The Antigen Presenting Potential of CD21low B Cells

JAK inhibitors attenuate hyperactivation of nonswitched memory B cells in rheumatoid arthritis patients in remission

OBJECTIVE

To investigate the distribution and activation of B-cell subpopulations in rheumatoid arthritis (RA) patients treated with Janus kinase inhibitors (JAKis) and to analyze their correlation with disease remission.

METHODS

Peripheral blood samples were collected from 23 adult healthy controls and 58 RA patients, 31 of whom were treated with JAKis and assessed during a 24-month follow-up. The number of peripheral B-cell subpopulations (including naive B cells, nonswitched memory B (NSMB) cells, switched memory B cells, and double-negative B cells), their activation, and phosphorylation of SYK and AKT upon B-cell receptor (BCR) stimulation in each population were analyzed by flow cytometry.

RESULTS

Compared with that in healthy controls, the frequency of NSMB cells was significantly lower in new-onset untreated RA patients. However, expression of CD40, CD80, CD95, CD21low and pAKT significantly increased in these NSMB cells. Additionally, the number of NSMB cells correlated negatively with DAS28-ESR and IgG and IgA levels in these patients; expression of CD80, CD95 and CD21low on NSMB cells correlated positively with DAS28-ESR and IgG and IgA levels. After treatment with JAKis, the serum IgG concentration significantly decreased in RA patients in remission, but CD40, CD95 and pAKT levels in NSMB cells significantly decreased.

CONCLUSION

RA patients present different B-cell subpopulations, in which the frequency of NSMB cells is negatively associated with disease activity. However, treatment with JAKis can inhibit activation of NSMB cells, restore the balance of kinase phosphorylation, and facilitate disease remission in RA patients.

Lymphocyte profile in peripheral blood of patients with multiple myeloma

Multiple myeloma (MM) is a disease which remains incurable. One of the main reasons is a weakened immune system that allows MM cells to survive. Therefore, the current research is focused on the study of immune system imbalance in MM to find the most effective immunotherapy strategies. Aiming to identify the key points of immune failure in MM patients, we analysed peripheral lymphocytes subsets from MM patients (n = 57) at various stages of the disease course and healthy individuals (HI, n = 15) focusing on T, NK, iNKT, B cells and NK-cell cytokines. Our analysis revealed that MM patients exhibited immune alterations in all studied immune subsets. Compared to HI, MM patients had a significantly lower proportion of CD4 + T cells (19.55% vs. 40.85%; p < 0.001) and CD4 + iNKT cells (18.8% vs. 40%; p < 0.001), within B cells an increased proportion of CD21LCD38L subset (4.5% vs. 0.4%; p < 0.01) and decreased level of memory cells (unswitched 6.1% vs. 14.7%; p < 0.001 and switched 7.8% vs. 11.2%; NS), NK cells displaying signs of activation and exhaustion characterised by a more than 2-fold increase in SLAMF7 MFI (p < 0.001), decreased expression of NKG2D (MFI) and NKp46 (%) on CD16 + 56 + and CD16 + 56- subset respectively (p < 0.05), Effective immunotherapy needs to consider these immune defects and monitoring of the immune status of MM patients is essential to define better interventions in the future.

A comprehensive analysis of the immune system in healthy Vietnamese people

Lifestyle, diet, socioeconomic status and genetics all contribute to heterogeneity in immune responses. Vietnam is plagued with a variety of health problems, but there are no available data on immune system values in the Vietnamese population. This study aimed to establish reference intervals for immune cell parameters specific to the healthy Vietnamese population by utilizing multi-color flow cytometry (MCFC). We provide a comprehensive analysis of total leukocyte count, quantitative and qualitative shifts within lymphocyte subsets, serum and cytokine and chemokine levels and functional attributes of key immune cells including B cells, T cells, natural killer (NK) cells and their respective subpopulations. By establishing these reference values for the Vietnamese population, these data contribute significantly to our understanding of the human immune system variations across diverse populations. These data will be of substantial comparative value and be instrumental in developing personalized medical approaches and optimizing diagnostic strategies for individuals based on their unique immune profiles.

CD32 (FcγRIIB) expression is low on CD21low B cells from systemic sclerosis patients with digital ulcers, interstitial lung disease, and anti-topoisomerase I autoantibodies

CD21low B cells have recently been found increased in SSc-associated digital ulcers (DUs) or interstitial lung disease (ILD). To further characterize CD21low B cells which encompass autoreactive cells, we analyzed their expression of the inhibitory CD32 receptor in SSc. Peripheral blood mononuclear cells from 27 patients with SSc and 15 age-and sex-matched healthy controls (HCs) were analyzed with multicolor flow cytometry. CD21low B cells were significantly increased in patients with DUs (51.3%) compared to HCs (28.1%) and in patients with ILD (53.1%) compared to HCs. CD21lowCD32low B cells were significantly increased in patients with DUs (23.8%) compared to HCs (4.4%), in patients with ILD (28.4%) compared to HCs, and in anti-topoisomerase I (+) patients (21.5%) compared to HCs and to anti-topoisomerase I (-) patients (2.4%). Autoreactive B cells recognizing Topoisomerase I were predominantly within CD32low cell fraction. Our study further supports the autoreactive status of CD21lowCD32low B cells in SSc patients.

B cells and the coordination of immune checkpoint inhibitor response in patients with solid tumors

Immunotherapy profoundly changed the landscape of cancer therapy by providing long-lasting responses in subsets of patients and is now the standard of care in several solid tumor types. However, immunotherapy activity beyond conventional immune checkpoint inhibition is plateauing, and biomarkers are overall lacking to guide treatment selection. Most studies have focused on T cell engagement and response, but there is a growing evidence that B cells may be key players in the establishment of an organized immune response, notably through tertiary lymphoid structures. Mechanisms of B cell response include antibody-dependent cellular cytotoxicity and phagocytosis, promotion of CD4+ and CD8+ T cell activation, maintenance of antitumor immune memory. In several solid tumor types, higher levels of B cells, specific B cell subpopulations, or the presence of tertiary lymphoid structures have been associated with improved outcomes on immune checkpoint inhibitors. The fate of B cell subpopulations may be widely influenced by the cytokine milieu, with versatile roles for B-specific cytokines B cell activating factor and B cell attracting chemokine-1/CXCL13, and a master regulatory role for IL-10. Roles of B cell-specific immune checkpoints such as TIM-1 are emerging and could represent potential therapeutic targets. Overall, the expanding field of B cells in solid tumors of holds promise for the improvement of current immunotherapy strategies and patient selection.

CD11chigh B Cell Expansion Is Associated With Severity and Brain Atrophy in Neuromyelitis Optica

BACKGROUND AND OBJECTIVES

Neuromyelitis optica (NMO) is an autoimmune astrocytopathy mediated by anti-AQP4 antibody-producing B cells. Recently, a B-cell subset highly expressing CD11c and T-bet, originally identified as age-associated B cells, has been shown to be involved in the pathogenesis of various autoimmune diseases. The objective of this study was to determine the relationship between the frequency of CD11chigh B cells per CD19+ B cells in the peripheral blood of patients with NMO and the clinical profiles including the brain volume.

METHODS

In this observational study, 45 patients with anti-AQP4 antibody-positive NMO in remission and 30 healthy control subjects (HCs) were enrolled. Freshly isolated peripheral blood mononuclear cells were analyzed for immune cell phenotypes. The frequency of CD11chigh B cells per CD19+ B cells was assessed by flow cytometry and was evaluated in association with the clinical profiles of patients. Brain MRI data from 26 patients were included in the study for the analysis on the correlation between CD11chigh B-cell frequency and brain atrophy.

RESULTS

We found that the frequency of CD11chigh B cells in CD19+ B cells was significantly increased in patients with NMO compared with HCs. The expansion of CD11chigh B cells significantly correlated with EDSS, past relapse numbers, and disease duration. In addition, a higher frequency of CD11chigh B cells negatively correlated with total brain, white matter, and gray matter volumes and positively correlated with T2/FLAIR high lesion volumes. When the past clinical relapse episodes of patients with or without the expansion of CD11chigh B cells were compared, relapses in the brain occurred more frequently in patients with CD11chigh B-cell expansion. CD11chigh B cells had distinct features including expression of chemokine receptors associated with migration into peripheral inflammatory tissues and antigen presentation. CD11chigh B-cell frequency was positively correlated with T peripheral helper-1 (Tph-1) cell frequency.

DISCUSSION

Even during the relapse-free period, CD11chigh B cells could expand in the long disease context, possibly through the interaction with Tph-1 cells. The increased frequency of CD11chigh B cells associated with brain atrophy and disease severity, indicating that this cell population could be involved in chronic neuroinflammation in NMO.

Association Between Cytometric Biomarkers, Clinical Phenotype, and Complications of Common Variable Immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) is a heterogeneous group of immune disorders. The patients are classified according to the clinical manifestation with the infection-only phenotype (CVIDinf) and CVID with immune dysregulation (CVIDid).

METHODS

We performed a retrospective clinical analysis of 64 CVID patients (34 males, 53.13%; mean age: 41.4 years; SD: ±21.4 years). We divided the patients into subgroups according to the clinical manifestation (CVIDinf and CVIDid) and according to B cell phenotypic profiling after performing flow cytometry with the use of the EUROclass classification. We compared clinical manifestations, selected laboratory parameters, and therapy in these groups. All CVIDid patients were tested after the manifestation of complications associated with immune dysregulation and in eight patients during the immunosuppressive treatment (systemic corticosteroids and hydroxychloroquine).

RESULTS

Two-thirds of patients in our cohort had symptoms resulting from immune dysregulation. Almost half of the patients had autoimmune complications. A higher proportion of marginal zone B cells was associated with autoimmune complications. A lower percentage of naïve B cells was connected to autoimmunity, whereas a lower proportion of transitional B cells was associated with rheumatic diseases and splenomegaly. Patients with lymphadenopathy had a higher percentage of double-negative T cells and a lower percentage of switched memory B cells. We performed molecular-genetic testing in 28% (n = 17) of patients and found a causal pathogenic variant in 23.5% (n = 4) of this group.

CONCLUSION

Based on our results, there is an association between specific cytometric parameters, clinical phenotype, and complications of CVID. The use of the subpopulations of B cells can be helpful in the diagnosis of these specific clinical complications in CVID patients and could help to personalise the therapeutic approach.

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

Many autoimmune diseases (AIDs) are characterized by the persistence of autoreactive B cell responses, which have been directly implicated in disease pathogenesis. How and why these cells are generated or how they are maintained for years is largely unknown. Rheumatoid arthritis (RA) is among the most common AIDs and is characterized by autoantibodies recognizing proteins with posttranslational modifications (PTMs). This PTM-directed autoreactive B cell compartment is ill defined. Here, we visualized the B cell response against the three main types of PTM antigens implicated in RA by spectral flow cytometry. Our results showed extensive cross-reactivity of PTM-directed B cells against all three PTM antigens (citrulline, homocitrulline, and acetyllysine). Unsupervised clustering revealed several distinct memory B cell (mBC) populations. PTM-directed cells clustered with the most recently activated class-switched mBC phenotype, with high CD80, low CD24, and low CD21 expression. Notably, patients also harbored large fractions of PTM-directed plasmablasts (PBs). Both PTM-directed mBCs and PBs showed high expression of CXCR3, a receptor for chemokines present in abundance in arthritic joints. Together, our data provide detailed insight into the biology of B cell autoreactivity and its remarkable, seemingly exhaustless persistence in a prominent human AID.

Recent updates in the diagnosis and management of cryoglobulinemic vasculitis

INTRODUCTION

Cryoglobulinemic vasculitis (CV), also known as mixed cryoglobulinemic syndrome (MCS), is a systemic vasculitis that affects small blood vessels. It exhibits a wide range of clinical manifestations, making its treatment a continuing challenge for physicians.

AREAS COVERED

We conducted a comprehensive review to evaluate the current status of diagnosis, management, and treatment of mixed cryoglobulinemia (MC). The accurate clinical and serological evaluation plays a vital role in diagnosing MC, identifying potential comorbidities, and monitoring its main manifestations and complications. Treatment strategies should be individualized based on the underlying etiopathogenesis, the severity of organ involvement, and the associated underlying disease. At present, the two mainstays of CV treatment are direct antiviral agents (for HCV-related CV) and B-cell-targeted therapy.

EXPERT OPINION

MC remains one of the few autoimmune diseases where the etiology is known, at least for the majority of patients. Its pathogenetic mechanism offers a unique opportunity to investigate the interplay between infections and the immune system. Moving forward, the primary challenge will continue to lie in the treatment of resistant or refractory cases of CV, particularly those associated with autoimmune diseases, or cases classified as 'essential' CV.

Human memory B cells show plasticity and adopt multiple fates upon recall response to SARS-CoV-2

The B cell response to different pathogens uses tailored effector mechanisms and results in functionally specialized memory B (Bm) cell subsets, including CD21+ resting, CD21-CD27+ activated and CD21-CD27- Bm cells. The interrelatedness between these Bm cell subsets remains unknown. Here we showed that single severe acute respiratory syndrome coronavirus 2-specific Bm cell clones showed plasticity upon antigen rechallenge in previously exposed individuals. CD21- Bm cells were the predominant subsets during acute infection and early after severe acute respiratory syndrome coronavirus 2-specific immunization. At months 6 and 12 post-infection, CD21+ resting Bm cells were the major Bm cell subset in the circulation and were also detected in peripheral lymphoid organs, where they carried tissue residency markers. Tracking of individual B cell clones by B cell receptor sequencing revealed that previously fated Bm cell clones could redifferentiate upon antigen rechallenge into other Bm cell subsets, including CD21-CD27- Bm cells, demonstrating that single Bm cell clones can adopt functionally different trajectories.

Treatment of inflammatory complications in common variable immunodeficiency (CVID): current concepts and future perspectives

INTRODUCTION

Patients with Common variable immunodeficiency (CVID) have a high frequency of inflammatory complications like autoimmune cytopenias, interstitial lung disease and enteropathy. These patients have poor prognosis and effective, timely and safe treatment of inflammatory complications in CVID are essential, but guidelines and consensus on therapy are often lacking.

AREAS COVERED

This review will focus on current medical treatment of inflammatory complications in CVID and point out some future perspectives based on literature indexed in PubMed. There are a number of good observational studies and case reports on treatment of specific complications but randomized controlled trials are scarce.

EXPERT OPINION

In clinical practice, the most urgent issues that need to be addressed are the preferred treatment of GLILD, enteropathy and liver disease. Treating the underlying immune dysregulation and immune exhaustion in CVID is an alternative approach that potentially could alleviate these and other organ-specific inflammatory complications. Therapies of potential interest and wider use in CVID include mTOR-inhibitors like sirolimus, JAK-inhibitors like tofacitinib, the monoclonal IL-12/23 antibody ustekinumab, the anti-BAFF antibody belimumab and abatacept. For all inflammatory complications, there is a need for prospective therapeutic trials, preferably randomized controlled trials, and multi-center collaborations with larger cohorts of patients will be essential.

T-bethighCD21low B cells: the need to unify our understanding of a distinct B cell population in health and disease

After many years of a niche research in a few laboratories of the world, T-bet^highCD21^low B cells have entered the limelight during the last years after the discovery of T-bet as common transcription factor of this unconventional B cell population and the increasing awareness of the expansion of these cells in autoimmune and infectious diseases. This population consists of different subsets which share large parts of their transcriptome, essential phenotypic markers, and reduced B cell receptor (BCR) signaling capacity. Inborn errors of immunity have helped to delineate essential signals for their differentiation. While our comprehension of their origin has improved, future research will hopefully profit from a common definition of the different T-bet^highCD21^low subpopulations in order to better define their specific roles during normal and aberrant immune responses.

Evaluation of tumor antigen-specific antibody responses in patients with metastatic triple negative breast cancer treated with cyclophosphamide and pembrolizumab

The role of B cells in antitumor immunity is becoming increasingly appreciated, as B cell populations have been associated with response to immune checkpoint blockade (ICB) in patients with breast cancer and murine models of breast cancer. Deeper understanding of antibody responses to tumor antigens is needed to clarify the function of B cells in determining response to immunotherapy. We evaluated tumor antigen-specific antibody responses in patients with metastatic triple negative breast cancer treated with pembrolizumab following low-dose cyclophosphamide therapy using computational linear epitope prediction and custom peptide microarrays. We found that a minority of predicted linear epitopes were associated with antibody signal, and signal was associated with both neoepitopes and self-peptides. No association was observed between signal presence and subcellular localization or RNA expression of parent proteins. Patient-specific patterns of antibody signal boostability were observed that were independent of clinical response. Intriguingly, measures of cumulative antibody signal intensity relative to immunotherapy treatment showed that the one complete responder in the trial had the greatest increase in total antibody signal, which supports a potential association between ICB-dependent antibody boosting and clinical response. The antibody boost in the complete responder was largely driven by increased levels of IgG specific to a sequence of N-terminal residues in native Epidermal Growth Factor Receptor Pathway Substrate 8 (EPS8) protein, a known oncogene in several cancer types including breast cancer. Structural protein prediction showed that the targeted epitope of EPS8 was in a region of the protein with mixed linear/helical structure, and that this region was solvent-exposed and not predicted to bind to interacting macromolecules. This study highlights the potential importance of the humoral immune response targeting neoepitopes as well as self epitopes in shaping clinical response to immunotherapy.

Gastrointestinal Involvement in Primary Antibody Deficiencies

Primary antibody deficiencies (PADs) are the most frequent group of inborn errors of immunity. Impaired B-cell development, reduced production of immunoglobulins (mainly IgG and IgA), and specific antibodies resulting in recurrent infections are their hallmarks. Infections typically affect the respiratory tract; however, gastrointestinal involvement is also common. These include infection with Helicobacter pylori, Salmonella, Campylobacter species, Giardia, and noroviruses. Impaired IgA production also contributes to dysbiosis and thereby an increase in abundance of species with proinflammatory properties, resulting in immune system dysregulation. Dysregulation of the immune system results in a broad spectrum of non-infectious manifestations, including autoimmune, lymphoproliferative, and granulomatous complications. Additionally, it increases the risk of malignancy, which may be present in more than half of patients with PADs. Higher prevalence is often seen in monogenic causes, and gastrointestinal involvement may clinically mimic various conditions including inflammatory bowel diseases and celiac disease but possess different immunological features and response to standard treatment, which make diagnosis and therapy challenging. The spectrum of malignancies includes gastric cancer and lymphoma. Thus, non-infectious manifestations significantly affect mortality and morbidity. In this overview, we provide a comprehensive insight into the epidemiology, genetic background, pathophysiology, and clinical manifestations of infectious and non-infectious complications.

Targeting B cells and plasma cells in autoimmune diseases: From established treatments to novel therapeutic approaches

Autoimmune diseases are characterized by the recognition of self-antigens by the immune system, which leads to inflammation and tissue damage. B cells are directly and indirectly involved in the pathophysiology of autoimmunity, both via antigen-presentation to T cells and production of proinflammatory cytokines and/or autoantibodies. Consequently, B lineage cells have been identified as therapeutic targets in autoimmune diseases. B cell depleting strategies have proven beneficial in the treatment of rheumatoid arthritis (RA), systemic lupus erythematous (SLE), ANCA-associated vasculitis (AAV), multiple sclerosis (MS), and a wide range of other immune-mediated inflammatory diseases (IMIDs). However, not all patients respond to treatment or may not reach (drug-free) remission. Moreover, B cell depleting therapies do not always target all B cell subsets, such as short-lived and long-lived plasma cells. These cells play an active role in autoimmunity and in certain diseases their depletion would be beneficial to achieve disease remission. In the current review article, we provide an overview of novel strategies to target B lineage cells in autoimmune diseases, with the focus on rheumatic diseases. Both advanced therapies that have recently become available and more experimental treatments that may reach the clinic in the near future are discussed.

Cross-platform immunophenotyping of human peripheral blood mononuclear cells with four high-dimensional flow cytometry panels

Immunophenotyping using high dimensional flow cytometry is a central component of human immune system multi-omic studies. We present four high parameter flow cytometry panels for deep immunophenotyping of human peripheral blood mononuclear cells (PBMC). This set of four 25+ color panels include 64 cell surface markers to resolve broad immune compartment populations, as well as activation and memory of specific T, B, natural killer (NK), and myeloid lineages. Common lineage bridging markers are integrated into each panel to allow for inter-panel quality control through major lineage frequency verification. These panels were developed using a five laser BD Symphony A5 conventional cytometer and successfully transferred to a five laser Cytek Aurora spectral cytometer capable of acquiring the panels. Nine representative PBMC samples were stained with the four phenotyping panels and acquired on both instruments to evaluate population frequency and visual staining patterns for gating between the systems. Both instruments produced comparable high quality flow cytometry data and supported our decision to acquire samples on the spectral cytometer moving forward. This modular set of panels and instrument performance metrics provide guidelines for designing flow cytometry experiments suitable for longitudinal or cross-sectional immune profiling.

TLR7 agonism accelerates disease in a mouse model of primary Sjögren's syndrome and drives expansion of T-bet+ B cells

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by chronic inflammation of exocrine tissue, resulting in loss of tears and saliva. Patients also experience many extra-glandular disease manifestations. Treatment for pSS is palliative, and there are currently no treatments available that target disease etiology. Previous studies in our lab demonstrated that MyD88 is crucial for pSS pathogenesis in the NOD.B10Sn-H2^b (NOD.B10) pSS mouse model, although the way in which MyD88-dependent pathways become activated in disease remains unknown. Based on its importance in other autoimmune diseases, we hypothesized that TLR7 activation accelerates pSS pathogenesis. We administered the TLR7 agonist Imiquimod (Imq) or sham treatment to pre-disease NOD.B10 females for 6 weeks. Parallel experiments were performed in age and sex-matched C57BL/10 controls. Imq-treated pSS animals exhibited cervical lymphadenopathy, splenomegaly, and expansion of TLR7-expressing B cells. Robust lymphocytic infiltration of exocrine tissues, kidney and lung was observed in pSS mice following treatment with Imq. TLR7 agonism also induced salivary hypofunction in pSS mice, which is a hallmark of disease. Anti-nuclear autoantibodies, including Ro (SSA) and La (SSB) were increased in pSS mice following Imq administration. Cervical lymph nodes from Imq-treated NOD.B10 animals demonstrated an increase in the percentage of activated/memory CD4+ T cells. Finally, T-bet⁺ B cells were expanded in the spleens of Imq-treated pSS mice. Thus, activation of TLR7 accelerates local and systemic disease and promotes expansion of T-bet-expressing B cells in pSS.

Characterization of intrahepatic B cells in acute-on-chronic liver failure

Background and objectives

Acute on chronic liver failure (ACLF) is characterized by the immunologic dissonance during the prolonged pathogenic development. Both abnormal innate immune response and adaptive T-cell response have been reported in patients with ACLF; however, less is known regarding B cells in ACLF pathogenesis. Previous reports were only based on immunophenotyping of peripheral blood samples. Here, we aim to dissect liver-infiltrating B-cell subpopulation in ACLF.

Methods

Paired liver perfusate and peripheral blood were freshly collected from healthy living donors and recipients during liver transplantation. Liver tissues were obtained from patients with ACLF, cirrhosis, and healthy controls. Flow cytometry was used to characterize the phenotypic and functional alterations in intrahepatic and circulating B-cell populations from ACLF, cirrhosis, and healthy controls. The expression of CD19⁺ and CD138⁺ on liver tissues was examined by immunohistochemistry staining.

Results

In this study, we first deciphered the intrahepatic B cells subsets of patients with ACLF. We found that the ACLF liver harbored reduced fraction of naïve B cells and elevated percentage of CD27⁺CD21^- activated memory B cells (AM), CD27^-CD21^- atypical memory B cells (atMBC), CD27⁺IgD^-IgM⁺(IgM⁺ memory B cells), and CD27⁺CD38⁺⁺ plasma cells than cirrhosis and healthy controls. Moreover, these B subpopulations demonstrated enhanced activation and altered effector functions. Specifically, the ACLF liver was abundant in atMBC expressing higher CD11c and lower CD80 molecule, which was significantly correlated to alanine aminotransferase and aspartate aminotransferase. In addition, we found that intrahepatic CD27⁺CD38⁺⁺plasma cells were preferentially accumulated in ACLF, which expressed more CD273 (PD-L2) and secreted higher granzyme B and IL-10. Finally, the enriched hepatic plasma B cells were in positive association with disease severity indices including alkaline phosphatase and gamma-glutamyl transferase.

Conclusions

In this pilot study, we showed an intrahepatic B-cell landscape shaped by the ACLF liver environment, which was distinct from paired circulating B-cell subsets. The phenotypic and functional perturbation in atMBC and plasma cells highlighted the unique properties of infiltrating B cells during ACLF progression, thereby denoting the potential of B-cell intervention in ACLF therapy.

The Effect of SARS-CoV-2 Vaccination on B-Cell Phenotype in Systemic Sclerosis Patients

Objective: to assess the influence of SARS-CoV-2 mRNA vaccine on B-cell phenotypes in systemic sclerosis (SSc). Methods: peripheral blood B-cell subpopulations were evaluated before (t1) and 3 months (t3) after the second dose of vaccine in 28 SSc patients. Peripheral blood B-cell subpopulations were evaluated in 21 healthy controls (HCs) only at t1. Anti-spike IgG levels were evaluated at t3 in both cohorts. Results: SSc patients presented higher naive, double-negative, and CD21low B cells compared to HCs. IgM-memory and switched-memory B cells were lower in SSc patients than HCs. No differences in anti-spike IgG levels after vaccination were observed between SSc patients and HCs. Anti-spike IgG levels after vaccination were lower in SSc patients with increased CD21low B cells at baseline compared to SSc patients with normal CD21low B cells. A positive correlation was found between IgG levels and naive B cells. A negative linear correlation was shown between IgG levels and IgM-memory, switched-memory, double-negative, and CD21low B cells. Conclusions: SARS-CoV-2 mRNA vaccine response is normal in SSc patients not undergoing immunosuppressive therapy. The normal number of naive B cells is a positive marker of antibody response. The increased percentage of CD21low B cells represents a negative marker of antibody response.

Human T-bet governs the generation of a distinct subset of CD11chighCD21low B cells

High-level expression of the transcription factor T-bet characterizes a phenotypically distinct murine B cell population known as "age-associated B cells" (ABCs). T-bet-deficient mice have reduced ABCs and impaired humoral immunity. We describe a patient with inherited T-bet deficiency and largely normal humoral immunity including intact somatic hypermutation, affinity maturation and memory B cell formation in vivo, and B cell differentiation into Ig-producing plasmablasts in vitro. Nevertheless, the patient exhibited skewed class switching to IgG1, IgG4, and IgE, along with reduced IgG2, both in vivo and in vitro. Moreover, T-bet was required for the in vivo and in vitro development of a distinct subset of human B cells characterized by reduced expression of CD21 and the concomitantly high expression of CD19, CD20, CD11c, FCRL5, and T-bet, a phenotype that shares many features with murine ABCs. Mechanistically, human T-bet governed CD21^loCD11c^hi B cell differentiation by controlling the chromatin accessibility of lineage-defining genes in these cells: FAS, IL21R, SEC61B, DUSP4, DAPP1, SOX5, CD79B, and CXCR4. Thus, human T-bet is largely redundant for long-lived protective humoral immunity but is essential for the development of a distinct subset of human CD11c^hiCD21^lo B cells.

Alternative B Cell Differentiation During Infection and Inflammation

Long-term protective immunity to infectious disease depends on cell-mediated and humoral immune responses. Induction of a strong humoral response relies on efficient B cell activation and differentiation to long-lived plasma cells and memory B cells. For many viral or bacterial infections, a single encounter is sufficient to induce such responses. In malaria, the induction of long-term immunity can take years of pathogen exposure to develop, if it occurs at all. This repeated pathogen exposure and suboptimal immune response coincide with the expansion of a subset of B cells, often termed atypical memory B cells. This subset is present at low levels in healthy individuals as well but it is observed to expand in an inflammatory context during acute and chronic infection, autoimmune diseases or certain immunodeficiencies. Therefore, it has been proposed that this subset is exhausted, dysfunctional, or potentially autoreactive, but its actual role has remained elusive. Recent reports have provided new information regarding both heterogeneity and expansion of these cells, in addition to indications on their potential role during normal immune responses to infection or vaccination. These new insights encourage us to rethink how and why they are generated and better understand their role in our complex immune system. In this review, we will focus on recent advances in our understanding of these enigmatic cells and highlight the remaining gaps that need to be filled.

Measurement of circulating CD21-CD27- B lymphocytes in SLE patients is associated with disease activity independently of conventional serological biomarkers

Determining disease activity in systemic lupus erythematosus (SLE) patients is challenging and limited by the lack of reliable biomarkers. Abnormally activated B cells play a key role in the pathogenesis of SLE, but their measure in clinical practice is currently not recommended. Here, we studied peripheral B cells to identify a valid biomarker. We analyzed peripheral B cells in a discovery cohort of 30 SLE patients compared to 30 healthy controls (HC) using mass cytometry and unsupervised clustering analysis. The relevant B cell populations were subsequently studied by flow cytometry in a validation cohort of 63 SLE patients, 28 autoimmune diseases controls and 39 HC. Our data show an increased frequency of B cell populations with activated phenotype in SLE compared to healthy and autoimmune diseases controls. These cells uniformly lacked the expression of CD21 and CD27. Measurement of CD21⁻CD27⁻ B cells in the blood identified patients with active disease and their frequency correlated with disease severity. Interestingly, we did not observe an increase in the frequency of CD21⁻CD27⁻ B cells in patients with clinically inactive disease but with elevated conventional biomarkers (anti-dsDNA and complement levels). Accordingly, measurement of CD21⁻CD27⁻ B cells represents a robust and easily accessible biomarker to assess the activity of the disease in SLE patients.

Elevated CD21low B Cell Frequency Is a Marker of Poor Immunity to Pfizer-BioNTech BNT162b2 mRNA Vaccine Against SARS-CoV-2 in Patients with Common Variable Immunodeficiency

PURPOSE

Limited data is available on the effect of COVID-19 vaccination in immunocompromised individuals. Here, we provide the results from vaccinating a single-center cohort of patients with common variable immunodeficiency (CVID).

METHODS

In a prospective, open-label clinical trial, 50 patients with CVID and 90 age-matched healthy controls (HC) were analyzed for SARS-CoV-2 spike antibody (Ab) production after one or two doses of the Pfizer-BioNTech BNT162b2 mRNA vaccine. Additionally, in selected patients, SARS-CoV-2 spike-specific T-cells were assessed.

RESULTS

A potent vaccine-induced anti-spike-specific IgG Ab response was observed in all the HC. In contrast, only 68.3% of the CVID patients seroconverted, with median titers of specific Ab being 83-fold lower than in HC. In fact, only 4/46 patients (8.6%) of patients who were seronegative at baseline reached the threshold for an optimal response (250 U/mL). Using the EUROclass definition, patients with either a reduced proportion, but not absolute counts, of switched memory B-cells or having an increased frequency of CD21low B-cells generally generated poor vaccine responses. Overall, CVID-patients had reduced spike-specific IFN-γ positive CD4+ T cell responses 2 weeks after the second dose, compared to HC. The total CD4 and CD4 central memory cell counts correlated with humoral immunity to the vaccine.

CONCLUSIONS

CVID patients with low frequency of switched memory B-cells or an increased frequency of CD21low B-cells according to the EUROclass definition demonstrated poor responses to Pfizer-BioNTech BNT162b2 mRNA vaccination. Cellular immune responses were significantly affected, affirming that the defect in CVID is not limited to humoral immunity.

High Dimensional Immune Profiling Reveals Different Response Patterns in Active and Latent Tuberculosis Following Stimulation With Mycobacterial Glycolipids

Upon infection with Mycobacterium tuberculosis (Mtb) the host immune response might clear the bacteria, control its growth leading to latent tuberculosis (LTB), or fail to control its growth resulting in active TB (ATB). There is however no clear understanding of the features underlying a more or less effective response. Mtb glycolipids are abundant in the bacterial cell envelope and modulate the immune response to Mtb, but the patterns of response to glycolipids are still underexplored. To identify the CD45⁺ leukocyte activation landscape induced by Mtb glycolipids in peripheral blood of ATB and LTB, we performed a detailed assessment of the immune response of PBMCs to the Mtb glycolipids lipoarabinomannan (LAM) and its biosynthetic precursor phosphatidyl-inositol mannoside (PIM), and purified-protein derivate (PPD). At 24 h of stimulation, cell profiling and secretome analysis was done using mass cytometry and high-multiplex immunoassay. PIM induced a diverse cytokine response, mainly affecting antigen-presenting cells to produce both pro-inflammatory and anti-inflammatory cytokines, but not IFN-γ, contrasting with PPD that was a strong inducer of IFN-γ. The effect of PIM on the antigen-presenting cells was partly TLR2-dependent. Expansion of monocyte subsets in response to PIM or LAM was reduced primarily in LTB as compared to healthy controls, suggesting a hyporesponsive/tolerance pattern derived from Mtb infection.

CD27-CD38lowCD21low B-Cells Are Increased in Axial Spondyloarthritis

B-cells have received little attention in axial spondyloarthritis (axSpA) and for this reason their role in pathogenesis remains unclear. However, there are indications that B-cells may be involved in the disease process. Our objective was to obtain insights into the composition of the peripheral B-cell compartment of axSpA patients compared to healthy donors (HD) and patients with primary Sjögren’s syndrome (pSS), a typical B-cell-associated autoimmune disease. Special emphasis was given to CD27-negative B-cells expressing low levels of CD21 (CD21^low B-cells), since this subset is implicated in autoimmune diseases with strong involvement of B-cells. Transitional B-cells (CD38^hi) were excluded from the analysis of the CD27^-CD21^low B-cell compartment. This study included 45 axSpA patients, 20 pSS patients and 30 HDs. Intriguingly, compared to HDs the frequency of CD27^-CD38^lowCD21^low B-cells was significantly elevated in both axSpA and pSS patients (P<0.0001 for both comparisons). The frequency of CD27^-CD38^lowCD21^low B-cells expressing the activation-induced immune markers T-bet and CD11c was decreased in axSpA patients compared to HDs. A higher proportion of CD27^-CD38^lowCD21^low B-cells expressed the chemokine receptor CXCR3 in axSpA compared to HDs, suggestive for active involvement of these cells in an inflammatory process. The frequency of CD27^-CD38^lowCD21^low B-cells in axSpA patients correlated positively with age and erythrocyte sedimentation rate. Furthermore, axSpA patients with extra-skeletal manifestations (ESM) showed increased frequencies of CD27^-CD38^lowCD21^low B-cells compared to patients without ESM. In conclusion, our findings are suggestive of active B-cell involvement in the pathogenesis of axSpA, against prevailing dogma.

The Multiple Roles of B Cells in the Pathogenesis of Sjögren's Syndrome

Primary Sjögren’s syndrome (pSS) is a chronic autoimmune disease characterized by lymphocytic infiltration and tissue destruction of exocrine glands such as salivary glands. Although the formation of ectopic lymphoid tissue in exocrine glands and overproduction of autoantibodies by autoreactive B cells highlight the critical involvement of B cells in disease development, the precise roles of various B cell subsets in pSS pathogenesis remain partially understood. Current studies have identified several novel B cell subsets with multiple functions in pSS, among which autoreactive age-associated B cells, and plasma cells with augmented autoantibody production contribute to the disease progression. In addition, tissue-resident Fc Receptor-Like 4 (FcRL4)⁺ B cell subset with enhanced pro-inflammatory cytokine production serves as a key driver in pSS patients with mucosa-associated lymphoid tissue (MALT)-lymphomas. Recently, regulatory B (Breg) cells with impaired immunosuppressive functions are found negatively correlated with T follicular helper (Tfh) cells in pSS patients. Further studies have revealed a pivotal role of Breg cells in constraining Tfh response in autoimmune pathogenesis. This review provides an overview of recent advances in the identification of pathogenic B cell subsets and Breg cells, as well as new development of B-cell targeted therapies in pSS patients.

Atypical phenotype and response of B cells in patients with seropositive rheumatoid arthritis

Patients with rheumatoid arthritis (RA) may be classified as seropositive or seronegative according to the presence of autoantibodies. An abnormal B cell phenotype and function could be one of the main components of the immunopathology of seropositive patients; however, there is little information regarding B cell defects in these patients. This study shows a broad characterization of the B cell phenotype and function in patients with seropositive RA. We focused mainly on the evaluation of subsets, the expression of modulatory molecules of cell activation (CD22, FcɣRIIb and FcµR), calcium mobilization, global tyrosine phosphorylation, expression of activation markers, cytokine and immunoglobulin (Ig) production, proliferation and the in-vitro generation of plasma cells. Increased frequency of CD27^- IgM^- IgD^- and CD21^- B cells was observed in patients with seropositive RA compared with healthy donors (HD). Decreased expression of CD22 was primarily found in memory B cells of patients with RA regardless of seropositivity. B cells from seropositive patients exhibited normal proliferation, calcium mobilization kinetics and global tyrosine phosphorylation, but showed an increased frequency of CD86⁺ B cells compared with HD. B cells of seropositive patients secrete less interleukin-10 after in-vitro activation and showed a decreased frequency of plasma cell differentiation and IgM production compared with HD. Our data indicate that patients with seropositive RA have an increased frequency of atypical B cell populations previously associated with chronic activation and antigen exposure. This may result in the observed low responsiveness of these cells in vitro.

Jo-1 autoantigen-specific B cells are skewed towards distinct functional B cell subsets in anti-synthetase syndrome patients

Background

Anti-Jo-1 autoantibodies which recognize histidyl-tRNA synthetase identify patients with the rare rheumatologic disease, anti-histidyl-tRNA synthetase syndrome (Jo-1 ARS), a phenotypically distinct subset of idiopathic inflammatory myopathies (IIM). Jo-1-binding B cells (JBCs) are implicated in disease pathogenesis, yet they have not been studied directly. We therefore aimed to characterize JBCs to better understand how they expand and function in Jo-1 ARS.

Methods

We enrolled 10 IIM patients diagnosed with Jo-1 ARS, 4 patients with non-Jo-1 IIM, and 8 age- and sex-matched healthy controls. We phenotypically characterized peripheral blood mononuclear cells (PBMCs) ex vivo using flow cytometry to define the B cell subsets in which JBCs reside. We further tested their ability to differentiate into antibody-secreting cells following stimulation in vitro.

Results

The majority of JBCs were IgM⁺ (not class-switched). Compared to non-JBCs in the same donors, JBCs contained a higher percentage of autoimmune-prone CD21^lo cells and were increased in the CD21^lo IgM⁺ IgD⁻ CD27⁺ memory subset relative to healthy donor B cells. Whereas non-JBCs were present in the anergic B_ND B cell subset, JBCs were nearly absent from this compartment. JBCs were detected among plasmablasts in some donors, but a reduced frequency of JBCs differentiated into CD38^hi24⁻ plasmablasts compared to non-JBCs present in the same wells following in vitro stimulation.

Conclusions

JBCs are enriched for autoimmune-prone CD21^lo B cells, some of which exhibit a memory phenotype in the peripheral repertoire of Jo-1 ARS patients. JBCs undergo limited class switch and show reduced capacity to differentiate into antibody-secreting cells. This suggests complex B cell biology exists beyond class-switched cells that differentiate to secrete anti-Jo-1 autoantibody (i.e., what is captured through serum autoantibody studies). New Jo-1 ARS therapies should thus ideally target non-class-switched JBCs in addition to those that have undergone IgG class-switching to most effectively block cross-talk with autoreactive T cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-020-02412-8.