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

Celiac Disease-Narrative Review on Progress in Celiac Disease

Celiac disease is defined as a systemic immunological disorder caused by gluten (gliadin and other prolamin) in genetically predisposed individuals, who present with a variety of gluten-dependent symptoms, specific antibodies, the presence of the HLA DQ2 and DQ8 histocompatibility antigen, and enteropathy. Its prevalence, depending on the studied population and methodology, is estimated at 0.75-1.6% of the general population. During the complex immune reaction it induces, most cells involved in inflammatory processes are activated, which leads to the gradual atrophy of intestinal villi and the proliferation of enterocytes within intestinal crypts. The pathogenesis of celiac disease is extremely complicated and is still the subject of research. According to the current diagnostic guidelines, the following criteria should be taken into account: clinical symptoms (intestinal and extraintestinal), the presence of antibodies against tissue transglutaminase in the IgA class, the level of total IgA, and the presence of typical histological changes in duodenal biopsies. Diet-resistant celiac disease is one of the most important clinical challenges, causing serious complications. Currently, the basic method for treating celiac disease is an elimination diet (i.e., the exclusion of products that may contain gluten from the diet), however, new therapeutic strategies are still being sought, mainly based on supplementation with exogenous endopeptidases, modification of the immune response, and the use of zonulin inhibitors and transglutaminase 2 inhibitors. Clinical trials of new drugs are ongoing. The gradually expanding knowledge about the pathogenesis of celiac disease may allow for the development of new therapeutic strategies for both patients with a mild disease course, as well as those that are diet-resistant.

A randomized, double-blind, placebo-controlled, multiple dose, parallel study to investigate the effects of a cathepsin S inhibitor in celiac disease

Celiac disease is a chronic, immune-mediated enteropathy with symptoms triggered by exposure to dietary gluten in genetically predisposed individuals. The only available management option is lifelong adherence to a gluten-free diet. This randomized, double-blind, placebo-controlled, parallel-group, single-center study tested the effects of the cathepsin S inhibitor RO5459072 on the immune response to a 13-day gluten challenge in 19 participants with celiac disease (ClinicalTrials.gov: NCT02679014). Nine participants in the RO5459072 arm received 100 mg study drug b.i.d. (200 mg daily); 10 received a placebo. The primary end point was the number of responders to the gluten challenge (defined as individuals with an increase in the number of gliadin-specific, IFNγ-secreting T cells detected using an ELISPOT assay). However, there was a weak response to the gluten challenge across both arms. Few participants had an increase in gliadin-specific, IFNγ-secreting T cells, and the antigen-specific responses (anti-tTG and anti-DGP antibodies) were weaker than expected in both arms. Therefore, the primary end point was not met, although the study was underpowered to detect a treatment effect under these circumstances. Pharmacodynamic findings suggested that RO5459072 had some beneficial effects. Fewer participants in the RO5459072 arm exhibited gliadin-specific IFNγ-secreting T cells after 6 days' gluten intake. Participants in the RO5459072 arm also showed decreased intestinal permeability, and a decrease in the number of circulating B cells, CD4+ and CD8+ T cells compared to baseline. Nevertheless, the absence of clear effects on the response to a gluten challenge indicates that inhibition of cathepsin S may not be an effective treatment strategy for celiac disease.

Analytical and functional approaches to assess the immunogenicity of gluten proteins

Gluten proteins are the causative agents of celiac disease (CD), a lifelong and worldwide spread food intolerance, characterized by an autoimmune enteropathy. Gluten is a complex mixture of high homologous water-insoluble proteins, characterized by a high content of glutamine and proline amino acids that confers a marked resistance to degradation by gastrointestinal proteases. As a consequence of that, large peptides are released in the gut lumen with the potential to activate inflammatory T cells, in CD predisposed individuals. To date, several strategies aimed to detoxify gluten proteins or to develop immunomodulatory drugs to recover immune tolerance to gluten are under investigation. This review overviews the state of art of both analytical and functional methods currently used to assess the immunogenicity potential of gluten proteins from different cereal sources, including native raw seed flours and complex food products, as well as drug-treated samples. The analytical design to assess the content and profile of gluten immunogenic peptides, described herein, is based on the oral-gastro-intestinal digestion (INFOGEST model) followed by extensive characterization of residual gluten peptides by proteomic and immunochemical analyses. These approaches include liquid chromatography-high-resolution mass spectrometry (LC-MS/MS) and R5/G12 competitive ELISA. Functional studies to assess the immune stimulatory capabilities of digested gluten peptides are based on gut mucosa T cells or peripheral blood cells obtained from CD volunteers after a short oral gluten challenge.

Oral Consumption of Bread from an RNAi Wheat Line with Strongly Silenced Gliadins Elicits No Immunogenic Response in a Pilot Study with Celiac Disease Patients

Celiac disease (CD) is a genetically predisposed, T cell-mediated and autoimmune-like disorder caused by dietary exposure to the storage proteins of wheat and related cereals. A gluten-free diet (GFD) is the only treatment available for CD. The celiac immune response mediated by CD4+ T-cells can be assessed with a short-term oral gluten challenge. This study aimed to determine whether the consumption of bread made using flour from a low-gluten RNAi wheat line (named E82) can activate the immune response in DQ2.5-positive patients with CD after a blind crossover challenge. The experimental protocol included assessing IFN-γ production by peripheral blood mononuclear cells (PBMCs), evaluating gastrointestinal symptoms, and measuring gluten immunogenic peptides (GIP) in stool samples. The response of PBMCs was not significant to gliadin and the 33-mer peptide after E82 bread consumption. In contrast, PBMCs reacted significantly to Standard bread. This lack of immune response is correlated with the fact that, after E82 bread consumption, stool samples from patients with CD showed very low levels of GIP, and the symptoms were comparable to those of the GFD. This pilot study provides evidence that bread from RNAi E82 flour does not elicit an immune response after a short-term oral challenge and could help manage GFD in patients with CD.

The use of peripheral blood mononuclear cells in celiac disease diagnosis and treatment

Introduction: Celiac disease is characterized by an abnormal immune activation driven by the ingestion of gluten from wheat, barley, and rye. Gluten-specific CD4⁺ T cells play an important role in disease pathogenesis and are detectable among peripheral blood mononuclear cells (PBMCs). Areas covered: This review summarizes the use of celiac disease patient PBMCs in clinical applications focusing on their exploitation in the development of diagnostic approaches and novel drugs to replace or complement gluten-free diet. Expert opinion: The most used PBMC-based methods applied in celiac disease research include ELISpot and HLA-DQ:gluten tetramer technology. ELISpot has been utilized particularly in research aiming to develop a celiac disease vaccine and in studies addressing the toxicity of different grains in celiac disease. HLA-DQ:gluten tetramer technology on the other hand initially focused on improving current diagnostics but in combination with additional markers it is also a useful outcome measure in clinical trials to monitor the efficacy of drug candidates. In addition, the technology serves well in the more detailed characterization of celiac disease-specific T cells, thereby possibly revealing novel therapeutic targets. Future studies may also reveal clinical applications for PBMC microRNAs and/or dendritic cells or monocytes present among PBMCs.

New celiac disease biomarkers

Advances in the knowledge regarding celiac disease have enabled the development of diagnostic markers, such as anti-tissue transglutaminase and anti-deaminated gliadin antibodies. The wide availability of these antibodies, genetic studies of HLA-DQ and duodenal biopsies constitute the pillars necessary for a definitive diagnosis. However, difficulties sometimes arise in both the diagnosis and follow-up of celiac patients, which cannot be resolved using these tools. This article reviews the scientific evidence and possible clinical utility of different biomarkers. This review is structured according to biomarkers that have been evaluated pathophysiologically in relation to intestinal damage or immune response and their potential clinical utility in the diagnosis and follow-up of celiac disease patients.

In Celiac Disease Patients the In Vivo Challenge with the Diploid Triticum monococcum Elicits a Reduced Immune Response Compared to Hexaploid Wheat

SCOPE

Gluten from the diploid wheat Triticum monococcum (TM) has low content of immunostimulatory sequences and a high gastro-intestinal digestibility. Gluten-reactive T cells elicited by diploid and hexaploid (Triticum aestivum-TA) wheat in celiac disease (CD) patients upon a brief oral challenge are analyzed.

METHODS AND RESULTS

Seventeen patients with CD (median age 13 years) consumed for 3 days sandwiches made with TM (cultivar Norberto-ID331, N=11), or TA (cultivar Sagittario, N=11) flours, corresponding to 12 gr of gluten/die. Immunostimulatory properties are assessed in blood by measuring the IFN-γ-secreting T cells by EliSpot and the expression of inflammatory cytokines/receptors (IL-12A, IL-15, IL-18RAP, IFN-γ) by qPCR. TA mobilizes a remarkable number of gliadin-specific, IFN-γ-secreting T cells (p<0.05), while no significant cell mobilization is induced by TM (p=ns). Similar results are obtained in response to five immunogenic peptides from α-, ω-, and γ-gliadins, although with a large individual variability. An increased mRNA expression for IL-12A and IFN-γ is detected in the group eating TA compared to those consuming TM (p<0.05).

CONCLUSIONS

Although T. monococcum is a cereal not suitable for the diet of celiacs, this diploid wheat elicits a reduced in vivo T-cell response compared to T. aestivum in celiac patients.

The intestinal expansion of TCRγδ+ and disappearance of IL4+ T cells suggest their involvement in the evolution from potential to overt celiac disease

Celiac disease (CD) is characterized by a spectrum of intestinal inflammatory lesions. Most patients have villous atrophy (overt-CD), while others have a morphologically normal mucosa, despite the presence of CD-specific autoantibodies (potential-CD). As the mechanism responsible for villous atrophy is not completely elucidated, we investigated biomarkers specific for the different celiac lesions. Phenotype and cytokine production of intestinal mucosa cells were analyzed by flow cytometry in gut biopsies of children with overt- or potential-CD and in healthy controls. Density of TCRγδ⁺ T cells was found markedly enhanced in intestinal mucosa of children with overt-CD compared to potential-CD or controls. By contrast, very few IL4⁺ T cells infiltrated the mucosa with villous atrophy compared to morphologically normal mucosa. IL4⁺ T cells were classical CD4⁺ T-helper cells (CD161^- ), producing or not IFN-γ, and negative for IL17A. Our study demonstrated that the transition to villous atrophy in CD patients is characterized by increased density of TCRγδ⁺ T cells, and concomitant disappearance of IL4⁺ cells. These findings suggest that immunomodulatory mechanisms are active in potential-CD to counteract the inflammatory cascade responsible of villous atrophy. Further studies are required to validate the use of IL4⁺ and TCRγδ⁺ T cells as biomarkers of the different CD forms.

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.

The Transcriptomic Analysis of Circulating Immune Cells in a Celiac Family Unveils Further Insights Into Disease Pathogenesis

Celiac disease (CD), the most common chronic enteropathy worldwide, is triggered and sustained by a dysregulated immune response to dietary gluten in genetically susceptible individuals. Up to date either the role of environmental factors and the pathways leading to mucosal damage have been only partially unraveled. Therefore, we seized the unique opportunity to study a naturally-occurring experimental model of a family composed of both parents suffering from CD (one on a gluten-free diet) and two non-celiac daughters. The control group consisted in four unrelated cases, two celiac and two non-celiac subjects, all matching with family members for both disease status and genetic susceptibility. In this privileged setting, we sought to investigate gene expression in peripheral blood mononuclear cells (PBMCs), a population known to mirror the immune response state within the gut. To this purpose, PBMCs were obtained from the four biopsied-proven CD patients and the four non-celiac cases. Each group included two family members and two unrelated control subjects. After RNA purification and cDNA synthesis, each sample underwent a microarray screen on a whole-transcriptome scale, and the hybridization results were visualized by hierarchical clustering. Differentially expressed genes (DEG) were partitioned into clusters displaying comparable regulations among samples. These clusters were subjected to both functional and pathway analysis by using the Kyoto Encyclopedia of Genes and Genomes. Interestingly, on a global gene expression level, the family members clustered together, regardless of their disease status. A relevant fraction of DEG belonged to a limited number of pathways, and could be differentiated based on disease status: active CD vs. treated CD and CD vs. controls. These pathways were mainly involved in immune function regulation, cell-cell junctions, protein targeting and degradation, exosome trafficking, and signal transduction. Worth of noting, a small group of genes mapping on the male-specific region of the Y chromosome, and previously linked to cardiovascular risk, was found to be strongly upregulated in the active CD case belonging to the family, who suddenly died of a heart attack. Our results provide novel information on CD pathogenesis and may be useful in identifying new therapeutic tools and risk factors associated with this condition.

Celiac Disease: A Review of Current Concepts in Pathogenesis, Prevention, and Novel Therapies

Our understanding of celiac disease and how it develops has evolved significantly over the last half century. Although traditionally viewed as a pediatric illness characterized by malabsorption, it is now better seen as an immune illness with systemic manifestations affecting all ages. Population studies reveal this global disease is common and, in many countries, increasing in prevalence. These studies underscore the importance of specific HLA susceptibility genes and gluten consumption in disease development and suggest that other genetic and environmental factors could also play a role. The emerging data on viral and bacterial microbe-host interactions and their alterations in celiac disease provides a plausible mechanism linking environmental risk and disease development. Although the inflammatory lesion of celiac disease is complex, the strong HLA association highlights a central role for pathogenic T cells responding to select gluten peptides that have now been defined for the most common genetic form of celiac disease. What remains less understood is how loss of tolerance to gluten occurs. New insights into celiac disease are now providing opportunities to intervene in its development, course, diagnosis, and treatment.