Generation of circulating autoreactive pre-plasma cells fueled by naive B cells in celiac disease.

Autoantibodies against the enzyme transglutaminase 2 (TG2) are characteristic of celiac disease (CeD), and TG2-specific immunoglobulin (Ig) A plasma cells are abundant in gut biopsies of patients. Here, we describe the corresponding population of autoreactive B cells in blood. Circulating TG2-specific IgA cells are present in untreated patients on a gluten-containing diet but not in controls. They are clonally related to TG2-specific small intestinal plasma cells, and they express gut-homing molecules, indicating that they are plasma cell precursors. Unlike other IgA-switched cells, the TG2-specific cells are negative for CD27, placing them in the double-negative (IgD-CD27-) category. They have a plasmablast or activated memory B cell phenotype, and they harbor fewer variable region mutations than other IgA cells. Based on their similarity to naive B cells, we propose that autoreactive IgA cells in CeD are generated mainly through chronic recruitment of naive B cells via an extrafollicular response involving gluten-specific CD4+ T cells.

Gluten-Free Diet Induces Rapid Changes in Phenotype and Survival Properties of Gluten-Specific T Cells in Celiac Disease.

BACKGROUND & AIMS: The treatment of celiac disease (CeD) with gluten-free diet (GFD) normalizes gut inflammation and disease-specific antibodies. CeD patients have HLA-restricted, gluten-specific T cells persisting in the blood and gut even after decades of GFD, which are reactivated and disease driving upon gluten exposure. Our aim was to examine the transition of activated gluten-specific T cells into a pool of persisting memory T cells concurrent with normalization of clinically relevant biomarkers during the first year of treatment. METHODS: We followed 17 CeD patients during their initial GFD year, leading to disease remission. We assessed activation and frequency of gluten-specific CD4+ blood and gut T cells with HLA-DQ2.5:gluten tetramers and flow cytometry, disease-specific serology, histology, and symptom scores. We assessed gluten-specific blood T cells within the first 3 weeks of GFD in 6 patients and serology in an additional 9 patients. RESULTS: Gluten-specific CD4+ T cells peaked in blood at day 14 while up-regulating Bcl-2 and down-regulating Ki-67 and then decreased in frequency within 10 weeks of GFD. CD38, ICOS, HLA-DR, and Ki-67 decreased in gluten-specific cells within 3 days. PD-1, CD39, and OX40 expression persisted even after 12 months. IgA-transglutaminase 2 decreased significantly within 4 weeks. CONCLUSIONS: GFD induces rapid changes in the phenotype and number of gluten-specific CD4+ blood T cells, including a peak of nonproliferating, nonapoptotic cells at day 14. Subsequent alterations in T-cell phenotype associate with the quiescent but chronic nature of treated CeD. The rapid changes affecting gluten-specific T cells and disease-specific antibodies offer opportunities for clinical trials aiming at developing nondietary treatments for patients with newly diagnosed CeD.

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

Gut intraepithelial γδ and CD8+ αß T lymphocytes have been connected to celiac disease (CeD) pathogenesis. Based on the previous observation that activated (CD38+), gut-homing (CD103+) γδ and CD8+ αß 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+ αß T cells, respectively, while 16 had increase in gluten-specific CD4+ T cells. We obtained γδ and αß 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+ αß T-cell clonotypes even prior to gluten challenge. In subjects with challenge-induced surge of γδ and/or CD8+ αß 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+ αß T-cell clonotypes that may not be specific for the gluten antigen.

Single-cell TCR repertoire analysis reveals highly polyclonal composition of human intraepithelial CD8+ αß T lymphocytes in untreated celiac disease.

We compared the αß T-cell receptor repertoires of CD8+ αß intraepithelial lymphocytes from celiac disease patients and healthy subjects by single-cell sequencing. We demonstrate that the repertoires of untreated celiac disease patients were more polyclonal and more diverse than what was observed in both treated patients and healthy subjects.

Single-cell TCR sequencing of gut intraepithelial γδ T cells reveals a vast and diverse repertoire in celiac disease.

A hallmark of celiac disease (CeD), a chronic condition driven by cereal gluten exposure, is increase of gut intraepithelial γδ T cells. This may indicate pathogenic involvement of γδ T cells and existence of disease-specific γδ T-cell receptors (TCRs) recognizing defined antigen(s). We performed high-throughput and paired γδ TCR sequencing of single intraepithelial γδ T cells of untreated CeD patients (n = 8; 1821 cells), CeD patients treated with a gluten-free diet (n = 5; 436 cells) and controls (n = 7; 1068 cells). We found that CeD patients, both untreated and treated, had larger and more diverse γδ TCR repertoires, more frequent usage of TRDV1 and TRDV3 and different patterns of TCRγ/TCRδ-pairing compared with controls. Although we observed no public CDR3δ sequences, there were several public CDR3γ sequences-many of which were shared by not only the CeD patients, but also by the controls. These public CDR3s were characterized by few N/P nucleotide insertions with germline and near-germline configuration, hence being easy to generate. Previous findings of CeD-specific CDR3 motifs were not replicated. Thus, being unable to raise evidence for CeD-specific γδ TCRs in this first large, paired γδ TCR single-cell sequencing study, we project challenges for identification of CeD-relevant γδ TCR ligands.

Resident memory CD8 T cells persist for years in human small intestine.

Resident memory CD8 T (Trm) cells have been shown to provide effective protective responses in the small intestine (SI) in mice. A better understanding of the generation and persistence of SI CD8 Trm cells in humans may have implications for intestinal immune-mediated diseases and vaccine development. Analyzing normal and transplanted human SI, we demonstrated that the majority of SI CD8 T cells were bona fide CD8 Trm cells that survived for >1 yr in the graft. Intraepithelial and lamina propria CD8 Trm cells showed a high clonal overlap and a repertoire dominated by expanded clones, conserved both spatially in the intestine and over time. Functionally, lamina propria CD8 Trm cells were potent cytokine producers, exhibiting a polyfunctional (IFN-γ+ IL-2+ TNF-α+) profile, and efficiently expressed cytotoxic mediators after stimulation. These results suggest that SI CD8 Trm cells could be relevant targets for future oral vaccines and therapeutic strategies for gut disorders.

Therapeutic and Diagnostic Implications of T Cell Scarring in Celiac Disease and Beyond.

Few therapeutic and diagnostic tools specifically aim at T cells in autoimmune disorders, but are T cells a narrow target in these diseases? Lessons may be learned from celiac disease (CeD), one of the few autoimmune disorders where the T cell driving antigens are known, i.e. dietary gluten proteins. T cell clonotypes specific to gluten are expanded, persist for decades and express a distinct phenotype in CeD patients. Cells with this phenotype are increased also in other autoimmune conditions. Accordingly, disease-specific CD4+ T cells form an immunological scar in CeD and probably other autoimmune disorders. We discuss approaches how such T cells may be targeted for better treatment and diagnosis via their antigen specificity or via their expression of characteristic phenotypic markers.

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 -ß 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-ß, or paired TCR-αß 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.

HLA-DQ:gluten tetramer test in blood gives better detection of coeliac patients than biopsy after 14-day gluten challenge.

OBJECTIVE: Initiation of a gluten-free diet without proper diagnostic work-up of coeliac disease is a frequent and demanding problem. Recent diagnostic guidelines suggest a gluten challenge of at least 14 days followed by duodenal biopsy in such patients. The rate of false-negative outcome of this approach remains unclear. We studied responses to 14-day gluten challenge in subjects with treated coeliac disease. DESIGN: We challenged 20 subjects with biopsy-verified coeliac disease, all in confirmed mucosal remission, for 14 days with 5.7 grams per oral gluten daily. Duodenal biopsies were collected. Blood was analysed by multiplex assay for cytokine detection, and by flow cytometry using HLA-DQ:gluten tetramers. RESULTS: Nineteen participants completed the challenge. Villous blunting appeared at end of challenge in 5 of 19 subjects. Villous height to crypt depth ratio reduced with at least 0.4 concomitantly with an increase in intraepithelial lymphocyte count of at least 50% in 9 of 19 subjects. Interleukin-8 plasma concentration increased by more than 100% after 4 hours in 7 of 19 subjects. Frequency of blood CD4+ effector-memory gut-homing HLA-DQ:gluten tetramer-binding T cells increased by more than 100% on day 6 in 12 of 15 evaluated participants. CONCLUSION: A 14-day gluten challenge was not enough to establish significant mucosal architectural changes in majority of patients with coeliac disease (sensitivity ≈25%-50%). Increase in CD4+ effector-memory gut-homing HLA-DQ:gluten tetramer-binding T cells in blood 6 days after gluten challenge is a more sensitive and less invasive biomarker that should be validated in a larger study. TRIAL REGISTRATION NUMBER: NCT02464150.

Structures of Preferred Human IgV Genes-Based Protective Antibodies Identify How Conserved Residues Contact Diverse Antigens and Assign Source of Specificity to CDR3 Loop Variation.

The human Ab response to certain pathogens is oligoclonal, with preferred IgV genes being used more frequently than others. A pair of such preferred genes, IGVK3-11 and IGVH3-30, contributes to the generation of protective Abs directed against the 23F serotype of the pneumonococcal capsular polysaccharide of Streptococcus pneumoniae and against the AD-2S1 peptide of the gB membrane protein of human CMV. Structural analyses of Fab fragments of mAbs 023.102 and pn132p2C05 in complex with portions of the 23F polysaccharide revealed five germline-encoded residues in contact with the key component, l-rhamnose. In the case of the AD-2S1 peptide, the KE5 Fab fragment complex identified nine germline-encoded contact residues. Two of these germline-encoded residues, Arg91L and Trp94L, contact both the l-rhamnose and the AD-2S1 peptide. Comparison of the respective paratopes that bind to carbohydrate and protein reveals that stochastic diversity in both CDR3 loops alone almost exclusively accounts for their divergent specificity. Combined evolutionary pressure by human CMV and the 23F serotype of S. pneumoniae acted on the IGVK3-11 and IGVH3-30 genes as demonstrated by the multiple germline-encoded amino acids that contact both l-rhamnose and AD-2S1 peptide.

Healthy HLA-DQ2.5+ Subjects Lack Regulatory and Memory T Cells Specific for Immunodominant Gluten Epitopes of Celiac Disease.

Celiac disease (CD) is an HLA-associated disorder characterized by a harmful T cell response to dietary gluten. It is not understood why most individuals who carry CD-associated HLA molecules, such as HLA-DQ2.5, do not develop CD despite continuous gluten exposure. In this study, we have used tetramers of HLA-DQ2.5 bound with immunodominant gluten epitopes to explore whether HLA-DQ2.5(+) healthy individuals mount a specific CD4(+) T cell response to gluten. We found that gluten tetramer-binding memory cells were rare in blood of healthy individuals. These cells showed lower tetramer-binding intensity and no signs of biased TCR usage compared with gluten tetramer-binding memory T cells from patients. After sorting and in vitro expansion, only 18% of the tetramer-binding memory cells from healthy subjects versus 79% in CD patients were gluten-reactive upon tetramer restaining. Further, T cell clones of tetramer-sorted memory cells of healthy individuals showed lower gluten-specific proliferative responses compared with those of CD patients, indicating that tetramer-binding memory cells in healthy control subjects may be cross-reactive T cells. In duodenal biopsy specimens of healthy control subjects, CD4(+) T cells were determined not to be gluten reactive. Finally, gluten tetramer-binding cells of healthy individuals did not coexpress regulatory T cell markers (Foxp3(+) CD25(+)) and cultured T cell clones did not express a cytokine profile that indicated immune-dampening properties. The results demonstrate that healthy HLA-DQ2.5(+) individuals do not mount a T cell response to immunodominant gluten epitopes of CD.