Celiac disease (CeD) is a complex immune-mediated disorder that is triggered by dietary gluten in genetically predisposed individuals. CeD is characterized by inflammation and villous atrophy of the small intestine, which can lead to gastrointestinal complaints, malnutrition, and malignancies. Currently, diagnosis of CeD relies on serology (antibodies against transglutaminase and endomysium) and small-intestinal biopsies. Since small-intestinal biopsies require invasive upper-endoscopy, and serology cannot predict CeD in an early stage or be used for monitoring disease after initiation of a gluten-free diet, the search for non-invasive biomarkers is ongoing. Here, we summarize current and up-and-coming non-invasive biomarkers that may be able to predict, diagnose, and monitor the progression of CeD. We further discuss how current and emerging techniques, such as (single-cell) transcriptomics and genomics, can be used to uncover the pathophysiology of CeD and identify non-invasive biomarkers.

Celiac disease is an auto-immune disease in which an immune response to dietary gluten leads to inflammation and subsequent atrophy of small intestinal villi, causing severe bowel discomfort and malabsorption of nutrients. The major instigating factor for the immune response in celiac disease is the activation of gluten-specific CD4+ T cells expressing T cell receptors that recognize gluten peptides presented in the context of HLA-DQ2 and DQ8. Here we provide an in-depth characterization of 28 gluten-specific T cell clones. We assess their transcriptional and epigenetic response to T cell receptor stimulation and link this to genetic factors associated with celiac disease. Gluten-specific T cells have a distinct transcriptional profile that mostly resembles that of Th1 cells but also express cytokines characteristic of other types of T-helper cells. This transcriptional response appears not to be regulated by changes in chromatin state, but rather by early upregulation of transcription factors and non-coding RNAs that likely orchestrate the subsequent activation of genes that play a role in immune pathways. Finally, integration of chromatin and transcription factor binding profiles suggest that genes activated by T cell receptor stimulation of gluten‑specific T cells may be impacted by genetic variation at several genetic loci associated with celiac disease.

In coeliac disease (CeD), the epithelial lining (EL) of the small intestine is severely damaged by a complex auto-inflammatory response, leading intraepithelial lymphocytes to attack epithelial cells. To understand the intestinal changes and genetic regulation in CeD, we investigated the heterogeneity in the transcriptomic profile of the duodenal EL using RNA-seq and eQTL analysis on predicted cell types. The study included duodenal biopsies from 82 patients, grouped into controls, gluten-free diet treated CeD and untreated CeD. We identified 1 862 differential expressed genes, which clustered into four sets. Two sets, one upregulated for cell cycle function (n = 366) and one downregulated for digestion, transmembrane transport, and laminin pathways (n = 543), defined three sample groups based on inflammation status: non-inflamed, mild inflammation or severe inflammation. The remaining two sets of genes were enriched for immune (n = 458) and extracellular matrix and barrier functions (n = 495) and were sufficient to classify samples into their disease conditions. Finally, deconvoluting eQTL effects from epithelial and immune cells identified 6 and 15 cell-type-mediated eQTL genes, respectively. In sum, we identified genes expressed in the duodenal EL whose expression reflect heterogeneity in CeD and that may be used as biomarkers to assess CeD condition and its mucosal and immune status.

In coeliac disease (CeD), the epithelial lining (EL) of the small intestine is severely damaged through a complex auto-inflammatory response that results in intraepithelial lymphocytes (IELs) attacking epithelial cells (ECs). To better understand the changes occurring in the EL in CeD, including after initiation of a gluten-free diet, and the regulatory mechanisms that affect mucosal homeostasis, we investigated ECs and IELs in the CeD duodenal EL using RNA-seq and eQTL analysis on predicted cell types. The study included 82 duodenal biopsies from volunteers, grouped into controls (CTRL), gluten-free diet treated CeD (TCD) and untreated CeD (UCD). We identified 2,868 differential expressed genes, which clustered into four sets with specific functions related to CeD. Two sets, one upregulated for cell cycle function and one downregulated for digestion, transmembrane transport, and laminin pathways, defined three groups of samples based on inflammation status: non-inflamed, mild inflammation or severe inflammation. These inflammation states correlated with but were not specific to disease state. The remaining two sets of genes were enriched for immune, extracellular matrix, and barrier functions. These latter two sets allowed the classification of samples into their disease conditions: CTRL, TCD, and UCD. Finally, deconvoluting eQTL effects from ECs and immune cells in the EL identified 7 and 9 cell-type-mediated eQTL genes, respectively. In sum, we identified genes expressed in the duodenal EL whose expression might be used as biomarkers to assess CeD condition and its mucosal and immune status. Highlights Gene expression in epithelial lining in CeD patients reflects inflammation status The transcriptome can classify epithelium as no, mild, or severe inflammation Cell cycle, absorption, and basal lamina genes are indicators of mucosal damage Immune and extracellular matrix genes distinguish untreated from treated cases Predicted-cell-type eQTLs pinpoint effects in immune and epithelial cells

Interactions between intraepithelial lymphocytes (IELs) and the intestinal epithelium are central to mucosal homeostasis and disease. However, mechanistic in vitro studies describing their crosstalk in humans are limited by scarceness of primary material and insufficient knowledge about co-culture requirements. Here, we establish an autologous human duodenal IEL–organoid co-culture system encompassing expandable and bankable IEL and organoid protocols, with co-culture conditions that allow viability of both cell types. This system enables successive interrogation of lympho-epithelial interactions starting from minimal biopsy material. Under baseline conditions, CD45⁺CD8⁺CD103⁺TCRαβ⁺ IELs retain tissue-residency and effector features and induce an epithelial interferon response and chemokine production, without overt epithelial apoptosis. IL-15 and IL-21, essential cytokines involved in IEL-activation in intestinal enteropathies like celiac disease, increases granzyme B expression and interferon-γ secretion but do not trigger epithelial cell death. However, enforcing IEL-epithelial contact using an anti-CD3-anti-Ep-CAM bispecific antibody induces epithelial apoptosis accompanied by increased tumor necrosis factor (TNF) and FAS-ligand (FASLG) secretion. These findings validate the platform’s ability to resolve non-destructive and cytotoxic lympho-epithelial interaction and provide a tractable system for studying intestinal inflammation and immune-mediated epithelial cell death.