Tolerance-inducing therapies in coeliac disease - mechanisms, progress and future directions

Coeliac disease is an autoinflammatory condition caused by immune reactions to cereal gluten proteins. Currently, the only available treatment for the condition is a lifelong avoidance of gluten proteins in the diet. There is an unmet need for alternative therapies. Coeliac disease has a strong association with certain HLA-DQ allotypes (DQ2.5, DQ2.2 and DQ8), and these disease-associated HLA-DQ molecules present deamidated gluten peptides to gluten-specific CD4+ T cells. The gluten-specific CD4+ T cells are the drivers of the immune reactions leading to coeliac disease. Once established, the clonotypes of gluten-specific CD4+ T cells persist for decades, explaining why patients must adhere to a gluten-free diet for life. Given the key pathogenic role of gluten-specific CD4+ T cells, tolerance-inducing therapies that target these T cells are attractive for treatment of the disorder. Lessons learned from coeliac disease might provide clues for treatment of other HLA-associated diseases for which the disease-driving antigens are unknown. Thus, intensive efforts have been and are currently implemented to bring an effective tolerance-inducing therapy for coeliac disease. This Review discusses mechanisms of the various approaches taken, summarizing the progress made, and highlights future directions in this field.

The Immunobiology and Pathogenesis of Celiac Disease

Among human leukocyte antigen (HLA)-associated disorders, celiac disease has an immunopathogenesis that is particularly well understood. The condition is characterized by hypersensitivity to cereal gluten proteins, and the disease lesion is localized in the gut. Still, the diagnosis can be made by detection of highly disease-specific autoantibodies to transglutaminase 2 in the blood. We now have mechanistic insights into how the disease-predisposing HLA-DQ molecules, via presentation of posttranslationally modified gluten peptides, are connected to the generation of these autoantibodies. This review presents our current understanding of the immunobiology of this common disorder that is positioned in the border zone between food hypersensitivity and autoimmunity.

Intestinal and blood lymphograms as new diagnostic tests for celiac disease

Accurate celiac disease (CD) diagnosis is still challenging for some specific patients or circumstances. Thus, much effort has been expended last decades focused on seronegative or low grade enteropathy CD and, especially, on enable early diagnosis of individuals on a gluten-free diet (GFD). We discuss here two diagnostic approaches based on immunophenotyping by flow cytometry that we expect to reduce the persistent low diagnostic rates and the common diagnostic delay. The intraepithelial lymphogram is based on determining the percentage of TCRγδ+ and surface CD3- lymphocytes in the intestinal epithelium. The concomitant increase in TCRγδ+ and decrease in surface CD3- intraepithelial lymphocytes has been termed the celiac lymphogram and has been proved to be discriminative in seronegative, low grade enteropathy and potential CD, as well as in most CD patients on a GFD. A blood lymphogram based on the analysis of activated gut-homing CD8+ T cells combined with a 3-day gluten challenge is also considered, which has shown high sensitivity and specificity to diagnose seropositive Marsh 1 and Marsh 3 CD in individuals following a GFD. In addition, flow cytometry can be extremely useful in cases of refractory CD type II to identify aberrant cells. Those approaches represent highly accurate methods for CD diagnosis, being simple, fast, highly reproducible and of easy implementation in clinical practice.

Review article: Diagnosis of coeliac disease: a perspective on current and future approaches

Diagnostics will play a central role in addressing the ongoing dramatic rise in global prevalence of coeliac disease, and in deploying new non-dietary therapeutics. Clearer understanding of the immunopathogenesis of coeliac disease and the utility of serology has led to partial acceptance of non-biopsy diagnosis in selected cases. Non-biopsy diagnosis may expand further because research methods for measuring gluten-specific CD4+ T cells and the acute recall response to gluten ingestion in patients is now relatively straightforward. This perspective on diagnosis in the context of the immunopathogenesis of coeliac disease sets out to highlight current consensus, limitations of current practices, gluten food challenge for diagnosis and the potential for diagnostics that measure the underlying cause for coeliac disease, gluten-specific immunity.

Phenotype-Based Isolation of Antigen-Specific CD4+ T Cells in Autoimmunity: A Study of Celiac Disease

The pathogenic immune response in celiac disease (CeD) is orchestrated by phenotypically distinct CD4+ T cells that recognize gluten epitopes in the context of disease-associated HLA-DQ allotypes. Cells with the same distinct phenotype, but with elusive specificities, are increased across multiple autoimmune conditions. Here, whether sorting of T cells based on their distinct phenotype (Tphe cells) yields gluten-reactive cells in CeD is tested. The method's efficiency is benchmarked by parallel isolation of gluten-reactive T cells (Ttet cells), using HLA-DQ:gluten peptide tetramers. From gut biopsies of 12 untreated HLA-DQ2.5+ CeD patients, Ttet+ /Tphe+ , Ttet- /Tphe+ , and Ttet- /Tphe- cells are sorted for single-cell T-cell receptor (TCR)-sequencing (n = 8) and T-cell clone (TCC)-generation (n = 5). The generated TCCs are TCR sequenced and tested for their reactivity against deamidated gluten. Gluten-reactivity is observed in 91.2% of Ttet+ /Tphe+ TCCs, 65.3% of Ttet- /Tphe+ TCCs and 0% of Ttet- /Tphe- TCCs. TCR sequencing reveals clonal expansion and sequence sharing across patients, features reflecting antigen-driven responses. The feasibility to isolate antigen-specific CD4+ T cells by the sole use of phenotypic markers in CeD outlines a potential avenue for characterizing disease-driving CD4+ T cells in autoimmune conditions.

Structural bases of T cell antigen receptor recognition in celiac disease

Celiac disease (CeD) is a human leukocyte antigen (HLA)-linked autoimmune-like disorder that is triggered by the ingestion of gluten or related storage proteins. The majority of CeD patients are HLA-DQ2.5⁺, with the remainder being either HLA-DQ8⁺ or HLA-DQ2.2⁺. Structural studies have shown how deamidation of gluten epitopes engenders binding to HLA-DQ2.5/8, which then triggers an aberrant CD4⁺ T cell response. HLA tetramer studies, combined with structural investigations, have demonstrated that repeated patterns of TCR usage underpins the immune response to some HLADQ2.5/8 restricted gluten epitopes, with distinct TCR motifs representing common landing pads atop the HLA-gluten complexes. Structural studies have provided insight into TCR specificity and cross-reactivity towards gluten epitopes, as well as cross-reactivity to bacterial homologues of gluten epitopes, suggesting that environmental factors may directly play a role in CeD pathogenesis. Collectively, structural immunology-based studies in the CeD axis may lead to new therapeutics/diagnostics to treat CeD, and also serve as an exemplar for other T cell mediated autoimmune diseases.

Gut tissue-resident memory T cells in coeliac disease

This mini-review describes observations of the 1990ies with culturing of gluten-specific and astrovirus-specific CD4⁺ T cells from duodenal biopsies from subjects who presumably had a long time between the exposure to gluten or astrovirus antigens and the sampling of the biopsy. In these studies, it was also observed that antigen-specific CD4⁺ T cells migrated out of the gut biopsies during overnight culture. The findings are suggestive of memory T cells in tissue which are resident, but which also can be mobilised on antigen stimulation. Of note, these findings were made years before the term tissue-resident memory T cells was invoked. Since that time, many observations have accumulated on these gut T cells, particularly the gluten-specific T cells, and we have insight into the turnover of CD4⁺ T cells in the gut lamina propria. These data make it evident that human antigen-specific CD4⁺ T cells that can be cultured from gut biopsies indeed are bone fide tissue-resident memory T cells.

Emergence of an adaptive immune paradigm to explain celiac disease: a perspective on new evidence and implications for future interventions and diagnosis

INTRODUCTION

Recent patient studies have shown that gluten-free diet is less effective in treating celiac disease than previously believed, and additionally patients remain vulnerable to gluten-induced acute symptoms and systemic cytokine release. Safe and effective pharmacological adjuncts to gluten-free diet are in preclinical and clinical development. Clear understanding of the pathogenesis of celiac disease is critical for drug target identification, establishing efficacy endpoints and to develop non-invasive biomarkers suitable to monitor and potentially diagnose celiac disease.

AREAS COVERED

The role and clinical effects of CD4+ T cells directed against deamidated gluten in the context of an "adaptive immune paradigm" are reviewed. Alternative hypotheses of gluten toxicity are discussed and contrasted. In the context of recent patient studies, implications of the adaptive immune paradigm for future strategies to prevent, diagnose, and treat celiac disease are outlined.

EXPERT OPINION

Effective therapeutics for celiac disease are likely to be approved and necessitate a variety of new clinical instruments and tests to stratify patient need, monitor remission, and confirm diagnosis in uncertain cases. Sensitive assessments of CD4+ T cells specific for deamidated gluten are likely to play a central role in clinical management, and to facilitate research and pharmaceutical development.

Insights from tissue "omics" analysis on intestinal remodeling in celiac disease

Celiac disease (CeD) is a prevalent intestinal disorder that only develops in genetically susceptible individuals when they mount a harmful CD4+ T-cell response towards gluten peptides. Intake of gluten leads to inflammation and remodeling of the small intestine with symptoms such as nausea and diarrhea. The only current treatment is a lifelong gluten free diet. The immunological basis for CeD is well characterized but the mechanisms that drive intestinal remodeling are still poorly understood. Transcriptome or proteome analysis of intestinal biopsies gives a global snapshot of all processes that occur in the tissue, including alterations in the epithelial cell layer. This paper will introduce concepts of intestinal remodeling, recapitulate the current understanding of CeD pathogenesis and discuss findings from relevant tissue "omics" studies. On the basis of this review, I give perspectives on what tissue "omics" studies can tell us about disease pathogenesis with a particular focus on the gluten induced intestinal remodeling.

Differential expression profile of gluten-specific T cells identified by single-cell RNA-seq

Gluten-specific CD4⁺ T cells drive the pathogenesis of celiac disease and circulating gluten-specific T cells can be identified by staining with HLA-DQ:gluten tetramers. In this first single-cell RNA-seq study of tetramer-sorted T cells from untreated celiac disease patients blood, we found that gluten-specific T cells showed distinct transcriptomic profiles consistent with activated effector memory T cells that shared features with Th1 and follicular helper T cells. Compared to non-specific cells, gluten-specific T cells showed differential expression of several genes involved in T-cell receptor signaling, translational processes, apoptosis, fatty acid transport, and redox potentials. Many of the gluten-specific T cells studied shared T-cell receptor with each other, indicating that circulating gluten-specific T cells belong to a limited number of clones. Moreover, the transcriptional profiles of cells that shared the same clonal origin were transcriptionally more similar compared with between clonally unrelated gluten-specific cells.

A high-affinity human TCR-like antibody detects celiac disease gluten peptide-MHC complexes and inhibits T cell activation

Antibodies specific for peptides bound to human leukocyte antigen (HLA) molecules are valuable tools for studies of antigen presentation and may have therapeutic potential. Here, we generated human T cell receptor (TCR)-like antibodies toward the immunodominant signature gluten epitope DQ2.5-glia-α2 in celiac disease (CeD). Phage display selection combined with secondary targeted engineering was used to obtain highly specific antibodies with picomolar affinity. The crystal structure of a Fab fragment of the lead antibody 3.C11 in complex with HLA-DQ2.5:DQ2.5-glia-α2 revealed a binding geometry and interaction mode highly similar to prototypic TCRs specific for the same complex. Assessment of CeD biopsy material confirmed disease specificity and reinforced the notion that abundant plasma cells present antigen in the inflamed CeD gut. Furthermore, 3.C11 specifically inhibited activation and proliferation of gluten-specific CD4⁺ T cells in vitro and in HLA-DQ2.5 humanized mice, suggesting a potential for targeted intervention without compromising systemic immunity.

Circulating CD103+ γδ and CD8+ T cells are clonally shared with tissue-resident intraepithelial lymphocytes in celiac disease

Gut intraepithelial γδ and CD8⁺ αβ T lymphocytes have been connected to celiac disease (CeD) pathogenesis. Based on the previous observation that activated (CD38⁺), gut-homing (CD103⁺) γδ and CD8⁺ αβ T cells increase in blood upon oral gluten challenge, we wanted to shed light on the pathogenic involvement of these T cells by examining the clonal relationship between cells of blood and gut during gluten exposure. Of 20 gluten-challenged CeD patients, 8 and 10 had increase in (CD38⁺CD103⁺) γδ and CD8⁺ αβ T cells, respectively, while 16 had increase in gluten-specific CD4⁺ T cells. We obtained γδ and αβ TCR sequences of >2500 single cells from blood and gut of 5 patients, before and during challenge. We observed extensive sharing between blood and gut γδ and CD8⁺ αβ T-cell clonotypes even prior to gluten challenge. In subjects with challenge-induced surge of γδ and/or CD8⁺ αβ T cells, as larger populations of cells analyzed, we observed more expanded clonotypes and clonal sharing, yet no discernible TCR similarities between expanded and/or shared clonotypes. Thus, CD4⁺ T cells appear to drive expansion of clonally diverse γδ or CD8⁺ αβ T-cell clonotypes that may not be specific for the gluten antigen.

Frequency of Gluten-Reactive T Cells in Active Celiac Lesions Estimated by Direct Cell Cloning

Chronic inflammation of the small intestine in celiac disease is driven by activation of CD4+ T cells that recognize gluten peptides presented by disease-associated HLA-DQ molecules. We have performed direct cell cloning of duodenal biopsies from five untreated and one refractory celiac disease patients, and three non-celiac disease control subjects in order to assess, in an unbiased fashion, the frequency of gluten-reactive T cells in the disease-affected tissue as well as the antigen fine specificity of the responding T cells. From the biopsies of active disease lesions of five patients, 19 T-cell clones were found to be gluten-reactive out of total 1,379 clones tested. This gave an average of 1.4% (range 0.7% - 1.9%) of gluten-reactive T cells in lamina propria of active celiac lesions. Interestingly, also the patient with refractory celiac disease had gluten-reactive T cell clones in the lamina propria (5/273; 1.8%). In comparison, we found no gluten-reactive T cells in any of the total 984 T-cell clones screened from biopsies from three disease control donors. Around two thirds of the gluten-reactive clones were reactive to a panel of peptides representing known gluten T-cell epitopes, of which two thirds were reactive to the immunodominant DQ2.5-glia-α1/DQ2.5-glia-α2 and DQ2.5-glia-ω1/DQ2.5-glia-ω2 epitopes. This study shows that gluten-reactive T cells in the inflamed duodenal tissue are prevalent in the active disease lesion, and that many of these T cells are reactive to T-cell epitopes that are not yet characterized. Knowledge of the prevalence and epitope specificity of gluten-specific T cells is a prerequisite for therapeutic efforts that target disease-specific T cells in celiac disease.

Evaluating Responses to Gluten Challenge: A Randomized, Double-Blind, 2-Dose Gluten Challenge Trial

BACKGROUND & AIMS

Gluten challenge is used to diagnose celiac disease (CeD) and for clinical research. Sustained gluten exposure reliably induces histologic changes but is burdensome. We investigated the relative abilities of multiple biomarkers to assess disease activity induced by 2 gluten doses, and aimed to identify biomarkers to supplement or replace histology.

METHODS

In this randomized, double-blind, 2-dose gluten-challenge trial conducted in 2 US centers (Boston, MA), 14 adults with biopsy-proven CeD were randomized to 3 g or 10 g gluten/d for 14 days. The study was powered to detect changes in villous height to crypt depth, and stopped at planned interim analysis on reaching this end point. Additional end points included gluten-specific cluster of differentiation (CD)4 T-cell analysis with HLA-DQ2-gluten tetramers and enzyme-linked immune absorbent spot, gut-homing CD8 T cells, interleukin-2, symptoms, video capsule endoscopy, intraepithelial leukocytes, and tissue multiplex immunofluorescence.

RESULTS

All assessments showed changes with gluten challenge. However, time to maximal change, change magnitude, and gluten dose-response relationship varied. Villous height to crypt depth, video capsule endoscopy enteropathy score, enzyme-linked immune absorbent spot, gut-homing CD8 T cells, intraepithelial leukocyte counts, and HLA-DQ2-restricted gluten-specific CD4 T cells showed significant changes from baseline at 10 g gluten only; symptoms were significant at 3 g. Symptoms and plasma interleukin-2 levels increased significantly or near significantly at both doses. Interleukin-2 appeared to be the earliest, most sensitive marker of acute gluten exposure.

CONCLUSIONS

Modern biomarkers are sensitive and responsive to gluten exposure, potentially allowing less invasive, lower-dose, shorter-duration gluten ingestion. This work provides a preliminary framework for rational design of gluten challenge for CeD research. ClinicalTrials.gov number, NCT03409796.

T cell receptor repertoire as a potential diagnostic marker for celiac disease

An individual's T cell repertoire is skewed towards some specificities as a result of past antigen exposure and subsequent clonal expansion. Identifying T cell receptor signatures associated with a disease is challenging due to the overall complexity of antigens and polymorphic HLA allotypes. In celiac disease, the antigen epitopes are well characterised and the specific HLA-DQ2-restricted T-cell repertoire associated with the disease has been explored in depth. By investigating T cell receptor repertoires of unsorted lamina propria T cells from 15 individuals, we provide the first proof-of-concept study showing that it could be possible to infer disease state by matching against a priori known disease-associated T cell receptor sequences.

Coeliac Disease Pathogenesis: The Uncertainties of a Well-Known Immune Mediated Disorder

Coeliac disease is a common small bowel enteropathy arising in genetically predisposed individuals and caused by ingestion of gluten in the diet. Great advances have been made in understanding the role of the adaptive immune system in response to gluten peptides. Despite detailed knowledge of these adaptive immune mechanisms, the complete series of pathogenic events responsible for development of the tissue lesion remains less certain. This review contributes to the field by discussing additional mechanisms which may also contribute to pathogenesis. These include the production of cytokines such as interleukin-15 by intestinal epithelial cells and local antigen presenting cells as a pivotal event in the disease process. A subset of unconventional T cells called gamma/delta T cells are also persistently expanded in the coeliac disease (CD) small intestinal epithelium and recent analysis has shown that these cells contribute to pathogenic inflammation. Other unconventional T cell subsets may play a local immunoregulatory role and require further study. It has also been suggested that, in addition to activation of pathogenic T helper cells by gluten peptides, other peptides may directly interact with the intestinal mucosa, further contributing to the disease process. We also discuss how myofibroblasts, a major source of tissue transglutaminase and metalloproteases, may play a key role in intestinal tissue remodeling. Contribution of each of these factors to pathogenesis is discussed to enhance our view of this complex disorder and to contribute to a wider understanding of chronic immune-mediated disease.

Peptide-MHC class I and class II tetramers: From flow to mass cytometry

To develop better vaccines and more targeted treatments for cancer and autoimmune disorders, the disease-specific T cells and their cognate antigens need to be better characterized. For more than two decades, peptide-major histocompatibility complex (pMHC) tetramers and flow cytometry have been the gold standard for detection of CD8+ and CD4+ T cells specific to antigens in the context of MHC class I and class II, respectively. Nonetheless, more recent studies combining such reagents with mass cytometry, that is, cytometry by time of flight (CyTOF), have offered far more comprehensive profiling of antigen-specific T-cell responses. In addition, mass cytometry has enabled ex vivo screening of CD8+ T-cell reactivities against hundreds of MHC class I restricted candidate epitopes. MHC class II molecules, on the other hand, have been challenging to combine with mass cytometry as they are more complex and bind with lower affinities to cognate T-cell receptors than MHC class I molecules. In this review, I discuss how techniques originally developed to improve the staining capacity of pMHC tetramers in flow cytometry led to the successful combination of such reagents with mass cytometry. Especially, I will highlight very recent advances facilitating the combination with pMHC class II tetramers. Together, these mass cytometry-based studies can help develop more targeted treatments for cancer and autoimmune disorders.

Cytokine release and gastrointestinal symptoms after gluten challenge in celiac disease

Celiac disease (CeD), caused by immune reactions to cereal gluten, is treated with gluten -elimination diets. Within hours of gluten exposure, either perorally or extraorally by intradermal injection, treated patients experience gastrointestinal symptoms. To test whether gluten exposure leads to systemic cytokine production time -related to symptoms, series of multiplex cytokine measurements were obtained in CeD patients after gluten challenge. Peptide injection elevated at least 15 plasma cytokines, with IL-2, IL-8, and IL-10 being most prominent (fold-change increase at 4 hours of 272, 11, and 1.2, respectively). IL-2 and IL-8 were the only cytokines elevated at 2 hours, preceding onset of symptoms. After gluten ingestion, IL-2 was the earliest and most prominent cytokine (15-fold change at 4 hours). Supported by studies of patient-derived gluten-specific T cell clones and primary lymphocytes, our observations indicate that gluten-specific CD4⁺ T cells are rapidly reactivated by antigen -exposure likely causing CeD-associated gastrointestinal symptoms.

Distinct phenotype of CD4+ T cells driving celiac disease identified in multiple autoimmune conditions

Combining HLA-DQ-gluten tetramers with mass cytometry and RNA sequencing analysis, we find that gluten-specific CD4+ T cells in the blood and intestines of patients with celiac disease display a surprisingly rare phenotype. Cells with this phenotype are also elevated in patients with systemic sclerosis and systemic lupus erythematosus, suggesting a way to characterize CD4+ T cells specific for disease-driving antigens in multiple autoimmune conditions.

Plasma Cells Are the Most Abundant Gluten Peptide MHC-expressing Cells in Inflamed Intestinal Tissues From Patients With Celiac Disease

BACKGROUND & AIMS

Development of celiac disease is believed to involve the transglutaminase-dependent response of CD4⁺ T cells toward deamidated gluten peptides in the intestinal mucosa of individuals with specific HLA-DQ haplotypes. We investigated the antigen presentation process during this mucosal immune response.

METHODS

We generated monoclonal antibodies (mAbs) specific for the peptide-MHC (pMHC) complex of HLA-DQ2.5 and the immunodominant gluten epitope DQ2.5-glia-α1a using phage display. We used these mAbs to assess gluten peptide presentation and phenotypes of presenting cells by flow cytometry and enzyme-linked immune absorbent spot (ELISPOT) in freshly prepared single-cell suspensions from intestinal biopsies from 40 patients with celiac disease (35 untreated and 5 on a gluten-free diet) as well as 18 subjects with confirmed noninflamed gut mucosa (controls, 12 presumed healthy, 5 undergoing pancreatoduodenectomy, and 1 with potential celiac disease).

RESULTS

Using the mAbs, we detected MHC complexes on cells from intestinal biopsies from patients with celiac disease who consume gluten, but not from patients on gluten-free diets. We found B cells and plasma cells to be the most abundant cells that present DQ2.5-glia-α1a in the inflamed mucosa. We identified a subset of plasma cells that expresses B-cell receptors (BCR) specific for gluten peptides or the autoantigen transglutaminase 2 (TG2). Expression of MHC class II (MHCII) was not restricted to these specific plasma cells in patients with celiac disease but was observed in an average 30% of gut plasma cells from patients and controls.

CONCLUSIONS

A population of plasma cells from intestinal biopsies of patients with celiac disease express MHCII; this is the most abundant cell type presenting the immunodominant gluten peptide DQ2.5-glia-α1a in the tissues from these patients. These results indicate that plasma cells in the gut can function as antigen-presenting cells and might promote and maintain intestinal inflammation in patients with celiac disease or other inflammatory disorders.

Antigen-specific therapeutic approaches for autoimmunity

The main function of the immune system in health is to protect the host from infection by microbes and parasites. Because immune responses to nonself bear the risk of unleashing accidental immunity against self, evolution has endowed the immune system with central and peripheral mechanisms of tolerance, including regulatory T and B cells. Although the past two decades have witnessed the successful clinical translation of a whole host of novel therapies for the treatment of chronic inflammation, the development of antigen-based approaches capable of selectively blunting autoimmune inflammation without impairing normal immunity has remained elusive. Earlier autoantigen-specific approaches employing peptides or whole antigens have evolved into strategies that seek to preferentially deliver these molecules to autoreactive T cells either indirectly, via antigen-presenting cells, or directly, via major histocompatibility complex molecules, in ways intended to promote clonal deletion and/or immunoregulation. The disease specificity, mechanistic underpinnings, developability and translational potential of many of these strategies remain unclear.

Evaluation of T cells in blood after a short gluten challenge for coeliac disease diagnosis

BACKGROUND AND AIM

To diagnose coeliac disease (CD) in individuals on a gluten free diet (GFD), we aimed to assess the utility of detecting activated γδ and CD8 T cells expressing gut-homing receptors after a short gluten challenge.

METHODS

We studied 15 CD patients and 35 non-CD controls, all exposed to three days of gluten when following a GFD. Peripheral blood was collected before and six days after starting gluten consumption, and the expression of CD103, β7 and CD38 in γδ and CD8 T cells was assessed by flow cytometry. Determination of IFN-γ and IP-10 was performed by means of ELISPOT and/or Luminex technology.

RESULTS

We observed both γδ and CD8 T cells coexpressing CD103, β7^hi and CD38 in every patient with CD on day six, but only in one control. The studied CD8 T subpopulation was easier to detect than the γδ subpopulation. Increased IFN-γ and IP-10 levels after challenge were observed in patients with CD, but not in controls.

CONCLUSION

A short three-day gluten challenge elicits the activation of CD103⁺ β7^hi CD8⁺ T cells in CD. These cells can be detected by flow cytometry in peripheral blood, opening new possibilities for CD diagnosis in individuals on a GFD.

Disease-driving CD4+ T cell clonotypes persist for decades in celiac disease

Little is known about the repertoire dynamics and persistence of pathogenic T cells in HLA-associated disorders. In celiac disease, a disorder with a strong association with certain HLA-DQ allotypes, presumed pathogenic T cells can be visualized and isolated with HLA-DQ:gluten tetramers, thereby enabling further characterization. Single and bulk populations of HLA-DQ:gluten tetramer-sorted CD4+ T cells were analyzed by high-throughput DNA sequencing of rearranged TCR-α and -β genes. Blood and gut biopsy samples from 21 celiac disease patients, taken at various stages of disease and in intervals of weeks to decades apart, were examined. Persistence of the same clonotypes was seen in both compartments over decades, with up to 53% overlap between samples obtained 16 to 28 years apart. Further, we observed that the recall response following oral gluten challenge was dominated by preexisting CD4+ T cell clonotypes. Public features were frequent among gluten-specific T cells, as 10% of TCR-α, TCR-β, or paired TCR-αβ amino acid sequences of total 1813 TCRs generated from 17 patients were observed in 2 or more patients. In established celiac disease, the T cell clonotypes that recognize gluten are persistent for decades, making up fixed repertoires that prevalently exhibit public features. These T cells represent an attractive therapeutic target.

Characterization of the Small Intestinal Lesion in Celiac Disease by Label-Free Quantitative Mass Spectrometry

Global characterization of tissue proteomes from small amounts of biopsy material has become feasible because of advances in mass spectrometry and bioinformatics tools. In celiac disease (CD), dietary gluten induces an immune response that is accompanied by pronounced remodeling of the small intestine. Removal of gluten from the diet abrogates the immune response, and the tissue architecture normalizes. In this study, differences in global protein expression of small intestinal biopsy specimens from CD patients were quantified by analyzing formalin-fixed, paraffin-embedded material using liquid chromatography-mass spectrometry and label-free protein quantitation. Protein expression was compared in biopsy specimens collected from the same patients before and after 1-year treatment with gluten-free diet (n = 10) or before and after 3-day gluten provocation (n = 4). Differential expression of proteins in particular from mature enterocytes, neutrophils, and plasma cells could distinguish untreated from treated CD mucosa, and Ig variable region IGHV5-51 expression was found to serve as a CD-specific marker of ongoing immune activation. In patients who had undergone gluten challenge, coordinated up-regulation of wound response proteins, including the CD autoantigen transglutaminase 2, was observed. Our study provides a global and unbiased assessment of antigen-driven changes in protein expression in the celiac intestinal mucosa.

T-cell repertoires in refractory coeliac disease

OBJECTIVE

Refractory coeliac disease (RCD) is a potentially hazardous complication of coeliac disease (CD). In contrast to RCD type I, RCD type II is a precursor entity of enteropathy-associated T-cell lymphoma (EATL), which is associated with clonally expanding T-cells that are also found in the sequentially developing EATL. Using high-throughput sequencing (HTS), we aimed to establish the small-intestinal T-cell repertoire (TCR) in CD and RCD to unravel the role of distinct T-cell clonotypes in RCD pathogenesis.

DESIGN

DNA extracted from duodenal mucosa specimens of controls (n=9), active coeliacs (n=10), coeliacs on a gluten-free diet (n=9), RCD type I (n=8), RCD type II (n=8) and unclassified Marsh I cases (n=3) collected from 2002 to 2013 was examined by TCRβ-complementarity-determining regions 3 (CDR3) multiplex PCR followed by HTS of the amplicons.

RESULTS

On average, 10⁶ sequence reads per sample were generated consisting of up to 900 individual TCRβ rearrangements. In RCD type II, the most frequent clonotypes (ie, sequence reads with identical CDR3) represent in average 42.6% of all TCRβ rearrangements, which was significantly higher than in controls (6.8%; p<0.01) or RCD type I (6.7%; p<0.01). Repeat endoscopies in individual patients revealed stability of clonotypes for up to several years without clinical symptoms of EATL. Dominant clonotypes identified in individual patients with RCD type II were unique and not related between patients. CD-associated, gliadin-dependent CDR3 motifs were only detectable at low frequencies.

CONCLUSIONS

TCRβ-HTS analysis unravels the TCR in CD and allows detailed analysis of individual TCRβ rearrangements. Dominant TCRβ sequences identified in patients with RCD type II are unique and not homologous to known gliadin-specific TCR sequences, supporting the assumption that these clonal T-cells expand independent of gluten stimulation.

T Cells in Celiac Disease

Celiac disease is a human T cell-mediated autoimmune-like disorder caused by exposure to dietary gluten in genetically predisposed individuals. This review will discuss how CD4 T cell responses directed against an exogenous Ag can cause an autoreactive B cell response and participate in the licensing of intraepithelial lymphocytes to kill intestinal epithelial cells. Furthermore, this review will examine the mechanisms by which intraepithelial cytotoxic T cells mediate tissue destruction in celiac disease.

Similar Responses of Intestinal T Cells From Untreated Children and Adults With Celiac Disease to Deamidated Gluten Epitopes

BACKGROUND & AIMS

Celiac disease is a chronic small intestinal inflammatory disorder mediated by an immune response to gluten peptides in genetically susceptible individuals. Celiac disease is often diagnosed in early childhood, but some patients receive a diagnosis late in life. It is uncertain whether pediatric celiac disease is distinct from adult celiac disease. It has been proposed that gluten-reactive T cells in children recognize deamidated and native gluten epitopes, whereas T cells from adults only recognize deamidated gluten peptides. We studied the repertoire of gluten epitopes recognized by T cells from children and adults.

METHODS

We examined T-cell responses against gluten by generating T-cell lines and T-cell clones from intestinal biopsies of adults and children and tested proliferative response to various gluten peptides. We analyzed T cells from 14 children (2-5 years old) at high risk for celiac disease who were followed for celiac disease development. We also analyzed T cells from 6 adults (26-55 years old) with untreated celiac disease. All children and adults were positive for HLA-DQ2.5. Biopsies were incubated with gluten digested with chymotrypsin (modified or unmodified by the enzyme transglutaminase 2) or the peptic-tryptic digest of gliadin (in native and deamidated forms) before T-cell collection.

RESULTS

Levels of T-cell responses were higher to deamidated gluten than to native gluten in children and adults. T cells from children and adults each reacted to multiple gluten epitopes. Several T-cell clones were cross-reactive, especially clones that recognized epitopes from γ-and ω-gliadin. About half of the generated T-cell clones from children and adults reacted to unknown epitopes.

CONCLUSIONS

T-cell responses to different gluten peptides appear to be similar between adults and children at the time of diagnosis of celiac disease.

Epitope-specific immunotherapy targeting CD4-positive T cells in coeliac disease: two randomised, double-blind, placebo-controlled phase 1 studies

BACKGROUND

A gluten-free diet is the only means to manage coeliac disease, a permanent immune intolerance to gluten. We developed a therapeutic vaccine, Nexvax2, designed to treat coeliac disease. Nexvax2 is an adjuvant-free mix of three peptides that include immunodominant epitopes for gluten-specific CD4-positive T cells. The vaccine is intended to engage and render gluten-specific CD4-positive T cells unresponsive to further antigenic stimulation. We assessed the safety and pharmacodynamics of the vaccine in patients with coeliac disease on a gluten-free diet.

METHODS

We did two randomised, double-blind, placebo-controlled, phase 1 studies at 12 community sites in Australia, New Zealand, and the USA, in HLA-DQ2·5-positive patients aged 18-70 years who had coeliac disease and were on a gluten-free diet. In the screening period for ascending dose cohorts, participants were randomly assigned (1:1) by central randomisation with a simple block method to a double-blind crossover, placebo-controlled oral gluten challenge. Participants with a negative interferon γ release assay to Nexvax2 peptides after the screening oral gluten challenge were discontinued before dosing. For the biopsy cohorts, the screening period included an endoscopy, and participants with duodenal histology who had a Marsh score of greater than 1 were discontinued before dosing. Participants were subsequently randomly assigned to either Nexvax2 or placebo in ascending dose cohorts (2:1) and in biopsy cohorts (1:1) by central randomisation with a simple block method. In the three-dose study, participants received either Nexvax2 60 μg, 90 μg, or 150 μg weekly, or placebo over 15 days; in a fourth biopsy cohort, patients received either Nexvax2 at the maximum tolerated dose (MTD) or placebo. In the 16-dose study, participants received Nexvax2 150 μg or 300 μg or placebo twice weekly over 53 days; in a third biopsy cohort, patients also received either Nexvax2 at the MTD or placebo. In the 4-week post-treatment period, ascending dose cohorts underwent a further double-blind crossover, placebo-controlled oral gluten challenge, which had a fixed sequence, and biopsy cohorts had a gastroscopy with duodenal biopsies and quantitative histology within 2 weeks without oral gluten challenge. Participants, investigators, and study staff were masked to the treatment assignment, except for the study pharmacist. The primary endpoint was the number and percentage of adverse events in the treatment period in an intention-to-treat analysis. Both trials were completed and closed before data analysis. Trials were registered with the Australian New Zealand Clinical Trials Registry, numbers ACTRN12612000355875 and ACTRN12613001331729.

FINDINGS

Participants were enrolled from Nov 28, 2012, to Aug 14, 2014, in the three-dose study, and from Aug 3, 2012, to Sept 10, 2013, in the 16-dose study. Overall, 62 (57%) of 108 participants were randomly assigned after oral gluten challenge and 20 (71%) of 28 participants were randomly assigned after endoscopy. In the three-dose study, nine participants were randomly allocated to Nexvax2 60 μg and three to placebo (first cohort), nine were allocated to Nexvax2 90 μg and four to placebo (second cohort), eight were allocated to Nexvax2 150 μg and four to placebo (third cohort), and three were allocated to Nexvax2 150 μg and three to placebo (biopsy cohort). In the 16-dose study, eight participants were randomly allocated to Nexvax2 150 μg and four to placebo (first cohort), ten were allocated to Nexvax2 300 μg and three to placebo (second cohort), and seven were allocated to Nexvax2 150 μg and seven to placebo (biopsy cohort). The MTD for Nexvax2 was 150 μg because of transient, acute gastrointestinal adverse events with onset 2-5 h after initial doses of the vaccine, similar to those caused by gluten ingestion. In the ascending dose cohorts in the three-dose study, six (55%) of 11 placebo recipients, five (56%) of nine who received Nexvax2 60 μg, seven (78%) of nine who received Nexvax2 90 μg, and five (63%) of eight who received Nexvax2 150 μg had at least one treatment-emergent adverse event, as did all three (100%) placebo recipients and one (33%) of three Nexvax2 150 μg recipients in the biopsy cohort. In the ascending dose cohorts of the 16-dose study, five (71%) of seven placebo-treated participants, six (75%) of eight who received Nexvax2 150 μg, and all ten (100%) who received Nexvax2 300 μg had at least one treatment-emergent adverse event, as did six (86%) of seven placebo recipients and five (71%) of seven Nexvax2 150 μg recipients in the biopsy cohort. Vomiting, nausea, and headache were the only treatment-emergent adverse events that occurred in at least 5% of participants in either study. Among participants given the MTD, eight gastrointestinal treatment-emergent adverse events occurred in four (50%) of eight participants in the third cohort and none (0%) of three participants in the biopsy cohort in the three-dose study, and five events occurred in five (63%) of eight participants in the first cohort and three events in two (29%) of seven participants in the biopsy cohort of the 16-dose study. Median villous height to crypt depth ratio in distal duodenal biopsies was not significantly different between those who received the vaccine at the MTD on either schedule and those who received placebo. Of the participants who completed the post-treatment oral gluten challenge per protocol, interferon γ release assay to Nexvax2 peptides was negative (responders to treatment) in two (22%) of nine placebo-treated participants in the three-dose study versus two (33%) of six who received Nexvax2 60 μg, five (63%) of eight who received Nexvax2 90 μg, and six (100%) of six who received Nexvax2 150 μg (p=0·007); in the 16-dose study, none (0%) of five placebo-treated participants had a negative assay versus six (75%) of eight who received Nexvax2 150 μg (p=0·021).

INTERPRETATION

The MTD of Nexvax2 was 150 μg for twice weekly intradermal administration over 8 weeks, which modified immune responsiveness to Nexvax2 peptides without deterioration in duodenal histology. The gastrointestinal symptoms that followed the first intradermal administration of the vaccine resembled those associated with oral gluten challenge. These findings support continued clinical development of this potential therapeutic vaccine for coeliac disease.

FUNDING

ImmusanT.

Gliadin-Specific T-Cells Mobilized in the Peripheral Blood of Coeliac Patients by Short Oral Gluten Challenge: Clinical Applications

Celiac disease (CD) is a common lifelong food intolerance triggered by dietary gluten affecting 1% of the general population. Gliadin-specific T-cell lines and T-cell clones obtained from intestinal biopsies have provided great support in the investigation of immuno-pathogenesis of CD. In the early 2000 a new in vivo, less invasive, approach was established aimed to evaluate the adaptive gliadin-specific T-cell response in peripheral blood of celiac patients on a gluten free diet. In fact, it has been demonstrated that three days of ingestion of wheat-containing food induces the mobilization of memory T lymphocytes reactive against gliadin from gut-associated lymphoid tissue into peripheral blood of CD patients. Such antigen-specific T-cells releasing interferon-γ can be transiently detected by using the enzyme-linked immunospot (ELISPOT) assays or by flow cytometry tetramer technology. This paper discusses the suitability of this in vivo tool to investigate the repertoire of gluten pathogenic peptides, to support CD diagnosis, and to assess the efficacy of novel therapeutic strategies. A systematic review of all potential applications of short oral gluten challenge is provided.

Celiac disease: Autoimmunity in response to food antigen

Celiac disease (CD) is an increasingly common disease of the small intestine that occurs in genetically susceptible subjects by ingestion of cereal gluten proteins. Gluten is highly abundant in the modern diet and well tolerated by most individuals. In CD, however, an erroneous but highly specific, adaptive immune response is mounted toward certain parts of the gluten proteome. The resulting intestinal destruction is reversible and resolved upon removal of gluten from the diet. Post-translational modification (deamidation) of gluten peptides by transglutaminase 2 (TG2) is essential for the peptides to act as HLA-DQ-restricted T-cell antigens. Characteristically, deamidated gluten and the self-protein TG2 both become targets of highly disease specific B-cell responses. These antibodies share several peculiar characteristics despite being directed against vastly different antigens, which suggests a common mechanism of development. Importantly, no clear function has been ascribed to the antibodies and their contribution to disease may relate to their function as antigen receptors of the B cells rather than as soluble immunoglobulins. Adaptive immunity against gluten and TG2 appears not to be sufficient for establishment of the disease lesion, and it has been suggested that stress responses in the intestinal epithelium are essential for the development of full-blown disease and tissue damage. In this review we will summarize current concepts of the immune pathology of CD with particular focus on recent advances in our understanding of disease specific B-cell responses.

Consistency in polyclonal T-cell responses to gluten between children and adults with celiac disease

BACKGROUND & AIMS

Developing antigen-specific approaches for diagnosis and treatment of celiac disease requires a detailed understanding of the specificity of T cells for gluten. The existing paradigm is that T-cell lines and clones from children differ from those of adults in the hierarchy and diversity of peptide recognition. We aimed to characterize the T-cell response to gluten in children vs adults with celiac disease.

METHODS

Forty-one children with biopsy-proven celiac disease (median age, 9 years old; 17 male), who had been on strict gluten-free diets for at least 3 months, were given a 3-day challenge with wheat; blood samples were collected and gluten-specific T cells were measured. We analyzed responses of T cells from these children and from 4 adults with celiac disease to a peptide library and measured T-cell receptor bias. We isolated T-cell clones that recognized dominant peptides and assessed whether gluten peptide recognition was similar between T-cell clones from children and adults.

RESULTS

We detected gluten-specific responses by T cells from 30 of the children with celiac disease (73%). T cells from the children recognized the same peptides that were immunogenic to adults with celiac disease; deamidation of peptides increased these responses. Age and time since diagnosis did not affect the magnitude of T-cell responses to dominant peptides. T-cell clones specific for dominant α- or ω-gliadin peptides from children with celiac disease had comparable levels of reactivity to wheat, rye, and barley peptides as T-cell clones from adults with celiac disease. The α-gliadin-specific T cells from children had biases in T-cell receptor usage similar to those in adults.

CONCLUSIONS

T cells from children with celiac disease recognize similar gluten peptides as T cells from adults with celiac disease. The findings indicate that peptide-based diagnostics and therapeutics for adults may also be used for children.

Coeliac disease - from genetic and immunological studies to clinical applications

Coeliac disease is a common and important gastrointestinal disease. It affects at least 1%, most Western European populations and in Nordic countries it is even more frequent. It is strongly associated with certain Human Leukocyte Antigen-DQ genes and triggered by ingestion of wheat gluten and related cereals from rye and barley. The diagnosis relies on a combination of clinical signs, serology and small intestinal biopsy. Work during the last couple of decades has shown that gluten-specific, Human Leukocyte Antigen-DQ-restricted T-cells in the intestinal mucosa are of paramount importance in the disease process. The gluten peptides are chemically modified by the endogenous enzyme transglutaminase 2, the same enzyme that serves as target in today's sensitive serological tests for coeliac disease. The increasing knowledge on the disease process allows for development of improved diagnosis, patient care and new treatment modalities.

T-cell and B-cell immunity in celiac disease

Celiac disease is an inflammatory disorder with leukocyte infiltration and changes of tissue architecture of the small intestine. The condition develops in genetically susceptible individuals as the result of an inappropriate immune response to gluten proteins of wheat, barley and rye. The clinical manifestations and the histological changes normalize when gluten is eliminated from the diet. CD4(+) T cells that recognize gluten peptides bound to predisposing HLA-DQ molecules play a key role in the pathogenesis. These T cells recognize better gluten peptides that are deamidated, and this posttranslational modification is mediated by the enzyme transglutaminase 2 (TG2). Another hallmark of celiac disease is the production of antibodies to gluten as well as to TG2. A role for B cells in celiac disease pathogenesis is receiving increased recognition. This review will discuss the main discoveries in the field of T-cell and B-cell biology of celiac disease.

Coeliac disease and rheumatoid arthritis: similar mechanisms, different antigens

Rheumatoid arthritis (RA) and coeliac disease are inflammatory diseases that both have a strong association with class II HLAs: individuals carrying HLA-DQ2.5 and/or HLA-DQ8 alleles have an increased risk of developing coeliac disease, whereas those carrying HLA-DR shared epitope alleles exhibit an increased risk of developing RA. Although the molecular basis of the association with specific HLA molecules in RA remains poorly defined, an immune response against post-translationally modified protein antigens is a hallmark of each disease. In RA, understanding of the pathogenetic role of B-cell responses to citrullinated antigens, including vimentin, fibrinogen and α-enolase, is rapidly growing. Moreover, insight into the role of HLAs in the pathogenesis of coeliac disease has been considerably advanced by the identification of T-cell responses to deamidated gluten antigens presented in conjunction with predisposing HLA-DQ2.5 molecules. This article briefly reviews these advances and draws parallels between the immune mechanisms leading to RA and coeliac disease, which point to a crucial role for T-cell-B-cell cooperation in the development of full-blown disease. Finally, the ways in which these novel insights are being exploited therapeutically to re-establish tolerance in patients with RA and coeliac disease are described.

Determinants of gliadin-specific T cell selection in celiac disease

In HLA-DQ8-associated celiac disease (CD), the pathogenic T cell response is directed toward an immunodominant α-gliadin-derived peptide (DQ8-glia-α1). However, our knowledge of TCR gene usage within the primary intestinal tissue of HLA-DQ8 (+) CD patients is limited. We identified two populations of HLA-DQ8-glia-α1 tetramer(+) CD4(+) T cells that were essentially undetectable in biopsy samples from patients on a gluten-free diet but expanded rapidly and specifically after antigenic stimulation. Distinguished by expression of TRBV9, both T cell populations displayed biased clonotypic repertoires and reacted similarly against HLA-DQ8-glia-α1. In particular, TRBV9 paired most often with TRAV26-2, whereas the majority of TRBV9(-) TCRs used TRBV6-1 with no clear TRAV gene preference. Strikingly, both tetramer(+)/TRBV9(+) and tetramer(+)/TRBV9(-) T cells possessed a non-germline-encoded arginine residue in their CDR3α and CDR3β loops, respectively. Comparison of the crystal structures of three TRBV9(+) TCRs and a TRBV9(-) TCR revealed that, as a result of distinct TCR docking modes, the HLA-DQ8-glia-α1 contacts mediated by the CDR3-encoded arginine were almost identical between TRBV9(+) and TRBV9(-) TCRs. In all cases, this interaction centered on two hydrogen bonds with a specific serine residue in the bound peptide. Replacement of serine with alanine at this position abrogated TRBV9(+) and TRBV9(-) clonal T cell proliferation in response to HLA-DQ8-glia-α1. Gluten-specific memory CD4(+) T cells with structurally and functionally conserved TCRs therefore predominate in the disease-affected tissue of patients with HLA-DQ8-mediated CD.

Lessons from rodent models in celiac disease

Over the past 25 years, studies led in humans have considerably improved our understanding of celiac disease, a complex disease that is generally defined as an autoimmune-like enteropathy induced by dietary gluten in genetically predisposed individuals. Recently, large efforts were also invested in the development of mouse models in order to explore pathogenic hypotheses, and also with the goal to design pretherapeutic models that could be used to test innovative therapies. Yet, modeling this complex multifactorial disease has been a very challenging task. Herein, we review how approaches in rodents have provided insight into celiac disease pathophysiology and also highlight the difficulties met to fully recapitulate the human disease.