-2 enhance T cell activity [e.g., interleukin-2 (IL-2), interferon-gamma, IL-1beta], we chose to investigate the influence of IRX-2 on monocyte-derived dendritic cells (Mo-DCs) isolated from human peripheral blood in an effort to further understand the clinical findings. We show here that IRX-2 treatment of human monocyte-derived DC resulted in morphologic, phenotypic, and functional changes consistent with the development of mature activated DC. Specifically, IRX-2-treated DC increased expression of CD83 and CCR7, markers for DC maturation and migration, respectively, and increased the expression of HLA-DR, CD54, and the costimulatory molecules CD86 and CD40, which are critical mediators of T cell activation. Functional changes in DC induced by IRX-2 included a reduced endocytic capacity, increased ability to stimulate T cells and increased IL-12 cytokine production. These results provide a plausible mechanistic explanation for the in vivo clinical activity of IRX-2 and an additional rationale for the use of IRX-2-based immunotherapy in patients.

Cytomegalovirus exploits IL-10-mediated immune regulation in the salivary glands

The salivary glands represent a major site of cytomegalovirus replication and transmission to other hosts. Despite control of viral infection by strong T cell responses in visceral organs cytomegalovirus replication continues in the salivary glands of mice, suggesting that the virus exploits the mucosal microenvironment. Here, we show that T cell immunity in the salivary glands is limited by the induction of CD4 T cells expressing the regulatory cytokine interleukin (IL)-10. Blockade of IL-10 receptor (IL-10R) with an antagonist antibody dramatically reduced viral load in the salivary glands, but not in the spleen. The mucosa-specific protection afforded by IL-10R blockade was associated with an increased accumulation of CD4 T cells expressing interferon γ, suggesting that IL-10R signaling limits effector T cell differentiation. Consistent with this, an agonist antibody targeting the tumor necrosis factor receptor superfamily member OX40 (TNFRSF4) enhanced effector T cell differentiation and increased the number of interferon γ–producing T cells, thus limiting virus replication in the salivary glands. Collectively, the results indicate that modulating effector T cell differentiation can counteract pathogen exploitation of the mucosa, thus limiting persistent virus replication and transmission.

Anti-LFA-1 antibody postpones T-cell receptor triggering while preserving generation of regulatory T cells in T-cell receptor anti-HY transgenic mice

BACKGROUND

Anti-LFA-1 (CD11a) antibody increases allograft survival and/or induces tolerance in murine models, but its mechanisms of action remain to be elucidated.

METHODS

Rag-2-/- H-2b recipient mice, bearing a transgenic T-cell receptor specific for the male antigen HY presented by MHC class II molecule, were transplanted with a C57BL/6 (H-2b) male heart with or without administration of anti-LFA-1 antibody from days -1 to 9.

RESULTS

Treatment prevented the transient episode of acute graft rejection observed in nontreated mice and maintained a naive phenotype and proliferative characteristics comparable to that of naive transgenic lymphocytes on day 7 during treatment, with decreased IFN-gamma mRNA and increased IL-4 mRNA. On day 14, phenotype and proliferative response of lymphocytes in treated mice was comparable to those of untreated animals. Furthermore, treatment did not interfere with the generation of CD4+Vbeta6+CD25+ (Foxp3) cells that were observed in long-term nontreated tolerant mice.

CONCLUSIONS

This in vivo model demonstrates that anti-LFA-1 treatment induced a transient blockade of antigen recognition, which inhibited and postponed induction of signal 1 via the TCR and decreased the intensity of the Th1 response. Importantly, LFA-1 blockade did not disturb spontaneous generation of regulatory mechanism. This treatment would be compatible in clinical settings with other therapeutics inducing regulatory mechanisms.

CD28 and ICOS: Similar or separate costimulators of T cells?

Numerous studies have revealed that the B7.1/B7.2-CD28 and B7RP-1-ICOS (Inducible COStimulator) pathways provide crucial costimulatory signals to T cells. We have compared the contribution of these pathways during primary and effector responses, in vitro and in vivo, molecularly as well as functionally. This comparison between CD28 an ICOS after initiation of T cell activation demonstrates that both CD28 and ICOS function similarly during expansion, survival and differentiation of T cells and that both CD28 and ICOS are necessary for proper IgG responses. The major differences between CD28 and ICOS are differences in expression of both receptors and ligands, and the fact that CD28 induces IL-2 production, whereas ICOS does not. In addition, ICOS is more potent in the induction of IL-10 production, a cytokine important for suppressive function of T regulatory cells. All data available at present indicate that both molecules are very suitable candidates for immunotherapy, each in their own unique way.