Distinct Effector B Cells Induced by Unregulated Toll-like Receptor 7 Contribute to Pathogenic Responses in Systemic Lupus Erythematosus

Aberrant B cell receptor signaling responses in circulating double-negative 2 B cells from radiographic axial spondyloarthritis patients

Objective

Radiographic axial spondyloarthritis (r-axSpA) is a chronic rheumatic disease in which innate immune cells and T cells are thought to play a major role. However, recent studies also hint at B cell involvement. Here, we performed an in-depth analysis on alterations within the B-cell compartment from r-axSpA patients.

Methods

We performed immune gene expression profiling on total peripheral blood B cells from 8 r-axSpA patients and 8 healthy controls (HCs). Next, we explored B cell subset distribution and B-cell receptor (BCR) signaling responses in circulating B cells from 28 r-axSpA patients and 15 HCs, by measuring spleen tyrosine kinase, phosphoinositide 3-kinase and extracellular signal regulated kinase 1/2 phosphorylation upon α-Ig stimulation using phosphoflow cytometry.

Results

Immune gene expression profiling indicated an elevated pathway score for BCR signaling in total B cells from r-axSpA patients compared with HCs. Flow cytometric analysis revealed an increase in frequency of both total and double-negative 2 (DN2) B cells in r-axSpA patients compared with HCs. In r-axSpA patients, DN2 B cells displayed an isotype shift towards IgA. Remarkably, where DN2 B cells from HCs were hyporesponsive, these cells displayed significant proximal BCR signaling responses in r-axSpA patients. Enhanced BCR signaling responses were also observed in the transitional and naïve B cell population from r-axSpA patients compared with HCs. The enhanced BCR signaling responses in DN2 B cells correlated with clinical disease parameters.

Conclusion

In r-axSpA patients, circulating DN2 B cells are expanded and, together with transitional and naïve B cells, display significantly enhanced BCR signaling responses upon stimulation. Together, our data suggest B cell involvement in the pathogenesis of r-axSpA.

Long-lasting B cell convergence to distinct broadly reactive epitopes following vaccination with chimeric influenza virus hemagglutinins

In a phase 1 clinical trial, a chimeric hemagglutinin (cHA) immunogen induced antibody responses against the conserved hemagglutinin (HA) stalk domain as designed. Here, we determined the specificity, function, and subsets of B cells induced by cHA vaccination by pairing single-cell RNA sequencing and B cell receptor repertoire sequencing. We have shown that the cHA-inactivated vaccine with a squalene-based adjuvant induced a robust activated B cell and memory B cell (MBC) phenotype against two broadly neutralizing epitopes in the stalk domain. The overall specificities of the acute plasmablast (PB) and MBC responses clonally overlapped, suggesting B cell convergence to these broadly protective epitopes. At 1 year post immunization, we identified that cHA vaccination reshaped the HA-specific MBC pool to enrich for stalk-binding B cells. Altogether, these data indicate the cHA vaccine induced robust and durable B cell responses against broadly protective epitopes of the HA stalk domain, in line with serological data.

Efficacy, safety and optimal intervention of belimumab for proliferative lupus nephritis patients in real-world settings: LOOPS registry

OBJECTIVES

This study investigated the efficacy, safety and predictive factors of belimumab (BEL) in induction therapy for patients with proliferative lupus nephritis (LN) in real-world settings.

METHODS

Patients with biopsy-proven ISN/RPS class III or IV LN, with or without coexisting class V LN, who underwent standard of care (SoC), glucocorticoid (GC) and either mycophenolate mofetil or cyclophosphamide treatments were included. Participants were treated with SoC (SoC group, n = 32) or BEL and SoC (BEL+SoC group, n = 30). The primary end point was complete renal response (CRR) at 52 weeks.

RESULTS

Baseline patient characteristics were not significantly different between the two groups. The 52-week retention rate of BEL was 90.0%. The BEL+SoC group showed significantly higher CRR and primary efficacy renal response achievement at 52 weeks and significantly lower GC dosage, adverse events and Systemic Lupus International Collaborating Clinics damage index scores. Multivariate analysis of CRR achievement at 52 weeks revealed that the lack of estimated glomerular filtration rate (eGFR) improvement at 4 weeks was associated with CRR failure in the SoC group. A shorter duration (cut-off of 42 days) between the start of induction therapy and addition of BEL was also related to the CRR in the BEL+SoC group.

CONCLUSION

BEL, in addition to SoC, controls disease activity, reduces GC use and suppresses organ damage in case of proliferative LN. Earlier BEL induction within 6 weeks may help achieve CRR in treatment-resistant cases without eGFR improvement at 4 weeks after induction therapy.

Early decrease of T-bet+ B cells during subcutaneous belimumab predicts response to therapy in systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is characterized by B cell dysregulation and expansion of atypical B cells that may correlate with disease manifestations and activity. This study investigated the impact of subcutaneous (sc) Belimumab (BLM) on the peripheral B cell compartment and on the functional properties of CD21low, T-bet+ and CD11c+ atypical B cells, in 21 active SLE patients over a 12-month period. At baseline, active SLE patients displayed reduced unswitched IgM memory B cells and expansion of atypical B cells, compared to healthy donors and to SLE patients in remission. sc BLM therapy promptly restored B cell homeostasis with a reduction of T-bet+ B cells, observed early in patients responsive to therapy. These findings highlight the pathogenic role of T-bet+ B cells in SLE disease and suggest their potential utility as biomarker of clinical response.

Allogeneic umbilical cord-derived mesenchymal stromal cells as treatment for systemic lupus erythematosus: a single-centre, open-label, dose-escalation, phase 1 study

BACKGROUND

Patients with systemic lupus erythematosus (SLE) with inadequate responses to standard therapies have unmet therapeutic needs. The immunomodulatory, proangiogenic, and antifibrotic properties of mesenchymal stromal cells support their use in treating patients with SLE. We aimed to assess the safety of a single intravenous infusion of allogeneic umbilical cord-derived mesenchymal stromal cells in patients with severe SLE.

METHODS

This prospective, single-centre, open-label, dose-escalation, Bayesian phase 1 study was done at the Saint-Louis University Hospital (Paris, France). Eligible patients were aged 18-70 years, were diagnosed with SLE according to American College of Rheumatology criteria with positive antinuclear antibodies, had a baseline Safety of Estrogens in Lupus Erythematosus National Assessment-SLE Disease Activity Index (SELENA-SLEDAI) score of 6 or more, and had disease that was refractory to first and second line SLE therapies. Patients were to receive a single intravenous infusion of 1 × 106, 2 × 106, or 4 × 106 umbilical cord-derived mesenchymal stromal cells per kg (manufactured from a single umbilical cord) in cohorts of five patients per dose, starting at 2 × 106 cells per kg. The primary endpoint was the rate of treatment-related severe adverse events (grade ≥3) in the first 10 days after infusion of umbilical cord-derived mesenchymal stromal cells. People with lived experience were involved in study design, patient enrolment, and dissemination of the study findings. This study is registered with ClinicalTrials.gov, NCT03562065, and the EU Clinical Trials Register, EudraCT2017-001400-29.

FINDINGS

From May 14, 2019, to March 6, 2023, 29 patients were screened for eligibility, eight of whom were enrolled in the study. Enrolment was terminated early after inclusion of eight patients and no patients received the 1 × 106 dose of umbilical cord-derived mesenchymal stromal cells. Seven (88%) of eight participants were cisgender women and one (13%) was a cisgender man. The median age was 35 years (range 26-57) and the median SLE disease duration was 12 years (5-19). All patients received at least 2 × 106 cells per kg (range 2 × 106 to 4 × 106). No severe adverse events and three infusion-related adverse events (two grade 1 and one grade 2) occurred in two patients in the first 10 days after infusion. After 12·4 months (range 12-13) of follow-up, no treatment-related severe adverse events and three non-treatment-related severe adverse events occurred in one patient after relapse.

INTERPRETATION

Our results suggest that a single infusion of 2 × 106 cells per kg or 4 × 106 cells per kg of allogeneic umbilical cord-derived mesenchymal stromal cells was safe in patients with severe SLE. Placebo-controlled trials are needed to confirm clinical efficacy and the role of B-cell modifications in clinical benefit.

FUNDING

Fondation du Rein, Alliance Maladies Rares AFM-Téléthon, Direction de la Recherche Clinique et de l'Innovation AP-HP, and ANR eCellFrance.

Long-lasting antibody B-cell responses to SARS-CoV-2 three years after the onset of the pandemic

Immune memory is essential for the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. In the current context of the pandemic, with a diminished vaccine efficacy against emerging variants, it remains crucial to perform long-term studies to evaluate the durability and quality of immune responses. Here, we examined the antibody and memory B-cell responses in a cohort of 113 healthcare workers with distinct exposure histories over a 3-year period. Previously infected and naive participants developed comparable humoral responses by 17 months after receiving a full three-dose mRNA vaccination. In addition, both maintained a substantial SARS-CoV-2-reactive memory B-cell pool, associated with a lower incidence of breakthrough infections in naive participants. Of note, previously infected participants developed an expanded SARS-CoV-2-reactive CD27-CD21- atypical B-cell population that remained stable throughout the follow-up period. Thus, previous SARS-CoV-2 infection differentially imprints the memory B-cell compartment without compromising the development of long-lasting humoral responses.

Nucleic acid triggers of autoimmunity and autoinflammation

The key role of nucleic acid sensing receptors in the development of autoimmune and autoinflammatory diseases is becoming increasingly apparent. Activation of these sensors has been attributed to the failure of professional scavenger cells to adequately clear cell debris, in many cases due to defective scavenger receptors. However, as now summarized in this review, numerous gain-of-function mutations in the nucleic acid sensing receptors, or in molecules that regulate sensor activity, have now been evaluated in gene-targeted murine strains, and critical components of their downstream pathways have been identified as therapeutic targets. In addition, we are beginning to understand how DNases and RNases play crucial roles in both generating and eliminating the distinct ligands that engage the various nucleic acid sensors. Murine models of disease have further provided important insights regarding the function of and synergy between individual endosomal and cytosolic receptors, as well as cell type restricted functions.

T-bet+CD11c+ age-associated B cells resist BLyS- and CD20-targeted ablation in murine lupus models

OBJECTIVE

B cell ablation strategies show promise for treating humoral autoimmune diseases, but their impact on pathogenic tissue-localized T-bet+CD11c+ age-associated B cells (ABCs) is poorly defined. We assessed whether mAb-mediated B cell depletion impacts ABCs and other splenic B cell subsets in two mouse models of lupus.

METHODS

Following disease onset, we injected NZBxNZWF1 mice (NZBWF1; n = 72) or bm12 chronic graft versus host disease mice (cGVHD; n = 59) with 0.2 mg or 1 mg of anti-BLyS (10F4), anti-CD20 (18B12), combined treatment, or saline. Spleens were harvested after two weeks and B cell subset representation was analyzed via flow cytometry.

RESULTS

In the NZBWF1 model, lymphopenia and resistance to 10F4 and 18B12 that arose concomitant with disease onset complicated interpretation, as ablative activity was partial and variable in the follicular (FO) and marginal zone (MZ) pools. Conversely, the T-bet+CD11c+ ABC pool was unchanged or enlarged versus controls and was entirely refractory to antibody treatments. In the cGVHD model, both 10F4 and 18B12 treatments ablated nearly all FO B cells. MZ B cells were profoundly ablated by 10F4 but spared by 18B12 treatment, whereas 10F4 treatment spared a small, undefined subset of splenic B cells that was ablated by 18B12. In contrast, T-bet+CD11c+ ABCs were minimally impacted by either reagent alone or combined, regardless of dose.

CONCLUSION

The spleen-resident T-bet+CD11c+ ABC pool resists anti-BLyS and anti-CD20 ablative treatment. These findings have implications for antibody-mediated ablative strategies in patients with autoimmune diseases.

Multiple sclerosis and infection: history, EBV, and the search for mechanism

SUMMARYInfection has long been hypothesized as the cause of multiple sclerosis (MS), and recent evidence for Epstein-Barr virus (EBV) as the trigger of MS is clear and compelling. This clarity contrasts with yet uncertain viral mechanisms and their relation to MS neuroinflammation and demyelination. As long as this disparity persists, it will invigorate virologists, molecular biologists, immunologists, and clinicians to ascertain how EBV potentiates MS onset, and possibly the disease's chronic activity and progression. Such efforts should take advantage of the diverse body of basic and clinical research conducted over nearly two centuries since the first clinical descriptions of MS plaques. Defining the contribution of EBV to the complex and multifactorial pathology of MS will also require suitable experimental models and techniques. Such efforts will broaden our understanding of virus-driven neuroinflammation and specifically inform the development of EBV-targeted therapies for MS management and, ultimately, prevention.

The immunological processes behind aquaporin 4-antibody seropositive neuromyelitis optica spectrum disorders

Ever since the discovery of pathogenic aquaporin 4-specific antibodies in the serum of patients with neuromyelitis optica spectrum disorders current knowledge about clinical observations and diagnosis, and about the underlying pathology and resulting therapies have been put forward in excellent reviews and primary publications. However, in order to further develop novel strategies for the treatment of this disease, there is an urgent need to understand the immunological processes associated with the formation of the pathogenic antibodies, and with aberrant immune responses observed in affected patients. In this review, we will highlight and evaluate important studies on these processes.

Cochlin-Expressing Memory B (COMB) Cells Are Enriched in Autoimmune Diseases and Display a Distinct Activation Profile

Rheumatoid arthritis (RA) is the most common chronic autoimmune arthritis, causing joint damage and affecting multiple organs over time. B cells play a key role in driving the disease by producing autoantibodies, releasing cytokines, and presenting antigens to T cells. While B cell depletion therapies can help reduce inflammation, they remove all CD20+B cells indiscriminately, which can increase infection risk and interfere with important regulatory immune functions. To better define pathogenic B cell subsets, we performed single-cell RNA and ATAC sequencing on circulating and synovial B cells from patients with early, untreated RA. We identified a novel population of memory B cells expressing cochlin (COCH), termed cochlin - expressing memory B (COMB) cells. While detectable at low levels in healthy controls, COMB cells are significantly expanded in RA and exhibit a distinct transcriptional profile indicative of immune activation. Epigenetic analysis showed that COMB cells have more open chromatin at key immune regulatory regions, including sites bound by NF-κB family transcription factors like RELA and REL. This suggests that these cells are primed to respond to inflammatory signals. We also looked at publicly available datasets and found COMB-like cells in the blood of people with systemic lupus erythematosus (SLE) and Sjögren's syndrome (SjS), as well as in inflamed kidney tissue from patients with SLE. COMB cells across these diseases share a conserved gene expression signature, pointing to a common memory B cell programme associated with autoimmunity. These findings define COMB cells as a previously unrecognised, transcriptionally and epigenetically distinct memory B cell subset enriched across autoimmune diseases, offering new insights into B cell-mediated pathology and potential therapeutic targets.

Distinct features of a peripheral T helper subset that drives the B cell response in dengue virus infection

Dengue-virus-induced humoral immunity can increase the risk of severe disease, but the factors influencing this response are poorly understood. Here, we investigate the contribution of CD4+ T cells to B cell responses in human dengue infection. We identify a dominant peripheral PD-1+ T cell subset that accumulates in severe patients and could induce B cell differentiation via interleukin-21 (IL-21)-related pathway. Single-cell analyses reveal heterogeneity within PD-1+ cells, demonstrating the coexistence of subsets with "helper" (IL-21+) or "cytotoxic" characteristics. The IL-21+ subset displays a distinct clonotypic and transcriptomic signature compared to follicular helper T cells and persists as a memory in lymph nodes. Notably, we show that the IL-21+ subset seems to majorly drive the extrafollicular B cell responses in dengue. Our study establishes the peripheral IL-21+ subset as a potential determinant of the humoral response to dengue virus infection. These findings provide important insights into the T-cell-dependent regulation of humoral responses and can inform the design of effective dengue vaccines.

Immunosenescence in autoimmune diseases

Autoimmune diseases (AIDs) are a group of disorders in which the immune system mistakenly attacks the body's own tissues, characterized by the loss of tolerance to self-antigens and destruction of tissues. Aging is a natural process of physiological decline that also alters the immune system, a condition known as immunosenescence. During immunosenescence, the immune system undergoes various changes, including modifications and antigenicity of self-antigens, abnormalities in the quantity, phenotype, and function of lymphocytes and antibodies, as well as a narrowing of the B and T cell receptor repertoire, changes that may increase susceptibility to AIDs. Additionally, senescent immune cells and the senescence-associated secretory phenotype (SASP) contribute to target organ involvement in AIDs, exacerbating chronic inflammation and tissue damage. Mitochondrial dysfunction and metabolic imbalances in AIDs lead to the accumulation of senescent cells, which act as upstream drivers of immunosenescence. In this review, we summarize the bidirectional relationship between AIDs and immunosenescence, as well as its potential mechanisms. Therapeutic approaches targeting immunosenescence in AIDs remain at an early stage. Strategies aimed at resetting or reversing the aging immune system are expected to become a novel direction in the future.

Unraveling Novel Subsets of Lymphocytes Involved in Sac Expansion in the Tertiary Lymphoid Structure Within an Abdominal Aortic Aneurysm

BACKGROUND

Chronic inflammation is involved in the development of abdominal aortic aneurysm (AAA). A tertiary lymphoid structure (TLS) within vascular lesions has recently been focused on for its role in modulation of inflammation in local tissues. We aimed to elucidate the relationships between TLS and pathophysiology of AAA.

METHODS

Abdominal aortic samples obtained from 37 patients with AAA (men/women: 34/3, age: 72.8±9.9 years) and 15 autopsied patients who died from non-aortic events (men/women: 11/4, age: 65.5±9.8 years) were investigated.

RESULTS

TLSs in AAA lesions were confirmed by focal infiltration of CD3-positive cells surrounding germinal center-like structures containing CD20-positive cells between the tunica adventitia and tunica media layers. The formation of a TLS was significantly more prevalent in AAA patients than in autopsied patients. The number of TLSs in AAA lesions was positively correlated with sac diameter (r=0.357, P=0.035) and the amount of intraluminal thrombosis (r=0.466, P=0.005). T cells and B cells were predominant cellular populations among CD45+ cells in AAA lesions. There was a significantly positive correlation between the proportions of interfollicular T follicular helper (CD3+CD4+CD45RA-CXCR5+PD-1+) cells and double negative B (CD3-CD19+IgD-CD27-) cells, and they were positively correlated with sac diameter, intraluminal thrombosis, and serum lipids. Deposited single-cell RNA-sequencing data for AAA showed that T follicular helper cells and double negative B cells were associated with lipid metabolism, T cell activation/proliferation and inflammation.

CONCLUSIONS

The formation of a TLS in AAA lesions is associated with sac diameter and intraluminal thrombosis in connection with interfollicular T follicular helper cells and double negative B cells, which may contribute to the pathophysiology of AAA and might be novel therapeutic targets for the development of AAA.

Polarization of the memory B-cell response

Memory B cells are long-lived cells that are induced following infection or vaccination. Upon antigen re-encounter, memory B cells rapidly differentiate into antibody-secreting or germinal center B cells. While memory B cells are an important component of long-term protective immunity following vaccination, they also contribute to the progression of diseases such as autoimmunity and allergy. Numerous subsets of memory B cells have been identified in mice and humans that possess important phenotypic and functional differences. Here, we review the transcriptional circuitry governing memory B-cell differentiation and function. We then summarize emerging evidence that the inflammatory environment in which memory B cells develop has an important role in shaping their phenotype and examine the pathways regulating the development of memory B cells during a type 1-skewed and type 2-skewed immune response.

IL-4 alters TLR7-induced B cell developmental program in lupus

TLR7 stimulation of T-bet+CD11c+IgD-CD27- double-negative 2 (DN2) B cells is crucial for autoantibody formation in systemic lupus erythematosus (SLE). Here, we show that administration of IL-4 for five weeks significantly reduced autoantibodies and T-bet+CD11c+ IgD- B cells in autoimmune BXD2 mice treated with R848, a TLR7 agonist. Single-cell transcriptomics analysis indicates that following two doses of in vivo administration, IL-4 redirected development toward follicular, CD23+ germinal center (GC), and DN4-like memory B cells compared to treatment with R848 alone. While IL-4 enhanced genes related to antigen processing and presentation, it also suppressed R848-induced Ki67+ GC B cells in vivo. In vitro stimulation of SLE patient B cells with a DN2 polarizing cocktail revealed that IL-4 reduced the expression of interferon response and DN2 signature genes, promoting a population of CD23+T-bet- DN4 B population. These findings suggest that developmental reprogramming by IL-4 counteracts TLR7-promoted DN2 and GC B cells in SLE.

Know Your ABCs: Discovery, Differentiation, and Targeting of T-Bet+ B Cells

Since their first description in 2008, T-bet+ B cells have emerged as a clinically important B cell subset. Now commonly known as ABCs (Age-associated B Cells), they are uniquely characterized by their expression of the transcription factor T-bet. Indeed, this singular factor defines this B cell subset. This review will describe the discovery of T-bet+ B cells, their role in bacterial infection as T cell-independent (TI) plasmablasts, as well as long-term follicular helper T cell-dependent (TD) IgM+ and switched memory cells (i.e., T-bet+ ABCs), and later discoveries of their role(s) in diverse immunological responses. These studies highlight a critical, although limited, role of T-bet in IgG2a class switching, a function central to the cells' role in immunity and autoimmunity. Given their association with autoimmunity, pharmacological targeting is an attractive strategy for reducing or eliminating the B cells. T-bet+ ABCs express a number of characteristic cell surface markers, including CD11c, CD11b, CD73, and the adenosine 2a receptor (A2aR). Accordingly, A2aR agonist administration effectively targeted T-bet+ ABCs in vivo. Moreover, agonist treatment of lupus-prone mice reduced autoantibodies and disease symptoms. This latter work highlights the potential therapeutic use of adenosine agonists for treating autoimmune diseases involving T-bet+ ABCs.

Signaling Activation and Modulation in Extrafollicular B Cell Responses

The differentiation of naive follicular B cells into either the germinal center (GC) or extrafollicular (EF) pathway plays a critical role in shaping the type, affinity, and longevity of effector B cells. This choice also governs the selection and survival of autoreactive B cells, influencing their potential to enter the memory compartment. During the first 2-3 days following antigen encounter, initially activated B cells integrate activating signals from T cells, Toll-like receptors (TLRs), and cytokines, alongside inhibitory signals mediated by inhibitory receptors. This integration modulates the intensity of signaling, particularly of the PI3K/AKT/mTOR pathway, which plays a central role in guiding developmental decisions. These early signaling events determine whether B cells undergo GC maturation or differentiate rapidly into antibody-secreting cells (ASCs) via the EF pathway. Dysregulation of these signaling pathways-whether through excessive activation or defective regulatory mechanisms-can disrupt the balance between GC and EF fates, predisposing individuals to autoimmunity. Accordingly, aberrant PI3K/AKT/mTOR signaling has been implicated in the defective selection of autoreactive B cells, increasing the risk of autoimmune disease. This review focuses on the signaling events in newly activated B cells, with an emphasis on the induction and regulation of the PI3K/AKT/mTOR pathway. It also highlights gaps in our understanding of how alternative B cell fates are regulated. Both the physiological context and the implications of inborn errors of immunity (IEIs) and complex autoimmune conditions will be discussed in this regard.

IgA class-switched CD27-CD21+ B cells in IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is characterized by the production of galactose-deficient IgA1 (GdIgA1) antibodies. As the source of pathogenic antibodies, B cells are central to IgAN pathogenesis, but the B cell activation pathways as well as the potential B cell source of dysregulated IgA secretion remain unknown.

METHODS

We carried out flow cytometry analysis of peripheral blood B cells in patients with IgAN and control subjects with a focus on IgA-expressing B cells to uncover the pathways of B cell activation in IgAN and how these could give rise to pathogenic GdIgA1 antibodies.

RESULTS

In addition to global changes in the B cell landscape-expansion of naïve and reduction in memory B cells-IgAN patients present with an increased frequency of IgA-expressing B cells that lack the classical memory marker CD27, but are CD21+. IgAN patients furthermore have an expanded population of IgA+ antibody-secreting cells, which correlate with serum IgA levels. Both IgA+ plasmabalsts and CD27- B cells co-express GdIgA1. Implicating dysregulation at mucosal surfaces as the driver of such B cell differentiation, we found a correlation between lipopolysaccharide in the serum and IgA+CD27- B cell frequency.

CONCLUSION

We propose that dysregulated immunity in the mucosa may drive de novo B cell activation within germinal centres, giving rise to IgA+CD27- B cells and subsequently IgA-producing plasmablasts. These data integrate B cells into the paradigm of IgAN pathogenesis and allow further investigation of this pathway to uncover biomarkers and develop therapeutic interventions.

Blood gene expression of Toll-like receptors in SLE patients with lupus nephritis or neuropsychiatric systemic lupus erythematosus

BACKGROUND

To determine differences in the blood innate gene expression signatures of systemic lupus erythematosus (SLE) patients across various organ manifestations and disease activity, with a focus on lupus nephritis (LN) and central nervous system (CNS) involvement.

METHODS

Toll-like receptor family (TLR 1-10) mRNA expression was investigated in peripheral blood mononuclear cells from patients with SLE (n = 74) and healthy controls (n = 34). We compared patients with histologically confirmed active LN or neuropsychiatric systemic lupus erythematosus (NPSLE) with patients without these symptoms. The expression of TLR mRNA was determined by RT‒qPCR using a high-throughput SmartChip Real-Time-qPCR system (WaferGen). Multivariate analysis and nonparametric statistics were used for data analysis to assess the associations between TLRs and disease activity and severity.

RESULTS

TLR4 (0.044 vs. 0.081, p = 0.012) was upregulated and TLR10 (0.009 vs. 0.006, p = 0.0007) was downregulated in the whole cohort of SLE patients compared to healthy controls. A comparison of the active LN group with participants without kidney involvement revealed increased expression of TLR2 (0.078 vs. 0.03, p = 0.009), and TLR5 (0.035 vs. 0.017, p = 0.03). Moreover, a significant difference was observed in TLR9 expression between inactive LN and the control group (0.014 vs. 0.009, p = 0.01), together with borderline correlation in TLR2 expression (0.04 vs. 0.03, p = 0.06). Receiver operating characteristic (ROC) curve analysis revealed that TLR1 and TLR2 expression were the best potential diagnostic markers for active LN. The NPSLE group showed upregulation of TLR1 (0.088 vs. 0.048, p = 0.01), TLR4 (0.173 vs. 0.066, p = 0.0003) and TLR6 (0.087 vs. 0.036, 0.007). Our correlation analysis supported the close relationships among the expression of individual TLRs in the whole lupus cohort and its subgroups.

CONCLUSION

Our study revealed differences in TLR expression between a lupus cohort and healthy controls. Additionally, our analysis provides insight into specific TLR expression in cases with severe organ manifestations, such as LN and NPSLE. The multiple mutual relationships of TLRs demonstrate the activation of innate immunity in SLE and suggest promising targets for future therapies or diagnostics.

T-bet-expressing B cells promote atherosclerosis in apolipoprotein E-deficient mice

The humoral immune system influences the development of atherosclerosis, but the contributions of specific memory B cell subsets and IgG isotypes are poorly understood. We assessed the relationship between atherosclerosis and age-associated B cells (ABCs), a T-bet-expressing memory B cell subset that is enriched for IgG2c production and implicated in humoral autoimmunity. We found increased numbers of splenic CD11c+ ABCs in 6-mo-old, chow-fed Apoe-/- mice versus C57BL/6 control mice, which were exacerbated by high-fat diet. Deletion of T-bet in the B lineage in high-fat diet-fed Apoe-/- mice reduced aortic lesion area, and this correlated with decreased splenic CD11c+ B cells and reduced serum oxidized low-density lipoprotein-specific IgG2c. Our findings suggest that T-bet-expressing B cells are atherogenic agents in the Apoe-/- model and indicate that interventions to inhibit a T-bet-driven humoral response may improve atherosclerotic disease.

Atypical memory B cells acquire Breg phenotypes in hepatocellular carcinoma

The functional plasticity of tumor-infiltrating lymphocyte B-cells (TIL-B) spans from antitumor responses to noncanonical immune suppression. Yet, how the tumor microenvironment (TME) influences TIL-B development is still underappreciated. Our current study integrated single-cell transcriptomics and B cell receptor (BCR) sequencing to profile TIL-B phenotypes and clonalities in hepatocellular carcinoma (HCC). Using trajectory and gene regulatory network analysis, we were able to characterize plasma cells and memory and naive B cells within the HCC TME and further revealed a downregulation of BCR signaling genes in plasma cells and a subset of inflammatory TNF+ memory B cells. Within the TME, a nonswitched memory B cell subset acquired an age-associated B cell phenotype (TBET+CD11c+) and expressed higher levels of PD-L1, CD25, and granzyme B. We further demonstrated that the presence of HCC tumor cells could confer suppressive functions on peripheral blood B cells that in turn, dampen T cell costimulation. To the best of our knowledge, these findings represent novel mechanisms of noncanonical immune suppression in HCC. While previous studies identified atypical memory B cells in chronic hepatitis and across several solid cancer types, we further highlighted their potential role as regulatory B cells (Bregs) within both the TME and peripheral blood of HCC patients.

Altered immune landscape of cervical lymph nodes reveals Epstein-Barr virus signature in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, and Epstein-Barr virus (EBV) infection is a prerequisite for developing the disease. However, the pathogenic mechanisms that lead to MS remain to be determined. Here, we characterized the immune landscape of deep cervical lymph nodes (dcLNs) in newly diagnosed untreated patients with MS (pwMS) using fine-needle aspirations. By combining single-cell RNA sequencing and cellular indexing of transcriptomes and epitopes by sequencing, we observed increased memory B cells and reduced germinal center B cells with decreased clonality in pwMS. Double-negative memory B cells were increased in pwMS that transcriptionally resembled B cells with a lytic EBV infection. Moreover, EBV-targeting memory CD8 T cells were detected in a subset of pwMS. We also detected increased EBV DNA in dcLNs and elevated viral loads in patient saliva. These findings suggest that EBV-driven B cell dysregulation is a critical mechanism in MS pathogenesis.

Deep profiling of B cells responding to various pathogens uncovers compartments in IgG memory B cell and antibody-secreting lineages

Improving our understanding of B cell transition to memory B cells (MBCs) and antibody-secreting cells (ASCs) is crucial for clinical monitoring and vaccine strategies. To explore these dynamics, we compared prepandemic antigen responses (influenza hemagglutinin, respiratory syncytial virus fusion glycoprotein, and tetanus toxoid) with recently encountered severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen responses in convalescent COVID-19 patients using spectral flow cytometry. Our analysis revealed the CD43+CD71+IgG+ activated B cell subset, highly enriched for SARS-CoV-2 specificities, as a juncture for ASC and MBC differentiation, with CD86+ phenotypically similar to ASCs and CD86- to IgG+ MBCs. Moreover, subpopulations within IgG+ MBCs were further identified based on CD73 and CD24 expression. Activated MBCs (CD73-/CD24lo) were predominantly SARS-CoV-2-specific, while resting MBCs (CD73+/CD24hi) recognized prepandemic antigens. A CD95- subcluster within resting MBCs accounted for over 40% of prepandemic-specific cells, indicating long-lasting memory. These findings advance our understanding of IgG+ MBC and ASC development stages, shedding light on the decision-making process guiding their differentiation.

Dysfunctional CD11c-CD21- extrafollicular memory B cells are enriched in the periphery and tumors of patients with cancer

Many patients with recurrent and metastatic cancer fail to produce a durable response to immunotherapy, highlighting the need for additional therapeutic targets to improve the immune landscape in tumors. Recent studies have highlighted the importance of B cells in the antitumor response, with memory B cells (MBCs) being prognostic in a variety of solid tumors. MBCs are a heterogenous B cell subset and can be generated through both germinal center reactions and extrafollicular (EF) responses. EF-derived MBCs have been recently linked to poor prognosis and treatment resistance in solid tumors and thus may represent candidate biomarkers or immunotherapy targets. EF-derived MBCs, termed "double-negative" (DN) MBCs may be further classified on the basis of surface expression of CD11c and CD21 into DN1, DN2, and DN3 MBCs. CD11c-CD21+ DN1 MBCs and CD11c+CD21- DN2 MBCs have been well studied across inflammatory diseases; however, the biology and clinical relevance of CD11c-CD21- DN3 MBCs remain unknown. Here, we report an accumulation of DN3 MBCs in the blood and tumors of patients with head and neck squamous cell carcinoma (HNSCC) and an increase in DN3 MBCs in locally advanced HNSCC tumors. Circulating and intratumoral DN3 MBCs were hyporesponsive to antigen stimulation, had low antibody production, and failed to differentiate into antibody-secreting cells. Moreover, DN3 MBCs accumulated selectively outside of tertiary lymphoid structures. Last, circulating DN3 MBCs correlated with poor therapeutic response, advanced disease, and worse outcomes in patients with HNSCC and melanoma, supporting further assessment of EF-derived MBCs as potential biomarkers and therapeutic targets.

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.

Cellular and molecular determinants mediating the dysregulated germinal center immune dynamics in systemic lupus erythematosus

Introduction

Systemic lupus erythematosus (SLE) is characterized by dysregulated humoral immunity, leading to the generation of autoreactive B cells that can differentiate both within and outside of lymph node (LN) follicles.

Methods

Here, we employed spatial transcriptomics and multiplex imaging to investigate the follicular immune landscaping and the in situ transcriptomic profile in LNs from SLE individuals.

Results

Our spatial transcriptomic analysis revealed robust type I IFN and plasma cell signatures in SLE compared to reactive, control follicles. Cell deconvolution revealed that follicular T cell subsets are mainly affected by the type I IFN fingerprint of SLE follicles. Dysregulation of TFH differentiation was documented by i) the significant reduction of Bcl6hi TFH cells, ii) the reduced cell density of potential IL-4 producing TFH cell subsets associated with the impaired transcriptomic signature of follicular IL-4 signaling and iii) the loss of their correlation with GC-B cells. This profile was accompanied by a marked reduction of Bcl6hi B cells and an enrichment of extrafollicular CD19hiCD11chiTbethi, age-associated B cells (ABCs), known for their autoreactive potential. The increased prevalence of follicular IL-21hi cells further reveals a hyperactive microenvironment in SLE compared to control.

Discussion

Taken together, our findings highlight the altered immunological landscape of SLE follicles, likely fueled by potent inflammatory signals such as sustained type I IFN and/or IL-21 signaling. Our work provides novel insights into the spatial molecular and cellular signatures of SLE follicular B and TFH cell dynamics, and points to druggable targets to restore immune tolerance and enhance vaccine responses in SLE patients.

Long-term safety and efficacy of the combination of belimumab and rituximab in the treatment of severe and refractory SLE: a preliminary report

OBJECTIVE

Combination therapy with rituximab and belimumab is a novel treatment strategy for severe SLE and lupus nephritis. Phase II studies have shown promising results, although long-term data are currently lacking. To address this, we analysed outcomes of patients with severe treatment-refractory SLE who previously participated in the phase II Synbiose Study, with a particular focus on immunological parameters.

METHODS

Eight patients continued belimumab treatment beyond the 2-year duration of the original trial. We conducted a descriptive study to evaluate the course of treatment and immunological parameters over an extended follow-up. Our analyses include blood cell counts, immunoglobulins, autoantibodies, complement markers and clinical disease activity parameters. Additionally, we examined long-term effects on the B cell compartment employing high-sensitivity flow cytometry.

RESULTS

Over a median follow-up period of 6.8 years, six out of eight previously treatment-refractory patients maintained long-term clinical remission, while two experienced a major flare. Among those in remission, two patients achieved immunosuppression-free remission, and four continued belimumab. Long-term effects on humoral (auto-)immunity were a persistent decrease in IgM levels, while IgG normalised. Most patients maintained low autoantibody titres, and complement markers remained normal. On the cellular level, belimumab treatment after rituximab prevented B cell repopulation. Notably, patients exhibited a stable reduction of double-negative (DN) B cells, irrespective of continuing or stopping belimumab.

CONCLUSIONS

Long-lasting remission was observed in patients with SLE following combination treatment with rituximab and belimumab. We observed no significant hypogammaglobulinaemia and, notably, persistent reduction of DN B cells.

Congenital T-cell activation impairs transitional-to-follicular B-cell maturation in humans

ABSTRACT

Patients with cytotoxic T-lymphocyte-associated protein 4 (CTLA4) deficiency exhibit profound humoral immune dysfunction, yet the basis for the B-cell defect is not known. We observed a marked reduction in transitional-to-follicular (FO) B-cell development in patients with CTLA4 deficiency, correlating with decreased CTLA4 function in regulatory T cells, increased CD40L levels in effector CD4+ T cells, and increased mammalian target of rapamycin complex 1 (mTORC1) signaling in transitional B cells (TrBs). Treatment of TrBs with CD40L was sufficient to induce mTORC1 signaling and inhibit FO B-cell maturation in vitro. Frequent cell-to-cell contacts between CD40L+ T cells and immunoglobulin D-positive CD27- B cells were observed in patient lymph nodes. FO B-cell maturation in patients with CTLA4 deficiency was partially rescued after CTLA4 replacement therapy in vivo. We conclude that functional regulatory T cells and the containment of excessive T-cell activation may be required for human TrBs to mature and attain metabolic quiescence at the FO B-cell stage.

CD38 deficiency leads to a defective short-lived transcriptomic response to chronic graft-versus-host disease induction, involving purinergic signaling-related genes and distinct transcriptomic signatures associated with lupus

This study aimed to elucidate the transcriptomic signatures and dysregulated pathways associated with the autoimmune response in Cd38-/- mice compared to wild-type (WT) mice within the bm12 chronic graft-versus-host disease (cGVHD) lupus model. We conducted bulk RNA sequencing on peritoneal exudate cells (PECs) and spleen cells (SPC) at two and four weeks following adoptive cell transfer. We also analyzed cells from healthy, untreated mice. These analyses revealed a sustained upregulation of a transcriptional profile of purinergic receptors and ectonucleotidases in cGVHD WT PECs, which displayed a coordinated expression with several type I interferon-stimulated genes (ISGs) and with key molecules involved in the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling pathway, two hallmarks in the lupus pathology. A second purinergic receptor transcriptomic profile, which included P2rx7 and P2rx4, showed a coordinated gene expression of the components of the NLRP3 inflammasome with its potential activators. These processes were transcriptionally less active in cGVHD Cd38-/- PECs than in WT PECs. We have also shown evidence of a distinct enrichment in pathways signatures that define processes such as Ca2+ ion homeostasis, cell division, phagosome, autophagy, senescence, cytokine/cytokine receptor interactions, Th17 and Th1/Th2 cell differentiation in Cd38-/- versus WT samples, which reflected the milder inflammatory and autoimmune response elicited in Cd38-/- mice relative to WT counterparts in response to the allogeneic challenge. Last, we have shown an intense metabolic reprogramming toward oxidative phosphorylation in PECs and SPC from cGVHD WT mice, which may reflect an increased cellular demand for oxygen consumption, in contrast to PECs and SPC from cGVHD Cd38-/- mice, which showed a short-lived metabolic effect at the transcriptomic level. Overall, these findings support the pro-inflammatory and immunomodulatory role of CD38 during the development of the cGVHD-lupus disease.

IRF7 controls spontaneous autoimmune germinal center and plasma cell checkpoints

How IRF7 promotes autoimmune B cell responses and systemic autoimmunity is unclear. Analysis of spontaneous SLE-prone mice deficient in IRF7 uncovered the IRF7 role in regulating autoimmune germinal center (GC), plasma cell (PC) and autoantibody responses and disease. IRF7, however, was dispensable for foreign antigen driven GC, PC and antibody responses. Competitive bone marrow (BM) chimeras highlighted the importance of IRF7 in hematopoietic cells in spontaneous GC and PC differentiation. Single-cell-RNAseq of SLE-prone B cells indicated IRF7 mediated B cell differentiation through GC and PC fates. Mechanistic studies revealed that IRF7 promoted B cell differentiation through GC and PC fates by regulating the transcriptome, translation, and metabolism of SLE-prone B cells. Mixed BM chimeras demonstrated a requirement for B cell-intrinsic IRF7 in IgG autoantibody production but not sufficient for promoting spontaneous GC and PC responses. Altogether, we delineate previously unknown B cell-intrinsic and -extrinsic mechanisms of IRF7-promoted spontaneous GC and PC responses, loss of tolerance, autoantibody production and SLE development.

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.

Rheumatoid Arthritis Related B-Cell Changes Are Found Already in the Risk-RA Phase

Anti-cyclic citrullinated peptide2 (CCP2) antibody positivity in rheumatoid arthritis (RA) and in the predisease phase, together with the success of B-cell depletion, support a crucial role for B cells in RA pathogenesis. Yet, knowledge of B cells in the transition from autoimmunity to RA is limited, and therefore we here investigated B-cell changes during the risk-RA phase. B-cell phenotypes in 18 CCP2-positive risk-RA individuals with musculoskeletal complaints were studied, parallel with ten CCP2-positive RA patients and nine healthy controls. Nine of the risk-RA individuals progressed to RA. B-cell phenotypes were investigated using spectral flow cytometry. The results demonstrate that unswitched and switched memory B-cell frequencies in the risk-RA cohort were more similar to controls than RA patients. Yet, risk-RA progressors displayed an early activation profile amongst naïve B cells. Deeper characterization of the memory compartment revealed expansion of CD27-negative IgG+ B cells both in RA compared with controls (p = 0.0172) and in risk-RA progressors versus non-progressors (p = 0.0295). Overall, we demonstrate that the phenotypic distribution of B cells is altered in the risk-RA phase. This includes changes in CD27-negative class-switched B cells, which have been attributed to autoreactive and anergic features implicating a possible contribution to RA development.

Opportunities and limitations of B cell depletion approaches in SLE

B cell depletion with rituximab, a chimeric monoclonal antibody that selectively targets B cells by binding CD20, has been used off label in severe and resistant systemic lupus erythematosus (SLE) for over two decades. Several biological mechanisms limit the efficacy of rituximab, including immunological reactions towards the chimeric molecule, increased numbers of residual B cells, including plasmablasts and plasma cells, and a post-treatment surge in B cell-activating factor (BAFF) levels. Consequently, rituximab induces remission in only a proportion of patients, and safety issues limit its use. However, the use of rituximab has established the value of B cell depletion strategies in SLE and has guided the development of several improved B cell depletion therapies for SLE. These include enhanced monoclonal antibodies, modalities that redirect the specificity of patient T cells using chimeric antigen receptor T cells or bispecific T cell engagers, and combination treatment that simultaneously inhibits the BAFF pathway. In this Review, we consider evidence gathered from over two decades of using rituximab in SLE and examine how B cell depletion therapies could be further optimized to achieve immunological and clinical efficacy. In addition, we discuss the prospects of B cell depletion strategies for personalized treatment in SLE based on genetic research and studies in pre-symptomatic individuals.

Circulatory age-associated B cells: Their distinct transcriptomic characteristics and clinical significance in drug-naïve patients with rheumatoid arthritis

Age-associated B cells (ABCs) have been implicated in the pathogenesis of autoimmune diseases. However, the global gene expression and clinical significance of circulatory ABCs in rheumatoid arthritis (RA) remain poorly understood. Here, single-cell RNA sequencing identified nine B cell subsets in peripheral blood of RA patients, including ABCs. Increased phagocytosis and antigen presentation were functionally enriched by the genes expressed differentially in ABCs. Network analysis and in vitro experiments demonstrated SYK as a key regulator defining the myeloid-like phenotypes in ABCs. Flow cytometry showed that the proportion of ABCs correlated with RA activity and serum tumor necrosis factor-alpha level. Notably, ABCs above a cutoff threshold specifically distinguished RA from healthy controls and indicated higher disease activity. This study highlights the myeloid characteristics of circulatory ABCs regulated by SYK in RA. Increased ABCs may reflect disease activity and could serve as a potential biomarker in RA.

Deciphering the secret codes in N7-methylguanosine modification: Context-dependent function of methyltransferase-like 1 in human diseases

N7-methylguanosine (m7G) is one of the most prevalent post-transcriptional modifications of RNA and plays a critical role in RNA translation and stability. As a pivotal m7G regulator, methyltransferase-like 1 (METTL1) is responsible for methyl group transfer during the progression of m7G modification and contributes to the structure and functional regulation of RNA. Accumulating evidence in recent years has revealed that METTL1 plays key roles in various diseases depending on its m7G RNA methyltransferase activity. Elevated levels of METTL1 are typically associated with disease development and adverse consequences. In contrast, METTL1 may act as a disease suppressor in several disorders. While the roles of m7G modifications in disease have been extensively reviewed, the critical functions of METTL1 in various types of disease and the potential targeting of METTL1 for disease treatment have not yet been highlighted. This review describes the various biological functions of METTL1, summarises recent advances in understanding its pathogenic and disease-suppressive functions and discusses the underlying molecular mechanisms. Given that METTL1 can promote or inhibit disease processes, the possibility of applying METTL1 inhibitors and agonists is further discussed, with the goal of providing novel insights for future disease diagnosis and potential intervention targets. KEY POINTS: METTL1-mediated m7G modification is crucial for various biological processes, including RNA stability, maturation and translation. METTL1 has emerged as a critical epigenetic modulator in human illnesses, with its dysregulated expression correlating with multiple diseases progression and presenting opportunities for both diagnostic biomarker development and molecular-targeted therapy. Enormous knowledge gaps persist regarding context-dependent regulatory networks of METTL1 and dynamic m7G modification patterns, necessitating mechanistic interrogation to bridge basic research with clinical translation in precision medicine.

Immunosenescence and age-related immune cells: causes of age-related diseases

Immunosenescence is a weakening of the immune system due to aging, characterized by changes in immune cells and dysregulated immune function. Age-related immune cells are increasing with aging. They are associated with chronic prolonged inflammation, causing tissue dysfunction and age-related diseases. Here, we discuss increased pro-inflammatory activity of aged macrophages, accumulation of lymphocytes with an age-associated phenotype, and specific alterations in both functions and characteristics of these immune cells. These cellular changes are associated with development of age-related diseases. Additionally, we reviewed various therapeutic strategies targeting age-related immunosenescence, providing pathways to mitigate effects of age-related diseases.

Human immune organoids to decode B cell response in healthy donors and patients with lymphoma

Antibodies are produced when naive B cells differentiate into plasma cells within germinal centres (GCs) of lymphoid tissues. Patients with B cell lymphoma on effective immunotherapies exhibit diminished antibody production, leading to higher infection rates and reduced vaccine efficacy, even after B cell recovery. Current ex vivo models fail to sustain long-term GC reactions and effectively test B cell responses. Here we developed synthetic hydrogels mimicking the lymphoid tissue microenvironment, enabling human GCs from tonsils and peripheral blood mononuclear cell-derived B cells. Immune organoids derived from peripheral blood mononuclear cells maintain GC B cells and plasma cells longer than tonsil-derived ones and exhibit unique B cell programming, including GC compartments, somatic hypermutation, immunoglobulin class switching and B cell clones. Chemical inhibition of transcriptional and epigenetic processes enhances plasma cell formation. While integrating polarized CXCL12 protein in a lymphoid organ-on-chip modulates GC responses in healthy donor B cells, it fails with B cells derived from patients with lymphoma. Our system allows rapid, controlled modelling of immune responses and B cell disorders.

Clonal relationships between Tph and Tfh cells in patients with SLE and in murine lupus

Pathologic T cell-B cell interactions drive disease in systemic lupus erythematosus (SLE). The T cells that activate B cell responses include T peripheral helper (Tph) and T follicular helper (Tfh) cells, yet the developmental and clonal relationships between these B cell-helper T cell populations are unclear. Here we use T cell receptor (TCR) profiling to demonstrate clonal overlap between Tph and Tfh cells in the circulation of patients with SLE. Expanded Tph and Tfh cell clones persist over the course of 1 year in patients with a new diagnosis of SLE, and clones are observed to shift both from Tfh to Tph cells and from Tph to Tfh cells over time. High resolution analysis of cells sorted as Tph cells (CXCR5- PD-1hi) and Tfh cells (CXCR5+ PD-1hi) from SLE patients revealed considerable heterogeneity among cells sorted as Tph cells and highlighted a specific cluster of cells that expressed transcriptomic features of activated B cell-helper T cells. This cell population, marked by expression of TOX and CXCL13, was found in both sorted Tph and Tfh cells, and was clonally linked in these two populations. Analysis of B cell-helper T cells in murine pristane-induced lupus demonstrated similar populations of Tph and Tfh cells in both lung and spleen with strong clonal overlap. T cell-specific loss of Bcl6 prevented accumulation of Tfh cells and reduced accumulation of Tph cells in pristane-treated mice, indicating a role for Bcl6 in the survival and expansion of both populations. Together, these observations demonstrate a shared developmental path among pathologically expanded Tph and Tfh cells in lupus. The persistence of expanded Tph and Tfh cells clones over time may impose barriers to induction of stable tolerance by immunosuppressive medications or by B cell depletion.

Evaluation of B cell related markers and autoantibodies in rheumatoid arthritis patients treated with abatacept

Objectives

To investigate whether biomarkers related to B cell activation and autoantibody production are associated with the response to abatacept in rheumatoid arthritis (RA) patients.

Methods

Twenty-five patients with RA were enrolled in this study. Responders (n=10) to abatacept were subjects who achieved ACR50 response at week 24. Serum levels of soluble biomarkers were measured with ProcartaPlex by Luminex or ELISA. Peripheral blood mononuclear cells were isolated and analysed for T cell and B cell subsets by flow cytometry. Patients were genotyped for human leukocyte antigen (HLA)-DRB1 shared epitope (SE) alleles. Baseline levels and longitudinal changes of markers were assessed between responders and nonresponders.

Results

Baseline levels of anti-cyclic citrullinated peptide (anti-CCP) antibodies (p=0.01), IgM rheumatoid factor (RF) (p=0.02), CXC chemokine ligand 13 (CXCL13, p=0.02), sCD23 (p<0.05), as well as frequencies of CD19+CD11c+IgD-CD27- B cells (p=0.04), were higher in responders than nonresponders. Among them, anti-CCP and frequencies of CD19+CD11c+IgD-CD27- B cells were independently associated with response to abatacept. The presence of two alleles of SE was associated with responders (p=0.04). Patients with 2 alleles of SE had higher levels of anti-CCP (p=0.02) and IgM RF (p=0.04) compared to patients with 0 or 1 allele. Further, IgM RF and CXCL13 levels decreased only in responders (p=0.02 and 0.004 respectively, at week 24), while anti-CCP levels did not decrease significantly in either responders or nonresponders.

Conclusion

Markers of B cell activation including anti-CCP and frequencies of CD19+CD11c+IgD-CD27- B cells in RA were associated with response to abatacept. IgM RF and CXCL13 decreased only in responders and could be potentially used as pharmacodynamic markers.

Organ-based characterization of B cells in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic, inflammatory, and progressive autoimmune disease. The unclear pathogenesis, high heterogeneity, and prolonged course of the disease present significant challenges for effective clinical management of lupus patients. Dysregulation of the immune system and disruption of immune tolerance, particularly through the abnormal activation of B lymphocytes and the production of excessive autoantibodies, lead to widespread inflammation and tissue damage, resulting in multi-organ impairment. Currently, there is no systematic review that examines the specificity of B cell characteristics and pathogenic mechanisms across various organs. This paper reviews current research on B cells in lupus patients and summarizes the distinct characteristics of B cells in different organs. By integrating clinical manifestations of organ damage in patients with a focus on the organ-specific features of B cells, we provide a new perspective on enhancing the efficacy of lupus-targeted B cell therapy strategies.

Multi-dimensional analysis of B cells reveals the expansion of memory and regulatory B-cell clusters in humans living in rural tropical areas

B-cells play a critical role in the formation of immune responses against pathogens by acting as antigen-presenting cells, by modulating immune responses, and by generating immune memory and antibody responses. Here, we studied B-cell subset distributions between regions with higher and lower microbial exposure, i.e. by comparing peripheral blood B-cells from people living in Indonesia or Ghana to those from healthy Dutch residents using a 36-marker mass cytometry panel. By applying an unbiased multidimensional approach, we observed differences in the balance between the naïve and memory compartments, with higher CD11c+ and double negative (DN-IgDnegCD27neg) memory (M)B-cells in individuals from rural tropical areas, and conversely lower naïve B-cells compared to residents from an area with less pathogen exposure. Furthermore, characterization of total B-cell populations, CD11c+, DN, and Breg cells showed the emergence of specific memory clusters in individuals living in rural tropical areas. Some of these differences were more pronounced in children compared to adults and suggest that a higher microbial exposure accelerates memory B-cell formation, which "normalizes" with age.

Functional validation of a novel STAT3 'variant of unknown significance' identifies a new case of STAT3 GOF syndrome and reveals broad immune cell defects

INTRODUCTION

Signal transducer and activator of transcription 3 (STAT3) orchestrates crucial immune responses through its pleiotropic functions as a transcription factor. Patients with germline monoallelic dominant negative or hypermorphic STAT3 variants, who present with immunodeficiency and/or immune dysregulation, have revealed the importance of balanced STAT3 signaling in lymphocyte differentiation and function, and immune homeostasis. Here, we report a novel missense variant of unknown significance in the DNA-binding domain of STAT3 in a patient who experienced hypogammaglobulinemia, lymphadenopathy, hepatosplenomegaly, immune thrombocytopenia, eczema, and enteropathy over a 35-year period.

METHODS

In vitro demonstration of prolonged STAT3 activation due to delayed dephosphorylation, and enhanced transcriptional activity, confirmed this to be a novel pathogenic STAT3 gain-of-function variant. Peripheral blood lymphocytes from this patient, and patients with confirmed STAT3 Gain-of-function Syndrome, were collected to investigate mechanisms of disease pathogenesis.

RESULTS

B cell dysregulation was evidenced by a loss of class-switched memory B cells and a significantly expanded CD19hiCD21lo B cell population, likely influenced by a skewed CXCR3+ TFH population. Interestingly, unlike STAT3 dominant negative variants, cytokine secretion by activated peripheral blood STAT3 GOF CD4+ T cells and frequencies of Treg cells were intact, suggesting CD4+ T cell dysregulation likely occurs at sites of disease rather than the periphery.

CONCLUSION

This study provides an in-depth case study in confirming a STAT3 gain-of-function variant and identifies lymphocyte dysregulation in the peripheral blood of patients with STAT3 gain-of-function syndrome. Identifying cellular biomarkers of disease provides a flow cytometric-based screen to guide validation of additional novel STAT3 gain-of-function variants as well as provide insights into putative mechanisms of disease pathogenesis.

IL-21-STAT3 axis negatively regulates LAIR1 expression in B cells

LAIR1 is an inhibitory receptor broadly expressed on human immune cells, including B cells. LAIR1 has been shown to modulate BCR signaling, however, it is still unclear whether its suppressive activity can be a negative regulator for autoreactivity. In this study, we demonstrate the LAIR1 expression profile on human B cells and prove its regulatory function and relationships to B cell autoreactivity. We show that both the frequency and level of LAIR1 expression decreases during B cell differentiation. LAIR1 expressing (LAIR1 + ) switched memory (SWM) B cells have a transcriptional profile less differentiated toward a plasma cell (PC) phenotype, harbor more autoreactive B cells and exhibit less PC differentiation in vitro than the LAIR1 negative (LAIR1 - ) counterpart. These data suggests that LAIR1 functions as a B cell tolerance checkpoint. We confirm previous data showing that patients with systemic lupus erythematosus (SLE) express less LAIR1 on B cells, implying a breakdown of the checkpoint, consistent with the enhanced PC differentiation seen in SLE. We further demonstrate that LAIR1 expression is down-regulated through the IL-21/STAT3 pathway which is known to be upregulated in SLE. These data suggest therapeutic targets that might decrease the aberrant PC differentiation observed in SLE.

Recent Evidence of the Role of CD4+ T Cell Subsets in IgG4-related Disease

CD4+ T cells, the so-called T helper cells, are one of the main players in the human immune system, which can regulate acquired immunity. Dysfunction of the acquired immune system induces various chronic inflammatory diseases such as malignancies and autoimmune diseases. IgG4-related disease (IgG4-RD) is also a chronic inflammatory disease that is characterized by elevated serum IgG4 concentration and infiltration of IgG4-positive plasma cells in affected tissues. Despite that remarkable advances in understanding the pathogenesis of IgG4-RD have been on the rise, the detailed mechanisms by which IgG4-RD develops are still unknown. In fact, CD4+ T cells abundantly infiltrate at lesions of IgG4-RD, and they are also associated with the pathogenesis of other refractory chronic inflammatory diseases. Therefore, our focus was on CD4+ T cells, and we previously reported the roles of their subsets including regulatory T cells, CD4 cytotoxic T lymphocytes, T follicular helper (Tfh) cells, T follicular regulatory cells, and T peripheral helper (Tph) cells in IgG4-RD. Among the subsets, Tph cells play an important role in generating ectopic lymphoid structures at inflammatory sites. Moreover, we found that circulating Tph cells are increased in IgG4-RD patients. Unlike Tfh cells, Tph cells express high levels of chemokine receptors and cytotoxic molecules. Thus, they can infiltrate affected tissues and exert a cytotoxic function. Additionally, our latest observations demonstrated that Tph cells interact with extrafollicular B cells in affected tissues. Hence, Tph cells may collaborate with a specific B-cell subset, and they play a role in the maintenance of persistent fibroinflammation in lesions of IgG4-RD. Tph cells may have an important role to play in the pathogenesis of not only IgG4-RD but also other chronic inflammatory diseases. This review summarizes and discusses the possible pathologic roles of CD4+ T cell subsets including Tph cells in IgG4-RD.

30-Color Longitudinal Full-Spectrum Immunophenotyping and Sorting of Human Circulating Immune Cell Subsets Implicated in Systemic Autoimmune Rheumatic Diseases

This 30-color panel was developed to enable the enumeration and purification of distinct circulating immune cell subsets implicated in the pathogenesis of systemic autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), systemic sclerosis (SSc; scleroderma), Sjögren's disease (SjD), idiopathic inflammatory myopathy (IIM), and others. While designed for application to peripheral blood mononuclear cells, the inclusion of CD45 coupled with the ability to extract cellular autofluorescence spectral signatures enables the application of this panel to other tissue types. Of the 30 total markers, this panel employs 18 markers to profile T cell subsets consisting of different memory subsets and T helper polarities, > 10 markers to profile B cell subsets including double-negative B cells, and a total of 8 lineage markers to identify immune lineages including monocyte and natural killer cell subsets, conventional dendritic cells, plasmacytoid dendritic cells, and basophils. This panel reproducibly identifies target populations with excellent resolution over several months of data acquisition with minimal batch effects, offering investigators a practical approach to sort immune cell subsets of interest for downstream applications while simultaneously collecting high parameter immunophenotypic information using a limited sample quantity.

Assessing human B cell responses to influenza virus vaccines and adjuvants in a PBMC-derived in vitro culture system

In vitro systems based on human peripheral blood mononuclear cells (PBMCs) can bridge the gap between preclinical and clinical vaccine evaluation but have so far mainly been exploited to assess vaccine effects on antigen-presenting cells and T cells. Our study aimed to assess whether B cells present in PBMCs also respond to vaccines and reflect the effects of different vaccine formulations and adjuvants. We stimulated PBMCs with whole inactivated virus (WIV) or split virus (SIV) H5N1 influenza vaccine, with or without the addition of the adjuvant cytosine phosphoguanine (CpG) ODN 2395, and collected the cells and supernatants at different timepoints. B cell subsets were measured by flow cytometry, immunoglobulin (IgG) levels by ELISA, B cell-related genes by qPCR, and cytokine levels by intracellular staining. B cells differentiated more readily to plasmablasts and plasma cells and produced more IgG when PBMC cultures were stimulated with WIV than when stimulated with SIV. In line, PRDM1, XBP1, and AICDA, genes associated with the differentiation of B cells to antibody-secreting cells, were expressed at higher levels in WIV- than in SIV-stimulated PBMCs. The combination of WIV and CpG consistently induced the highest levels of antibody-secreting cell differentiation, IgG production, and B-cells secreting IL-6 and IL-10. Taken together, B cells in human PBMC cultures show distinct responses to different types of vaccines and vaccine/CpG combinations. This underlines the suitability of unfractionated PBMCs for evaluating vaccine effects on different types of human immune cells before running costly clinical trials.

Function and Regulation of Age-Associated B Cells in Diseases

The aging process often leads to immune-related diseases, including infections, tumors, and autoimmune disorders. Recently, researchers identified a special subpopulation of B cells in elderly female mice that increases with age and accumulates prematurely in mouse models of autoimmune diseases or viral infections; these B cells are known as age-related B cells (ABCs). These cells possess distinctive cell surface phenotypes and transcriptional characteristics, and the cell population is widely recognized as CD11c+CD11b+T-bet+CD21-CD23- cells. Research has shown that ABCs are a heterogeneous group of B cells that originate independently of the germinal center and are insensitive to B-cell receptor (BCR) and CD40 stimulation, differentiating and proliferating in response to toll-like receptor 7 (TLR7) and IL-21 stimulation. Additionally, they secrete self-antibodies and cytokines to regulate the immune response. These issues have aroused widespread interest among researchers in this field. This review summarizes recent research progress on ABCs, including the functions and regulation of ABCs in aging, viral infection, autoimmune diseases, and organ transplantation.

Disease-associated B cells and immune endotypes shape adaptive immune responses to SARS-CoV-2 mRNA vaccination in human SLE

Severe acute respiratory syndrome coronavirus 2 mRNA vaccination has reduced effectiveness in certain immunocompromised individuals. However, the cellular mechanisms underlying these defects, as well as the contribution of disease-induced cellular abnormalities, remain largely unexplored. In this study, we conducted a comprehensive serological and cellular analysis of patients with autoimmune systemic lupus erythematosus (SLE) who received the Wuhan-Hu-1 monovalent mRNA coronavirus disease 2019 vaccine. Our findings revealed that patients with SLE exhibited reduced avidity of anti-receptor-binding domain antibodies, leading to decreased neutralization potency and breadth. We also observed a sustained anti-spike response in IgD-CD27- 'double-negative (DN)' DN2/DN3 B cell populations persisting during memory responses and with greater representation in the SLE cohort. Additionally, patients with SLE displayed compromised anti-spike T cell immunity. Notably, low vaccine efficacy strongly correlated with higher values of a newly developed extrafollicular B and T cell score, supporting the importance of distinct B cell endotypes. Finally, we found that anti-BAFF blockade through belimumab treatment was associated with poor vaccine immunogenicity due to inhibition of naive B cell priming and an unexpected impact on circulating T follicular helper cells.