Quantification of polyreactive immunoglobulin G facilitates the diagnosis of autoimmune hepatitis.

BACKGROUND AND AIMS: Detection of autoantibodies is a mainstay of diagnosing autoimmune hepatitis (AIH). However, conventional autoantibodies for the workup of AIH lack either sensitivity or specificity, leading to substantial diagnostic uncertainty. We aimed to identify more accurate serological markers of AIH with a protein macroarray. APPROACH AND RESULTS: During the search for more-precise autoantibodies to distinguish AIH from non-AIH liver diseases (non-AIH-LD), IgG antibodies with binding capacities to many human and foreign proteins were identified with a protein macroarray and confirmed with solid-phase ELISAs in AIH patients. Subsequently, polyreactive IgG (pIgG) was exemplarily quantified by reactivity against human huntingtin-interacting protein 1-related protein in bovine serum albumin blocked ELISA (HIP1R/BSA). The diagnostic fidelity of HIP1R/BSA binding pIgG to diagnose AIH was assessed in a retrospective training, a retrospective multicenter validation, and a prospective validation cohort in cryoconserved samples from 1,568 adults from 10 centers from eight countries. Reactivity against HIP1R/BSA had a 25% and 14% higher specificity to diagnose AIH than conventional antinuclear and antismooth muscle antibodies, a significantly higher sensitivity than liver kidney microsomal antibodies and antisoluble liver antigen/liver pancreas antigen, and a 12%-20% higher accuracy than conventional autoantibodies. Importantly, HIP1R/BSA reactivity was present in up to 88% of patients with seronegative AIH and in up to 71% of AIH patients with normal IgG levels. Under therapy, pIgG returns to background levels of non-AIH-LD. CONCLUSIONS: pIgG could be used as a promising marker to improve the diagnostic workup of liver diseases with a higher specificity for AIH compared to conventional autoantibodies and a utility in autoantibody-negative AIH. Likewise, pIgG could be a major source of assay interference in untreated AIH.

Mechanisms of autoimmune hepatitis.

PURPOSE OF REVIEW: Autoimmune hepatitis (AIH) is a chronic disease characterized by a lymphocyte infiltrate in the liver. For decades, nonspecific immunosuppression has been used to limit chronic liver inflammation. The high risk of relapse, the treatments side effects, and the significant number of refractory patients are the main clinical issues that require efforts to understand AIH immune mechanisms. RECENT FINDINGS: The balance between regulatory CD4 T cells, known to control autoimmunity, and effector CD4 T cells, that recognize liver self-antigens and mediate the liver inflammation, appears central in AIH immune mechanisms. Recent advances in the identification of pathogenic auto-reactive CD4 T cells, and of new mechanisms of immune regulatory defects in AIH patients, give new insights into the pathophysiology of this disease. SUMMARY: In this review, we propose an overview of the central role of CD4 T cells (both regulatory and pathogenic) in mechanisms of AIH, with a focus on recent advances regarding defective regulatory mechanisms and immune profile of auto-reactive CD4 T cells. These findings may have implication for the orientation of new therapeutic strategies to treat AIH, such as regulatory T-cell infusion or targeting B cells and cytokines released by pathogenic CD4 T cells.

Integrative molecular profiling of autoreactive CD4 T cells in autoimmune hepatitis.

BACKGROUND & AIMS: In most autoimmune disorders, crosstalk of B cells and CD4 T cells results in the accumulation of autoantibodies. In autoimmune hepatitis (AIH), the presence of anti-soluble liver antigen (SLA) autoantibodies is associated with reduced overall survival, but the associated autoreactive CD4 T cells have not yet been characterised. Herein, we isolated and deeply characterised SLA-specific CD4 T cells in patients with AIH. METHODS: We used brief ex vivo restimulation with overlapping SLA peptides to isolate and phenotype circulating SLA-specific CD4 T cells, and integrative single-cell RNA-seq (scRNA-seq) to characterise their transcriptome and T-cell receptor (TCR) repertoire. Autoreactive TCRs were cloned and used to identify dominant SLA-derived epitopes. SLA-specific CD4 T cells were tracked in peripheral blood through TCR sequencing to identify their phenotypic niche. We further characterised disease-associated peripheral blood T cells by high-content flow cytometry in 42 patients with AIH and 17 controls with non-alcoholic steatohepatitis. RESULTS: Autoreactive SLA-specific CD4 T cells were only detected in patients with anti-SLA autoantibodies and had a memory PD-1+CXCR5-CCR6-CD27+ phenotype. ScRNA-seq revealed their pro-inflammatory/B-helper profile. SLA81-100 and SLA177-204 contain dominant T-cell epitopes. Autoreactive TCR clonotypes were predominantly found in the memory PD-1+CXCR5-CD4 T cells, which were significantly increased in the blood of patients with AIH and supported B-cell differentiation through IL-21. Finally, we identified specific T-cell phenotypes linked to disease activity and IgG level during AIH. CONCLUSIONS: We provide a deep characterisation of rare circulating autoreactive CD4 T cells and identify their peripheral reservoir in AIH. We also propose a specific phenotype of autoreactive T cells related to AIH disease activity, which will be essential to track, delineate, and potentially target these pathogenic cells. LAY SUMMARY: One principal characteristic of autoimmune hepatitis (AIH), like for many other autoimmune diseases, is the accumulation of autoantibodies produced by B lymphocytes following their interaction with autoreactive CD4 T lymphocytes. In this study, we identified and characterised with high resolution these CD4 T cells. This will be essential to track, delineate, and potentially target them during AIH.

Synchronous immune alterations mirror clinical response during allergen immunotherapy.

BACKGROUND: Three years of treatment with either sublingual or subcutaneous allergen immunotherapy has been shown to be effective and to induce long-term tolerance. The Gauging Response in Allergic Rhinitis to Sublingual and Subcutaneous Immunotherapy (GRASS) trial demonstrated that 2 years of treatment through either route was effective in suppressing the response to nasal allergen challenge, although it was insufficient for inhibition 1 year after discontinuation. OBJECTIVE: We sought to examine in the GRASS trial the time course of immunologic changes during 2 years of sublingual and subcutaneous immunotherapy and for 1 year after treatment discontinuation. METHODS: We performed multimodal immunomonitoring to assess allergen-specific CD4 T-cell properties in parallel with analysis of local mucosal cytokine responses induced by nasal allergen exposure and humoral immune responses that included IgE-dependent basophil activation and measurement of serum inhibitory activity for allergen-IgE binding to B cells (IgE-facilitated allergen binding). RESULTS: All 3 of these distinct arms of the immune response displayed significant and coordinate alterations during 2 years of allergen desensitization, followed by reversal at 3 years, reflecting a lack of a durable immunologic effect. Although frequencies of antigen-specific TH2 cells in peripheral blood determined by using HLA class II tetramer analysis most closely paralleled clinical outcomes, IgE antibody-dependent functional assays remained inhibited in part 1 year after discontinuation. CONCLUSION: Two years of allergen immunotherapy were effective but insufficient for long-term tolerance. Allergen-specific TH2 cells most closely paralleled the transient clinical outcome, and it is likely that recurrence of the T-cell drivers of allergic immunity abrogated the potential for durable tolerance. On the other hand, the persistence of IgE blocking antibody 1 year after discontinuation might be an early indicator of a protolerogenic mechanism.

Chronic cat allergen exposure induces a TH2 cell-dependent IgG4 response related to low sensitization.

BACKGROUND: In human subjects, allergen tolerance has been observed after high-dose allergen exposure or after completed allergen immunotherapy, which is related to the accumulation of anti-inflammatory IgG4. However, the specific T-cell response that leads to IgG4 induction during chronic allergen exposure remains poorly understood. OBJECTIVE: We sought to evaluate the relationship between cat allergen-specific T-cell frequency, cat allergen-specific IgE and IgG4 titers, and clinical status in adults with cat allergy with and without cat ownership and the cellular mechanism by which IgG4 is produced. METHODS: Fel d 1-, Fel d 4-, Fel d 7-, and Fel d 8-specific T-cell responses were characterized by CD154 expression after antigen stimulation. RESULTS: In allergic subjects without cat ownership, the frequency of cat allergen (Fel d 1 and Fel d 4)-specific TH2 (sTH2) cells correlates with higher IgE levels and is linked to asthma. Paradoxically, we observed that subjects with cat allergy and chronic cat exposure maintain a high frequency of sTH2 cells, which correlates with higher IgG4 levels and low sensitization. B cells from allergic, but not nonallergic subjects, are able to produce IgG4 after cognate interactions with sTH2 clones and Fel d 1 peptide or the Fel d 1 recombinant protein. CONCLUSION: These experiments suggest that (1) allergen-experienced B cells with the capacity to produce IgG4 are present in allergic subjects and (2) cat allergen exposure induces an IgG4 response in a TH2 cell-dependent manner. Thus IgG4 accumulation could be mediated by chronic activation of the TH2 response, which in turn drives desensitization.

T cell immuno-phenotyping : a source of predictive biomarkers for autoimmune hepatitis relapse.

Relapse after immunosuppression (IS) treatment withdrawal is frequent in patients with Autoimmune Hepatitis (AIH), and non-invasive biomarkers predictive of this risk are lacking. We assessed the frequency of circulating T cell subsets as potential biomarkers of disease activity and predictor of the risk of relapse after IS withdrawal. Serum levels of the cytokine B-cell Activating Factor (BAFF) were also investigated. Blood samples from 58 patients with active AIH, 56 AIH patients in remission, and 31 patients with NASH were analyzed. The frequency of activated CD4+ T peripheral helper (TPH) cells (CD4+CD45RA-CXCR5-PD1+CD38+) and of activated CD8+ T cells (CD8+CD45RA-PD1+CD38+) were assessed by flow cytometry. BAFF levels were determined by ELISA. Activated TPH and CD8+ T cell frequencies were significantly increased in patients with active AIH compared to remission AIH or NASH (TPH: 0.88% of total CD3+ vs. 0.42% and 0.39% respectively, p < 0.0001; CD8+ subset: 1.42% vs. 0.09% and 0.11% p < 0.0001). Among patients in remission undergoing treatment withdrawal (n = 18), those with increased frequencies of activated TPH (> 0.5% of total CD3+) and/or activated CD8+ T cells (> 0.18% total CD3+) had a higher risk of relapse (80% vs. 15% after 2 years, p = 0.0071). High BAFF serum concentration (> 213pg/ml) was also associated to a higher risk of relapse (57% vs. 11%, p = 0.0452). In conclusion, high frequency of activated TPH and of activated CD8+, as well as high levels of BAFF, before IS discontinuation, were significantly associated to a greater risk of relapse during the first two years. Thus, they represent promising biomarkers to provide personalized clinical follow-up for patients with AIH.

Detection of polyreactive immunoglobulin G facilitates diagnosis in children with autoimmune hepatitis.

OBJECTIVE: The detection of autoantibodies is essential to diagnose autoimmune hepatitis (AIH). Particularly in children, specificity of autoantibodies decreases due to lower titers being diagnostic and being present not only in AIH but also in other liver diseases. Recently, quantification of polyreactive IgG (pIgG) for detection of adult AIH showed the highest overall accuracy compared to antinuclear antibodies (ANA), anti-smooth muscle antibodies (anti-SMA), anti-liver kidney microsomal antibodies (anti-LKM) and anti-soluble liver antigen/liver pancreas antibodies (anti-SLA/LP). We aimed to evaluate the diagnostic value of pIgG for pediatric AIH. DESIGN: pIgG, quantified using HIP1R/BSA coated ELISA, and immunofluorescence on rodent tissue sections were performed centrally. The diagnostic fidelity to diagnose AIH was compared to conventional autoantibodies of AIH in training and validation cohorts from a retrospective, European multi-center cohort from nine centers from eight European countries composed of existing biorepositories from expert centers (n = 285). RESULTS: IgG from pediatric AIH patients exhibited increased polyreactivity to multiple protein and non-protein substrates compared to non-AIH liver diseases and healthy children. pIgG had an AUC of 0.900 to distinguish AIH from non-AIH liver diseases. pIgG had a 31-73% higher specificity than ANA and anti-SMA and comparable sensitivity that was 6-20 times higher than of anti-SLA/LP, anti-LC1 and anti-LKM. pIgG had a 21-34% higher accuracy than conventional autoantibodies, was positive in 43-75% of children with AIH and normal IgG and independent from treatment response. CONCLUSION: Detecting pIgG improves the diagnostic evaluation of pediatric AIH compared to conventional autoantibodies, primarily owing to higher accuracy and specificity.

IL-17-producing invariant NKT cells in lymphoid organs are recent thymic emigrants identified by neuropilin-1 expression.

Despite increasing knowledge on the mechanisms of invariant natural killer T (iNKT)-cell development in the thymus, the function of recent thymic emigrant (RTE) iNKT cells remains largely unexplored, principally because of a lack of bona fide markers to distinguish RTE from long-lived iNKT cells. Whether the recently described IL-17-producing iNKT cell subset is part of RTE has notably not been addressed. In the present study, we show that neuropilin-1 (Nrp-1), a transmembrane receptor mainly found on T-regulatory (Treg) cells in the murine immune system, is specifically expressed on RTE iNKT cells in naive mice. We used the Nrp-1 marker to discriminate RTE from mature iNKT cells and compare their functions. We show that RTE iNKT cells proliferate more than mature iNKT cells after in vitro activation; that, unlike mature iNKT cells, most RTE iNKT cells fail to rapidly produce IFN-γ and IL-4 after in vivo activation; and, most importantly, that IL-17-producing iNKT cells in lymphoid organs of naive mice are contained within the RTE iNKT cell pool. Our results establish an accurate marker of RTE iNKT cells and reveal that continuous thymic output is required for pro-inflammatory IL-17 secretion, a key function of adult iNKT cells.

Rationale and efficacy of interleukin-1 targeting in Erdheim-Chester disease.

Erdheim-Chester disease (ECD) pathophysiology remains largely unknown. Its treatment is not codified and usually disappointing. Interferon (IFN)-α therapy lacks efficacy for some life-threatening manifestations and has a poor tolerance profile. Because interleukin (IL)-1Ra synthesis is naturally induced after stimulation by IFN-α, we hypothesized that recombinant IL-1Ra (anakinra) might have some efficacy in ECD. We treated 2 patients who had poor tolerance or contraindication to IFN-α with anakinra as a rescue therapy and measured their serum C-reactive protein, IL-1ß, IL-6, and monocytic membranous IL-1α (mIL-1α) levels before, under, and after therapy. Another untreated ECD patient and 5 healthy subjects were enrolled as controls. After treatment, fever and bone pains rapidly disappeared in both patients, as well as eyelid involvement in one patient. In addition, retroperitoneal fibrosis completely or partially regressed, and C-reactive protein, IL-6, and mIL-1α levels decreased to within the normal and control range. Beside injection-site reactions, no adverse event was reported. Therefore, our results support a central role of the IL-1 network, which seemed to be overstimulated in ECD. Its specific blockade using anakinra thereby opens new pathophysiology and therapeutic perspectives in ECD.

Mast cell leukemia: identification of a new c-Kit mutation, dup(501-502), and response to masitinib, a c-Kit tyrosine kinase inhibitor.

OBJECTIVE: Most patients with systemic mastocytosis bear mutations in the tyrosine kinase receptor gene c-Kit. Limited treatment options exist for mast cell leukemia, a rare form of systemic mastocytosis associated with a dire prognosis. Our aim was to investigate c-Kit mutations associated with mast cell leukemia and find new treatment for this severe form of mastocytosis. PATIENT AND METHODS: We describe here a patient with mast cell leukemia characterized by 42% of circulating mast cells associated with a previously unidentified c-Kit mutation in adult mastocytosis: dup(501-502). MAIN FINDINGS: This patient was treated with masitinib, a novel c-Kit tyrosine kinase inhibitor, with a dramatic response observed following 3 months of treatment, including clinical improvement, disappearance of circulating mast cells, and decrease in both serum histamine and tryptase levels. In vitro and ex vivo research was performed on the patient's cells and revealed constitutive c-Kit phosphorylation in mast cell leukemia. CONCLUSIONS: This case highlights the importance of sequencing all c-Kit exons when the classical D816V c-Kit mutation is not found, even in adults with SM. It also indicates that masitinib may be safe and effective for the treatment for some mast cell leukemia.

Neuropilin-1 cooperates with PD-1 in CD8+ T cells predicting outcomes in melanoma patients treated with anti-PD1.

Targeting immune checkpoints, such as Programmed cell Death 1 (PD1), has improved survival in cancer patients by restoring antitumor immune responses. Most patients, however, relapse or are refractory to immune checkpoint blocking therapies. Neuropilin-1 (NRP1) is a transmembrane glycoprotein required for nervous system and angiogenesis embryonic development, also expressed in immune cells. We hypothesized that NRP1 could be an immune checkpoint co-receptor modulating CD8+ T cells activity in the context of the antitumor immune response. Here, we show that NRP1 is recruited in the cytolytic synapse of PD1+CD8+ T cells, cooperates and enhances PD-1 activity. In mice, CD8+ T cells specific deletion of Nrp1 improves anti-PD1 antibody antitumor immune responses. Likewise, in human metastatic melanoma, the expression of NRP1 in tumor infiltrating CD8+ T cells predicts poor outcome of patients treated with anti-PD1. NRP1 is a promising target to overcome resistance to anti-PD1 therapies.

Regulatory T-cell depletion in angioimmunoblastic T-cell lymphoma.

Angioimmunoblastic T-cell lymphoma (AITL) is the most frequent nodal T-cell lymphoma and is characterized by a polymorphic lymph node infiltrate, various dysimmune disorders, and a poor prognosis. Regulatory T-cells (Treg) play an emerging role in the prognosis of non-Hodgkin B-cell lymphoma and mediate significant autoreactive T-cell suppression. In this report, we demonstrate that numbers of Treg are significantly decreased in AITL lymph nodes [n = 30, 91 (40-195) per high power fields] compared with follicular lymphoma [n = 19, 179 (86-355)] and reactive lymph nodes [n = 8, 186 (140-265)]. Moreover, the few Treg in lymph nodes of AITL are resting Treg (rTreg) and have a naive CD45RA+, PD1-, and ICOS- phenotype [n = 5, 57% of Treg are CD45RA+ (16-96)], in contrast to the Treg in follicular lymphomas [n = 5, 7.4% (1-13)] or reactive lymph nodes [n = 7, 18.6% (6-48)]. Interestingly, Treg depletion was not observed in AITL peripheral blood at diagnosis. Altogether, these data suggest that Treg depletion could contribute to the nodal neoplastic T(FH) expansion and dysimmune symptoms in AITL.

Neuropilin-1 is not a marker of human Foxp3+ Treg.

Treg are immune cells that play a critical role in the regulation of the immune response. Although the transcription factor Foxp3 is widely accepted as the standard marker of Treg, specific surface markers are needed to better characterize these cells and decipher their mechanisms of action. Neuropilin-1 (Nrp-1), a membrane protein primarily involved in the nervous system, was identified as a specific marker of murine Treg, but its expression has not been rigorously investigated in human Treg. Here we show that in contrast to murine Treg and regardless of their origins (blood, thymus, spleen, lymph node or tonsil), human Foxp3(+) Treg do not specifically express Nrp-1. However, a population of Foxp3(-) Nrp-1(+) T cells can be detected in human secondary lymphoid organs, and Nrp-1 expression is induced on peripheral blood T lymphocytes upon in vitro activation. We conclude that Nrp-1 cannot be used as a specific marker of human Treg, but might represent a novel activation marker of human T cells both in vitro and in vivo.

Role of GM-CSF in tolerance induction by mobilized hematopoietic progenitors.

Mechanisms of protection against autoimmune diseases by transplantation of autologous hematopoietic progenitors remain poorly defined. We recently demonstrated that, unlike medullary hematopoietic stem cells (HSCs), mobilized hematopoietic progenitors (HPCs) stimulate peripheral Foxp3(+) regulatory T cell (Treg)-expansion through cell-contact activation of Notch signaling and through as yet undetermined soluble factor(s), distinct from TGF-beta1. Herein we identified one such soluble factor as granulocyte macrophage-colony stimulating factor (GM-CSF), which is produced at higher levels by HPCs than HSCs and whose neutralization significantly reduces the growth-promoting effect of HPCs on Treg. Treg express a functional GM-CSF receptor alpha-chain CD116 and proliferate in response to this cytokine independently from IL2. GM-CSF-expanded Treg-like HPC-expanded Treg-display enhanced suppressive capacity relative to control Treg. Hence, mobilized progenitors stimulate Treg expansion both by cell-contact dependent mechanisms and by their production of GM-CSF.

Corrigendum: FB5P-seq: FACS-Based 5-Prime End Single-Cell RNA-seq for Integrative Analysis of Transcriptome and Antigen Receptor Repertoire in B and T Cells.

[This corrects the article DOI: 10.3389/fimmu.2020.00216.].

Corrigendum: FB5P-seq: FACS-Based 5-Prime End Single-Cell RNA-seq for Integrative Analysis of Transcriptome and Antigen Receptor Repertoire in B and T Cells.

[This corrects the article DOI: 10.3389/fimmu.2020.00216.].

FB5P-seq: FACS-Based 5-Prime End Single-Cell RNA-seq for Integrative Analysis of Transcriptome and Antigen Receptor Repertoire in B and T Cells.

Single-cell RNA sequencing (scRNA-seq) allows the identification, characterization, and quantification of cell types in a tissue. When focused on B and T cells of the adaptive immune system, scRNA-seq carries the potential to track the clonal lineage of each analyzed cell through the unique rearranged sequence of its antigen receptor (BCR or TCR, respectively) and link it to the functional state inferred from transcriptome analysis. Here we introduce FB5P-seq, a FACS-based 5'-end scRNA-seq method for cost-effective, integrative analysis of transcriptome and paired BCR or TCR repertoire in phenotypically defined B and T cell subsets. We describe in detail the experimental workflow and provide a robust bioinformatics pipeline for computing gene count matrices and reconstructing repertoire sequences from FB5P-seq data. We further present two applications of FB5P-seq for the analysis of human tonsil B cell subsets and peripheral blood antigen-specific CD4 T cells. We believe that our novel integrative scRNA-seq method will be a valuable option to study rare adaptive immune cell subsets in immunology research.

Heterogeneity of Ara h Component-Specific CD4 T Cell Responses in Peanut-Allergic Subjects.

Understanding the peanut-specific CD4 T cell responses in peanut-allergic (PA) subjects should provide new insights into the development of innovative immunotherapies for the treatment of peanut allergy. Although peanut-specific CD4 T cells have a TH2 profile in PA subjects, the immunogenicity of different Ara h components in eliciting specific CD4 T cell responses and the heterogeneity of these Ara h-reactive TH2 cells remains unclear. In this study, we investigated Ara h 1, 2, 3, 6, and 8-specific T cell responses in PA and sensitized non-peanut-allergic (sNPA) subjects, using the CD154 upregulation assay and the class II tetramer technology. In the PA group, T cells directed against Ara h 1, 2, 3, and 6 have a heterogeneous TH2 phenotype characterized by differential expression of CRTH2, CD27, and CCR6. Reactivity toward these different components was also distinct for each PA subject. Two dominant Ara h 2 epitopes associated with DR1501 and DR0901 were also identified. Frequencies of Ara h-specific T cell responses were also linked to the peanut specific-IgE level. Conversely, low peanut-IgE level in sNPA subjects was associated with a weak or an absence of the allergen-specific T cell reactivity. Ara h 8-specific T cell reactivity was weak in both PA and sNPA subjects. Thus, peanut-IgE level was associated with a heterogeneous Ara h (but not Ara h 8)-specific T cell reactivity only in PA patients. This suggests an important immunogenicity of each Ara h 1, 2, 3, and 6 in inducing peanut allergy. Targeting Ara h 1-, 2-, 3-, and 6-specific effector-TH2 cells can be the future way to treat peanut allergy.