An Altered Self-Peptide with Superagonist Activity Blocks a CD8-Mediated Mouse Model of Type 1 Diabetes

A Single L/D-Substitution at Q4 of the mInsA2-10 Epitope Prevents Type 1 Diabetes in Humanized NOD Mice

Autoreactive CD8⁺ T cells play an indispensable key role in the destruction of pancreatic islet β-cells and the initiation of type 1 diabetes (T1D). Insulin is an essential β-cell autoantigen in T1D. An HLA-A*0201-restricted epitope of insulin A chain (mInsA_2-10) is an immunodominant ligand for autoreactive CD8⁺ T cells in NOD.β2m^null .HHD mice. Altered peptide ligands (APLs) carrying amino acid substitutions at T cell receptor (TCR) contact positions within an epitope are potential to modulate autoimmune responses via triggering altered TCR signaling. Here, we used a molecular simulation strategy to guide the generation of APL candidates by substitution of L-amino acids with D-amino acids at potential TCR contact residues (positions 4 and 6) of mInsA_2-10, named mInsA_2-10DQ4 and mInsA_2-10DC6, respectively. We found that administration of mInsA_2-10DQ4, but not DC6, significantly suppressed the development of T1D in NOD.β2m^null .HHD mice. Mechanistically, treatment with mInsA_2-10DQ4 not only notably eliminated mInsA_2-10 autoreactive CD8⁺ T cell responses but also prevented the infiltration of CD4⁺ T and CD8⁺ T cells, as well as the inflammatory responses in the pancreas of NOD.β2m^null.HHD mice. This study provides a new strategy for the development of APL vaccines for T1D prevention.

Manipulating the TCR signaling network for cellular immunotherapy: Challenges & opportunities

T cells can help confer protective immunity by eliminating infections and tumors or drive immunopathology by damaging host cells. Both outcomes require a series of steps from the activation of naïve T cells to their clonal expansion, differentiation and migration to tissue sites. In addition to specific recognition of the antigen via the T cell receptor (TCR), multiple accessory signals from costimulatory molecules, cytokines and metabolites also influence each step along the progression of the T cell response. Current efforts to modify effector T cell function in many clinical contexts focus on the latter - which encompass antigen-independent and broad, contextual regulators. Not surprisingly, such approaches are often accompanied by adverse events, as they also affect T cells not relevant to the specific treatment. In contrast, fine tuning T cell responses by precisely targeting antigen-specific TCR signals has the potential to radically alter therapeutic strategies in a focused manner. Development of such approaches, however, requires a better understanding of functioning of the TCR and the biochemical signaling network coupled to it. In this article, we review some of the recent advances which highlight important roles of TCR signals throughout the activation and differentiation of T cells during an immune response. We discuss how, an appreciation of specific signaling modalities and variant ligands that influence the function of the TCR has the potential to influence design principles for the next generation of pharmacologic and cellular therapies, especially in the context of tumor immunotherapies involving adoptive cell transfers.

T-cell receptor affinity in the age of cancer immunotherapy

The strength of the interaction between T-cell receptors (TCRs) and their ligands, peptide/major histocompatibility complex complexes (pMHCs), is one of the most frequently discussed and investigated features of T cells in immuno-oncology today. Although there are many molecules on the surface of T cells that interact with ligands on other cells, the TCR/pMHC is the only receptor-ligand pair that offers antigen specificity and dictates the functional response of the T cell. The strength of the TCR/pMHC interaction, along with the environment in which this interaction takes place, is key to how the T cell will respond. The TCR repertoire of T cells that interact with tumor-associated antigens is vast, although typically of low affinity. Here, we focus on the low-affinity interactions between TCRs from CD8+ T cells and different models used in immuno-oncology.

An altered CD8+ T cell epitope of insulin prevents type 1 diabetes in humanized NOD mice

Autoreactive CD8⁺ T cells, which play an indispensable role in β cell destruction, represent an emerging target for the prevention of type 1 diabetes (T1D). Altered peptide ligands (APLs) can efficiently induce antigen-specific T cells anergy, apoptosis or shifts in the immune response. Here, we found that HLA-A*0201-restricted CD8⁺ T cell responses against a primary β-cell autoantigen insulin epitope InsB1_5-14 were present in both NOD.β2m^null.HHD NOD mice and T1D patients. We generated several APL candidates for InsB1_5-14 by residue substitution at the p6 position. Only H6F exhibited an inhibitory effect on mInsB1_5-14-specific CD8⁺ T cell responses in vitro. H6F treatment significantly reduced the T1D incidence, which was accompanied by diminished autoreactive CD8⁺ T cell responses to mInsB1_5-14, inhibited infiltration of CD8⁺ and CD4⁺ T cells in the pancreas and reduced pro-inflammatory cytokine production in pancreatic and splenic T cells in NOD.β2m^null.HHD mice. Mechanistically, H6F treatment significantly augmented a tiny portion of CD8⁺CD25⁺Foxp3⁺ T cells in the spleen and especially in the pancreas. This subset exhibited typical Treg phenotypes and required peptide-specific restimulation to exert immunosuppressive activity. Therefore, this APL H6F may be a promising candidate with potential clinical application value for antigen-specific prevention of T1D.

Contribution of TCR signaling strength to CD8+ T cell peripheral tolerance mechanisms

Peripheral tolerance mechanisms are in place to prevent T cells from mediating aberrant immune responses directed against self and environmental Ags. Mechanisms involved in the induction of peripheral tolerance include T cell-intrinsic pathways, such as anergy or deletion, or exogenous tolerance mediated by regulatory T cells. We have previously shown that the density of peptide-MHC class I recognized by the TCR determines whether CD8(+) T cells undergo anergy or deletion. Specifically, using a TCR-transgenic CD8(+) T cell model, we demonstrated that persistent peripheral exposure to low- or high-dose peptides in the absence of inflammatory signals resulted in clonal deletion or anergy of the T cell, respectively. In this study, by altering the affinity of the peptide-MHC tolerogen for TCR, we have confirmed that this mechanism is dependent on the level of TCR signaling that the CD8(+) T cell receives. Using altered peptide ligands (APLs) displaying high TCR affinities, we show that increasing the TCR signaling favors anergy induction. Conversely, using APLs displaying a decreased TCR affinity tilted our system in the direction of deletional tolerance. We demonstrate how differential peripheral CD8(+) T cell tolerance mechanisms are controlled by both the potency and density of MHC class I-peptide tolerogen.

Fungal β-glucan, a Dectin-1 ligand, promotes protection from type 1 diabetes by inducing regulatory innate immune response

β-Glucans are naturally occurring polysaccharides in cereal grains, mushrooms, algae, or microbes, including bacteria, fungi, and yeast. Immune cells recognize these β-glucans through a cell surface pathogen recognition receptor called Dectin-1. Studies using β-glucans and other Dectin-1 binding components have demonstrated the potential of these agents in activating the immune cells for cancer treatment and controlling infections. In this study, we show that the β-glucan from Saccharomyces cerevisiae induces the expression of immune regulatory cytokines (IL-10, TGF-β1, and IL-2) and a tolerogenic enzyme (IDO) in bone marrow-derived dendritic cells as well as spleen cells. These properties can be exploited to modulate autoimmunity in the NOD mouse model of type 1 diabetes (T1D). Treatment of prediabetic NOD mice with low-dose β-glucan resulted in a profound delay in hyperglycemia, and this protection was associated with increase in the frequencies of Foxp3(+), LAP(+), and GARP(+) T cells. Upon Ag presentation, β-glucan-exposed dendritic cells induced a significant increase in Foxp3(+) and LAP(+) T cells in in vitro cultures. Furthermore, systemic coadministration of β-glucan plus pancreatic β cell Ag resulted in an enhanced protection of NOD mice from T1D as compared with treatment with β-glucan alone. These observations demonstrate that the innate immune response induced by low-dose β-glucan is regulatory in nature and can be exploited to modulate T cell response to β cell Ag for inducing an effective protection from T1D.

Altered influenza virus haemagglutinin (HA)-derived peptide is potent therapy for CIA by inducing Th1 to Th2 shift

There has been an increase in interest in the use of altered peptides as antigen-specific therapeutic agents in autoimmune diseases. Here we investigated the inhibitory effect and possible mechanism of an altered influenza virus haemagglutinin (HA)-derived peptide in collagen-induced arthritis (CIA). CIA was induced in DBA/1 mice by immunisation with type II collagen (CII). Altered HA308-317, wild-type HA308-317 or irrelevant peptide was administered intranasally beginning from arthritis onset. Clinical and histological scores were assessed, and cytokine levels in the serum or supernatants from splenocytes were determined. The percentages of Th1 and Th2 cells in response to different peptides were analysed by FACS both in vivo and in vitro. Our results showed that intranasal administration of altered HA308-317 peptide significantly ameliorated CIA. The therapeutic effect of altered HA308-317 peptide was associated with a substantial decrease in production of interferon (IFN)-γ, interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, anti-CII IgG, IgG1 and IgG2a antibodies, and an markedly increase in production of IL-10 and IL-4 in serum or supernatants from splenocytes treated with altered HA308-317 peptide. The percentage of Th2 (CD4(+)IL-4(+)) cells was upregulated significantly by altered HA308-317 peptide with a decreased percentage of Th1 (T helper 1; CD4(+)INF-γ(+)) cells both in vivo and in vitro. These findings suggest that altered HA308-317 peptide might be a promising candidate for rheumatoid arthritis (RA) treatment.

T lymphocyte responses to heterologous secondary dengue virus infections

The available evidence suggests that plasma leakage in dengue hemorrhagic fever is caused by the action of circulating mediators on the vascular endothelium, and that the host immune response is a critical determinant of this response. We have been exploring the role of dengue virus-specific T lymphocytes in the immunopathogenesis of plasma leakage. Memory dengue virus-specific T cells induced during a primary dengue virus infection are reactivated by the heterologous viral serotype during a secondary infection to expand to high levels and produce a skewed cytokine profile. Investigations are underway to identify the immunologic profiles associated with increased or decreased risk for severe disease.

Inhibition of the alloimmune response through the generation of regulatory T cells by a MHC class II-derived peptide

We have previously shown that HLA-DQA1, a peptide derived from a highly conserved region of MHC class II, prevents alloreactive T cell priming and effector function in vivo, although underlying mechanisms are obscure. In this study, we demonstrate that 28% of mice treated with HLA-DQA1 combined with low-dose rapamycin achieved permanent engraftment of fully MHC-disparate islet allografts and significantly prolonged survival in the remaining animals (log rank, p < 0.001). Immunohistologic examination of the grafts from HLA-DQA1/rapamycin-treated animals revealed up-regulated expression of TGF-ss and FoxP3. In vivo administration of blocking anti-TGF-ss or depleting anti-CD25 mAb augmented T cell alloimmunity and prevented the long-term engraft induced by HLA-DQA1. In vitro experiments further showed that HLA-DQA1 induced differentiation of CD4(+) T cells into CD4(+)CD25(+)FoxP3(+) regulatory T cells. Together, these data provide the first demonstration that HLA-DQA1, a MHC class II-derived peptide, can prolong allograft survival via a TGF-beta and regulatory T cell-dependent mechanisms.

Induction of anergy by antibody blockade of TCR in myelin oligodendrocyte glycoprotein-specific cells

Previous studies have found that a 95% reduction in TCR expression does not adversely affect response to foreign Ags, indicating that T cells have an excess of TCR for Ag recognition. Because self-reactive T cells may have low affinity for peptide:MHC, we investigated whether myelin-reactive T cells require these excess TCR for optimal response. To test this concept, mAb were used to effectively reduce the TCR of Valpha3.2 and Vbeta11 TCR transgenic mice (referred to as 2D2). After masking the TCR with either continuous or prepulsed anti-Valpha3.2 Ab, 2D2 cells were immediately stimulated with myelin oligodendrocyte glycoprotein (MOG)(35-55). These cells have a dramatic Ab dose-dependent reduction in proliferation, with a small reduction in TCR expression leading to a 50% reduction in proliferation in vitro. Additionally, 2D2 cells, treated with anti-Valpha3.2 Ab and peptide for 7 days, were re-stimulated with MOG and continue to have a dose-dependent reduction in proliferation. TCR quantitation identified the same amount of TCR on the Ab/peptide treatment compared with the peptide-only control. These results point out that the combination of reduced TCR and peptide challenge leads to a phenotypic change resulting in T cell anergy. Importantly, adoptive transfer of these anergic T cells upon autoimmune disease induction had a marked reduction in disease severity compared with untreated MOG-specific CD4(+) T cells, which had significant autoimmune disease manifested by optic neuritis and death. Thus, reduction of TCR expression may provide a potential therapy for self-reactive T cells involved in autoimmune diseases through the induction of anergy.

Enhanced Levels of Costimulation Lead to Reduced Effector/Memory CD8+ T Cell Functionality

The role of different levels of costimulation in conjunction with signal 1 in the activation of memory CD8+ T cells remains elusive. In this study, we demonstrate, in a mouse model with the influenza nucleoprotein epitope NP68, that mouse early memory (effector/memory) CD8+ T cells that were generated with high levels of costimulation have reduced CTL functionality compared with those that were generated with low levels of costimulation. This reduction is associated with increased phosphorylation of the negative regulatory site 292 on Zap70 and a decrease in granzyme B levels. Furthermore, we show that enhanced costimulation reduces proliferation and cytokine production of effector/memory CD8+ T cells in response to intermediate and weak TCR stimulation, in contrast to previously described positive effects of costimulation on naive CD8+ T cells. This effect is associated with the expression of ICAM-1 on APCs. Together, our results indicate that enhanced costimulation can lead to reduced functionality in effector/memory CD8+ T cells. This compromised effector function of effector/memory CD8+ T cells in response to high levels of costimulation can have important implications for designing immunotherapeutic strategies to enhance immune responses.

Mapping the human proteome for non-redundant peptide islands

We describe immune-proteome structures using libraries of protein fragments that define a structural immunological alphabet. We propose and validate such an alphabet as i) composed of letters of five consecutive amino acids, pentapeptide units being sufficient minimal antigenic determinants in a protein, and ii) characterized by low-similarity to human proteins, so representing structures unknown to the host and potentially able to evoke an immune response. In this context, we have thoroughly sifted through the entire human proteome searching for non-redundant protein motifs. Here, for the first time, a complete sequence redundancy dissection of the human proteome has been conducted. The non-redundant peptide islands in the human proteome have been quantified and catalogued according to the amino acid length. The library of uniquely occurring n-peptide sequences that was obtained is characterized by a logarithmic decrease of the number of non-redundant peptides as a function of the peptide length. This library represents a highly specific catalogue of molecular protein signatures, the possible use of which in cancer/autoimmunity research is discussed, with a major focus on non-redundant dodecamer sequences.

Immunization of HLA Class I Transgenic Mice Identifies Autoantigenic Epitopes Eliciting Dominant Responses in Type 1 Diabetes Patients

Type 1 diabetes (T1D) results from the autoimmune destruction of pancreatic beta cells. CD8(+) T cells have recently been assigned a major role in beta cell injury. Consequently, the identification of autoreactive CD8(+) T cells in humans remains essential for development of therapeutic strategies and of assays to identify aggressive cells. However, this identification is laborious and limited by quantities of human blood samples available. We propose a rapid and reliable method to identify autoantigen-derived epitopes recognized by human CD8(+) T lymphocytes in T1D patients. Human histocompatibility leukocyte Ags-A*0201 (HLA-A*0201) transgenic mice were immunized with plasmids encoding the T1D-associated autoantigens: 65 kDa glutamic acid decarboxylase (GAD) or insulinoma-associated protein 2 (IA-2). Candidate epitopes for T1D were selected from peptide libraries by testing the CD8(+) reactivity of vaccinated mice. All of the nine-candidate epitopes (five for GAD and four for IA-2) identified by our experimental approach were specifically recognized by CD8(+) T cells from newly diagnosed T1D patients (n = 19) but not from CD8(+) T cells of healthy controls (n = 20). Among these, GAD(114-123), GAD(536-545) and IA-2(805-813) were recognized by 53%, 25%, and 42% of T1D patients, respectively.

Lymphopenia-driven CD8+ T cells are resistant to antigen-induced tolerance in NOD.scid mice

T cells undergoing lymphopenia-driven proliferation acquire effector and memory properties that can be pathogenic. Indeed, generalized lymphopenia is associated with a variety of autoimmune diseases such as type 1 diabetes. The current study was carried out to determine how CD8(+) T cells undergoing acute lymphopenic expansion respond to antigen under tolerizing conditions in vivo. Adoptive transfer of diabetes by TCR-transgenic CD8(+) T cells was enhanced following treatment of NOD. scid recipients with a high dose of soluble peptide. Furthermore, whereas TCR-transgenic CD8(+) T cells underwent clonal deletion and failed to differentiate into CTL in peptide-treated lymphoreplete recipient mice, TCR-transgenic CD8(+) T cells in a lymphopenic environment were resistant to clonal deletion, and CTL differentiation was enhanced by a high dose of soluble peptide. Moreover, peptide treatment had distinct effects on expression of the anti-apoptotic protein Bcl-X(L) in TCR-transgenic CD8(+) T cells under lymphopenic versus lymphoreplete conditions. These results demonstrate that CD8(+) T cells undergoing lymphopenia-driven expansion in NOD. scid recipients are resistant to antigen-induced tolerance, and readily differentiate into CTL upon stimulation with a high dose of soluble peptide.

Invariant NKT cells exacerbate type 1 diabetes induced by CD8 T cells

Invariant NKT (iNKT) cells have been implicated in the regulation of autoimmune diseases. In several models of type 1 diabetes, increasing the number of iNKT cells prevents the development of disease. Because CD8 T cells play a crucial role in the pathogenesis of diabetes, we have investigated the influence of iNKT cells on diabetogenic CD8 T cells. In the present study, type 1 diabetes was induced by the transfer of CD8 T cells specific for the influenza virus hemagglutinin into recipient mice expressing the hemagglutinin Ag specifically in their beta pancreatic cells. In contrast to previous reports, high frequency of iNKT cells promoted severe insulitis and exacerbated diabetes. Analysis of diabetogenic CD8 T cells showed that iNKT cells enhance their activation, their expansion, and their differentiation into effector cells producing IFN-gamma. This first analysis of the influence of iNKT cells on diabetogenic CD8 T cells reveals that iNKT cells not only fail to regulate but in fact exacerbate the development of diabetes. Thus, iNKT cells can induce opposing effects dependent on the model of type 1 diabetes that is being studied. This prodiabetogenic capacity of iNKT cells should be taken into consideration when developing therapeutic approaches based on iNKT cell manipulation.

T cell epitope-containing peptides of the major dog allergen Can f 1 as candidates for allergen immunotherapy

One prerequisite for developing peptide-based allergen immunotherapy is knowing the T cell epitopes of an allergen. In this study, human T cell reactivity against the major dog allergen Can f 1 was investigated to determine peptides suitable for immunotherapy. Seven T cell epitope regions (A-G) were found in Can f 1 with specific T cell lines and clones. The localization of the epitope regions shows similarities with those of the epitopes found in Bos d 2 and Rat n 1. On average, individuals recognized three epitopes in Can f 1. Our results suggest that seven 16-mer peptides (p15-30, p33-48, p49-64, p73-88, p107-122, p123-138, and p141-156), each from one of the epitope regions, show widespread T cell reactivity in the population studied, and they bind efficiently to seven HLA-DRB1 molecules (DRB1*0101, DRB1*0301, DRB1*0401, DRB1*0701, DRB1*1101, DRB1*1301, and DRB1*1501) predominant in Caucasian populations. Therefore, these peptides are potential candidates for immunotherapy of dog allergy.

Immunomodulatory potential of heteroclitic analogs of the dominant T-cell epitope of lipocalin allergen Bos d 2 on specific T cells

Peptide-based allergen immunotherapy is a novel alternative for conventional allergen immunotherapy. Here, we have characterized the immunomodulatory potential of heteroclitic peptide analogs of the immunodominant epitope of lipocalin allergen Bos d 2 on specific human T-cell clones. The TCR affinity of Bos d 2-specific T-cell clones for the natural peptide ligand and its heteroclitic analogs was assessed with fluorescent-labeled MHC class II tetramers. The activation and cytokine production of the clones were analyzed upon stimulation with the different ligands. Moreover, the capacity of the heteroclitic analogs to induce hyporesponsiveness and cell death was examined. The T-cell clones F1-9 and K3-2 bound MHC class II tetramers loaded with the heteroclitic peptide analogs of the immunodominant epitope of Bos d 2 with increased affinity. At similar peptide concentrations, stimulation of the clones with the heteroclitic analogs favored increased IFN-gamma/IL-4 and IFN-gamma/IL-5 ratios in comparison with stimulation with the natural peptide ligand. Moreover, the T-cell clones stimulated with the heteroclitic analogs exhibited an increased susceptibility to cell death or hyporesponsiveness upon re-stimulation. Our results suggest that heteroclitic analogs of a T-cell epitope of an allergen may enhance the efficacy of peptide-based allergen immunotherapy.

Modulation of Memory CD4 T Cell Function and Survival Potential by Altering the Strength of the Recall Stimulus

Optimization of long term immunity depends on the functional persistence of memory T cells; however, there are no defined strategies for promoting memory T cell function and survival. In this study, we hypothesized that varying the strength of the recall stimulus could modulate the function and survival potential of memory CD4 T cells. We tested the ability of peptide variants of influenza hemagglutinin (HA) exhibiting strong and weak avidity for an HA-specific TCR, to modulate HA-specific memory CD4 T cells in vitro and in vivo. In vitro stimulation with a weak avidity peptide (L115) uncoupled memory CD4 T proliferation from effector cytokine production with low apoptosis, whereas stimulation with a strong avidity peptide (Y117) fully recalled memory T cell functions but triggered increased apoptosis. To determine how differential recall would affect memory T cells in vivo, we boosted BALB/c hosts of transferred, CFSE-labeled HA-specific memory CD4 T cells with native HA, Y117, and L115 variant peptides and found differences in early Ag-driven memory T cell proliferation and IL-7R expression, with subsequent changes in memory T cell yield. High avidity boosting resulted in rapid proliferation, extensive IL-7R down-regulation, and the lowest yield of HA-specific memory cells, whereas low avidity boosting triggered low in vivo proliferation, maintenance of IL-7R expression, and the highest memory T cell yield. Our results indicate that memory CD4 T cell function and survival can be modulated at the recall level, and can be optimized by low level stimulation that minimizes apoptosis and enhances responses to survival factors.

Autoimmune diabetes: ongoing development of immunological intervention strategies targeted directly against autoreactive T cells

It is well known that autoimmunity associated with the onset of insulin-dependent diabetes mellitus (IDDM) involves the generation of autoreactive T and B cells. The findings that diabetics mount humoral and cellular immune responses against islet cell antigens (ICAs) have led to the testing of ICAs and their analogs as candidates for therapeutic agents for better treatment of IDDM at its prediabetic and diabetic stages. Apart from this type of approach, various immunological intervention strategies aimed at direct targeting of the autoreactive T cells have also been investigated. The present review covers the ongoing aspects of these developments focusing on the preclinical findings made in NOD (nonobese diabetic) mice which have been commonly used as a disease model for human autoimmune diabetes. Other types of approaches involving the mobilization of regulatory T cells to indirectly control or modulate the pathological activity of autoreactive T cells will not be discussed within this scope.