Naive T cells are resistant to anergy induction by anti-CD3 antibodies

Revisiting the Principles of Designing a Vaccine

Immune principles formulated by Jenner, Pasteur, and early immunologists served as fundamental propositions for vaccine discovery against many dreadful pathogens. However, decisive success in the form of an efficacious vaccine still eludes for diseases such as tuberculosis, leishmaniasis, and trypanosomiasis. Several antileishmanial vaccine trials have been undertaken in past decades incorporating live, attenuated, killed, or subunit vaccination, but the goal remains unmet. In light of the above facts, we have to reassess the principles of vaccination by dissecting factors associated with the hosts' immune response. This chapter discusses the pathogen-associated perturbations at various junctures during the generation of the immune response which inhibits antigenic processing, presentation, or remodels memory T cell repertoire. This can lead to ineffective priming or inappropriate activation of memory T cells during challenge infection. Thus, despite a protective primary response, vaccine failure can occur due to altered immune environments in the presence of pathogens.

Mechanobiology of T Cell Activation: To Catch a Bond

T cell activation is a critical event in the adaptive immune response, indispensable for cell-mediated and humoral immunity as well as for immune regulation. Recent years have witnessed an emerging trend emphasizing the essential role that physical force and mechanical properties play at the T cell interface. In this review, we integrate current knowledge of T cell antigen recognition and the different models of T cell activation from the perspective of mechanobiology, focusing on the interaction between the T cell receptor (TCR) and the peptide-major histocompatibility complex (pMHC) antigen. We address the shortcomings of TCR affinity alone in explaining T cell functional outcomes and the rising status of force-regulated TCR bond lifetimes, most notably the TCR catch bond. Ultimately, T cell activation and the ensuing physiological responses result from mechanical interaction between TCRs and the pMHC. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Conversion of Anergic T Cells Into Foxp3- IL-10+ Regulatory T Cells by a Second Antigen Stimulus In Vivo

T cell anergy is a common mechanism of T cell tolerance. However, although anergic T cells are retained for longer time periods in their hosts, they remain functionally passive. Here, we describe the induction of anergic CD4⁺ T cells in vivo by intravenous application of high doses of antigen and their subsequent conversion into suppressive Foxp3^- IL-10⁺ Tr1 cells but not Foxp3⁺ Tregs. We describe the kinetics of up-regulation of several memory-, anergy- and suppression-related markers such as CD44, CD73, FR4, CD25, CD28, PD-1, Egr-2, Foxp3 and CTLA-4 in this process. The conversion into suppressive Tr1 cells correlates with the transient intracellular CTLA-4 expression and required the restimulation of anergic cells in a short-term time window. Restimulation after longer time periods, when CTLA-4 is down-regulated again retains the anergic state but does not lead to the induction of suppressor function. Our data require further functional investigations but at this stage may suggest a role for anergic T cells as a circulating pool of passive cells that may be re-activated into Tr1 cells upon short-term restimulation with high and systemic doses of antigen. It is tentative to speculate that such a scenario may represent cases of allergen responses in non-allergic individuals.

Comprehensive analysis of epigenetically regulated genes in anergic T cells

T cell anergy is one of the important mechanisms for immune tolerance. The results of many studies investigating the mechanism for T cell anergy induction have revealed that the expression of several genes was up-regulated in anergic T cells. It has also been demonstrated that the molecules encoded on those genes played a critical role in anergy induction. However, the mechanism for their up-regulation has not previously been clarified. We examined in this study the changes in gene expression and DNA methylation status caused by anergy induction. Our results demonstrate that the expression of many genes was changed by anergy induction, and that the DNA methylation status of some of these genes was also changed. We show here by a GO analysis that the extent of the change in methylation status caused by anergy induction was distinct between the groups of genes that were categorized.

Induction of CD4(+) Regulatory and Polarized Effector/helper T Cells by Dendritic Cells

Dendritic cells (DCs) are considered to play major roles during the induction of T cell immune responses as well as the maintenance of T cell tolerance. Naive CD4(+) T cells have been shown to respond with high plasticity to signals inducing their polarization into effector/helper or regulatory T cells. Data obtained from in vitro generated bone-marrow (BM)-derived DCs as well as genetic mouse models revealed an important but not exclusive role of DCs in shaping CD4(+) T cell responses. Besides the specialization of some conventional DC subsets for the induction of polarized immunity, also the maturation stage, activation of specialized transcription factors and the cytokine production of DCs have major impact on CD4(+) T cells. Since in vitro generated BM-DCs show a high diversity to shape CD4(+) T cells and their high similarity to monocyte-derived DCs in vivo, this review reports data mainly on BM-DCs in this process and only touches the roles of transcription factors or of DC subsets, which have been discussed elsewhere. Here, recent findings on 1) the conversion of naive into anergic and further into Foxp3(-) regulatory T cells (Treg) by immature DCs, 2) the role of RelB in steady state migratory DCs (ssmDCs) for conversion of naive T cells into Foxp3(+) Treg, 3) the DC maturation signature for polarized Th2 cell induction and 4) the DC source of IL-12 for Th1 induction are discussed.

Treatment of new onset type 1 diabetes with teplizumab: successes and pitfalls in development

INTRODUCTION

Type 1 diabetes is an organ-specific autoimmune disease, characterized by selective destruction of insulin-producing pancreatic β-cells by T-cell-mediated inflammation. Beginning with studies of cyclosporin A in the 1980s, but with more activity in the past decade, there have been a number of clinical trials to test whether immunotherapies can arrest the decline in C-peptide, which is associated with progression of type 1 diabetes leading to the metabolic instability that characterizes the disease. One of the most promising agents, teplizumab , is an FcR-nonbinding anti-CD3 monoclonal antibody that has been tested in Phase II - III clinical trials and was shown to preserve the C-peptide levels and reduce the need for exogenous insulin.

AREAS COVERED

In this review, we discuss the recent update on clinical data obtained from trials of teplizumab in type 1 diabetes, the drug's postulated mechanism of action and the identification of responders to therapy. We highlight the results of recent trials as well as the lessons that have been learned from the clinical trials involving selection of end points and the inclusion of diverse study populations.

EXPERT OPINION

Teplizumab has been shown to preserve β cell function in patients; however, it does not represent a 'cure' for patients, and its efficacy does entail a significant advance in arresting the progression of the disease toward complete insulin deficiency and reliance on exogenous insulin.

Immature dendritic cells convert anergic nonregulatory T cells into Foxp3- IL-10+ regulatory T cells by engaging CD28 and CTLA-4

Anergic T cells can survive for long time periods passively in a hyporesponsive state without obvious active functions. Thus, the immunological reason for their maintenance is unclear. Here, we induced peptide-specific anergy in T cells from mice by coculturing these cells with immature murine dendritic cells (DCs). We found that these anergic, nonsuppressive IL-10(-) Foxp3(-) CTLA-4(+) CD25(low) Egr2(+) T cells could be converted into suppressive IL-10(+) Foxp3(-) CTLA-4(+) CD25(high) Egr2(+) cells resembling type-1 Treg cells (Tr1) when stimulated a second time by immature DCs in vitro. Addition of TGF-β during anergy induction favored Foxp3(+) Treg-cell induction, while TGF-β had little effect when added to the second stimulation. Expression of both CD28 and CTLA-4 molecules on anergic T cells was required to allow their conversion into Tr1-like cells. Suppressor activity was enabled via CD28-mediated CD25 upregulation, acting as an IL-2 sink, together with a CTLA-4-mediated inhibition of NFATc1/α activation to shut down IL-2-mediated proliferation. Together, these data provide evidence and mechanistical insights into how persistent anergic T cells may serve as a resting memory pool for Tr1-like cells.

CD4+ primary T cells expressing HCV-core protein upregulate Foxp3 and IL-10, suppressing CD4 and CD8 T cells

Adaptive T cell responses are critical for controlling HCV infection. While there is clinical evidence of a relevant role for regulatory T cells in chronic HCV-infected patients, based on their increased number and function; mechanisms underlying such a phenomena are still poorly understood. Accumulating evidence suggests that proteins from Hepatitis C virus can suppress host immune responses. We and others have shown that HCV is present in CD4+ lymphocytes from chronically infected patients and that HCV-core protein induces a state of unresponsiveness in the CD4+ tumor cell line Jurkat. Here we show that CD4+ primary T cells lentivirally transduced with HCV-core, not only acquire an anergic phenotype but also inhibit IL-2 production and proliferation of bystander CD4+ or CD8+ T cells in response to anti-CD3 plus anti-CD28 stimulation. Core-transduced CD4+ T cells show a phenotype characterized by an increased basal secretion of the regulatory cytokine IL-10, a decreased IFN-γ production upon stimulation, as well as expression of regulatory T cell markers, CTLA-4, and Foxp3. A significant induction of CD4+CD25+CD127(low)PD-1(high)TIM-3(high) regulatory T cells with an exhausted phenotype was also observed. Moreover, CCR7 expression decreased in HCV-core expressing CD4+ T cells explaining their sequestration in inflamed tissues such as the infected liver. This work provides a new perspective on de novo generation of regulatory CD4+ T cells in the periphery, induced by the expression of a single viral protein.

Conditional deletion of PTEN in peripheral T cells augments TCR-mediated activation but does not abrogate CD28 dependency or prevent anergy induction

PTEN is thought to play a critical role in T cell activation by negatively regulating the PI3K signaling pathway important for cellular activation, growth, and proliferation. To directly eliminate PTEN in postthymic T cells for studies of functional effects, we used CAR transgenic × PTEN(flox/flox) mice, which enabled gene deletion using a Cre adenovirus in vitro. These mice were also immunized to generate stable Th1 clones that could have PTEN deleted when desired. PTEN-deleted T cells exhibited enhanced IL-2 production, proliferation, and Akt phosphorylation upon TCR/CD28 engagement, whereas T cell survival was not potentiated. Gene expression profiling revealed a small subset of induced genes that were augmented upon PTEN deletion. However, PTEN-deficient T cells still required CD28 costimulation for IL-2 production and remained susceptible to anti-CD3-induced anergy. The absence of PTEN within the CD8 T cell compartment led to markedly increased cytolytic activity following an allogeneic MLR in vitro, without increasing autologous MLR activity. Our results indicate that deletion of PTEN can augment the activation of postthymic T cells but does not mediate CD28 independence or anergy resistance. Nonetheless, PTEN inhibition may be a viable target for immune potentiation owing to increased cytokine production by activated CD4(+) cells and increased cytotoxicity by CD8(+) T cells.

Peripheral blood T lymphocyte subsets in children with congenital asplenia

The aim of the current study was to examine whether a congenital lack of the spleen changes distribution, state of activation and function of peripheral lymphocyte T subsets. Seven children with congenital asplenia (CA) aged 1.5-17 years and seven age-matched controls were tested. By triple-color flow cytometry we examined: (1) the expression of CD3(+), CD4(+), CD8(+), CD19(+), and CD56(+) on lymphocytes; (2) the distribution of CD45RA(+) and CD45RO(+) in CD4(+) and CD8(+); (3) the expression of CD27(+) in the CD4(+) and CD8(+) T-cell-bearing CD45RA(+), CD45RO(+), or CD45RB(+). Lymphocyte proliferative responses and cytokines production (IFN-gamma, IL-6, TNF-alfa, and IL-10) in anti-CD3-induced peripheral blood mononuclear cells were tested. The results indicate (1) a normal distribution of the basic lymphocyte subsets, (2) low CD3(+)/CD8(+) percentage but expressing CD8(+high) and non-significantly elevated CD4(+)/CD8(+) ratio, (3) CD45RA(+high) and CD27(+high) in the CD4(+) and CD8(+) T cell, and (4) CD45RB(+high) in the CD4(+) and CD45RO(+high) in the CD8(+). The distribution of CD27(+) in the CD45RA(+) and CD45RO(+) CD4(+) T cells remained unchanged. However, the percentage of CD8(+)/CD45RO(+)/CD27(+) T cells tended to be elevated. Altogether, these data indicate that CA is connected with (1) the presence CD4(+) T cells expressing the "naive" phenotype (CD45RA(+high) RB(+high) and CD27(+high)), (2) high numbers of activated CD8(+) T cells shifted toward the memory phenotype (CD45RO(+high)) but still showing high CD27(+) expression, which may indicate failure in T CD8(+) cytotoxic effectors differentiation, and (3) a tendency to the rather pro-inflammatory status of cells, low IL-10 expression, and suboptimal lymphocytes responses to mitogenic stimulation.

Memory T-cell-specific therapeutics attenuate allograft rejection via mediation of alloreactivity in memory cells

Many means in inbred rodent models promoted long-term graft survival or donor-specific tolerance, but less so in nonhuman primates, outbred rodents or human patients. A diverse repertoire of memory T cells, derived from heterologous immunity or prior to exposure to alloantigen, has been believed to be an important part of this barrier. Memory T cells have a unique capacity to generate effector functions quickly upon re-exposure to antigen, and this capacity is achieved by reduced activation thresholds, and expressed high level trafficking and adhesion molecules, which is likely responsible for their exhibiting differential susceptibility to immune therapeutics compared with naïve T cells. This review outlines recent progress on characteristics of memory T cells and focuses on these potential therapies targeting memory T cells which are likely to ameliorate allograft rejection by inducing transplant tolerance.

Negative feedback control of the autoimmune response through antigen-induced differentiation of IL-10-secreting Th1 cells

Regulation of the immune response to self- and foreign antigens is vitally important for limiting immune pathology associated with both infections and hypersensitivity conditions. Control of autoimmune conditions can be reinforced by tolerance induction with peptide epitopes, but the mechanism is not currently understood. Repetitive intranasal administration of soluble peptide induces peripheral tolerance in myelin basic protein (MBP)–specific TCR transgenic mice. This is characterized by the presence of anergic, interleukin (IL)-10–secreting CD4⁺ T cells with regulatory function (IL-10 T reg cells). The differentiation pathway of peptide-induced IL-10 T reg cells was investigated. CD4⁺ T cells became anergic after their second encounter with a high-affinity MBP peptide analogue. Loss of proliferative capacity correlated with a switch from the Th1-associated cytokines IL-2 and interferon (IFN)-γ to the regulatory cytokine IL-10. Nevertheless, IL-10 T reg cells retained the capacity to produce IFN-γ and concomitantly expressed T-bet, demonstrating their Th1 origin. IL-10 T reg cells suppressed dendritic cell maturation, prevented Th1 cell differentiation, and thereby created a negative feedback loop for Th1-driven immune pathology. These findings demonstrate that Th1 responses can be self-limiting in the context of peripheral tolerance to a self-antigen.

Adenosine and anergy

T cells must integrate multiple environmental cues when deciding whether to mount an immunogenic or tolerogenic response. Since not all self-reactive T cells are eliminated during thymic development, mechanisms of peripheral tolerance such as T cell anergy contribute to preventing autoimmunity. Recent studies have implicated extracellular adenosine and the adenosine A(2A) receptor as playing an important role in inhibiting T cell effector function. Herein, we review the current literature regarding T cell anergy and the emerging literature implicating the A(2A) receptor as critical regulator of immune activation. Finally, we present evidence to suggest a possible role for adenosine A(2A) receptor signaling in T cell anergy.

Differential regulation of naïve and memory CD4+ T cells by alternatively activated dendritic cells

Promising immunotherapeutic tools for T cell-mediated pathologies are alternatively activated dendritic cells (aaDC), which exert their effect through the regulation and tolerization of T cells. As naïve and memory T cells have different susceptibilities to tolerogenic signals, it is important to understand the modulatory effects of aaDC on these T cell subsets. We have examined regulation of naïve and memory CD4⁺ T cells by human aaDC generated with dexamethasone, the active form of vitamin D3, 1α,25-dihydroxyvitamin D3, and LPS. Although aaDC induced low, primary, allogeneic responses by naïve and memory T cells, aaDC regulated the differentiation of these T cell subsets in a distinct manner. Naïve T cells primed by aaDC retained a strong, proliferative capacity upon restimulation but were skewed toward a low IFN-γ/high IL-10 cytokine profile. In contrast, memory T cells primed by aaDC became hyporesponsive in terms of proliferation and cytokine production. Induction of anergy in memory T cells by aaDC was not a result of the presence of CD25^hi regulatory T cells and could be partially reversed by IL-2. Both T cell subsets acquired regulatory activity and inhibited primary CD4 and CD8 responses. Addition of exogenous IL-12p70 during T cell priming by aaDC prevented anergy induction in memory T cells and cytokine polarization in naïve T cells, indicating that the lack of IL-12p70 is a key feature of aaDC. Our finding that aaDC differentially regulate naïve and memory T cells is important for understanding and maximizing the therapeutic potential of aaDC.

Induction of T-cell activation or anergy determined by the combination of intensity and duration of T-cell receptor stimulation, and sequential induction in an individual cell

It has been shown that anergic T cells have important roles in peripheral tolerance, although the precise mechanism for inducing anergy is still unclear. We analysed the kinetics of anergy induction at an individual cell level by flow cytometry. We first successfully obtained T helper type 1 (Th1) cells that had been made uniform with the level of interferon-gamma (IFN-gamma) production induced by antigen stimulation. We then used these Th1 cells to evaluate the degree of anergy for each Th1 cell treated with an anti-CD3 monoclonal antibody according to the level of IFN-gamma secretion. Our results demonstrate that anergic stimulation could induce both activation and anergy, depending on the duration and intensity of stimulation at the level of an individual cell. Each Th1 cell was first activated and then gradually became anergic depending on the duration of stimulation. The duration of the stimulus required for inducing anergy became shorter as the intensity of stimulation became stronger. We also show that the calcineurin signal controlled the induction of activation or anergy depending on the activity. This study contributes to better understanding of the precise mechanism for inducing T-cell anergy.

Nicotinamide inhibits B lymphocyte activation by disrupting MAPK signal transduction

Nicotinamide (NAm) represents both a pharmacological agent known to express cell preserving and anti-inflammatory properties, and a useful investigational tool to elucidate cellular pathways regulating a wide range of cellular functions. We demonstrate in this study that exogenous NAm, when used at pharmacological doses, inhibits activation of primary murine B lymphocytes in response to multiple ligands. NAm appears to affect a membrane proximal event leading to MAPKs activation, a transduction pathway shared by multiple receptors including the antigen-specific B cell receptor, CD38, CD40 and TLR4 receptors. NAm inhibited phospho-ERK accumulation, and only marginally affected phospho-p38 and phospho-JNK induction upon BCR stimulation of naive B lymphocytes. Accordingly, NAm also affected the expression of known targets of the MAPK ERK pathway such as CD69 and cyclin D2. Based on a comparison with well-characterized pharmacological inhibitors, we suggest in this work that NAm may inhibit a post-translational modification mediated by a yet unidentified mono(ADP-ribose)transferase. Collectively, our observations indicate that in addition to its previously described effect on cells of the innate immune system, NAm is able to modulate the activity of B lymphocytes suggesting a potential role of this vitamin in regulating antibody-mediated autoimmune disorders.

Reshaping the past: Strategies for modulating T-cell memory immune responses

Memory T cells are generated following an initial encounter with antigen, persist over the lifetime of an individual, and mediate rapid and robust functional responses upon antigenic recall. While immune memory is generally associated with protective immune response to pathogens, memory T cells can be generated to diverse types of antigens including autoantigens and alloantigens through homologous or crossreactive priming and comprise the majority of circulating T cells during adulthood. Memory T cells can therefore play critical roles in propagating and perpetuating autoimmune disease and in mediating allograft rejection, although the precise pathways for regulation of memory immune responses remain largely undefined. Moreover, evaluating and designing strategies to modulate memory T-cell responses are challenging given the remarkable heterogeneity of memory T cells, with different subsets predominating in lymphoid versus non-lymphoid tissue sites. In this review, we discuss what is presently known regarding the effect of current immunomodulation strategies on the memory T-cell compartment and potential strategies for controlling immunological recall.

T-cell tolerance or function is determined by combinatorial costimulatory signals

Activated in immune responses, T lymphocytes differentiate into effector cells with potent immune function. CD28 is the most prominent costimulatory receptor for T-cell activation. However, absence of CD28 costimulation did not completely impair effector function of CD4 or CD8 T cells. Moreover, increasing number of costimulatory molecules are recently found on antigen-presenting cells to regulate T-cell activation. To understand the molecular mechanisms that determine T-cell function or tolerance, we have collectively examined the roles of positive and negative costimulatory molecules. Antigen-specific naïve CD4 and CD8 T cells, only when activated in the absence of both CD28 and ICOS pathways, were completely impaired in effector function. These tolerant T cells not only were anergic with profound defects in TcR signal transduction but also completely lacked expression of effector-specific transcription factors. T-cell tolerance induction in this system requires the action by negative costimulatory molecules; T-cell proliferation and function was partially restored by inhibiting PD-1, B7-H3 or B7S1. This work demonstrates that T-cell function or tolerance is controlled by costimulatory signals.

The induction and maintenance of T cell anergy

While the "true" role of T cell anergy in promoting peripheral tolerance continues to be debated, it is clear that studying the various models of anergy have led to important insight in terms of understanding the pathways and molecules responsible for T cell activation and inhibition. This review will examine our current understanding of CD4+ T cell anergy. In particular, it will focus on the signaling pathways responsible for both the induction and maintenance of anergy. Furthermore, it will examine how specifically targeting these pathways can be exploited clinically in terms of promoting tolerance in transplantation and autoimmunity and inhibiting tumor-induced tolerance in the case of tumor-immunotherapy.