CD4+ T cells from type 1 diabetic and healthy subjects exhibit different thresholds of activation to a naturally processed proinsulin epitope

First-in-human, double-blind, randomized phase 1b study of peptide immunotherapy IMCY-0098 in new-onset type 1 diabetes: an exploratory analysis of immune biomarkers

BACKGROUND

IMCY-0098, a synthetic peptide developed to halt disease progression via elimination of key immune cells in the autoimmune cascade, has shown a promising safety profile for the treatment of type 1 diabetes (T1D) in a recent phase 1b trial. This exploratory analysis of data from that trial aimed to identify the patient biomarkers at baseline associated with a positive response to treatment and examined the associations between immune response parameters and clinical efficacy endpoints (as surrogates for mechanism of action endpoints) using an artificial intelligence-based approach of unsupervised explainable machine learning.

METHODS

We conducted an exploratory analysis of data from a phase 1b, dose-escalation, randomized, placebo-controlled study of IMCY-0098 in patients with recent-onset T1D. Here, a panel of markers of T cell activation, memory T cells, and effector T cell response were analyzed via descriptive statistics. Artificial intelligence-based analyses of associations between all variables, including immune responses and clinical responses, were performed using the Knowledge Extraction and Management (KEM®) v 3.6.2 analytical platform.

RESULTS

The relationship between all available patient data was investigated using unsupervised machine learning implemented in the KEM® environment. Of 15 associations found for the dose C group (450 μg subcutaneously followed by 3 × 225 μg subcutaneously), seven involved human leukocyte antigen (HLA) type, all of which identified improvement/absence of worsening of disease parameters in DR4+ patients and worsening/absence of improvement in DR4- patients. This association with DR4+ and non-DR3 was confirmed using the endpoints normalized area under the curve C-peptide from mixed meal tolerance tests where presence of DR4 HLA haplotype was associated with an improvement in both endpoints. Exploratory immune analysis showed that IMCY-0098 dose B (150 μg subcutaneously followed by 3 × 75 μg subcutaneously) and dose C led to an increase in presumed/potentially protective antigen-specific cytolytic CD4+ T cells and a decrease in pathogenic CD8+ T cells, consistent with the expected mechanism of action of IMCY-0098. The analysis identified significant associations between immune and clinical responses to IMCY-0098.

CONCLUSIONS

Promising preliminary efficacy results support the design of a phase 2 study of IMCY-0098 in patients with recent-onset T1D.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03272269; EudraCT: 2016-003514-27.

Technical Validation and Utility of an HLA Class II Tetramer Assay for Type 1 Diabetes: A Multicenter Study

CONTEXT

Validated assays to measure autoantigen-specific T-cell frequency and phenotypes are needed for assessing the risk of developing diabetes, monitoring disease progression, evaluating responses to treatment, and personalizing antigen-based therapies.

OBJECTIVE

Toward this end, we performed a technical validation of a tetramer assay for HLA-DRA-DRB1*04:01, a class II allele that is strongly associated with susceptibility to type 1 diabetes (T1D).

METHODS

HLA-DRA-DRB1*04:01-restricted T cells specific for immunodominant epitopes from islet cell antigens GAD65, IGRP, preproinsulin, and ZnT8, and a reference influenza epitope, were enumerated and phenotyped in a single staining tube with a tetramer assay. Single and multicenter testing was performed, using a clone-spiked specimen and replicate samples from T1D patients, with a target coefficient of variation (CV) less than 30%. The same assay was applied to an exploratory cross-sectional sample set with 24 T1D patients to evaluate the utility of the assay.

RESULTS

Influenza-specific T-cell measurements had mean CVs of 6% for the clone-spiked specimen and 11% for T1D samples in single-center testing, and 20% and 31%, respectively, for multicenter testing. Islet-specific T-cell measurements in these same samples had mean CVs of 14% and 23% for single-center and 23% and 41% for multicenter testing. The cross-sectional study identified relationships between T-cell frequencies and phenotype and disease duration, sex, and autoantibodies. A large fraction of the islet-specific T cells exhibited a naive phenotype.

CONCLUSION

Our results demonstrate that the assay is reproducible and useful to characterize islet-specific T cells and identify correlations between T-cell measures and clinical traits.

Pancreatic islet-specific engineered Tregs exhibit robust antigen-specific and bystander immune suppression in type 1 diabetes models

Adoptive transfer of regulatory T cells (T_regs) is therapeutic in type 1 diabetes (T1D) mouse models. T_regs that are specific for pancreatic islets are more potent than polyclonal T_regs in preventing disease. However, the frequency of antigen-specific natural T_regs is extremely low, and ex vivo expansion may destabilize T_regs, leading to an effector phenotype. Here, we generated durable, antigen-specific engineered T_regs (EngT_regs) from primary human CD4⁺ T cells by combining FOXP3 homology-directed repair editing and lentiviral T cell receptor (TCR) delivery. Using TCRs derived from clonally expanded CD4⁺ T cells isolated from patients with T1D, we generated islet-specific EngT_regs that suppressed effector T cell (T_eff) proliferation and cytokine production. EngT_regs suppressed T_effs recognizing the same islet antigen in addition to bystander T_effs recognizing other islet antigens through production of soluble mediators and both direct and indirect mechanisms. Adoptively transferred murine islet-specific EngT_regs homed to the pancreas and blocked diabetes triggered by islet-specific T_effs or diabetogenic polyclonal T_effs in recipient mice. These data demonstrate the potential of antigen-specific EngT_regs as a targeted therapy for preventing T1D.

Insulin B-chain hybrid peptides are agonists for T cells reactive to insulin B:9-23 in autoimmune diabetes

Insulin is considered to be a key antigenic target of T cells in Type 1 Diabetes (T1D) and autoimmune diabetes in the NOD mouse with particular focus on the B-chain amino acid sequence B:9-23 as the primary epitope. Our lab previously discovered that hybrid insulin peptides (HIPs), comprised of insulin C-peptide fragments fused to other β-cell granule peptides, are ligands for several pathogenic CD4 T cell clones derived from NOD mice and for autoreactive CD4 T cells from T1D patients. A subset of CD4 T cell clones from our panel react to insulin and B:9-23 but only at high concentrations of antigen. We hypothesized that HIPs might also be formed from insulin B-chain sequences covalently bound to other endogenously cleaved ß-cell proteins. We report here on the identification of a B-chain HIP, termed the 6.3HIP, containing a fragment of B:9-23 joined to an endogenously processed peptide of ProSAAS, as a strong neo-epitope for the insulin-reactive CD4 T cell clone BDC-6.3. Using an I-Ag7 tetramer loaded with the 6.3HIP, we demonstrate that T cells reactive to this B-chain HIP can be readily detected in NOD mouse islet infiltrates. This work suggests that some portion of autoreactive T cells stimulated by insulin B:9-23 may be responding to B-chain HIPs as peptide ligands.

Autoreactive T cell receptors with shared germline-like α chains in type 1 diabetes

Human islet antigen reactive CD4⁺ memory T cells (IAR T cells) play a key role in the pathogenesis of autoimmune type 1 diabetes (T1D). Using single-cell RNA sequencing (scRNA-Seq) to identify T cell receptors (TCRs) in IAR T cells, we have identified a class of TCRs that share TCRα chains between individuals (“public” chains). We isolated IAR T cells from blood of healthy, new-onset T1D and established T1D donors using multiplexed CD154 enrichment and identified paired TCRαβ sequences from 2767 individual cells. More than a quarter of cells shared TCR junctions between 2 or more cells (“expanded”), and 29/47 (~62%) of expanded TCRs tested showed specificity for islet antigen epitopes. Public TCRs sharing TCRα junctions were most prominent in new-onset T1D. Public TCR sequences were more germline like than expanded unique, or “private,” TCRs, and had shorter junction sequences, suggestive of fewer random nucleotide insertions. Public TCRα junctions were often paired with mismatched TCRβ junctions in TCRs; remarkably, a subset of these TCRs exhibited cross-reactivity toward distinct islet antigen peptides. Our findings demonstrate a prevalent population of IAR T cells with diverse specificities determined by TCRs with restricted TCRα junctions and germline-constrained antigen recognition properties. Since these “innate-like” TCRs differ from previously described immunodominant TCRβ chains in autoimmunity, they have implications for fundamental studies of disease mechanisms. Self-reactive restricted TCRα chains and their associated epitopes should be considered in fundamental and translational investigations of TCRs in T1D.

Proinsulin-specific T-cell responses correlate with estimated c-peptide and predict partial remission duration in type 1 diabetes

Objective

Type 1 diabetes (T1D) is an autoimmune disorder in which autoreactive T cells destroy insulin-producing β-cells. Interventions that preserve β-cell function represent a fundamental therapeutic goal in T1D and biomarkers that predict and monitor β-cell function, and changes in islet autoantigenic signatures are needed. As proinsulin and neoantigens derived from proinsulin peptides (hybrid insulin peptides, HIPs) are important T1D autoantigens, we analysed peripheral blood CD4⁺ T-cell autoantigen-specific proliferative responses and their relationship to estimated β-cell function.

Methods

We recruited 72 people with and 42 without T1D, including 17 pre-diabetic islet antibody-positive and 9 antibody-negative first-degree relatives and 16 unrelated healthy controls with T1D-risk HLA types. We estimated C-peptide level at 3-month intervals for 2 years post-diagnosis and measured CD4⁺ T-cell proliferation to proinsulin epitopes and HIPs using an optimised bioassay.

Results

We show that CD4⁺ T-cell proliferation to any islet peptide and to multiple epitopes were significantly more frequent in pre-diabetic islet antibody-positive siblings and participants with T1D ≤ 3 months of duration, than in participants with T1D > 3 months or healthy controls. Among participants with T1D and first-degree relatives, CD4⁺ T-cell proliferation occurred most frequently in response to proinsulin_33-63 (full-length C-peptide). Proinsulin_33-63-specific responses were associated with HLA-DR3-DQ2 and/or HLA-DR4/DQ8. In children with T1D, proinsulin_33-63-specific T-cell proliferation positively associated with concurrent estimated C-peptide and predicted survival in honeymoon.

Conclusion

CD4⁺ T-cell proliferative responses to proinsulin-containing autoantigens are common before and immediately after diagnosis of T1D but decline thereafter. Proinsulin_33-63-specific CD4⁺ T-cell response is a novel marker of estimated residual endogenous β-cell function and predicts a better 2-year disease outcome.

Characterization of Proinsulin T Cell Epitopes Restricted by Type 1 Diabetes-Associated HLA Class II Molecules

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which the insulin-producing β cells within the pancreas are destroyed. Identification of target Ags and epitopes of the β cell-reactive T cells is important both for understanding T1D pathogenesis and for the rational development of Ag-specific immunotherapies for the disease. Several studies suggest that proinsulin is an early and integral target autoantigen in T1D. However, proinsulin epitopes recognized by human CD4⁺ T cells have not been comprehensively characterized. Using a dye dilution-based T cell cloning method, we generated and characterized 24 unique proinsulin-specific CD4⁺ T cell clones from the peripheral blood of 17 individuals who carry the high-risk DR3-DQ2 and/or DR4-DQ8 HLA class II haplotypes. Some of the clones recognized previously reported DR4-restricted epitopes within the C-peptide (C25-35) or A-chain (A1-15) of proinsulin. However, we also characterized DR3-restricted epitopes within both the B-chain (B16-27 and B22-C3) and C-peptide (C25-35). Moreover, we identified DQ2-restricted epitopes within the B-chain and several DQ2- or DQ8-restricted epitopes within the C-terminal region of C-peptide that partially overlap with previously reported DQ-restricted epitopes. Two of the DQ2-restricted epitopes, B18-26 and C22-33, were shown to be naturally processed from whole human proinsulin. Finally, we observed a higher frequency of CDR3 sequences matching the TCR sequences of the proinsulin-specific T cell clones in pancreatic lymph node samples compared with spleen samples. In conclusion, we confirmed several previously reported epitopes but also identified novel (to our knowledge) epitopes within proinsulin, which are presented by HLA class II molecules associated with T1D risk.

Characterization of proinsulin-specific regulatory T cells in type 1 diabetes at different ages of onset

BACKGROUND AND OBJECTIVES

Regulatory T cells (Tregs) play an important role in maintaining tolerance to self-antigens. Defects in the frequency and function of polyclonal Tregs have been reported in type 1 diabetes (T1D). However, characteristics of proinsulin (PI)-specific Tregs in human T1D have not yet been explored. Therefore, we aimed to characterize PI-specific Tregs in two distinct pathophysiological subtypes of T1D, juvenile-onset T1D (JOT1D) and adult-onset T1D (AOT1D), distinguished by the age of onset.

METHODS

Peripheral blood mononuclear cells of the recruited subjects were stimulated in vitro with PI-derived peptides. PI-specific Tregs were characterized by flow cytometry using the combination of markers CD25, CD137, FOXP3 and CD45RA.

RESULTS

Firstly, we observed similar frequencies of polyclonal Tregs in the T1D (n = 25) and healthy control (HC) (n = 20) subjects (P = 0.96), with a positive correlation between age and frequency of polyclonal Tregs (r = +0.35, P = 0.04). While the frequency of polyclonal Tregs was higher in AOT1D group (P = 0.02), both JOT1D (n = 14) and AOT1D groups (n = 11) had a comparable frequency of PI-specific Tregs in their peripheral blood. The frequency of PI-specific memory Tregs was significantly high in both the JOT1D (P = 0.02) and AOT1D (P = 0.009) groups compared to their respective HC groups (n = 10). Finally, we observed no significant difference in the expression of FOXP3 and IL-2 receptor in PI-specific Tregs in all the groups.

CONCLUSIONS

Unlike polyclonal Tregs, both T1D subtypes harbor comparable frequencies of PI-specific Tregs. Chronic antigen presentation results in a distinct memory-like phenotype of PI-specific Tregs in these subjects irrespective of the age of disease onset.

Epitope Stealing as a Mechanism of Dominant Protection by HLA-DQ6 in Type 1 Diabetes

The heterozygous DQ2/8 (DQA1*05:01-DQB1*02:01/DQA1*03:01-DQB1*03:02) genotype confers the highest risk in type 1 diabetes (T1D), whereas the DQ6/8 (DQA1*02:01-DQB1*06:02/DQA1*03:01-DQB1*03:02) genotype is protective. The mechanism of dominant protection by DQ6 (DQB1*06:02) is unknown. We tested the hypothesis that DQ6 interferes with peptide binding to DQ8 by competition for islet epitope ("epitope stealing") by analysis of the islet ligandome presented by HLA-DQ6/8 and -DQ8/8 on dendritic cells pulsed with islet autoantigens preproinsulin (PPI), GAD65, and IA-2, followed by competition assays using a newly established "epitope-stealing" HLA/peptide-binding assay. HLA-DQ ligandome analysis revealed a distinct DQ6 peptide-binding motif compared with the susceptible DQ2/8 molecules. PPI and IA-2 peptides were identified from DQ6, of DQ6/8 heterozygous dendritic cells, but no DQ8 islet peptides were retrieved. Insulin B6-23, a highly immunogenic CD4 T-cell epitope in patients with T1D, bound to both DQ6 and DQ8. Yet, binding of InsB6-23 to DQ8 was prevented by DQ6. We obtained first functional evidence of a mechanism of dominant protection from disease, in which HLA molecules associated with protection bind islet epitopes in a different, competing, HLA-binding register, leading to "epitope stealing" and conceivably diverting the immune response from islet epitopes presented by disease-susceptible HLA molecules in the absence of protective HLA.

A Novel Approach of Identifying Immunodominant Self and Viral Antigen Cross-Reactive T Cells and Defining the Epitopes They Recognize

Infection and vaccination can lead to activation of autoreactive T cells, including the activation of cross-reactive T cells. However, detecting these cross-reactive T cells and identifying the non-self and self-antigen epitopes is difficult. The current study demonstrates the utility of a novel approach that effectively accomplishes both. We utilized surface expression of CD38 on newly activated CD4 memory T cells as a strategy to identify type 1 diabetes associated autoreactive T cells activated by influenza vaccination in healthy subjects. We identified an influenza A matrix protein (MP) specific CD4+ T cell clone that cross-recognizes an immunodominant epitope from Glutamic Acid Decarboxylase 65 (GAD65) protein. The sequences of the MP and GAD65 peptides are rather distinct, with only 2 identical amino acids within the HLA-DR binding region. This result suggests that activation of autoreactive T cells by microbial infection under certain physiological conditions can occur amongst peptides with minimum amino acid sequence homology. This novel strategy also provides a new research pathway in which to examine activation of autoreactive CD4+ T cells after vaccination or natural infection.

DRB4*01:01 Has a Distinct Motif and Presents a Proinsulin Epitope That Is Recognized in Subjects with Type 1 Diabetes

DRB4*01:01 (DRB4) is a secondary HLA-DR product that is part of the high-risk DR4/DQ8 haplotype that is associated with type 1 diabetes (T1D). DRB4 shares considerable homology with HLA-DR4 alleles that predispose to autoimmunity, including DRB1*04:01 and DRB1*04:04. However, the DRB4 protein sequence includes distinct residues that would be expected to alter the characteristics of its binding pockets. To identify high-affinity peptides that are recognized in the context of DRB4, we used an HLA class II tetramer-based approach to identify epitopes within multiple viral Ags. We applied a similar approach to identify antigenic sequences within glutamic acid decarboxylase 65 and pre-proinsulin that are recognized in the context of DRB4. Seven sequences were immunogenic, eliciting high-affinity T cell responses in DRB4⁺ subjects. DRB1*04:01-restricted responses toward many of these peptides have been previously described, but responses to a novel pre-proinsulin 9-28 peptide were commonly observed in subjects with T1D. Furthermore, T cells that recognized this peptide in the context of DRB4 were present at significantly higher frequencies in patients with T1D than in healthy controls, implicating this as a disease-relevant specificity that may contribute to the breakdown of β cell tolerance in genetically susceptible individuals. We then deduced a DRB4 motif and confirmed its key features through structural modeling. This modeling suggested that the core epitope within the pre-proinsulin 9-28 peptide has a somewhat unusual binding motif, with tryptophan in the fourth binding pocket of DRB4, perhaps influencing the availability of this complex for T cell selection.

Analysis of pancreatic beta cell specific CD4+ T cells reveals a predominance of proinsulin specific cells

CD4+ T cell responses are thought to play a role in type 1 diabetes (T1D). However, detection and characterization of T cells that respond to beta cell epitopes in subjects with T1D has been limited by technical obstacles, including the inherently low frequencies in peripheral blood and variable responsiveness of individual subjects to single epitopes. We implemented a multicolor staining approach that allows direct ex vivo characterization of multiple CD4+ T cell specificities in a single sample. Here we demonstrate and apply that multicolor approach to directly measure the frequency and phenotype of beta cell specific CD4+ T cells in T1D patients and HLA matched controls. For this work we utilized five DR0401 restricted peptides from proinsulin, GAD65, IA-2, and IGRP, which were previously reported as disease relevant epitopes. Surprisingly, although responses to each of these peptides can be readily detected after in vitro expansion, our results indicated that only proinsulin specific T cells were consistently detectable at moderate frequencies in subjects with T1D. Characterization of beta cell specific CD4+ T cells revealed only modest differences between subjects with T1D and healthy controls. Subjects with T1D did have higher proportions of CD45RA negative epitope specific T cells than controls. In patients epitope specific T cells were often CXCR3 positive and a substantial proportion were CCR7 negative, suggesting a Th1-like effector phenotype. Finally, we demonstrated that our multicolor staining approach is compatible with class I multimer analysis, facilitating the characterization of self-reactive CD4+ and CD8+ T cells using a single sample.

Inflammation-Induced Citrullinated Glucose-Regulated Protein 78 Elicits Immune Responses in Human Type 1 Diabetes

The β-cell has become recognized as a central player in the pathogenesis of type 1 diabetes with the generation of neoantigens as potential triggers for breaking immune tolerance. We report that posttranslationally modified glucose-regulated protein 78 (GRP78) is a novel autoantigen in human type 1 diabetes. When human islets were exposed to inflammatory stress induced by interleukin-1β, tumor necrosis factor-α, and interferon-γ, arginine residue R510 within GRP78 was converted into citrulline, as evidenced by liquid chromatography-tandem mass spectrometry. This conversion, known as citrullination, led to the generation of neoepitopes, which effectively could be presented by HLA-DRB1*04:01 molecules. With the use of HLA-DRB1*04:01 tetramers and ELISA techniques, we demonstrate enhanced antigenicity of citrullinated GRP78 with significantly increased CD4+ T-cell responses and autoantibody titers in patients with type 1 diabetes compared with healthy control subjects. Of note, patients with type 1 diabetes had a predominantly higher percentage of central memory cells and a lower percentage of effector memory cells directed against citrullinated GRP78 compared with the native epitope. These results strongly suggest that citrullination of β-cell proteins, exemplified here by the citrullination of GRP78, contributes to loss of self-tolerance toward β-cells in human type 1 diabetes, indicating that β-cells actively participate in their own demise.

Single-Cell RNA Sequencing Reveals Expanded Clones of Islet Antigen-Reactive CD4+ T Cells in Peripheral Blood of Subjects with Type 1 Diabetes

The significance of islet Ag-reactive T cells found in peripheral blood of type 1 diabetes (T1D) subjects is unclear, partly because similar cells are also found in healthy control (HC) subjects. We hypothesized that key disease-associated cells would show evidence of prior Ag exposure, inferred from expanded TCR clonotypes, and essential phenotypic properties in their transcriptomes. To test this, we developed single-cell RNA sequencing procedures for identifying TCR clonotypes and transcript phenotypes in individual T cells. We applied these procedures to analysis of islet Ag-reactive CD4⁺ memory T cells from the blood of T1D and HC individuals after activation with pooled immunodominant islet peptides. We found extensive TCR clonotype sharing in Ag-activated cells, especially from individual T1D subjects, consistent with in vivo T cell expansion during disease progression. The expanded clonotype from one T1D subject was detected at repeat visits spanning >15 mo, demonstrating clonotype stability. Notably, we found no clonotype sharing between subjects, indicating a predominance of "private" TCR specificities. Expanded clones from two T1D subjects recognized distinct IGRP peptides, implicating this molecule as a trigger for CD4⁺ T cell expansion. Although overall transcript profiles of cells from HC and T1D subjects were similar, profiles from the most expanded clones were distinctive. Our findings demonstrate that islet Ag-reactive CD4⁺ memory T cells with unique Ag specificities and phenotypes are expanded during disease progression and can be detected by single-cell analysis of peripheral blood.

Antigen-Specific T Cell Analysis Reveals That Active Immune Responses to β Cell Antigens Are Focused on a Unique Set of Epitopes

CD38 is an activation marker that is present on recently activated T cells, but absent on resting memory T cells. In this study, we show that CD45RO⁺CD38⁺ β cell Ag-specific CD4⁺ T cells were present at higher frequencies in type 1 diabetes subjects compared with those in healthy subjects. These results imply an ongoing β cell immunity years after onset of diabetes and suggest these activated T cells have an active role in the disease process. The Ag specificities of these activated T cells were determined by a novel CD154 T cell epitope mapping assay. Although each patient usually had a unique set of epitopes recognized by these T cells, two epitopes, DR0401-restricted modified preproinsulin peptide 78-90^K88S and zinc transport 8 266-285, were repeatedly identified in multiple subjects. Identifying these T cells and their specific antigenic epitopes might provide immunotherapeutic targets for personalized therapies.

T Cell-Mediated Beta Cell Destruction: Autoimmunity and Alloimmunity in the Context of Type 1 Diabetes

Type 1 diabetes (T1D) results from destruction of pancreatic beta cells by T cells of the immune system. Despite improvements in insulin analogs and continuous blood glucose level monitoring, there is no cure for T1D, and some individuals develop life-threatening complications. Pancreas and islet transplantation have been attractive therapeutic approaches; however, transplants containing insulin-producing cells are vulnerable to both recurrent autoimmunity and conventional allograft rejection. Current immune suppression treatments subdue the immune system, but not without complications. Ideally a successful approach would target only the destructive immune cells and leave the remaining immune system intact to fight foreign pathogens. This review discusses the autoimmune diabetes disease process, diabetic complications that warrant a transplant, and alloimmunity. First, we describe the current understanding of autoimmune destruction of beta cells including the roles of CD4 and CD8 T cells and several possibilities for antigen-specific tolerance induction. Second, we outline diabetic complications necessitating beta cell replacement. Third, we discuss transplant recognition, potential sources for beta cell replacement, and tolerance-promoting therapies under development. We hypothesize that a better understanding of autoreactive T cell targets during disease pathogenesis and alloimmunity following transplant destruction could enhance attempts to re-establish tolerance to beta cells.

Expanding antigen-specific regulatory networks to treat autoimmunity

Regulatory T cells hold promise as targets for therapeutic intervention in autoimmunity, but approaches capable of expanding antigen-specific regulatory T cells in vivo are currently not available. Here we show that systemic delivery of nanoparticles coated with autoimmune-disease-relevant peptides bound to major histocompatibility complex class II (pMHCII) molecules triggers the generation and expansion of antigen-specific regulatory CD4(+) T cell type 1 (TR1)-like cells in different mouse models, including mice humanized with lymphocytes from patients, leading to resolution of established autoimmune phenomena. Ten pMHCII-based nanomedicines show similar biological effects, regardless of genetic background, prevalence of the cognate T-cell population or MHC restriction. These nanomedicines promote the differentiation of disease-primed autoreactive T cells into TR1-like cells, which in turn suppress autoantigen-loaded antigen-presenting cells and drive the differentiation of cognate B cells into disease-suppressing regulatory B cells, without compromising systemic immunity. pMHCII-based nanomedicines thus represent a new class of drugs, potentially useful for treating a broad spectrum of autoimmune conditions in a disease-specific manner.

Enhanced Detection of Antigen-Specific CD4+ T Cells Using Altered Peptide Flanking Residue Peptide-MHC Class II Multimers

Fluorochrome-conjugated peptide-MHC (pMHC) class I multimers are staple components of the immunologist's toolbox, enabling reliable quantification and analysis of Ag-specific CD8(+) T cells irrespective of functional outputs. In contrast, widespread use of the equivalent pMHC class II (pMHC-II) reagents has been hindered by intrinsically weaker TCR affinities for pMHC-II, a lack of cooperative binding between the TCR and CD4 coreceptor, and a low frequency of Ag-specific CD4(+) T cell populations in the peripheral blood. In this study, we show that peptide flanking regions, extending beyond the central nonamer core of MHC-II-bound peptides, can enhance TCR-pMHC-II binding and T cell activation without loss of specificity. Consistent with these findings, pMHC-II multimers incorporating peptide flanking residue modifications proved superior for the ex vivo detection, characterization, and manipulation of Ag-specific CD4(+) T cells, highlighting an unappreciated feature of TCR-pMHC-II interactions.

T cell epitopes and post-translationally modified epitopes in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease in which progressive loss of self-tolerance, evidenced by accumulation of auto-antibodies and auto-reactive T cells that recognize diverse self-proteins, leads to immune-mediated destruction of pancreatic beta cells and loss of insulin secretion. In this review, we discuss antigens and epitopes in T1D and the role that post-translational modifications play in circumventing tolerance mechanisms and increasing antigenic diversity. Emerging data suggest that, analogous to other autoimmune diseases such as rheumatoid arthritis and celiac disease, enzymatically modified epitopes are preferentially recognized in T1D. Modifying enzymes such as peptidyl deiminases and tissue transglutaminase are activated in response to beta cell stress, providing a mechanistic link between post-translational modification and interactions with the environment. Although studies of such responses in the at-risk population have been limited, current data suggests that breakdown in tolerance through post-translational modification represents an important checkpoint in the development of T1D.

Role of viruses and bacteria-virus interactions in autoimmunity

A potential role for viral and bacterial-viral interactions in the pathogenesis of autoimmune disease has been long recognized. Recently, intensive investigation has begun to decipher interactions between specific microbes with the host that contribute toward autoimmunity. This work has primarily focused on known viral and bacterial pathogens. A major challenge is to determine the role of bacteria that are typically considered as commensals as well as chronic viruses. Furthermore, equally challenging is to prove causality given the potential complexity of microbe-microbe interactions. Important initial contributions to this field have shown that specific interactions of microbes with hosts that contain a background of genetic susceptibility can play a role in autoimmune pathogenesis. In this review, we describe principles of immune tolerance with a focus on its breakdown during pathogenic as well as commensal relationships between the host and the microbial world.

Autoreactive T cells specific for insulin B:11-23 recognize a low-affinity peptide register in human subjects with autoimmune diabetes

Previous studies in type 1 diabetes (T1D) in the nonobese diabetic mouse demonstrated that a crucial insulin epitope (B:9-23) is presented to diabetogenic CD4 T cells by IA(g7) in a weakly bound register. The importance of antigenic peptides with low-affinity HLA binding in human autoimmune disease remains less clear. The objective of this study was to investigate T-cell responses to a low-affinity self-epitope in subjects with T1D. HLA-DQ8 tetramers loaded with a modified insulin peptide designed to improve binding the low-affinity register were used to visualize T-cell responses following in vitro stimulation. Positive responses were only detectable in T1D patients. Because the immunogenic register of B:9-23 presented by DQ8 has not been conclusively demonstrated, T-cell assays using substituted peptides and DQ8 constructs engineered to express and present B:9-23 in fixed binding registers were used to determine the immunogenic register of this peptide. Tetramer-positive T-cell clones isolated from T1D subjects that responded to stimulation by B:11-23 peptide and denatured insulin protein were conclusively shown to recognize B:11-23 bound to HLA-DQ8 in the low-affinity register 3. These T cells also responded to homologous peptides derived from microbial antigens, suggesting that their initial priming could occur via molecular mimicry. These results are in accord with prior observations from the nonobese diabetic mouse model, suggesting a mechanism shared by mouse and man through which T cells that recognize a weakly bound peptide can circumvent tolerance mechanisms and play a role in the initiation of autoimmune diseases, such as T1D.

Avidity-dependent programming of autoreactive T cells in T1D

Fate determination for autoreactive T cells relies on a series of avidity-dependent interactions during T cell selection, represented by two general types of signals, one based on antigen expression and density during T cell development, and one based on genes that interpret the avidity of TCR interaction to guide developmental outcome. We used proinsulin-specific HLA class II tetramers to purify and determine transcriptional signatures for autoreactive T cells under differential selection in type 1 diabetes (T1D), in which insulin (INS) genotypes consist of protective and susceptible alleles that regulate the level of proinsulin expression in the thymus. Upregulation of steroid nuclear receptor family 4A (NR4A) and early growth response family genes in proinsulin-specific T cells was observed in individuals with susceptible INS-VNTR genotypes, suggesting a mechanism for avidity-dependent fate determination of the T cell repertoire in T1D. The NR4A genes act as translators of TCR signal strength that guide central and peripheral T cell fate decisions through transcriptional modification. We propose that maintenance of an NR4A-guided program in low avidity autoreactive T cells in T1D reflects their prior developmental experience influenced by proinsulin expression, identifying a pathway permissive for autoimmunity.

A humanized mouse model of autoimmune insulitis

Many mechanisms of and treatments for type 1 diabetes studied in the NOD mouse model have not been replicated in human disease models. Thus, the field of diabetes research remains hindered by the lack of an in vivo system in which to study the development and onset of autoimmune diabetes. To this end, we characterized a system using human CD4(+) T cells pulsed with autoantigen-derived peptides. Six weeks after injection of as few as 0.5 × 10(6) antigen-pulsed cells into the NOD-Scid Il2rg(-/-) mouse expressing the human HLA-DR4 transgene, infiltration of mouse islets by human T cells was seen. Although islet infiltration occurred with both healthy and diabetic donor antigen-pulsed CD4(+) T cells, diabetic donor injections yielded significantly greater levels of insulitis. Additionally, significantly reduced insulin staining was observed in mice injected with CD4(+) T-cell lines from diabetic donors. Increased levels of demethylated β-cell-derived DNA in the bloodstream accompanied this loss of insulin staining. Together, these data show that injection of small numbers of autoantigen-reactive CD4(+) T cells can cause a targeted, destructive infiltration of pancreatic β-cells. This model may be valuable for understanding mechanisms of induction of human diabetes.

Posttranslational modification of HLA-DQ binding islet autoantigens in type 1 diabetes

Posttranslational modification (PTM) of islet autoantigens can cause lack of central tolerance in type 1 diabetes (T1D). Tissue transglutaminase (tTG), involved in PTM of gluten antigens in celiac disease, creates negatively charged peptides favored by T1D-predisposing HLA-DQ molecules, offering an attractive candidate modifying islet autoantigens in T1D. The highly predisposing HLA-DQ8cis/trans molecules share preferences for negatively charged peptides, as well as distinct peptide-binding characteristics that distinguish their peptide-binding repertoire. We screened islet autoantigens with the tTG substrate motif for candidate-modified epitopes binding to HLA-DQ8cis/trans and identified 31 candidate islet epitopes. Deamidation was confirmed for 28 peptides (90%). Two of these epitopes preferentially bound to HLA-DQ8cis and six to HLA-DQ8trans upon deamidation, whereas all other peptides bound equally to HLA-DQ8cis/trans. HLA-DQ8cis-restricted T cells from a new-onset T1D patient could only be generated against a deamidated proinsulin peptide, but cross-reacted with native proinsulin peptide upon restimulation. The rate of T-cell autoreactivity in recent-onset T1D patients extended from 42% to native insulin to 68% adding responses to modified proinsulin, versus 20% and 37% respectively, in healthy donors. Most patients responded by interferon-γ, whereas most healthy donors produced interleukin-10 only. Thus, T-cell autoreactivity exists to modified islet epitopes that differs in quality and quantity between patients and healthy donors.

Decreased CD127 expression on CD4+ T-cells and elevated frequencies of CD4+CD25+CD127- T-cells in children with long-lasting type 1 diabetes

Pathobiology of type 1 diabetes (T1D) is predominantly associated with T-cell-related actions. Homeostasis of majority of T-cells is critically dependent on signals mediated by CD127 (interleukin-7 receptor, IL-7R). In contrast, regulatory T-cells express very little CD127 and thereby may be delineated by CD4+CD25+CD127− phenotype. Here we aimed to analyze CD127 expression on CD4+ and CD8+ T-cells and enumerate CD4+CD25+CD127− T-cells in long-lasting T1D. T-cells were analyzed by flow cytometry and immunologic data were correlated with vascular, metabolic, and inflammatory parameters. We demonstrated significantly decreased CD127 levels on CD4+, but not CD8+, T cells in T1D pediatric patients. Interestingly, frequencies of CD4+CD25+CD127− T-cells were significantly enhanced in T1D children and correlated well with frequencies of CD34+CD144+ endothelial progenitor cells and CD4+CD25− T-cells. Levels of CD127 on both CD4+ and CD8+ T-cells in T1D patients were not correlated to each other or HbA_1C. Interestingly, however, CD127 levels on CD4+ T-cells were significantly correlated to frequencies of CD4+CD25+CD127− T-cells, whereas CD127 levels on CD8+ T-cells were significantly correlated to concentrations of VEGF and triglycerides. Our data indicate that CD127 expression is differentially modulated on CD4+ and CD8+ T-cells in the course of T1D. Moreover, we demonstrated that, in contrast to recent-onset T1D, long-lasting T1D is associated with enhancement of T-cells with regulatory phenotype.

Revisiting the old link between infection and autoimmune disease with commensals and T helper 17 cells

Genetic composition and major histocompatibility complex polymorphisms unequivocally predispose to autoimmune disease, but environmental factors also play a critical role in precipitating disease in susceptible individuals. Notorious among these has been microbial infection. Older studies describing associations between microbial infection and autoimmune disease are now followed by new studies demonstrating correlations between susceptibility to autoimmune disease and commensal colonization of the intestinal tract. T helper 17 (T(H)17) cells have gained a prominent role in autoimmune disease, and notably, their development within the intestine has been linked to colonization with specific commensal bacteria. Here, we consider current views on how microbes, T(H)17 cells, and autoimmunity are connected. We speculate on how the intricate relationships among commensal, pathogen, and the host might ultimately determine susceptibility to autoimmune disease.

Immunobiology of beta-cell destruction

Type 1 diabetes is a chronic disease characterized by severe insulin deficiency and hyperglycemia, due to autoimmune destruction of pancreatic islets of Langerhans. A susceptible genetic background is necessary, but not sufficient, for the development of the disease. Epidemiological and clinical observations underscore the importance of environmental factors as triggers of type 1 diabetes, currently under investigation. Islet-specific autoantibodies precede clinical onset by months to years and are established tools for risk prediction, yet minor players in the pathogenesis of the disease. Many efforts have been made to elucidate disease-relevant defects in the key immune effectors of islet destruction, from the early failure of specific tolerance to the vicious circle of destructive insulitis. However, the events triggering islet autoimmunity as well as the transition to overt diabetes are still largely unknown, making prevention and treatment strategies still a challenge.

A functional framework for interpretation of genetic associations in T1D

Susceptibility to type 1 diabetes is attributable to genes that link disease progression to distinct steps in immune activation, expansion, and regulation. Recent studies illustrate examples of disease-associated variants that function in multiple cell types and independent pathways, some that impact different steps of a single mechanistic pathway, and some that are functionally interactive for deterministic events in setting thresholds for immune response.

MHC class II tetramers

MHC class II tetramers have emerged as an important tool for characterization of the specificity and phenotype of CD4 T cell immune responses, useful in a large variety of disease and vaccine studies. Issues of specific T cell frequency, biodistribution, and avidity, coupled with the large genetic diversity of potential class II restriction elements, require targeted experimental design. Translational opportunities for immune disease monitoring are driving the rapid development of HLA class II tetramer use in clinical applications, together with innovations in tetramer production and epitope discovery.

Immunology of Diabetes Society T-Cell Workshop: HLA class II tetramer-directed epitope validation initiative

BACKGROUND

Islet-antigen-specific CD4+ T cells are known to promote auto-immune destruction in T1D. Measuring T-cell number and function provides an important biomarker. In response to this need, we evaluated responses to proinsulin and GAD epitopes in a multicentre study.

METHODS

A tetramer-based assay was used in five participating centres to measure T-cell reactivities to DR0401-restricted epitopes. Three participating centres concurrently performed ELISPOT or immunoblot assays. Each centre used blind-coded, centrally distributed peptide and tetramer reagents.

RESULTS

All participating centres detected responses to auto-antigens and the positive control antigen, and in some cases cloned the corresponding T cells. However, response rates varied among centres. In total, 74% of patients were positive for at least one islet epitope. The most commonly recognized epitope was GAD270-285. Only a minority of the patients tested by tetramer and ELISPOT were concordant for both assays.

CONCLUSIONS

This study successfully detected GAD and proinsulin responses using centrally distributed blind-coded reagents. Centres with little previous experience using class II tetramer reagents implemented the assay. The variability in response rates observed for different centres suggests technical difficulties and/or heterogeneity within the local patient populations tested. Dual analysis by tetramer and ELISPOT or immunoblot assays was frequently discordant, suggesting that these assays detect distinct cell populations. Future efforts should investigate shared blood samples to evaluate assay reproducibility and longitudinal samples to identify changes in T-cell phenotype that correlate with changes in disease course.

Comparison of cryopreservation methods on T-cell responses to islet and control antigens from type 1 diabetic patients and controls

BACKGROUND

Type 1 diabetes (T1D) is a cell-mediated autoimmune disease characterized by destruction of the pancreatic islet cells. The use of cryopreserved cells is preferable to the use of freshly isolated cells to monitor clinical trials to decrease assay and laboratory variability.

METHODS

The T-Cell Workshop Committee of the Immunology of Diabetes Society compared two widely accepted T-cell freezing protocols (warm and cold) to freshly isolated peripheral blood mononuclear cells from patients with T1D and controls in terms of recovery, viability, cell subset composition, and performance in functional assays currently in use in T1D-related research. Nine laboratories participated in the study with four different functional assays included.

RESULTS

The cold freezing method yielded higher recovery and viability compared with the warm freezing method. Irrespective of freezing protocol, B cells and CD8+ T cells were enriched, monocyte fraction decreased, and islet antigen-reactive responses were lower in frozen versus fresh cells. However, these results need to take in to account that the overall response to islet autoantigens was low in some assays.

CONCLUSIONS

In the current study, none of the tested T-cell functional assays performed well using frozen samples. More research is required to identify a freezing method and a T-cell functional assay that will produce responses in patients with T1D comparable to responses using fresh peripheral blood mononuclear cells.

Increased frequencies of myelin oligodendrocyte glycoprotein/MHC class II-binding CD4 cells in patients with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease characterized by infiltration of pathogenic immune cells in the CNS resulting in destruction of the myelin sheath and surrounding axons. We and others have previously measured the frequency of human myelin-reactive T cells in peripheral blood. Using T cell cloning techniques, a modest increase in the frequency of myelin-reactive T cells in patients as compared with control subjects was observed. In this study, we investigated whether myelin oligodendrocyte glycoprotein (MOG)-specific T cells could be detected and their frequency was measured using DRB1*0401/MOG(97-109(107E-S)) tetramers in MS subjects and healthy controls expressing HLA class II DRB1*0401. We defined the optimal culture conditions for expansion of MOG-reactive T cells upon MOG peptide stimulation of PMBCs. MOG(97-109)-reactive CD4(+) T cells, isolated with DRB1*0401/MOG(97-109) tetramers, and after a short-term culture of PMBCs with MOG(97-109) peptides, were detected more frequently from patients with MS as compared with healthy controls. T cell clones from single cell cloning of DRB1*0401/MOG(97-109(107E-S)) tetramer(+) cells confirmed that these T cell clones were responsive to both the native and the substituted MOG peptide. These data indicate that autoantigen-specific T cells can be detected and enumerated from the blood of subjects using class II tetramers, and the frequency of MOG(97-109)-reactive T cells is greater in patients with MS as compared with healthy controls.

The potential of multimer technologies in type 1 diabetes prediction strategies

Type 1 diabetes is an autoimmune disease which occurs in (human leukocyte antigen) genetically predisposed individuals as a consequence of the organ-specific immune destruction of the insulin-producing β cells in the islets of Langherans within the pancreas. Type 1 diabetes is the result of a breakdown in immune regulation that leads to expansion of autoreactive CD4+ and CD8+ T cells, autoantibody-producing B lymphocytes and activation of the innate immune system. Islet-related autoantibodies revealed themselves to be good predictors of future onset of the disease, although they are not directly pathogenetic; T cells instead play a dominant role in disease initiation and progression. In this review, we first discuss the approaches that several laboratories attempted to measure human islet autoantigen-specific T-cell function in type 1 diabetes. T-cell assays could be used in combination with standardized autoantibody screenings to improve predictive strategies. They could also help to monitor in long-term follow-up the efficacy of tolerogenic immunotherapeutic strategies when established at the onset of the disease, and help to predict the recurrence of disease. Although some recent developments based on enzyme-linked immunosorbent spot and immunoblotting techniques have been able to distinguish with good sensitivity and specificity patients from controls, T-cell results, as revealed by international workshops, were indeed largely inconclusive. Nowadays, novel technologies have been exploited that could contribute to answering the tantalizing question of identifying autoreactive T cells. We particularly focus on and discuss MHC multimer tools and emphasize the advantages they can offer but also their weaknesses when used in combination with other T-cell assays. Copyright © 2011 John Wiley & Sons, Ltd.

Allergen-specific naïve and memory CD4+ T cells exhibit functional and phenotypic differences between individuals with or without allergy

Although allergen-specific CD4(+) T cells are detectable in the peripheral blood of both individuals with or without allergy, their frequencies and phenotypes within the memory as well as naïve repertoires are incompletely known. Here, we analyzed the DRB1*0401-restricted responses of peripheral blood-derived memory (CD4(+)CD45RO(+)) and naïve (CD4(+)CD45RA(+)) T cells from subjects with or without allergy against the immunodominant epitope of the major cow dander allergen Bos d 2 by HLA class II tetramers in vitro. The frequency of Bos d 2(127-142)-specific memory T cells in the peripheral blood-derived cultures appeared to be higher in subjects with allergy than those without, whereas naïve Bos d 2(127-142)-specific T cells were detectable in the cultures of both groups at nearly the same frequency. Surprisingly, the TCR avidity of Bos d 2(127-142)-specific T cells of naïve origin, as assessed by the intensity of HLA class II tetramer staining, was found to be higher in individuals with allergy. Upon restimulation, long-term Bos d 2(127-142)-specific T-cell lines generated from both memory and naïve T-cell pools from individuals with allergy proliferated more strongly, produced more IL-4 and IL-10, and expressed higher levels of CD25 but lower levels of CXCR3 than the T-cell lines from individuals without allergy, demonstrating differences also at the functional level. Collectively, our current results suggest that not only the memory but also the naïve allergen-specific T-cell repertoires differ between individuals with or without allergy.

Current approaches to measuring human islet-antigen specific T cell function in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease caused by the T cell-mediated destruction of the pancreatic insulin-producing beta cells. Currently there are no widely accepted and standardized assays available to analyse the function of autoreactive T cells involved in T1D. The development of such an assay would greatly aid efforts to understand the pathogenesis of T1D and is also urgently required to guide the development of antigen-based therapies intended to prevent, or cure, T1D. Here we describe some of the assays used currently to detect autoreactive T cells in human blood and review critically their strengths and weaknesses. The challenges and future prospects for the T cell assays are discussed.

Diagnostic challenges in celiac disease and the role of the tissue transglutaminase-neo-epitope

The diagnosis of celiac disease (CD) remains a clinical challenge based on the incomplete specificity and sensitivity rates of current non-invasive tests. Furthermore, histological assessments fail to identify all overt cases and, in particular, do not manifest pathognomonic alterations in silent cases. Accordingly, the majority of CD cases are diagnosed with great delay. Recent research into the pathogenesis of CD, allowed us to identify a neo-antigen that appears to be the most promising serological tool for the detection of anti-tissue transglutaminase as well as anti-gliadin antibodies.

Prediction and pathogenesis in type 1 diabetes

A combination of genetic and immunological features is useful for prediction of autoimmune diabetes. Patterns of immune response correspond to the progression from a preclinical phase of disease to end-stage islet damage, with biomarkers indicating transition from susceptibility to active autoimmunity, and to a final loss of immune regulation. Here, we review the markers that provide evidence for immunological checkpoint failure and that also provide tools for assessment of individualized disease risk. When viewed in the context of genetic variation that influences immune response thresholds, progression from susceptibility to overt disease displays predictable modalities of clinical presentation resulting from a sequential series of failed homeostatic checkpoints for selection and activation of immunity.

Insulin gene VNTR genotype associates with frequency and phenotype of the autoimmune response to proinsulin

Immune responses to autoantigens are in part controlled by deletion of autoreactive cells through genetically regulated selection mechanisms. We have directly analyzed peripheral CD4+ proinsulin (PI) 76–90 (SLQPLALEGSLQKRG)-specific T cells using soluble fluorescent major histocompatibility complex class II tetramers. Subjects with type I diabetes and healthy controls with high levels of peripheral proinsulin-specific T cells were characterized by the presence of a disease-susceptible polymorphism in the insulin variable number of tandem repeats (INS-VNTR) gene. Conversely, subjects with a ‘protective' polymorphism in the INS-VNTR gene had nearly undetectable levels of proinsulin tetramer-positive T cells. These results strongly imply a direct relationship between genetic control of autoantigen expression and peripheral autoreactivity, in which proinsulin genotype restricts the quantity and quality of the potential T-cell response. Using a modified tetramer to isolate low-avidity proinsulin-specific T cells from subjects with the susceptible genotype, transcript arrays identified several induced pro-apoptotic genes in the control, but not diabetic subjects, likely representing a second peripheral mechanism for maintenance of tolerance to self antigens.

Immunology of beta-cell destruction

The pancreatic islet beta-cells are the target for an autoimmune process that eventually results in an inability to control blood glucose due to the lack of insulin. The different steps that eventually lead to the complete loss of the beta-cells are reviewed to include the very first step of a triggering event that initiates the development of beta-cell autoimmunity to the last step of appearance of islet-cell autoantibodies, which may mark that insulitis is about to form. The observations that the initial beta-cell destruction by virus or other environmental factors triggers islet autoimmunity not in the islets but in the draining pancreatic lymph nodes are reviewed along with possible basic mechanisms of loss of tolerance to islet autoantigens. Once islet autoimmunity is established the question is how beta-cells are progressively killed by autoreactive lymphocytes which eventually results in chronic insulitis. Many of these series of events have been dissected in spontaneously diabetic mice or rats, but controlled clinical trials have shown that rodent observations are not always translated into mechanisms in humans. Attempts are therefore needed to clarify the step 1 triggering mechanisms and the step to chronic autoimmune insulitis to develop evidence-based treatment approaches to prevent type 1 diabetes.

Insufficient deactivation of the protein tyrosine kinase lck amplifies T-cell responsiveness in acute coronary syndrome

RATIONALE

In the vulnerable atherosclerotic plaque, T cells may destabilize the tissue structure through direct cell-injurious effector functions. T cells transmit environmental signals, such as recognition of antigen, into cellular responses through regulated phosphorylation of cytoplasmic proteins, with the Src family kinase Lck (lymphocyte-specific protein tyrosine kinase) in critical membrane-proximal position of the T-cell receptor (TCR) signaling cascade. The balance between protein phosphorylation and dephosphorylation defines the signal transduction threshold and determines appropriate T-cell responses.

OBJECTIVE

We have examined whether abnormal calibration of intracellular signaling pathways renders acute coronary syndrome (ACS) patients susceptible to disproportionate T-cell responses.

METHODS AND RESULTS

Intracellular signaling cascades were quantified in CD4 T cells from ACS patients and control individuals after stimulation with major histocompatibility complex class II-superantigen complexes. ACS T cells mobilized more intracellular calcium and accumulated higher levels of phosphotyrosine than control T cells. Proximal steps in TCR signaling, such as recruitment of ZAP-70 and clustering of TCR complexes in the immune synapse, were abnormally enhanced in ACS T cells. Acceleration of the signaling cascade derived from a proximal defect in ACS T cells, which failed to phosphorylate Lck at Tyr505, extending activation of the Src kinase. Abnormalities in TCR signaling did not correlate with systemic inflammation as measured by C-reactive protein.

CONCLUSIONS

An intrinsic abnormality in the signaling machinery of ACS T cells resulting in the accumulation of active Lck lowers the TCR threshold and renders lymphocytes hyperreactive and capable of unwanted immune responses.

Detection of GAD65 autoreactive T-cells by HLA class I tetramers in type 1 diabetic patients

Type 1 diabetes (T1D) is an autoimmune disease, in which pancreatic β cells are destroyed in genetically predisposed individuals. While the direct contribution of autoantibodies to the disease pathogenesis is controversial, it is generally recognised that the mechanism of β cell destruction is mediated by autoreactive T cells that had escaped the thymic selection. We aimed to design a method to detect circulating CD8+ T cells autoreactive against an epitope of the glutamic acid decarboxylase autoantigen, isoform 65 (GAD65) ex vivo in T1D patients by using HLA class I tetramers. Low frequencies of GAD65 peptide-specific CD8+ cytotoxic T lymphocytes were detected in peripheral blood lymphocytes (PBMC) of normal controls after GAD65 peptide-specific stimulation. Conversely, their frequencies were significantly higher than in controls in PBMC of T1D patients after GAD65 peptide stimulation. These preliminary data are encouraging in order to develop a reliable assay to be employed in large-scale screening studies.

Low-dose, low-dose-rate proton radiation modulates CD4(+) T cell gene expression

PURPOSE

To evaluate cluster of differentiation 4(+) (CD4(+)) T cell gene expression and related parameters after whole-body exposure to proton radiation as it occurs in the spaceflight environment.

MATERIALS AND METHODS

C57BL/6 mice were irradiated to total doses of 0, 0.01, 0.05, and 0.1 gray (Gy) at 0.1 cGy/h. On day 0 spleens were harvested from a subset in the 0, 0.01 and 0.1 Gy groups; (CD4(+)) T cells were isolated; and expression of 84 genes relevant to T helper (Th) cell function was determined using reverse transcriptase-polymerase chain reaction (RT-PCR). Remaining mice were euthanized on days 0, 4, and 21 for additional analyses.

RESULTS

Genes with >2-fold difference and p < 0.05 compared to 0 Gy were noted. After 0.01 Gy, five genes were up-regulated (Ccr5, Cd40, Cebpb, Igsf6, Tnfsf4) and three were down-regulated (Il4ra, Mapk8, Nfkb1). After 0.1 Gy there were nine up-regulated genes (Ccr4, Cd40, Cebpb, Cxcr3, Socs5, Stat4, Tbx21, Tnfrsf4, Tnfsf4); none were down-regulated. On day 0 after 0.01 Gy, CD4(+) T cell counts and CD4:CD8 ratio were low in the spleen (p < 0.05). Spontaneous DNA synthesis in both spleen and blood was lowest in the 0.01 Gy group on day 0; on days 4 and 21 all p values were >0.1.

CONCLUSION

The data show that the pattern of gene expression in CD4(+) T cells after protracted low-dose proton irradiation was significantly modified and highly dependent upon total dose. The findings also suggest that low-dose radiation, especially 0.01 Gy, may enhance CD4(+) T cell responsiveness.