Silencing of high-affinity insulin-reactive B lymphocytes by anergy and impact of the NOD genetic background in mice

Evaluation of proinsulin(F25D) as a targeting ligand for insulin-binding B cells in autoimmune diabetes

Insulin-binding B cells are implicated in Type 1 Diabetes (T1D) pathology. Antigen-specific immunotherapy (ASIT) holds promise in T1D. However, ASIT-targeted suppression of insulin-binding B cells is hampered by insulin's hormonal activity and the resulting binding and endocytosis of insulin by insulin receptors (INSR). To evaluate ASIT strategies that target insulin-binding B cells in vivo, non-hormonally active insulin variants are needed. In this work, we aimed to improve upon prior non-hormonal insulin variants by making mutations to the insulin precursor, proinsulin, and including a c-terminal sortase (SrtA) tag (LPETGGHG) to enable facile site-selective bioconjugation to scaffolds or payloads. Of the insulin variants investigated that retained low-nM binding to the murine-derived insulin autoantibody mAb 125, proinsulin(F25D)-SrtA had the lowest INSR binding and activity and the greatest fibrillation resistance. Compared to desoctapeptide insulin, a previously proposed non-hormonal insulin variant, proinsulin(F25D)-SrtA demonstrated 50-fold lower INSR binding and 100-fold greater fibrillation lag time. However, insulin(F25D)-SrtA bound to the anti-insulin antibody 12M4 isolated from a presymptomatic T1D individual, whereas proinsulin(F25D)-SrtA and desoctapeptide insulin did not, highlighting the potential for anti-insulin B cells to develop in human T1D that would escape this ASIT moiety. The characteristics of proinsulin(F25D)-SrtA make it a well-suited non-hormonal insulin variant for insulin-binding B cell targeting and warrants additional study with other anti-insulin B cell specificities derived from T1D individuals.

Deciphering the cellular and molecular landscape of pulmonary fibrosis through single-cell sequencing and machine learning

Pulmonary fibrosis is characterized by progressive lung scarring, leading to a decline in lung function and an increase in morbidity and mortality. This study leverages single-cell sequencing and machine learning to unravel the complex cellular and molecular mechanisms underlying pulmonary fibrosis, aiming to improve diagnostic accuracy and uncover potential therapeutic targets. By analyzing lung tissue samples from pulmonary fibrosis patients, we identified distinct cellular phenotypes and gene expression patterns that contribute to the fibrotic process. Notably, our findings revealed a significant enrichment of activated B cells, CD4 T cells, macrophages, and specific fibroblast subpopulations in fibrotic versus normal lung tissue. Machine learning analysis further refined these observations, resulting in the development of a diagnostic model with enhanced precision, based on key gene signatures including TMEM52B, PHACTR1, and BLVRB. Comparative analysis with existing diagnostic models demonstrates the superior accuracy and specificity of our approach. Through In vitro experiments involving the knockdown of PHACTR1, TMEM52B, and BLVRB genes demonstrated that these genes play crucial roles in inhibiting the expression of α-SMA and collagen in lung fibroblasts induced by TGF-β. Additionally, knockout of the PHACTR1 gene reduced inflammation and collagen deposition in a bleomycin-induced mouse model of pulmonary fibrosis in vivo. Additionally, our study highlights novel gene signatures and immune cell profiles associated with pulmonary fibrosis, offering insights into potential therapeutic targets. This research underscores the importance of integrating advanced technologies like single-cell sequencing and machine learning to deepen our understanding of pulmonary fibrosis and pave the way for personalized therapeutic strategies.

The Src-family kinase Lyn plays a critical role in establishing and maintaining B cell anergy by suppressing PI3K-dependent signaling

Although the Src family kinase (SFK) Lyn is known to be involved in induction and maintenance of peripheral B cell tolerance, the molecular basis of its action in this context remains unclear. This question has been approached using conventional as well as B cell-targeted knockouts of Lyn, with varied conclusions likely confused by collateral loss of Lyn functions in B cell and myeloid cell development and activation. Here we utilized a system in which Lyn gene deletion is tamoxifen inducible and B cell restricted. This system allows acute elimination of Lyn in B cells without off-target effects. This genetic tool was employed in conjunction with immunoglobulin transgenic mice in which peripheral B cells are autoreactive. DNA reactive Ars/A1 B cells require continuous inhibitory signaling, mediated by the inositol phosphatase SHIP-1 and the tyrosine phosphatase SHP-1, to maintain an unresponsive (anergic) state. Here we show that Ars/A1 B cells require Lyn to establish and maintain B cell unresponsiveness. Lyn primarily functions by restricting PI3K-dependent signaling pathways. This Lyn-dependent mechanism complements the impact of reduced mIgM BCR expression to restrict BCR signaling in Ars/A1 B cells. Our findings suggest that a subset of autoreactive B cells requires Lyn to become anergic and that the autoimmunity associated with dysregulated Lyn function may, in part, be due to an inability of these autoreactive B cells to become tolerized.

Factors Governing B Cell Recognition of Autoantigen and Function in Type 1 Diabetes

Islet autoantibodies predict type 1 diabetes (T1D) but can be transient in murine and human T1D and are not thought to be directly pathogenic. Rather, these autoantibodies signal B cell activity as antigen-presenting cells (APCs) that present islet autoantigen to diabetogenic T cells to promote T1D pathogenesis. Disrupting B cell APC function prevents T1D in mouse models and has shown promise in clinical trials. Autoantigen-specific B cells thus hold potential as sophisticated T1D biomarkers and therapeutic targets. B cell receptor (BCR) somatic hypermutation is a mechanism by which B cells increase affinity for islet autoantigen. High-affinity B and T cell responses are selected in protective immune responses, but immune tolerance mechanisms are known to censor highly autoreactive clones in autoimmunity, including T1D. Thus, different selection rules often apply to autoimmune disease settings (as opposed to protective host immunity), where different autoantigen affinity ceilings are tolerated based on variations in host genetics and environment. This review will explore what is currently known regarding B cell signaling, selection, and interaction with T cells to promote T1D pathogenesis.

Identification of an anergic BND cell-derived activated B cell population (BND2) in young-onset type 1 diabetes patients

Recent evidence suggests a role for B cells in the pathogenesis of young-onset type 1 diabetes (T1D), wherein rapid progression occurs. However, little is known regarding the specificity, phenotype, and function of B cells in young-onset T1D. We performed a cross-sectional analysis comparing insulin-reactive to tetanus-reactive B cells in the blood of T1D and controls using mass cytometry. Unsupervised clustering revealed the existence of a highly activated B cell subset we term BND2 that falls within the previously defined anergic BND subset. We found a specific increase in the frequency of insulin-reactive BND2 cells in the blood of young-onset T1D donors, which was further enriched in the pancreatic lymph nodes of T1D donors. The frequency of insulin-binding BND2 cells correlated with anti-insulin autoantibody levels. We demonstrate BND2 cells are pre-plasma cells and can likely act as APCs to T cells. These findings identify an antigen-specific B cell subset that may play a role in the rapid progression of young-onset T1D.

Comparative analysis of the repertoire of insulin-reactive B cells in type 1 diabetes-prone and resistant mice

Seropositivity for autoantibodies against multiple islet antigens is associated with development of autoimmune type 1 diabetes (T1D), suggesting a role for B cells in disease. The importance of B cells in T1D is indicated by the effectiveness of B cell-therapies in mouse models and patients. B cells contribute to T1D by presenting islet antigens, including insulin, to diabetogenic T cells that kill pancreatic beta cells. The role of B cell receptor (BCR) affinity in T1D development is unclear. Here, we employed single cell RNA sequencing to define the relationship between BCR affinity for insulin and B cell phenotype during disease development. We utilized immunoglobulin (Ig) heavy chain (VH125) mouse models in which high-affinity insulin-reactive B cells (IBCs) were previously shown to be anergic in diabetes-resistant VH125.C57BL/6-H2g7 and activated in VH125. NOD mice developing disease. Here, high-affinity IBCs were found in the spleen of prediabetic VH125. NOD mice and exhibited marginal zone or follicular phenotypes. Ig light chains expressed by these B cells are unmutated and biased toward Vκ4-74 and Vκ4-57 usage. Receptors expressed by anergic high-affinity IBCs of diabetes-resistant VH125.C57BL/6-H2g7 are also unmutated; however, in this genetic background light chains are polymorphic relative to those of NOD. Light chains derived from NOD and C57BL/6-H2g7 genetic backgrounds conferred divergent kinetics of binding to insulin when paired with the VH125 heavy chain. These findings suggest that relaxation of tolerance mechanisms in the NOD mouse leads to accumulation and partial activation of B cells expressing germline encoded high-affinity BCRs that support development of autoimmunity.

Polygenic autoimmune disease risk alleles impacting B cell tolerance act in concert across shared molecular networks in mouse and in humans

Most B cells produced in the bone marrow have some level of autoreactivity. Despite efforts of central tolerance to eliminate these cells, many escape to periphery, where in healthy individuals, they are rendered functionally non-responsive to restimulation through their antigen receptor via a process termed anergy. Broad repertoire autoreactivity may reflect the chances of generating autoreactivity by stochastic use of germline immunoglobulin gene segments or active mechanisms may select autoreactive cells during egress to the naïve peripheral B cell pool. Likewise, it is unclear why in some individuals autoreactive B cell clones become activated and drive pathophysiologic changes in autoimmune diseases. Both of these remain central questions in the study of the immune system(s). In most individuals, autoimmune diseases arise from complex interplay of genetic risk factors and environmental influences. Advances in genome sequencing and increased statistical power from large autoimmune disease cohorts has led to identification of more than 200 autoimmune disease risk loci. It has been observed that autoantibodies are detectable in the serum years to decades prior to the diagnosis of autoimmune disease. Thus, current models hold that genetic defects in the pathways that control autoreactive B cell tolerance set genetic liability thresholds across multiple autoimmune diseases. Despite the fact these seminal concepts were developed in animal (especially murine) models of autoimmune disease, some perceive a disconnect between human risk alleles and those identified in murine models of autoimmune disease. Here, we synthesize the current state of the art in our understanding of human risk alleles in two prototypical autoimmune diseases - systemic lupus erythematosus (SLE) and type 1 diabetes (T1D) along with spontaneous murine disease models. We compare these risk networks to those reported in murine models of these diseases, focusing on pathways relevant to anergy and central tolerance. We highlight some differences between murine and human environmental and genetic factors that may impact autoimmune disease development and expression and may, in turn, explain some of this discrepancy. Finally, we show that there is substantial overlap between the molecular networks that define these disease states across species. Our synthesis and analysis of the current state of the field are consistent with the idea that the same molecular networks are perturbed in murine and human autoimmune disease. Based on these analyses, we anticipate that murine autoimmune disease models will continue to yield novel insights into how best to diagnose, prognose, prevent and treat human autoimmune diseases.

Role of inhibitory signaling in peripheral B cell tolerance*

At least 20% of B cells in the periphery expresses an antigen receptor with a degree of self-reactivity. If activated, these autoreactive B cells pose a risk as they can contribute to the development of autoimmune diseases. To prevent their activation, both B cell-intrinsic and extrinsic tolerance mechanisms are in place in healthy individuals. In this review article, I will focus on B cell-intrinsic mechanisms that prevent the activation of autoreactive B cells in the periphery. I will discuss how inhibitory signaling circuits are established in autoreactive B cells, focusing on the Lyn-SHIP-1-SHP-1 axis, how they contribute to peripheral immune tolerance, and how disruptions of these circuits can contribute to the development of autoimmunity.

Increased plasmablasts enhance T cell-mediated beta cell destruction and promote the development of type 1 diabetes

BACKGROUND

Although type 1 diabetes (T1D) is typically described as a T cell-mediated autoimmune disease, increasing evidence for a role of B cells has emerged. However, the pivotal disease-relevant B cell subset and its contribution to islet autoimmunity remain elusive.

METHODS

The frequencies and phenotypic characteristics of circulating B cell subsets were analyzed using flow cytometry in individuals with new-onset T1D, long-term T1D, type 2 diabetes, and nondiabetic controls, and also in a prospective cohort of patients receiving mesenchymal stromal cell (MSC) transplantation. NOD mice and adoptive transfer assay were used to dissect the role of the certain B cell subset in disease progression. An in-vitro coculture system of islets with immune cells was established to examine the response against islets and the underlying mechanisms.

RESULTS

We identified that plasmablasts, a B cell subset at the antibody-secreting stage, were significantly increased and correlated with the deterioration of beta cell function in patients with new-onset T1D. Further, a fall of plasmablast number was associated with the preservation of beta cell function in patients who received MSC transplantation after 3 months of follow-up. Meanwhile, a gradual increase of plasmablasts in pancreatic lymph nodes during the natural progression of insulitis was observed in non-obese diabetic (NOD) mice; adoptive transfer of plasmablasts together with T cells from NOD mice accelerated diabetes onset in NOD/SCID recipients.

CONCLUSIONS

Our study revealed that plasmablasts may function as antigen-presenting cells and promote the activation and proinflammatory response of CD4+ T cells, further contributing to the T cell-mediated beta cell destruction. Our results provide insights into the pathogenic role of plasmablasts in islet autoimmunity and may offer new translational strategies for inhibiting T1D development.

Enrichment and Detection of Antigen-Binding B Cells for Mass Cytometry

Over the years, various techniques have been utilized to study the function and phenotype of antigen-binding B cells in the primary repertoire following immunization, infection, and development of autoimmunity. Due to the low frequency of antigen-reactive B cells (<0.05% of lymphocytes) in the periphery, preliminary enrichment of cells is necessary to achieve sufficient numbers for statistically sound characterization, especially when downstream analytic platform use, e.g., CyTOF, is low throughput. We previously described a method to detect and enrich antigen-reactive B cells from peripheral blood and tissues using biotinylated antigens in conjunction with magnetic nanoparticles, preparative to a downstream analysis by ELISPOT and flow cytometry. While mass cytometry (CyTOF) enables high dimensional immunophenotyping of over 40 unique parameters on a single-cell level, its low throughput compared to flow cytometry and requirement for removal of metal contaminants, such as nanoparticles, made it particularly unsuitable for studies of rare cells in a mixed population. Here we describe a novel CyTOF-compatible approach for multiplexed enrichment of antigen-reactive B cells, e.g., insulin and tetanus toxoid, using cleavable magnetic nanoparticles. This method allows improved monitoring of the phenotype and function of antigen-reactive B cells during the development of disease or after immunization while minimizing the amount of sample and run times needed.

Memory B cells targeting SARS-CoV-2 spike protein and their dependence on CD4+ T cell help

Memory B cells seem to be more durable than antibodies and thus crucial for the long-term immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Here we investigate SARS-CoV-2 spike-specific memory B cells and their dependence on CD4⁺ T cell help in different settings of coronavirus disease 2019 (COVID-19). Compared with severely ill individuals, those who recovered from mild COVID-19 develop fewer but functionally superior spike-specific memory B cells. Generation and affinity maturation of these cells is best associated with IL-21⁺CD4⁺ T cells in recovered individuals and CD40L⁺CD4⁺ T cells in severely ill individuals. The increased activation and exhaustion of memory B cells observed during COVID-19 correlates with CD4⁺ T cell functions. Intriguingly, CD4⁺ T cells recognizing membrane protein show a stronger association with spike-specific memory B cells than those recognizing spike or nucleocapsid proteins. Overall, we identify CD4⁺ T cell subsets associated with the generation of B cell memory during SARS-CoV-2 infection.

B Quiet: Autoantigen-Specific Strategies to Silence Raucous B Lymphocytes and Halt Cross-Talk with T Cells in Type 1 Diabetes

Islet autoantibodies are the primary biomarkers used to predict type 1 diabetes (T1D) disease risk. They signal immune tolerance breach by islet autoantigen-specific B lymphocytes. T-B lymphocyte interactions that lead to expansion of pathogenic T cells underlie T1D development. Promising strategies to broadly prevent this T-B crosstalk include T cell elimination (anti-CD3, teplizumab), B cell elimination (anti-CD20, rituximab), and disruption of T cell costimulation/activation (CTLA-4/Fc fusion, abatacept). However, global disruption or depletion of immune cell subsets is associated with significant risk, particularly in children. Therefore, antigen-specific therapy is an area of active investigation for T1D prevention. We provide an overview of strategies to eliminate antigen-specific B lymphocytes as a means to limit pathogenic T cell expansion to prevent beta cell attack in T1D. Such approaches could be used to prevent T1D in at-risk individuals. Patients with established T1D would also benefit from such targeted therapies if endogenous beta cell function can be recovered or islet transplant becomes clinically feasible for T1D treatment.

Tetrameric Fluorescent Antigen Arrays for Single-Step Identification of Antigen-Specific B Cells

Fluorescent antigen production is a critical step in the identification of antigen-specific B cells. Here, we detailed the preparation, purification, and the use of four-arm, fluorescent PEG-antigen conjugates to selectively identify antigen-specific B cells through avid engagement with cognate B cell receptors. Using modular click chemistry and commercially available fluorophore kit chemistries, we demonstrated the versatility of preparing customized fluorescent PEG-conjugates by creating distinct arrays for proteolipid protein (PLP139-151) and insulin, which are important autoantigens in murine models of multiple sclerosis and type 1 diabetes, respectively. Assays were developed for each fluorescent conjugate in its respective disease model using flow cytometry. Antigen arrays were compared to monovalent autoantigen to quantify the benefit of multimerization onto PEG backbones. Finally, we illustrated the utility of this platform by isolating and assessing anti-insulin B cell responses after antigen stimulation ex vivo. Labeling insulin-specific B cells enabled the amplified detection of changes to co-stimulation (CD86) that were otherwise dampened in aggregate B cell analysis. Together, this report enables the production and use of fluorescent antigen arrays as a robust tool for probing B cell populations.

Endotypes in T1D: B lymphocytes and early onset

PURPOSE OF REVIEW

Although type 1 diabetes (T1D) is characterized by destruction of the pancreatic beta cells by self-reactive T cells, it has become increasingly evident that B cells also play a major role in disease development, likely functioning as antigen-presenting cells. Here we review the biology of islet antigen-reactive B cells and their participation in autoimmune diabetes.

RECENT FINDINGS

Relative to late onset, individuals who develop T1D at an early age display increased accumulation of insulin-reactive B cells in islets. This B-cell signature is also associated with rapid progression of disease and responsiveness to B-cell depletion therapy. Also suggestive of B-cell participation in disease is loss of anergy in high-affinity insulin-reactive B cells. Importantly, loss of anergy is seen in patient's healthy first-degree relatives carrying certain T1D risk alleles, suggesting a role early in disease development.

SUMMARY

Recent studies indicate that islet-reactive B cells may play a pathogenic role very early in T1D development in young patients, and suggest utility of therapies that target these cells.

Phenotypically distinct anti-insulin B cells repopulate pancreatic islets after anti-CD20 treatment in NOD mice

AIMS/HYPOTHESIS

Autoreactive B cells escape immune tolerance and contribute to the pathogenesis of type 1 diabetes. While global B cell depletion is a successful therapy for autoimmune disease, the fate of autoreactive cells during this treatment in autoimmune diabetes is unknown. We aimed to identify and track anti-insulin B cells in pancreatic islets and understand their repopulation after anti-CD20 treatment.

METHODS

We generated a double transgenic system, the VH125.hCD20/NOD mouse. The VH125 transgenic mouse, expressing an increased frequency of anti-insulin B cells, was crossed with a human CD20 (hCD20) transgenic mouse, to facilitate B cell depletion using anti-CD20. B cells were analysed using multiparameter and ImageStream flow cytometry.

RESULTS

We demonstrated that anti-insulin B cells were recruited to the pancreas during disease progression in VH125.hCD20/NOD mice. We identified two distinct populations of anti-insulin B cells in pancreatic islets, based on CD19 expression, with both populations enriched in the CD138^int fraction. Anti-insulin B cells were not identified in the plasma-cell CD138^hi fraction, which also expressed the transcription factor Blimp-1. After anti-CD20 treatment, anti-insulin B cells repopulated the pancreatic islets earlier than non-specific B cells. Importantly, we observed that a CD138^intinsulin⁺CD19^- population was particularly enriched after B cell depletion, possibly contributing to the persistence of disease still observed in some mice after anti-CD20 treatment.

CONCLUSIONS/INTERPRETATION

Our observations may indicate why the loss of C-peptide is only temporarily delayed following anti-CD20 treatment in human type 1 diabetes.

Techniques to Study Antigen-Specific B Cell Responses

Antibodies against foreign antigens are a critical component of the overall immune response and can facilitate pathogen clearance during a primary infection and also protect against subsequent infections. Dysregulation of the antibody response can lead to an autoimmune disease, malignancy, or enhanced infection. Since the experimental delineation of a distinct B cell lineage in 1965, various methods have been developed to understand antigen-specific B cell responses in the context of autoimmune diseases, primary immunodeficiencies, infection, and vaccination. In this review, we summarize the established techniques and discuss new and emerging technologies for probing the B cell response in vitro and in vivo by taking advantage of the specificity of B cell receptor (BCR)-associated and secreted antibodies. These include ELISPOT, flow cytometry, mass cytometry, and fluorescence microscopy to identify and/or isolate primary antigen-specific B cells. We also present our approach to identify rare antigen-specific B cells using magnetic enrichment followed by flow cytometry. Once these cells are isolated, in vitro proliferation assays and adoptive transfer experiments in mice can be used to further characterize antigen-specific B cell activation, function, and fate. Transgenic mouse models of B cells targeting model antigens and of B cell signaling have also significantly advanced our understanding of antigen-specific B cell responses in vivo.

A Precision B Cell-Targeted Therapeutic Approach to Autoimmunity Caused by Phosphatidylinositol 3-Kinase Pathway Dysregulation

The inositol lipid phosphatases PTEN and SHIP-1 play a crucial role in maintaining B cell anergy and are reduced in expression in B cells from systemic lupus erythematosus and type 1 diabetes patients, consequent to aberrant regulation by miRNA-7 and 155. With an eye toward eventual use in precision medicine therapeutic approaches in autoimmunity, we explored the ability of p110δ inhibition to compensate for PI3K pathway dysregulation in mouse models of autoimmunity. Low dosages of the p110δ inhibitor idelalisib, which spare the ability to mount an immune response to exogenous immunogens, are able to block the development of autoimmunity driven by compromised PI3K pathway regulation resultant from acutely induced B cell-targeted haploinsufficiency of PTEN and SHIP-1. These conditions do not block autoimmunity driven by B cell loss of the regulatory tyrosine phosphatase SHP-1. Finally, we show that B cells in NOD mice express reduced PTEN, and low-dosage p110δ inhibitor therapy blocks disease progression in this model of type 1 diabetes. These studies may aid in the development of precision treatments that act by enforcing PI3K pathway regulation in patients carrying specific risk alleles.

Non-Antibody-Secreting Functions of B Cells and Their Contribution to Autoimmune Disease

B cells play multiple important roles in the pathophysiology of autoimmune disease. Beyond producing pathogenic autoantibodies, B cells can act as antigen-presenting cells and producers of cytokines, including both proinflammatory and anti-inflammatory cytokines. Here we review our current understanding of the non-antibody-secreting roles that B cells may play during development of autoimmunity, as learned primarily from reductionist preclinical models. Attention is also given to concepts emerging from clinical studies using B cell depletion therapy, which shed light on the roles of these mechanisms in human autoimmune disease.