Autoreactive B cells in rheumatoid arthritis include mainly activated CXCR3+ memory B cells and plasmablasts

Age-Associated B Cells in Autoimmune Diseases: Pathogenesis and Clinical Implications

As a heterogeneous B cell subset, age-associated B cells (ABCs) exhibit distinct transcription profiles, extrafollicular differentiation processes, and multiple functions in autoimmunity. TLR7 and TLR9 signals, along with IFN-γ and IL-21 stimulation, are both essential for ABC differentiation, which is also regulated by chemokine receptors including CXCR3 and CCR2 and integrins including CD11b and CD11c. Given their functions in antigen uptake and presentation, autoantibody and proinflammatory cytokine secretion, and T helper cell activation, ABCs display potential in the prognosis, diagnosis, and therapy for autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome, multiple sclerosis, neuromyelitis optica spectrum disorders, and ankylosing spondylitis. Specifically targeting ABCs by inhibiting T-bet and CD11c and activating CD11b and ARA2 represents potential therapeutic strategies for SLE and RA. Although single-cell sequencing technologies have recently revealed the heterogeneous characteristics of ABCs, further investigations to explore and validate ABC-target therapies are still warranted.

B Cell Receptor Repertoire Analysis of the CD21lo B Cell Compartment in Healthy Individuals, Patients With Sjögren's Disease, and Patients With Radiographic Axial Spondyloarthritis

B cells with low or absent expression of CD21 (CD21lo B cells) gained attention due to their expansion in the peripheral blood of patients with immune-mediated, rheumatic diseases. This is not only observed in typical autoimmune diseases like systemic lupus erythematosus and Sjögren's disease (SjD) but also in radiographic axial spondyloarthritis (r-axSpA), which is considered an autoinflammatory disease. To gain more insight into the origins of the heterogeneous CD21lo B-cell population, and its relation to the plasmablast (PB) compartment, we profiled the B-cell-receptor (BCR) repertoire in CD27- and CD27+ fractions of CD21lo B cells and early PBs using next-generation sequencing. Populations were sorted from peripheral blood of healthy individuals, SjD patients, and r-axSpA patients (n = 10 for each group). In healthy individuals and both patient groups, our findings indicate that CD27-CD21lo B cells, which exhibit few mutations in their BCR, may develop into CD27+CD21lo B cells and PBs, both marked by considerably more mutations. Given the known expansion of circulating CD27-CD21lo B cells in SjD and r-axSpA patients and clonal relationships with both CD27+CD21lo B cells and early PBs, these cells might actively contribute to (pathological) immune responses in rheumatic diseases with autoimmune and/or autoinflammatory characteristics.

Regulation of reactive oxygen species and the role of mitochondrial apoptotic-related genes in rheumatoid arthritis

Previous research suggests mitochondrial apoptosis alleviates rheumatoid arthritis (RA), but the role of mitochondrial apoptosis-related genes (MARGs) is unclear. Urgent exploration of RA-related mitochondrial apoptosis biomarkers is needed. Gene Expression Ontology (GEO)-derived RA datasets were used to identify differentially expressed genes (DEGs) compared to normal controls, intersected with MARGs to obtain differentially expressed mitochondrial apoptosis-related genes (DE-MARGs). Three ML algorithms screened diagnostic biomarkers. A nomogram was built and validated by receiver operating characteristic (ROC) analysis. Gene Set Enrichment Analysis (GSEA), regulatory network, and drug prediction explored biomarker mechanisms. Finally, key cells analysis included clustering, type annotation, pseudo-temporal study, and interaction, focusing on validated biomarker expression in those cells. A total of 147 DE-MARGs linked to energy & ROS metabolism were identified. Four validated biomarkers (MRPS10, EEF2, HSPA9, TUFM) formed a new RA diagnostic model. Moreover, GSEA linked them to oxidative phosphorylation. YY1 regulates EEF2, HSPA9, MRPS10; FOXO3 regulates EEF2, TUFM. Drugs like Nonoxynol-9, Nedocromil, Gadobutrol target these biomarkers. In addition, biomarkers are expressed in plasmablasts, with CD74 as a key receptor binding multiple ligands. RA biomarkers (MRPS10, EEF2, HSPA9, TUFM) linked to energy & ROS, progression tied to AMPK/mTOR, CD74-MIF crucial. Study advances RA pathogenesis knowledge, supporting clinical diagnosis.

Increased Phosphorylation of Intracellular Signaling Molecules Indicates Continuous Activation of Human Autoreactive B-Cells

Many human autoimmune diseases (AIDs) are hallmarked by the presence and persistence of autoreactive B-cells. While autoreactive B-cells may frequently encounter antigens, the signals required to balance and maintain their activation and survival are mostly unknown. Understanding such signals may be important for strategies aimed at eliminating human B-cell autoreactivity. Here, we assessed intracellular signaling pathways in B cells targeting citrullinated protein antigens isolated from patients with rheumatoid arthritis (RA), a common and well-characterized AID. Peripheral blood mononuclear cells of 15 RA patients positive for anti-citrullinated protein antibodies (ACPA) were analyzed directly ex vivo using spectral flow cytometry and B-cell differentiation markers, citrullinated antigen-biotin-streptavidin tetramers, and intracellular (phosphoflow) markers. Tetanus toxoid (TT)-specific B cells served as antigen-specific comparators. In absence of any in vitro BCR stimulation, ACPA-expressing memory B cells (MBCs) displayed enhanced expression of Ki-67 and increased SYK-, BTK-, AKT-, and S6-phosphorylation compared with TT-specific MBCs. We demonstrate the simultaneous detection of B cell antigen-specificity and intracellular protein phosphorylation on the single-cell level. The data reveal that autoreactive B-cells in RA, in contrast to B cells against recall antigens, display enhanced phosphorylation of signaling molecules that point toward continuous, presumably antigen-mediated activation of the autoreactive B-cell compartment.

Circulating Baseline CXCR3+Th2 and Th17 Cell Proportions Correlate With Trabecular Bone Loss After 48 Weeks of Biological Treatment in Early Rheumatoid Arthritis

OBJECTIVE

The high prevalence of osteoporosis in rheumatoid arthritis (RA) is due to inflammation that stimulates differentiation of osteoclasts, a process involving circulating monocytes and T cell-derived factors. The aim of this study was to evaluate relations between circulating monocytes, T cell subsets, and changes in bone characteristics before and after treatment with biological disease-modifying antirheumatic drugs (bDMARDs) in RA.

METHODS

Thirty patients with untreated early RA who met the American College of Rheumatology/EULAR 2010 criteria were included. Data were collected before and 48 weeks after treatment with methotrexate (MTX) together with one of three bDMARDs (abatacept, tocilizumab, or certolizumab pegol). Disease activity was measured using the Clinical Disease Activity Index, swollen or tender joint counts, C-reactive protein levels, and erythrocyte sedimentation rates. Proportions of monocyte and CD4+ T cell subsets in blood samples were analyzed by flow cytometry. Bone densitometry was performed using high-resolution peripheral quantitative computed tomography (HR-pQCT).

RESULTS

HR-pQCT revealed an overall decrease in cortical (P = 0.009) and trabecular (P = 0.034) bone mineral density, although a subset of patients showed no bone loss after 48 weeks of treatment. The overall bone loss was not associated with age, body mass index, sex, intraarticular glucocorticoid injections, or baseline disease activity. Loss of trabecular bone volume fraction correlated with high proportions of circulating CXCR3+Th2 cells (r = -0.38, P = 0.04) and CXCR3+Th17 cells (r = -0.36, P = 0.05) at baseline. Similarly, no loss of trabecular bone volume fraction correlated with high proportions of regulatory T cells (r = 0.4, P = 0.03) at baseline. However, the associations were not significant when corrected for confounders and multiple testing.

CONCLUSION

MTX together with bDMARDs efficiently reduce disease activity but only prevent bone loss in a subset of patients with RA after 48 weeks of treatment. The correlations of circulating baseline T helper cell and regulatory T cell populations with trabecular bone changes suggest a potential novel role for these cells in systemic bone homeostasis during early RA.

Citrullinated Autoantigen-Specific T and B Lymphocytes in Rheumatoid Arthritis: Focus on Follicular T Helper Cells and Expansion by Coculture

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by circulating anti-cyclic citrullinated peptide (CCP) autoantibodies (ACPAs), resulting in inflammation of the joints and other organs. We have established novel assays to assess immune cell subpopulations, including citrullinated antigen-specific (CAS) autoreactive B and T lymphocytes, in patients with RA.

METHODS AND RESULTS

We found that activated CD25+ T cells were markedly increased in patients with RA compared to healthy controls. Novel combinations of major histocompatibility complex class II citrulline epitope tetramers were developed, which enabled robust detection of CAS T cells and showed increases of CAS-naive T helper cells, Th1.17 cells, CAS total circulating T follicular helper (cTfh) cells, and cTfh1 cells in ACPA+ patients with RA. In addition, an innovative assay using dual labeling with CCP-biotin probes allowed for reproducible identification of primary CAS B cells after enrichment with advantages over existing detection methods. Furthermore, patient-derived immune cells were successfully expanded. Primary RA B cells were successfully cultured on novel feeder cell lines, whereas T cells were expanded ex vivo in the presence of interleukin-2 and citrullinated peptides, and subsequent alterations in cell frequencies were assessed.

CONCLUSION

Novel assays were established to reliably detect CAS T and B cells in patients with RA, and specific CAS-naive T helper cells, Th1.17 cells, cTfh cells, and cTfh1 cells were observed more frequently in RA. Based on these results, new coculture systems of disease-relevant cells are developed to simulate human secondary lymphoid tissues ex vivo. This technology will serve as a platform to identify therapies that modulate disease-specific immune cells.

CD19: a promising target for systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune disease characterized by immune dysregulation, vascular damage, and fibrosis. B cells play a significant role in SSc through autoantibody production, cytokine secretion, and T cell regulation. Autoantibodies like anti-topoisomerase I and anti-RNA polymerase III are specific to SSc and linked to clinical features such as skin and lung involvement. B cell depletion therapies, particularly anti-CD20 antibodies like rituximab, have shown benefits in treating SSc, improving skin and lung disease symptoms. However, CD19, another B cell marker, is more widely expressed and has emerged as a promising target in autoimmune diseases. CD19-targeted therapies, such as CAR T cells and Uplizna® (inebilizumab), have demonstrated potential in treating refractory autoimmune diseases, including SSc. Uplizna® offers advantages over rituximab by targeting a broader range of B cells and showing higher efficacy in specific patient subsets. Clinical trials currently investigate Uplizna®'s effectiveness in SSc, particularly in severe cases. While these therapies offer hope, long-term safety and efficacy remain unknown. SSc is still a complex disease, but advancing B cell-targeted treatments could significantly improve patient outcomes and knowledge about the pathogenesis.

Antigen-specific T cells and autoimmunity

Autoimmune diseases (ADs) showcase the intricate balance between the immune system's protective functions and its potential for self-inflicted damage. These disorders arise from the immune system's erroneous targeting of the body's tissues, resulting in damage and disease. The ability of T cells to distinguish between self and non-self-antigens is pivotal to averting autoimmune reactions. Perturbations in this process contribute to AD development. Autoreactive T cells that elude thymic elimination are activated by mimics of self-antigens or are erroneously activated by self-antigens can trigger autoimmune responses. Various mechanisms, including molecular mimicry and bystander activation, contribute to AD initiation, with specific triggers and processes varying across the different ADs. In addition, the formation of neo-epitopes could also be implicated in the emergence of autoreactivity. The specificity of T cell responses centers on the antigen recognition sequences expressed by T cell receptors (TCRs), which recognize peptide fragments displayed by major histocompatibility complex (MHC) molecules. The assortment of TCR gene combinations yields a diverse array of T cell populations, each with distinct affinities for self and non-self antigens. However, new evidence challenges the traditional notion that clonal expansion solely steers the selection of higher-affinity T cells. Lower-affinity T cells also play a substantial role, prompting the "two-hit" hypothesis. High-affinity T cells incite initial responses, while their lower-affinity counterparts perpetuate autoimmunity. Precision treatments that target antigen-specific T cells hold promise for avoiding widespread immunosuppression. Nevertheless, detection of such antigen-specific T cells remains a challenge, and multiple technologies have been developed with different sensitivities while still harboring several drawbacks. In addition, elements such as human leukocyte antigen (HLA) haplotypes and validation through animal models are pivotal for advancing these strategies. In brief, this review delves into the intricate mechanisms contributing to ADs, accentuating the pivotal role(s) of antigen-specific T cells in steering immune responses and disease progression, as well as the novel strategies for the identification of antigen-specific cells and their possible future use in humans. Grasping the mechanisms behind ADs paves the way for targeted therapeutic interventions, potentially enhancing treatment choices while minimizing the risk of systemic immunosuppression.

The peculiar features, diversity and impact of citrulline-reactive autoantibodies

Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations.

Immune response to post-translationally modified proteins in rheumatoid arthritis: what makes it special?

Rheumatoid arthritis (RA) exhibits common characteristics with numerous other autoimmune diseases, including the presence of susceptibility genes and the presence of disease-specific autoantibodies. Anti-citrullinated protein antibodies (ACPA) are the hallmarking autoantibodies in RA and the anti-citrullinated protein immune response has been implicated in disease pathogenesis. Insight into the immunological pathways leading to anti-citrullinated protein immunity will not only aid understanding of RA pathogenesis, but may also contribute to elucidation of similar mechanisms in other autoantibody-positive autoimmune diseases. Similarly, lessons learnt in other human autoimmune diseases might be relevant to understand potential drivers of RA. In this review, we will summarise several novel insights into the biology of the anti-citrullinated protein response and their clinical associations that have been obtained in recent years. These insights include the identification of glycans in the variable domain of ACPA, the realisation that ACPA are polyreactive towards other post-translational modifications on proteins, as well as new awareness of the contributing role of mucosal sites to the development of the ACPA response. These findings will be mirrored to emerging concepts obtained in other human (autoimmune) disease characterised by disease-specific autoantibodies. Together with an updated understanding of genetic and environmental risk factors and fresh perspectives on how the microbiome could contribute to antibody formation, these advancements coalesce to a progressively clearer picture of the B cell reaction to modified antigens in the progression of RA.

Autoantibodies in rheumatoid arthritis - rheumatoid factor, anticitrullinated protein antibodies and beyond

PURPOSE OF REVIEW

RA is characterized by the presence of autoantibodies among which rheumatoid factors (RFs) and antimodified protein antibodies (AMPA) are serological hallmarks of the disease. In recent years, several novel insights into the biology, immunogenetics and clinical relevance of these autoantibodies have been obtained, which deserve to be discussed in more detail.

RECENT FINDINGS

RFs from RA patients seem to target distinct epitopes which appear to be quite specific for RA. Determination of immunoglobulin A (IgA) isotypes of RF and anticitrullinated protein antibodies (ACPA) may provide prognostic information because their presence is associated with reduced therapeutic responses to TNF inhibitors. Furthermore, IgA levels are increased in RA patients and IgA immune complexes are more potent than immunoglobulin G (IgG) complexes in inducing NET formation. Concerning AMPAs, investigations on variable domain glycosylation (VDG) revealed effects on antigen binding and activation of autoreactive B cells. Studies on pathogenetic involvement of ACPA suggest Janus-faced roles: on the one hand, ACPA may be involved in joint destruction and pain perception while on the other hand protective anti-inflammatory effects may be attributed to a subset of ACPAs.

SUMMARY

The autoimmune response in RA is extremely complex and still far from being fully understood. Antibodies are not only valuable diagnostic biomarkers but also seem to play pivotal roles in the pathophysiology of RA.

An anti-CD19/CTLA-4 switch improves efficacy and selectivity of CAR T cells targeting CD80/86-upregulated DLBCL

Chimeric antigen receptor T cell (CAR T) therapy is a potent treatment for relapsed/refractory (r/r) B cell lymphomas but provides lasting remissions in only ∼40% of patients and is associated with serious adverse events. We identify an upregulation of CD80 and/or CD86 in tumor tissue of (r/r) diffuse large B cell lymphoma (DLBCL) patients treated with tisagenlecleucel. This finding leads to the development of the CAR/CCR (chimeric checkpoint receptor) design, which consists of a CD19-specific first-generation CAR co-expressed with a recombinant CTLA-4-linked receptor with a 4-1BB co-stimulatory domain. CAR/CCR T cells demonstrate superior efficacy in xenograft mouse models compared with CAR T cells, superior long-term activity, and superior selectivity in in vitro assays with non-malignant CD19+ cells. In addition, immunocompetent mice show an intact CD80-CD19+ B cell population after CAR/CCR T cell treatment. The results reveal the CAR/CCR design as a promising strategy for further translational study.

Single-cell insights into immune dysregulation in rheumatoid arthritis flare versus drug-free remission

Immune-mediated inflammatory diseases (IMIDs) are typically characterised by relapsing and remitting flares of inflammation. However, the unpredictability of disease flares impedes their study. Addressing this critical knowledge gap, we use the experimental medicine approach of immunomodulatory drug withdrawal in rheumatoid arthritis (RA) remission to synchronise flare processes allowing detailed characterisation. Exploratory mass cytometry analyses reveal three circulating cellular subsets heralding the onset of arthritis flare - CD45RO+PD1hi CD4+ and CD8+ T cells, and CD27+CD86+CD21- B cells - further characterised by single-cell sequencing. Distinct lymphocyte subsets including cytotoxic and exhausted CD4+ memory T cells, memory CD8+CXCR5+ T cells, and IGHA1+ plasma cells are primed for activation in flare patients. Regulatory memory CD4+ T cells (Treg cells) increase at flare onset, but with dysfunctional regulatory marker expression compared to drug-free remission. Significant clonal expansion is observed in T cells, but not B cells, after drug cessation; this is widespread throughout memory CD8+ T cell subsets but limited to the granzyme-expressing cytotoxic subset within CD4+ memory T cells. Based on our observations, we suggest a model of immune dysregulation for understanding RA flare, with potential for further translational research towards novel avenues for its treatment and prevention.