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Purpose Hyper activation of the JAK-STAT signaling underlies the pathophysiology of many human immune–mediated diseases. Herein, the study of 2 adult patients with SOCS1 haploinsufficiency illustrates the severe and pleomorphic consequences of its impaired regulation in the intestinal tract. Methods Two unrelated adult patients presented with gastrointestinal manifestations, one with Crohn’s disease-like ileo-colic inflammation refractory to anti-TNF and the other with lymphocytic leiomyositis causing severe chronic intestinal pseudo-occlusion. Next-generation sequencing was used to identify the underlying monogenic defect. One patient received anti-IL-12/IL-23 treatment while the other received the JAK1 inhibitor, ruxolitinib. Peripheral blood, intestinal tissues, and serum samples were analyzed before-and-after JAK1 inhibitor therapy using mass cytometry, histology, transcriptomic, and Olink assay. Results Novel germline loss-of-function variants in SOCS1 were identified in both patients. The patient with Crohn-like disease achieved clinical remission with anti-IL-12/IL-23 treatment. In the second patient with lymphocytic leiomyositis, ruxolitinib induced rapid resolution of the obstructive symptoms, significant decrease of the CD8+ T lymphocyte muscular infiltrate, and normalization of serum and intestinal cytokines. Decreased frequencies of circulating Treg cells, MAIT cells, and NK cells, with altered CD56bright:CD16lo:CD16hi NK subtype ratios were not modified by ruxolitinib. Conclusion SOCS1 haploinsufficiency can result in a broad spectrum of intestinal manifestations and need to be considered as differential diagnosis in cases of severe treatment-refractory enteropathies, including the rare condition of lymphocytic leiomyositis. This provides the rationale for genetic screening and considering JAK inhibitors in such cases.

Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a RHO-GTPase involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but has never been described so far. We studied eight male patients, from seven unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B lymphoblastoid cell lines (B-LCL) of patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. A DOCK11 knock-down recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells (MDDC) and primary activated T cells from healthy controls. Lastly, in line with the patients' autoimmune manifestations, we also observed abnormal regulatory T cells (Tregs) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found a reduced T cell proliferation and an impaired STAT5B phosphorylation upon IL2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and associated with abnormal actin cytoskeleton remodeling as well as Tregs phenotype culminating in immune dysregulation and severe early-onset autoimmunity.

International audience; Variants in aminoacyl-tRNA synthetases (ARSs) genes are associated to a broad spectrum of human inherited diseases. Patients with defective PheRS, encoded by FARSA and FARSB, display brain abnormalities, interstitial lung disease and facial dys-morphism. We investigated four children from two unrelated consanguineous families carrying two missense homozygous variants in FARSA with significantly reduced PheRS-mediated aminoacylation activity. In addition to the core ARS-phenotype, patients showed an inflammatory profile associated with autoimmunity and interferon score, a clinical feature not ascribed to PheRS-deficient patients to date. JAK inhibition improved lung disease in one patient. Our findings expand the genetic and clinical spectrum of FARSA-related disease

International audience; The interleukin-12 (IL-12) family comprises the only heterodimeric cytokines mediating diverse functional effects. We previously reported a striking bimodal IL-12p70 response to lipopolysaccharide (LPS) stimulation in healthy donors. Herein, we demonstrate that interferon β (IFNβ) is a major upstream determinant of IL-12p70 production, which is also associated with numbers and activation of circulating monocytes. Integrative modeling of proteomic, genetic, epigenomic, and cellular data confirms IFNβ as key for LPS-induced IL-12p70 and allowed us to compare the relative effects of each of these parameters on variable cytokine responses. Clinical relevance of our findings is supported by reduced IFNβ-IL-12p70 responses in patients hospitalized with acute severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or chronically infected with hepatitis C (HCV). Importantly, these responses are resolved after viral clearance. Our systems immunology approach defines a better understanding of IL-12p70 and IFNβ in healthy and infected persons, providing insights into how common genetic and epigenetic variation may impact immune responses to bacterial infection.

Mevalonate kinase deficiency should be considered in patients with severe very-early-onset inflammatory bowel disease (IBD), especially in patients with a history of recurrent or chronic fever, peritoneal adhesions, and atypical IBD pathology. Anti-interleukin-1 therapy may be efficacious in these patients with monogenic very-early-onset IBD.

The mechanisms that maintain intestinal homeostasis despite constant exposure of the gut surface to multiple environmental antigens and to billions of microbes have been scrutinized over the past 20 years with the goals to gain basic knowledge, but also to elucidate the pathogenesis of inflammatory bowel diseases (IBD) and to identify therapeutic targets for these severe diseases. Considerable insight has been obtained from studies based on gene inactivation in mice as well as from genome wide screens for genetic variants predisposing to human IBD. These studies are, however, not sufficient to delineate which pathways play key nonredundant role in the human intestinal barrier and to hierarchize their respective contribution. Here, we intend to illustrate how such insight can be derived from the study of human Mendelian diseases, in which severe intestinal pathology results from single gene defects that impair epithelial and or hematopoietic immune cell functions. We suggest that these diseases offer the unique opportunity to study in depth the pathogenic mechanisms leading to perturbation of intestinal homeostasis in humans. Furthermore, molecular dissection of monogenic intestinal diseases highlights key pathways that might be druggable and therapeutically targeted in common forms of IBD.

Indolent T cell lymphoproliferative disorder (LPD) of the gastrointestinal tract (GI-TLPD) is a rare human primary gastrointestinal T cell lymphoma that was recently included in the 2016 revision of the World Health Organization classification of lymphoid neoplasms. Low-grade intestinal T cell lymphoma (LGITL), an emerging disease in the domestic cat, shares a number of features with human GI-TLPD. In this prospective study, we determined whether feline LGITL might serve as a model of human GI-TLPD. We analyzed clinical, laboratory, and radiological data and performed histopathological and molecular studies on small intestinal biopsies from 22 domestic cats diagnosed with LGITL. This cancer mostly affects aging cats, is associated with nonspecific gastrointestinal tract signs, and is usually characterized by an indolent course. A histopathological analysis indicated that LGITL was mainly located in the jejunum. The small intestinal lamina propria was infiltrated by large numbers of small CD3+ T cell lymphocytes with various CD4 and CD8 expression profiles (CD4+ CD8- (4 out of 11, 36%), CD4- CD8+ (3 out of 11, 27%), and CD4- CD8- (4 out of 11, 36%)). Intraepithelial lymphocyte (IEL) counts were elevated in all cases. Ki67 was expressed in lamina propria lymphocytes and IELs at a low level (

Coeliac disease (CD) is a frequent immune enteropathy induced by gluten in genetically predisposed individuals. Its pathogenesis has been extensively studied and CD has emerged as a model disease to decipher how the interplay between environmental and genetic factors can predispose to autoimmunity and promote lymphomagenesis. The keystone event is the activation of a gluten-specific immune response that is driven by molecular interactions between gluten, the indispensable environmental factor, HLA-DQ2/8, the main predisposing genetic factor and transglutaminase 2, the CD-specific autoantigen. The antigluten response is however not sufficient to induce epithelial damage which requires the activation of cytotoxic CD8+intraepithelial lymphocytes (IEL). In a plausible scenario, cooperation between cytokines released by gluten-specific CD4+T cells and interleukin-15 produced in excess in the coeliac gut, licenses the autoimmune-like attack of the gut epithelium, likely via sustained activation of the Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway in IEL. Demonstration that lymphomas complicating CD arise from IEL that have acquired gain-of-functionJAK1orSTAT3mutations stresses the key role of this pathway and explains how gluten-driven chronic inflammation may promote this rare but most severe complication. If our understanding of CD pathogenesis has considerably progressed, several questions and challenges remain. One unsolved question concerns the considerable variability in disease penetrance, severity and presentation, pointing to the role of additional genetic and environmental factors that remain however uneasy to untangle and hierarchize. A current challenge is to transfer the considerable mechanistic insight gained into CD pathogenesis into benefits for the patients, notably to alleviate the gluten-free diet, a burden for many patients.

A subset of CD8

Summary Background Refractory coeliac disease type 2 is a rare subtype of coeliac disease with high mortality rates; interleukin 15 (IL-15) is strongly implicated in its pathophysiology. This trial aimed to investigate the effects of AMG 714, an anti-IL-15 monoclonal antibody, on the activity and symptoms of refractory coeliac disease type 2. Methods This was a randomised, double-blind, placebo-controlled, phase 2a study of adults with a confirmed diagnosis of refractory coeliac disease type 2. Patients were randomly assigned at a 2:1 ratio to receive seven intravenous doses over 10 weeks of AMG 714 (8 mg/kg) or matching placebo. Biopsy samples were obtained at baseline and week 12 for cellular analysis and histology. The change in the proportion of aberrant intraepithelial lymphocytes from baseline to week 12 with respect to all intraepithelial lymphocytes was the primary endpoint and was quantified using flow cytometry. Secondary endpoints were the change in aberrant intraepithelial lymphocytes with respect to intestinal epithelial cells; intestinal histological scores (villous height-to-crypt depth ratio; VHCD); intraepithelial lymphocyte counts; Marsh score; and patient-reported symptom measures, including the Bristol stool form scale (BSFS) and gastrointestinal symptom rating scale (GSRS). Main analyses were done in the per-protocol population of patients who received their assigned treatment, provided evaluable biopsy samples, and did not have major protocol deviations; only patients with non-atypical disease were included in the analyses of aberrant intraepithelial lymphocytes, including the primary analysis. Safety was assessed in all patients who received at least one dose of study drug. This study is registered at ClinicalTrials.gov (NCT02633020) and EudraCT (2015-004063-36). Findings From April 13, 2016, to Jan 19, 2017, 28 patients were enrolled and randomly assigned to AMG 714 (n=19) and placebo (n=9). Six patients were not included in the primary analysis because of protocol deviation (one in the AMG 714 group), insufficient biopsy samples (one in the AMG 714 group), and atypical intraepithelial lymphocytes (three in the AMG 714 group and one in the placebo group). At 12 weeks, the least square mean difference between AMG 714 and placebo in the relative change from baseline in aberrant intraepithelial lymphocyte percentage was −4·85% (90% CI −30·26 to 20·56; p=0·75). The difference between the AMG 714 and placebo groups in aberrant intraepithelial lymphocytes with respect to epithelial cells at 12 weeks was −38·22% (90% CI −95·73 to 19·29; nominal p=0·18); the difference in change in Marsh score from baseline was 0·09% (95% CI −1·60–1·90; nominal p=0·92); the difference in VHCD ratio was 10·67% (95% CI −38·97 to 60·31; nominal p=0·66); and the difference in change in total intraepithelial lymphocyte count was −12·73% (95% CI −77·57–52·12); nominal p=0·69). Regarding symptoms, the proportion of patients with diarrhoea per the BSFS score decreased from ten (53%) of 19 at baseline to seven (37%) of 19 at week 12 in the AMG 714 group and increased from two (22%) of nine at baseline to four (44%) of nine at week 12 in the placebo group (nominal p=0·0008); and the difference between the groups in change in GSRS score was −0·14 (SE 0·19; nominal p=0·48). Eight (89%) patients in the placebo group and 17 (89%) in the AMG 714 group had treatment-emergent adverse events, including one (11%) patient in the placebo group and five (26%) in the AMG 714 group who had serious adverse events. The most common adverse event in the AMG 714 group was nasopharyngitis (eight [42%] patients vs one [11%] in the placebo group). Interpretation In patients with refractory coeliac disease type 2 who were treated with AMG 714 or placebo for 10 weeks, there was no difference between the groups in terms of the primary endpoint of aberrant intraepithelial lymphocyte reduction from baseline. Effects on symptoms and other endpoints suggest that further research of AMG 714 may be warranted in patients with refractory coeliac disease type 2. Funding Celimmune and Amgen.

Background and Aims Nucleotide oligomerization domain 2 [NOD2] mutations are key risk factors for Crohn’s disease [CD]. NOD2 contributes to intestinal homeostasis by regulating innate and adaptive immunity together with intestinal epithelial function. However, the exact roles of NOD2 in CD and other NOD2-associated disorders remain poorly known. Methods We initially observed that NOD2 expression was increased in epithelial cells away from inflamed areas in CD patients. To explore this finding, Nod2 mRNA expression, inflammation, and cytokines expression were examined in the small bowel of wild-type [WT], Nod2 knockout and Nod2 mutant mice after rectal instillation of 2,4,6-trinitrobenzene sulphonic acid [TNBS]. Results In WT mice, Nod2 upregulation upstream to rectal injury was associated with pro-inflammatory cytokine expression but no overt histological inflammatory lesions. Conversely, in Nod2-deficient mice the inflammation spread from colitis to ileum and duodenum. Conclusions Nod2 protects the gut from colitis spreading to small intestine.

PTPN2 is an important protein tyrosine phosphatase (PTP) that plays a key role in cell signaling. Deletions or inactivating mutations of PTPN2 has been described in different pathologies and underline its critical role in hematopoiesis, auto-immunity and inflammation. Surprisingly, despite the major pathophysiological implications of PTPN2, the structural analysis of this PTP and notably of its pathogenic mutants remain poorly documented. Contrary to other human PTP enzymes, to date, only one structure of PTPN2 (wild-type form) has been reported. Here, we report the first crystal structure of a pathogenic mutant of PTPN2 (Cys216Gly) that causes an autoimmune enteropathy. We show in particular that this mutant adopts a classical PTP fold. More importantly, albeit inactive, the mutant retains its ability to bind substrates and to adopt the characteristic catalytically competent closed form of PTP enzymes. This novel PTPN2 structure may serve as a new tool to better understand PTP structures and the structural impacts of pathogenic mutations. Moreover, the C216G PTPN2 structure could also be helpful to design specific ligands/inhibitors. This article is protected by copyright. All rights reserved.

International audience; No abstract available

A subset of CD8 + T cells regulate chronic inflammation by killing pathogenic CD4 + T cells

Single genetic mutations predispose to very early onset inflammatory bowel disease (VEO-IBD). Here, we identify a de novo duplication of the 10p15.1 chromosomal region, including the IL2RA locus, in a 2-year-old girl with treatment-resistant pancolitis that was brought into remission by colectomy. Strikingly, after colectomy while the patient was in clinical remission and without medication, the peripheral blood CD4:CD8 ratio was constitutively high and CD25 expression was increased on circulating effector memory, Foxp3+, and Foxp3neg CD4+ T cells compared to healthy controls. This high CD25 expression increased IL-2 signaling, potentiating CD4+ T-cell-derived IFNγ secretion after T-cell receptor (TCR) stimulation. Restoring CD25 expression using the JAK1/3-inhibitor tofacitinib controlled TCR-induced IFNγ secretion in vitro. As diseased colonic tissue, but not the unaffected duodenum, contained mainly CD4+ T cells with a prominent IFNγ-signature, we hypothesize that local microbial stimulation may have initiated colonic disease. Overall, we identify that duplication of the IL2RA locus can associate with VEO-IBD and suggest that increased IL-2 signaling predisposes to colonic intestinal inflammation.

International audience; Dysregulated transforming growth factor TGF-beta signaling underlies the pathogenesis of genetic disorders affecting the connective tissue such as Loeys-Dietz syndrome. Here, we report 12 individuals with bi-allelic loss-of-function variants in IPO8 who presented with a syndromic association characterized by cardio-vascular anomalies, joint hyperlaxity, and various degree of dysmorphic features and developmental delay as well as immune dysregulation; the individuals were from nine unrelated families. Importin 8 belongs to the karyopherin family of nuclear transport receptors and was previously shown to mediate TGF-beta-dependent SMADs trafficking to the nucleus in vitro. The important in vivo role of IPO8 in pSMAD nuclear translocation was demonstrated by CRISPR/Cas9-mediated inactivation in zebrafish. Consistent with IPO8's role in BMP/TGF-beta signaling, ipo8(-/-) zebrafish presented mild to severe dorso-ventral patterning defects during early embryonic development. Moreover, ipo8(-/-) zebrafish displayed severe cardiovascular and skeletal defects that mirrored the human phenotype. Our work thus provides evidence that IPO8 plays a critical and non-redundant role in TGF-beta signaling during development and reinforces the existing link between TGF-beta signaling and connective tissue defects.

FOXP3 deficiency in mice and in patients with immune dysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome results in fatal autoimmunity by altering regulatory T (T-reg) cells. CD4(+) T cells in patients with IPEX syndrome and Foxp3-deficient mice were analyzed by single-cell cytometry and RNA-sequencing, revealing heterogeneous T-reg-like cells, some very similar to normal T-reg cells, others more distant. Conventional T cells showed no widespread activation or helper T cell bias, but a monomorphic disease signature affected all CD4(+) T cells. This signature proved to be cell extrinsic since it was extinguished in mixed bone marrow chimeric mice and heterozygous mothers of patients with IPEX syndrome. Normal T-reg cells exerted dominant suppression, quenching the disease signature and revealing in mutant T-reg-like cells a small cluster of genes regulated cell-intrinsically by FOXP3, including key homeostatic regulators. We propose a two-step pathogenesis model: cell-intrinsic downregulation of core FOXP3-dependent genes destabilizes T-reg cells, de-repressing systemic mediators that imprint the disease signature on all T cells, furthering T-reg cell dysfunction. Accordingly, interleukin-2 treatment improved the T-reg-like compartment and survival. FOXP3 deficiency leads to dramatic loss of immune homeostasis. This multicenter collaborative group finds that loss of FOXP3 function only disrupts a few core genes, but this unmasks a degree of systemic inflammation, and it is this environment that then strongly perturbs T-reg cells.

International audience; Proprotein convertase 1 (PCSK1, PC1/3) deficiency is an uncommon cause of neonatal malabsorptive diarrhoea associated with endocrinopathies that are due to the disrupted processing of a large number of prohormones, including proinsulin. To date, only 26 cases have been reported. Herein, we describe two siblings with typical features including severe congenital diarrhoea, central diabetes insipidus, growth hormone deficiency, and hypoadrenalism. Next generation sequencing found a homozygous missense mutation in exon 5 of PCSK1 gene, c.500A\textgreaterC (p.Asp167Ala), located within the catalytic domain. Both patients presented a high level of proinsulin. In the first years of life they required parenteral nutrition and hormone replacement therapy. The patients, aged 3 and 1.5 years, experienced several infectious episodes associated with septic shocks. While the mechanism underlying intestinal failure remains poorly investigated, parenteral nutrition is essential in order to ensure normal growth in early childhood.

The mechanisms that maintain intestinal homeostasis despite constant exposure of the gut surface to multiple environmental antigens and to billions of microbes have been scrutinized over the past 20 years with the goals to gain basic knowledge, but also to elucidate the pathogenesis of inflammatory bowel diseases (IBD) and to identify therapeutic targets for these severe diseases. Considerable insight has been obtained from studies based on gene inactivation in mice as well as from genome wide screens for genetic variants predisposing to human IBD. These studies are, however, not sufficient to delineate which pathways play key nonredundant role in the human intestinal barrier and to hierarchize their respective contribution. Here, we intend to illustrate how such insight can be derived from the study of human Mendelian diseases, in which severe intestinal pathology results from single gene defects that impair epithelial and or hematopoietic immune cell functions. We suggest that these diseases offer the unique opportunity to study in depth the pathogenic mechanisms leading to perturbation of intestinal homeostasis in humans. Furthermore, molecular dissection of monogenic intestinal diseases highlights key pathways that might be druggable and therapeutically targeted in common forms of IBD.

Background Chronic intestinal pseudo-obstruction (CIPO) is a rare condition that is not commonly associated with Crohn’s disease (CD). We performed a cohort study aiming at identifying clinical, immunological and genetic features as well as response to conventional CD treatments of patients co-affected with CIPO and CD. Methods We conducted an observational retrospective cohort study in two tertiary CIPO and IBD centers. Patients with parenteral nutrition-dependent CIPO and features of CD including large intestinal or perianal ulcers, strictures, abscesses and fistula with pathology findings compatible with CD, were included. We used flow-cytometry and targeted-next generation sequencing to identify immune defects and monogenic causes in 129 predefined genes responsible for monogenic enteropathies Results Eight unrelated patients were studied. 5 had a myogenic phenotype and 3 had a neurogenic form with histological exam for all patients. CD involved small bowel in all cases whereas one patient had ileocolonic involvement. Two patients had perianal complex fistula. Seven patients had a stricturing form and 1 had an inflammatory-only behavior. No patient had a penetrating form. All patients were diagnosed with CIPO prior to CD. Median age at CIPO diagnosis was 11.5 years old (IQR 0,31.5) while it was 22.5 (IQR 19,29) at CD diagnosis. At CD diagnosis, mean fecal calprotectin level was 551 ug/g (range 390 - 1200) and citrulline averaged 23.6 umol/l (range 15–35 umol/l). Histopathological analyses of intestinal specimens revealed ulcerations for half of the patients, increase in intraepithelial lymphocytes in 3, granuloma and cryptitis in 1 patient. Abnormalities in peripheral lymphocytes’ subsets were found in 2 patients. 5 patients were ultimately diagnosed with monogenic forms of enteropathy: 2 in ACTG2, with an autosomal dominant inheritance, 1 with a STAT1gain of function, (GOF) and two with recessive inheritance: TYMP. All patients received steroids with clinical response in 2. 6 patients received antiTNF, with only one sustained remission. Two patients received vedolizumab and 2 were treated with ustekinumab. Except for antiTNF in 1 patient, common CD treatments did not lead to any improvement. Of note, antiJAK therapy in a patient with STAT1GOF failed to induce remission. Conclusion Herein is described the first cohort of extensively genetically and immunologically explored patients co-affected with CIPO and CD. Immune defects were common and monogenic forms were found with a high prevalence. Rates of response to biologic treatment were very low. Identification of monogenic cause through immunological and genetic explorations is warranted in patient with CIPO-CD association as it could lead to targeted therapy and genetic counseling.

ObjectiveEnteropathy-associated T-cell lymphoma (EATL) is a rare but severe complication of celiac disease (CeD), often preceded by low-grade clonal intraepithelial lymphoproliferation, referred to as type II refractory CeD (RCDII). Knowledge on underlying oncogenic mechanisms remains scarce. Here, we analysed and compared the mutational landscape of RCDII and EATL in order to identify genetic drivers of CeD-associated lymphomagenesis.DesignPure populations of RCDII-cells derived from intestinal biopsies (n=9) or sorted from blood (n=2) were analysed by whole exome sequencing, comparative genomic hybridization and RNA-sequencing. Biopsies from RCDII (n=50), EATL (n=19), type I refractory CeD (n=7) and uncomplicated CeD (n=7) were analysed by targeted next-generation sequencing. Moreover, functional in vitro studies and drug testing were performed in RCDII-derived cell lines.Results80% of RCDII and 90% of EATL displayed somatic gain-of-functions mutations in the JAK1-STAT3 pathway, including a remarkable p.G1097 hotspot mutation in the JAK1 kinase-domain in approximately 50% of cases. Other recurrent somatic events were deleterious mutations in NFκB-regulators TNFAIP3 and TNIP3 and potentially oncogenic mutations in TET2, KMT2D and DDX3X. JAK1 inhibitors and the proteasome inhibitor bortezomib could block survival and proliferation of malignant RCDII-cell lines.ConclusionMutations activating the JAK1-STAT3 pathway appear to be the main drivers of CeD-associated lymphomagenesis. In concert with mutations in negative regulators of NFκB, they may favour the clonal emergence of malignant lymphocytes in the cytokine-rich coeliac intestine. The identified mutations are attractive therapeutic targets to treat RCDII and block progression towards EATL.

Indolent T cell lymphoproliferative disorder (LPD) of the gastrointestinal tract (GI-TLPD) is a rare human primary gastrointestinal T cell lymphoma that was recently included in the 2016 revision of the World Health Organization classification of lymphoid neoplasms. Low-grade intestinal T cell lymphoma (LGITL), an emerging disease in the domestic cat, shares a number of features with human GI-TLPD. In this prospective study, we determined whether feline LGITL might serve as a model of human GI-TLPD. We analyzed clinical, laboratory, and radiological data and performed histopathological and molecular studies on small intestinal biopsies from 22 domestic cats diagnosed with LGITL. This cancer mostly affects aging cats, is associated with nonspecific gastrointestinal tract signs, and is usually characterized by an indolent course. A histopathological analysis indicated that LGITL was mainly located in the jejunum. The small intestinal lamina propria was infiltrated by large numbers of small CD3+ T cell lymphocytes with various CD4 and CD8 expression profiles (CD4+ CD8- (4 out of 11, 36%), CD4- CD8+ (3 out of 11, 27%), and CD4- CD8- (4 out of 11, 36%)). Intraepithelial lymphocyte (IEL) counts were elevated in all cases. Ki67 was expressed in lamina propria lymphocytes and IELs at a low level (30%). Most LGITLs were labelled by antibodies against phosphorylated STAT5, but were negative for CD56 and phosphorylated STAT3. T cell receptor gamma chain gene monoclonality was found in 86% of cases. These findings confirmed that feline LGITL shares clinical and histopathological features with human GI-TLPD. Feline LGITL may therefore constitute a relevant model of the human disease.

FOXP3 deficiency in mice and IPEX syndrome patients results in fatal autoimmunity by altering T regulatory cells (Treg). CD4+ T cells in IPEX patients and Foxp3-deficient mice were analyzed by single-cell cytometry and RNAseq, revealing heterogeneous Treg-like cells, some very similar to normal Tregs, others more distant. Conventional T cells showed no widespread activation or Th bias, but a monomorphic disease signature affected all CD4+ T cells, cell-extrinsic signature since extinguished in mixed bone marrow chimeric mice and heterozygous mothers of IPEX patients. Normal Tregs exerted dominant suppression, extinguishing the disease signature, and revealing in mutant Treg-like cells a small cluster of genes regulated cell-intrinsically by FOXP3, including key homeostatic regulators. We propose a two-step pathogenesis model: cell-intrinsic downregulation of core genes destabilizes Tregs, de-repressing systemic mediators which imprint the disease signature on all T cells, furthering Treg dysfunction. Accordingly, IL2 treatment improved the Treg-like compartment and survival.

FOXP3 deficiency in humans with IPEX syndrome and mice results in fatal systemic autoimmunity by altering regulatory T cell (Treg) physiology, but actual cellular and molecular mechanisms of disease are unclear, part because Treg surface markers may be unreliable in disease states. We used deep profiling by flow cytometry, population and single-cell RNAseq to analyze Tregs and conventional (Tconv) CD4+ T lymphocytes in cohorts of IPEX patients with a range of genetic lesions, and in Foxp3-deficient mice. In all patients and mice, heterogeneous Treg-like cells with an active FOXP3 locus were observed, some differing very little from normal Tregs, others more distant. Tconv showed no widespread activation or Th bias. The dominant mark was a monomorphic signature equally affecting all CD4+ T cells, unexpectedly dampening tumor-Treg and cytokine-signaling modules. In mixed bone marrow chimeras, WT Tregs exerted dominant suppression, normalizing the states of mutant Treg and Tconv, extinguishing the disease signature, and revealing a small gene cluster truly regulated, cell-intrinsically, by FOXP3. These results suggest a two-step pathogenesis model, with therapeutic implications: limited downregulation of a few core Treg genes de-represses a systemic mediator(s), which imprints the disease signature on all T cells, and further dampens Treg function.

Background and Aims An expanding number of monogenic defects have been identified as causative of severe forms of very early-onset inflammatory bowel diseases [VEO-IBD]. The present study aimed at defining how next-generation sequencing [NGS] methods can be used to improve identification of known molecular diagnosis and to adapt treatment. Methods A total of 207 children were recruited in 45 paediatric centres through an international collaborative network [ESPGHAN GENIUS working group] with a clinical presentation of severe VEO-IBD [n = 185] or an anamnesis suggestive of a monogenic disorder [n = 22]. Patients were divided at inclusion into three phenotypic subsets: predominantly small bowel inflammation, colitis with perianal lesions, and colitis only. Methods to obtain molecular diagnosis included functional tests followed by specific Sanger sequencing, custom-made targeted NGS, and in selected cases whole exome sequencing [WES] of parents-child trios. Genetic findings were validated clinically and/or functionally. Results Molecular diagnosis was achieved in 66/207 children [32%]: 61% with small bowel inflammation, 39% with colitis and perianal lesions, and 18% with colitis only. Targeted NGS pinpointed gene mutations causative of atypical presentations, and identified large exonic copy number variations previously missed by WES. Conclusions Our results lead us to propose an optimised diagnostic strategy to identify known monogenic causes of severe IBD.

Indolent T-cell lymphoproliferative disorder of the GI tract (GI-TLPD) is a rare human gastrointestinal T cell lymphoma, with no therapeutic consensus. Meanwhile, an emerging indolent GI lymphoma affecting the ageing cat (T-cell low grade intestinal lymphoma ; T-LGIL) has been reported by the veterinary community. T-LGIL entity was prospectively defined at the clinical, paraclinical, histopathological and molecular levels in order to validate a potential model for the human disease. New histopathologic and immunohistochemical criteria were defined. Clonality analysis showed mainly monoclonal TCR rearrangement. The second part of the study led us to describe discriminating criteria to differentiate T-LGIL from lymphoplasmacytic enteritis. A new lymphomagenesis model was therefore suggested, evoking a continuity between an intestinal chronic antigenic stimulation and a clonal emergence of small T-cell lymphocytes within the intestinal mucosa. In conclusion, we assume that feline T-LGIL is a relevant model to better characterize human GI-TLPD., Les lymphoproliférations à cellules T du tractus gastro-intestinal (GI-TLPD) sont des lymphomes T rares chez l’Homme pour lesquels aucun consensus thérapeutique n’est établi. Par ailleurs, une lymphoprolifération digestive indolente à cellules T (T-LGIL) émergente est décrite dans l’espèce féline. La physiopathologie de ces entités est mal définie. Dans un premier temps, nous avons prospectivement analysé des prélèvements lésionnels chez 22 chats présentant un T-LGIL sur les plans clinique, paraclinique, histopathologique et moléculaire. Nos résultats valident que ce modèle animal est pertinent pour l’étude de la maladie humaine. Dans l’autre partie du travail, notre objectif a été l’identification de critères discriminant les lymphoproliférations indolentes félines des entérites lymphoplasmocytaires, ce diagnostic différentiel étant un défi chez le chat. Nous avons établi de nouveaux critères histologiques et immunohistochimiques. Un modèle de lymphomagenèse a été proposé : il repose sur un continuum entre une entéropathie inflammatoire chronique et l’émergence de clones néoplasiques T au sein de la muqueuse intestinale., Freiche Valérie, Cordonnier-Lefort Nathalie, Paulin Mathieu-Victor, Huet Hélène, Turba Maria-Elena, Macintyre Elizabeth, Malamut Georgia, Cerf-Bensussan Nadine, Molina Thierry Jo, Hermine Olivier, Bruneau Julie, Couronné Lucile. Lymphome intestinal de bas grade félin : validation d’un modèle spontané et émergent illustrant les lymphoproliférations digestives indolentes à cellules T de l’homme. In: Bulletin de l'Académie Vétérinaire de France tome 173, 2020. pp. 9-19.

Resume La maladie cœliaque (MC), ou intolerance au gluten, est une pathologie multifactorielle developpee sur un terrain genetique predisposant. Aujourd’hui encore sous diagnostiquee, elle toucherait pres de 1 % de la population mondiale. La presentation clinique classique d’enteropathie avec malabsorption n’est pas la plus frequente, elle est souvent asymptomatique, pauci-symptomatique ou de presentation clinique atypique. Son diagnostic est multidisciplinaire, et l’apport de l’histologie bien que discute, est souvent primordial, confirmant le diagnostic suspecte de MC et justifiant ainsi la mise en place d‘un regime sans gluten (RSG) a vie. L’histologie est utile egalement lors du suivi de la MC, afin de mettre en evidence une pathologie associee ou une evolution defavorable vers une MC refractaire au RSG. Enfin, il faut savoir remettre en question le diagnostic de MC si tous les parametres biologiques ne sont pas reunis et notamment un typage HLA compatible. En effet, la premiere cause d’atrophie villositaire est la MC, mais de nombreuses etiologies peuvent etre associees a une atrophie villositaire. Dans cette revue, les points essentiels du diagnostic, de la physiopathologie, de l’histopathologie et des complications de la MC seront developpes.