Long-lived plasma cells in autoimmunity: lessons from B-cell depleting therapy

Autoimmune effector mechanisms associated with a defective immunosuppressive axis in immune thrombocytopenia (ITP)

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by an isolated thrombocytopenia and variable phenotype as some patients suffer no bleeding whilst others have bleeding from mild to severe, which may be fatal. This variability probably reflects the disease's complex pathophysiology; a dysregulated hyperreactive immune effector cell response involving the entire adaptive immune system (e.g. B and T cell subsets) that leads to platelet and megakaryocyte (MK) destruction. It appears that these effector responses are due to a breakdown in immune tolerance, and this is characterized by defects in several immunosuppressive cell types. These include defective T regulatory cells (Tregs), B regulatory cells (Bregs) and Myeloid-derived suppressor cells (MDSC), all of which are all intimately associated with antigen presenting cells (APC) such as dendritic cells (DC). The loss of this immunosuppressive axis allows for the activation of unchecked autoreactive T cells and B cells, leading to the development of autoantibodies and cytotoxic T cells (CTL), which can directly destroy platelets in the periphery and inhibit MK platelet production in the bone marrow (BM). This review will focus on the effector cell mechanisms in ITP and highlight the defective immunosuppressive axis that appears responsible for this platelet-specific immune hyperreactivity.

B cell dysregulation and depletion therapy in primary membranous nephropathy: Prospects and potential challenges

B cells are crucial to the humoral immune response, originating in the bone marrow and maturing in the spleen and lymph nodes. They primarily function to protect against a wide range of infections through the secretion of antibodies. The role of B cells in primary membranous nephropathy (PMN) has gained significant attention, especially following the discovery of various autoantibodies that target podocyte antigens and the observed positive outcomes from B cell depletion therapy. Increasing evidence points to the presence of abnormal B cell subsets and functions in MN. B cells have varied roles during the different stages of disease onset, progression, and relapse. Initially, B cells facilitate self-antigen presentation, activate effector T cells, and initiate cellular immunity. Subsequently, the disruption of both central and peripheral immune tolerance results in the emergence of autoreactive B cells, with strong germinal center responses as a major source of MN autoantibodies. Additionally, critical B cell subsets, including Bregs, memory B cells, and plasma cells, play roles in the immune dysregulation observed in MN, assisting in predicting disease recurrence and guiding management strategies for MN. This review offers a detailed overview of research advancements on B cells and elucidates their pathological roles in MN.

An updated management approach of Pompe disease patients with high-sustained anti-rhGAA IgG antibody titers: experience with bortezomib-based immunomodulation

Introduction

High sustained anti-rhGAA antibody titers (HSAT; ≥12,800) are directly linked to reduced efficacy of enzyme replacement therapy (ERT) and subsequent clinical deterioration in infantile-onset Pompe disease (IOPD). We have previously demonstrated the safety and effectiveness of a bortezomib-based immune-tolerance induction (ITI) regimen (bortezomib, rituximab, methotrexate, and IVIG) in eliminating HSAT.

Methods

Here, we describe two IOPD cases (patients 6 and 8) who developed HSAT at 8 and 10 weeks on ERT despite transient low-dose methotrexate ITI administration in the ERT-naïve setting and were treated with a bortezomib-based ITI regimen, and we compare their courses to a series of six historical patients (patients 1-5, and 7) with a similar presentation who exemplify our evolving approach to treatment.

Results

In total, patients 6 and 8 received 16 and 8 doses of bortezomib (4 doses=1 cycle) respectively reducing titers from 25,600 to seronegative, but differences in the course of their therapy were instructive regarding the optimal approach to initial treatment of HSAT; specifically, patient 6 was treated initially with only a single course of bortezomib rescue therapy, while patient 8 received two back-to-back courses. Patient 8 received IVIG therapy throughout the immunosuppression whereas patient 6 received IVIG therapy and was switched to subcutaneous IgG replacement. Patient 6 had a transient reduction in anti-rhGAA antibodies, after receiving a single initial cycle of bortezomib, but had a recurrence of high anti-rhGAA antibody titer after 160 weeks that required 3 additional cycles of bortezomib to ultimately achieve tolerance. In contrast, patient 8 achieved tolerance after being given two consecutive cycles of bortezomib during their initial treatment and had B cell recovery by week 54. Since the reduction in anti-rhGAA antibodies, both patients are doing well clinically, and have decreasing ALT, AST, and CK. No major infections leading to interruption of treatment were observed in either patient. The bortezomib-based ITI was safe and well-tolerated, and patients continue to receive ERT at 40 mg/kg/week.

Discussion

These case studies and our previous experience suggest that to achieve an effective reduction of anti-rhGAA antibodies in the setting of HSAT, bortezomib should be initiated at the earliest sign of high anti-rhGAA antibodies with a minimum of two consecutive cycles as shown in the case of patient 8. It is important to note that, despite initiation of ERT at age 2.3 weeks, patient 8 quickly developed HSAT. We recommend close monitoring of anti-rhGAA antibodies and early intervention with ITI as soon as significantly elevated anti-rhGAA antibody titers are noted.

From neglect to spotlight: the underappreciated role of B cells in cutaneous inflammatory diseases

The skin, covering our entire body as its largest organ, manifests enormous complexities and a profound interplay of systemic and local responses. In this heterogeneous domain, B cells were considered strangers. Yet, recent studies have highlighted their existence in the skin and their distinct role in modulating cutaneous immunity across various immune contexts. Accumulating evidence is progressively shedding light on the significance of B cells in maintaining skin health and in skin disorders. Herein, we integrate current insights on the systemic and local contributions of B cells in three prevalent inflammatory skin conditions: Pemphigus Vulgaris (PV), Systemic Lupus Erythematosus (SLE), and Atopic Dermatitis (AD), underscoring the previously underappreciated importance of B cells within skin immunity. Moreover, we address the potential adverse effects of current treatments used for skin diseases, emphasizing their unintentional consequences on B cells. These comprehensive approaches may pave the way for innovative therapeutic strategies that effectively address the intricate nature of skin disorders.

Myasthenia gravis: the changing treatment landscape in the era of molecular therapies

Myasthenia gravis (MG) is an autoimmune disorder that affects the neuromuscular junction, leading to muscle weakness and fatigue. MG is caused by antibodies against the acetylcholine receptor (AChR), the muscle-specific kinase (MuSK) or other AChR-related proteins that are expressed in the postsynaptic muscle membrane. The standard therapeutic approach for MG has relied on acetylcholinesterase inhibitors, corticosteroids and immunosuppressants, which have shown good efficacy in improving MG-related symptoms in most people with the disease; however, these therapies can carry a considerable burden of long-term adverse effects. Moreover, up to 15% of individuals with MG exhibit limited or no response to these standard therapies. The emergence of molecular therapies, including monoclonal antibodies, B cell-depleting agents and chimeric antigen receptor T cell-based therapies, has the potential to revolutionize the MG treatment landscape. This Review provides a comprehensive overview of the progress achieved in molecular therapies for MG associated with AChR antibodies and MuSK antibodies, elucidating both the challenges and the opportunities these therapies present to the field. The latest developments in MG treatment are described, exploring the potential for personalized medicine approaches.

Therapeutic Outcomes and Electrophysiological Biomarkers in Anti-Myelin-Associated Glycoprotein Neuropathy: A Multicenter Cohort Study in South Korea

BACKGROUND AND PURPOSE

Unlike other immune-mediated neuropathies, anti-myelin-associated glycoprotein (MAG) neuropathy is often refractory to immunotherapy. It is necessary to compare the relative efficacies of various immunotherapies and develop objective biomarkers in order to optimize its clinical management.

METHODS

This study recruited 91 patients with high anti-MAG antibody titers from 7 tertiary hospitals in South Korea. We analyzed the baseline characteristics, therapeutic outcomes, and nerve conduction study (NCS) findings of 68 patients and excluded 23 false positive cases.

RESULTS

The rate of positive responses to treatment was highest using zanubrutinib (50%) and rituximab (36.4%), followed by corticosteroids (16.7%), immunosuppressants (9.5%), intravenous immunoglobulin (5%), and plasma exchange (0%). Disability and weakness were significantly associated with multiple NCS parameters at the time of diagnosis, especially distal compound muscle action potential (CMAP) amplitudes. Moreover, the longitudinal trajectory of the average CMAP amplitudes paralleled the clinical courses, with a 16.2 percentile decrease as an optimal cutoff for predicting a clinical exacerbation (area under the receiver operating characteristic curve=0.792).

CONCLUSIONS

Our study supports the use of NCS as an objective marker for estimating disease burden and tracking clinical changes in patients with anti-MAG neuropathy. We have described the beneficial effects of rituximab and a new drug, zanubrutinib, compared with conventional immunotherapies.

An interleukin 6 responsive plasma cell signature is associated with disease progression in systemic sclerosis interstitial lung disease

Systemic sclerosis (SSc) interstitial lung disease (ILD) is among the leading causes of SSc-related morbidity and mortality. Tocilizumab (TCZ, anti-IL6RA) has demonstrated a reduced rate of pulmonary function decline in two phase 2/3 trials (faSScinate and focuSSced) in SSc-ILD patients. We performed transcriptome analysis of skin biopsy samples collected in the studies to decipher gene networks that were potentially associated with clinical responses to TCZ treatment. One module correlated with disease progression showed pharmacodynamic changes with TCZ treatment, and was characterized by plasma cell (PC) genes. PC signature gene expression levels were also significantly increased in both fibrotic SSc and IPF lungs compared to controls. scRNAseq analyses confirmed that PC signature genes were co-expressed in CD38 and CD138 expressing PC subsets in SSc lungs. These data provide insights into the potential role of PC in disease progression and mechanisms of action of TCZ in fibrotic interstitial lung diseases.

Off-label use of rituximab in patients with systemic lupus erythematosus with extrarenal disease activity: a retrospective study and literature review

Introduction

Off-label rituximab is commonly used for patients with systemic lupus erythematosus (SLE) with extrarenal disease activity.

Methods

The outcomes and tolerability of rituximab in adult patients with non-renal SLE treated at our hospital from 2013 to 2020 were described. Patients were followed-up until December 2021. Data were retrieved from electronic medical records. Response was classified into complete, partial or no response according to the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI 2 K)-based definitions.

Results

A total of 44 cycles were administered to 33 patients. Median age was 45 years and 97% were female. Median follow-up was 5.9 years (IQR 3.7-7.2). The most frequent symptoms that motivated rituximab use were thrombocytopenia (30.3%), arthritis (30.3%), neurological manifestations (24.2%) and cutaneous lupus (15.2%). After most treatment cycles a partial remission was achieved. The median SLEDAI-2 K score declined from 9 (IQR 5-13) to 1.5 (IQR 0-4) (p < 0.00001). The median number of flares significantly declined after receiving rituximab. Platelet counts significantly improved in patients with thrombocytopenia and patients with skin disorders or neurological manifestations also had a partial or complete response. Only 50% of patients with a predominant joint involvement had either a complete or a partial response. The median time to relapse after the first cycle was 1.6 years (95% CI, 0.6-3.1). Anti-dsDNA levels decreased significantly after rituximab from a median of 64.3 (IQR 12-373.9) to 32.7 (IQR 10-173), p = 0.00338. The most frequent adverse events were infusion-related reactions (18.2%) and infections (57.6%). All patients needed further treatment to maintain remission or to treat new flares.

Conclusion

A partial or complete response was documented after most rituximab cycles in patients with non-renal SLE. Patients with thrombocytopenia, neurolupus, and cutaneous lupus had better response than those with a predominant joint involvement.

A Phase I Trial of SYK Inhibition with Fostamatinib in the Prevention and Treatment of Chronic Graft-Versus-Host Disease

Despite the exciting advancement of novel therapies, chronic graft-versus-host disease (cGVHD) remains the most common cause of non-relapse mortality after allogeneic hematopoietic stem cell transplantation (HCT). Frontline treatment of cGVHD involves systemic steroids, which are associated with significant morbidities. We previously found that inhibition of spleen tyrosine kinase (SYK) with fostamatinib preferentially eradicated aberrantly activated B cells in both ex vivo studies of cGVHD patient B cells, as well as in vivo mouse studies. These and other preclinical studies implicated hyper-reactive B-cell receptor signaling and increased SYK expression in the pathogenesis of cGVHD and compelled this first in-human allogeneic HCT clinical trial. We investigated the safety and efficacy of the oral SYK inhibitor, fostamatinib, for both the prevention and treatment of cGVHD. The primary objective was to evaluate the safety of fostamatinib and determine its maximum tolerated dose in the post-HCT setting. Secondary objectives included assessing the efficacy of fostamatinib in preventing and treating cGVHD, as well as examining alterations in B-cell compartments with treatment. This was a single-institution phase I clinical trial that evaluated the use of fostamatinib in allogeneic HCT patients before the development of cGVHD or at the time of steroid-refractory cGVHD (SR-cGVHD). Patients received fostamatinib at one of three dose levels using a continual reassessment algorithm to determine the maximum tolerated dose. Multiparameter flow cytometry was used to evaluate changes in B cell subpopulations over the first year of treatment with fostamatinib. Nineteen patients were enrolled in this phase I trial, with 5 in the prophylaxis arm and 14 in the therapeutic arm. One patient (5%) required discontinuation of therapy for a dose-limiting toxicity. At a median follow-up of over 3 years, no patients had cancer relapse while on fostamatinib treatment, and recurrent malignancy was observed in 1 patient 2 years after the end of therapy. In the prophylaxis arm, 1 of 5 patients (20%) developed cGVHD while on fostamatinib. In the therapeutic arm, the overall response rate was 77%, with a complete response rate of 31%. The median duration of response was 19.3 months and the 12-month failure-free survival was 69% (95% confidence interval, 48-100). Patients were able to reduce their steroid dose by a median of 80%, with 73% remaining on a lower dose at 1 year compared to baseline. There was an early reduction in the proportion of IgD-CD38hi plasmablast-like cells with fostamatinib treatment, particularly in those SR-cGVHD patients who had an eventual response. B-cell reconstitution was not significantly impacted by fostamatinib therapy after allogeneic HCT. Fostamatinib featured a favorable safety profile in the post-HCT setting. Our data suggests an early efficacy signal that was associated with effects on expected cell targets in both the prophylaxis and treatment of cGVHD, providing rationale for a phase II investigation.

Immune Mechanisms in Epileptogenesis: Update on Diagnosis and Treatment of Autoimmune Epilepsy Syndromes

Seizures and epilepsy can result from various aetiologies, yet the underlying cause of several epileptic syndromes remains unclear. In that regard, autoimmune-mediated pathophysiological mechanisms have been gaining attention in the past years and were included as one of the six aetiologies of seizures in the most recent classification of the International League Against Epilepsy. The increasing number of anti-neuronal antibodies identified in patients with encephalitic disorders has contributed to the establishment of an immune-mediated pathophysiology in many cases of unclear aetiology of epileptic syndromes. Yet only a small number of patients with autoimmune encephalitis develop epilepsy in the proper sense where the brain transforms into a state where it will acquire the enduring propensity to produce seizures if it is not hindered by interventions. Hence, the term autoimmune epilepsy is often wrongfully used in the context of autoimmune encephalitis since most of the seizures are acute encephalitis-associated and will abate as soon as the encephalitis is in remission. Given the overlapping clinical presentation of immune-mediated seizures originating from different aetiologies, a clear distinction among the aetiological entities is crucial when it comes to discussing pathophysiological mechanisms, therapeutic options, and long-term prognosis of patients. Moreover, a rapid and accurate identification of patients with immune-mediated epilepsy syndromes is required to ensure an early targeted treatment and, thereby, improve clinical outcome. In this article, we review our current understanding of pathogenesis and critically discuss current and potential novel treatment options for seizures and epilepsy syndromes of underlying or suspected immune-mediated origin. We further outline the challenges in proper terminology.

Selective Silencing of Disease-Associated B Lymphocytes from Hashimoto's Thyroiditis Patients by Chimeric Protein Molecules

Hashimoto's thyroiditis is one of the most common endocrine disorders, affecting up to 20% of the adult population. No treatment or prevention exists except hormonal substitution for hypothyroidism. We hypothesize that it may be possible to selectively suppress anti-thyroglobulin (Tg) IgG antibody-producing B lymphocytes from HT patients by a chimeric protein molecule containing a monoclonal antibody specific for the human inhibitory receptor CR1, coupled to peptide epitopes derived from Tg protein. We expect that this treatment will down-regulate B-cell autoreactivity by delivering a strong inhibitory signal. Three peptides-two epitope-predicted ones derived from Tg and another irrelevant peptide-were synthesized and then coupled with monoclonal anti-human CR1 antibody to construct three chimeric molecules. The binding to CD35 on human B cells and the effects of the chimeric constructs on PBMC and TMC from patients with HT were tested using flow cytometry, ELISpot assay, and immunoenzyme methods. We found that after the chemical conjugation, all chimeras retained their receptor-binding capacity, and the Tg epitopes could be recognized by anti-Tg autoantibodies in the patients' sera. This treatment downregulated B-cell autoreactivity and cell proliferation, inhibited Tg-specific B-cell differentiation to plasmablasts and promoted apoptosis to the targeted cells. The treatment of PBMCs from HT patients with Tg-epitope-carrying chimeric molecules affects the activity of Tg-specific autoreactive B lymphocytes, delivering to them a strong suppressive signal.

Autoantibodies as Biomarker and Therapeutic Target in Systemic Sclerosis

Systemic sclerosis (SSc) is a rare connective tissue disorder characterized by immune dysregulation evoking the pathophysiological triad of inflammation, fibrosis and vasculopathy. In SSc, several alterations in the B-cell compartment have been described, leading to polyclonal B-cell hyperreactivity, hypergammaglobulinemia and autoantibody production. Autoreactive B cells and autoantibodies promote and maintain pathologic mechanisms. In addition, autoantibodies in SSc are important biomarkers for predicting clinical phenotype and disease progression. Autoreactive B cells and autoantibodies represent potentially promising targets for therapeutic approaches including B-cell-targeting therapies, as well as strategies for unselective and selective removal of autoantibodies. In this review, we present mechanisms of the innate immune system leading to the generation of autoantibodies, alterations of the B-cell compartment in SSc, autoantibodies as biomarkers and autoantibody-mediated pathologies in SSc as well as potential therapeutic approaches to target these.

Systemic lupus erythematosus-complicating immune thrombocytopenia: From pathogenesis to treatment

Immune thrombocytopenia (ITP) is a common hematological manifestation of systemic lupus erythematosus (SLE). The heterogeneity of its clinical characteristics and therapeutic responses reflects a complex pathogenesis. A better understanding of its pathophysiological mechanisms and employing an optimal treatment regimen is therefore important to improve the response rate and prognosis, and avoid unwanted outcomes. Besides glucocorticoids, traditional immunosuppressants (i.e. cyclosporine, mycophenolate mofetil) and intravenous immunoglobulins, new therapies are emerging and promising for the treatment of intractable SLE-ITP, such as thrombopoietin receptor agonists (TPO-RAs), platelet desialylation inhibitors(i.e. oseltamivir), B-cell targeting therapy(i.e. rituximab, belimumab), neonatal Fc receptor(FcRn) inhibitor, spleen tyrosine kinase(Syk) inhibitor and Bruton tyrosine kinase(BTK) inhibitor et al., although more rigorous randomized controlled trials are needed to substantiate their efficacy. In this review, we update our current knowledge on the pathogenesis and treatment of SLE-ITP.

Glucocorticoid discontinuation in patients with SLE with prior severe organ involvement: a single-center retrospective analysis

Objective

Long-term glucocorticoid use in SLE may have significant side effects; however, glucocorticoid discontinuation is occasionally associated with disease flare-ups. Therefore, we evaluated the risk factors for disease flares and the flare rate on glucocorticoid tapering in patients with prior severe organ involvement.

Methods

Data of patients with SLE with glucocorticoid tapering at our institution were retrospectively analysed. We divided the patients by the presence of prior severe organ involvement and compared flare rates after glucocorticoid discontinuation. Furthermore, we determined risk factors for flares after glucocorticoid discontinuation.

Results

In total, 309 patients with SLE were screened, 73 of whom met the inclusion criteria; 49 were classified as SLE with prior severe organ involvement. No significant differences were noted in the 52-week flare rate after glucocorticoid discontinuation between patients with and without prior severe organ involvement (16.7% vs 18.2%, p=1.0). Hypocomplementaemia, elevated anti-dsDNA antibody titres more than twice the upper limit of the laboratory reference range, positive anti-Smith/anti-ribonucleoprotein antibody, and use of any immunosuppressant on the day of glucocorticoid discontinuation were negatively associated with flare-free remission.

Conclusions

Glucocorticoid discontinuation after gradual tapering can often be achieved in patients with SLE, even with prior severe organ involvement, especially when the disease is clinically and serologically stable.

Single-Cell Technologies for the Study of Antibody-Secreting Cells

Antibody-secreting cells (ASC), plasmablasts and plasma cells, are terminally differentiated B cells responsible for large-scale production and secretion of antibodies. ASC are derived from activated B cells, which may differentiate extrafollicularly or form germinal center (GC) reactions within secondary lymphoid organs. ASC therefore consist of short-lived, poorly matured plasmablasts that generally secrete lower-affinity antibodies, or long-lived, highly matured plasma cells that generally secrete higher-affinity antibodies. The ASC population is responsible for producing an immediate humoral B cell response, the polyclonal antibody repertoire, as well as in parallel building effective humoral memory and immunity, or potentially driving pathology in the case of autoimmunity. ASC are phenotypically and transcriptionally distinct from other B cells and further distinguishable by morphology, varied lifespans, and anatomical localization. Single cell analyses are required to interrogate the functional and transcriptional diversity of ASC and their secreted antibody repertoire and understand the contribution of individual ASC responses to the polyclonal humoral response. Here we summarize the current and emerging functional and molecular techniques for high-throughput characterization of ASC with single cell resolution, including flow and mass cytometry, spot-based and microfluidic-based assays, focusing on functional approaches of the secreted antibodies: specificity, affinity, and secretion rate.

Abnormalities of bone marrow B cells and plasma cells in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an autoantibody-mediated hemorrhagic disorder in which B cells play an essential role. Previous studies have focused on peripheral blood (PB), but B cells in bone marrow (BM) have not been well characterized. We aimed to explore the profile of B-cell subsets and their cytokine environments in the BM of patients with ITP to further clarify the pathogenesis of the disease. B-cell subpopulations and their cytokine/chemokine receptors were detected by using flow cytometry. Plasma concentrations of cytokines/chemokines were measured by using enzyme-linked immunosorbent assay. Messenger RNA levels of B cell-related transcription factors were determined by using quantitative polymerase chain reaction. Regulatory B cell (Breg) function was assessed by quantifying their inhibitory effects on monocytes and T cells in vitro. Decreased proportions of total B cells, naive B cells, and defective Bregs were observed in patients with ITP compared with healthy controls (HCs), whereas an elevated frequency of long-lived plasma cells was found in BM of autoantibody-positive patients. No statistical difference was observed in plasmablasts or in short-lived plasma cells between patients with ITP and HCs. The immunosuppressive capacity of BM Bregs from patients with ITP was considerably weaker than HCs. An in vivo study using an active ITP murine model revealed that Breg transfusion could significantly alleviate thrombocytopenia. Moreover, overactivation of CXCL13-CXCR5 and BAFF/APRIL systems were found in ITP patient BM. Taken together, B-cell subsets in BM were skewed toward a proinflammatory profile in patients with ITP, suggesting the involvement of dysregulated BM B cells in the development of the disease.

Efficacy, safety and immunological profile of combining rituximab with belimumab for adults with persistent or chronic immune thrombocytopenia: results from a prospective phase 2b trial

B-cell activating factor may be involved in the failure of B-cell depleting therapy with rituximab in immune thrombocytopenia (ITP) by promoting the emergence of splenic long-lived plasma cells. From results obtained in mouse models, we hypothesized that combining rituximab with sequential injections of belimumab could increase the rate of response at one year in patients with persistent or chronic ITP by preventing the emergence of these long-lived plasma cells. The study was a single-center, single arm, prospective phase 2b trial (RITUX-PLUS, NCT03154385) investigating the safety and efficacy of rituximab given at a fixed dose of 1,000 mg, two weeks apart, combined with five infusions of belimumab, 10 mg/kg at week 0 (W0)+2 days, W2+2 days, W4, W8 and W12 for adults with primary persistent or chronic ITP. The primary endpoint was the total number of patients achieving an overall response (complete response + response) at W52 according to a standard definition. In total, 15 non-splenectomized adults, nine (60%) with persistent IPT and six (40%) with chronic ITP, were included. No severe adverse event, infection, or severe hypogammaglobulinemia was observed. Thirteen patients achieved an initial overall response. At W52, 12 (80%) patients achieved an overall response, including ten (66.7%) with complete response. When compared with a cohort of patients receiving rituximab alone, the kinetics of B-cell repopulation appeared similar, but the number of circulating T follicular helper cells was significantly decreased with belimumab combination therapy. Combining rituximab and belimumab seems a promising strategy in ITP, with high efficacy and acceptable safety.

Update on biologic therapies for juvenile idiopathic arthritis-associated uveitis

Juvenile idiopathic arthritis (JIA) is the most common rheumatic disease of childhood, and juvenile idiopathic associated uveitis (JIA-U) is the most frequently noted extra-articular manifestation. JIA-U can present asymptomatically and lead to ocular complications, so regular screening and monitoring are needed to prevent potentially sight-threatening sequelae. Topical glucocorticoids such as prednisolone acetate are usually the first line of treatment for anterior uveitis associated with JIA-U, but long-term use may be associated with cataract, ocular hypertension and glaucoma. Disease modifying anti-rheumatic drugs (DMARDs) such as methotrexate allow tapering of the corticosteroids to prevent long-term complications. Biologic therapies have been increasingly used as targeted therapies for JIA-U, particularly monoclonal antibodies targeting the proinflammatory cytokine TNF-α such as adalimumab and infliximab. One recent, multicenter, prospective, randomized clinical trial provided evidence of the efficacy of adalimumab with methotrexate for JIA-U compared to methotrexate alone. Another clinical trial studying the interleukin-6 inhibitor tocilizumab for JIA-U showed promise in tapering topical corticosteroids. Additionally, JAK inhibitors are emerging biologic therapies for JIA-U in patients refractory to TNF-α inhibitors, with a clinical trial assessing the efficacy of baricitinib for JIA-U underway. While clinical trials on these novel biologics are limited, further investigation of these agents may provide additional therapeutic options for JIA-U.

Daratumumab therapy for post-HSCT immune-mediated cytopenia: experiences from two pediatric cases and review of literature

Background

Immune-mediated cytopenias (AIC) are challenging complications following allogeneic hematopoietic stem cell transplantation (HSCT). While broad-acting immunosuppressive agents like corticosteroids are often standard of care, several novel therapies which target specific immunological pathways have recently been developed and provide hope for patients with steroid-refractory courses and may limit long-term toxicity. The successful off-label use of the plasma cell depleting anti-CD38 antibody daratumumab was published in several case reports, suggesting efficacy, i.e., in patients with antibody-mediated AIC refractory to previous B cell depletion. We want to share our experience with two children, whom we treated with daratumumab, including one fatal course with uncontrolled disease. Given the absence of substantial data from HSCT registries or prospective trials, we furthermore provide a critical review of the literature on daratumumab treatment of AIC.

Case presentations

Patient 1 (P1), an 11-year-old girl with lipopolysaccharide-responsive and beige-like anchor protein (LRBA) deficiency who developed immune-mediated thrombocytopenia (AIT) from day +58 after HSCT, showed a complete response to daratumumab after the fourth of six total daratumumab doses. She remains transfusion independent for over a year of follow-up. Previously, her thrombocytopenia was refractory to corticosteroids, rituximab, intravenous immunoglobulins (IVIG), eltrombopag, cyclosporine A, and sirolimus. Patient 2 (P2), a 6-year-old boy with CD40 ligand (CD40L) deficiency, developed both AIT and hemolytic anemia (AIHA) after HSCT on days +58 and +83, respectively, and was also treated with daratumumab after being previously refractory to prednisolone, rituximab, and IVIG. Yet, he did neither respond to daratumumab nor the concomitantly administered methyprednisolone pulse, plasmapheresis, and eculizumab and succumbed due to refractory disease.

Conclusion

Reviewing the literature on the use of daratumumab for refractory AIC post-HSCT, we consider daratumumab a promising agent for this life-threatening disorder: ten of the twelve patients reached transfusion independency in the literature. However, treatment failures are likely to be underreported. Thus, controlled trials are needed to explore the safety and efficacy of daratumumab in this rare post-HSCT complication.

The Successful Treatment of a Case of HCV-associated Cryoglobulinemic Glomerulonephritis with Rituximab, Direct-acting Antiviral Agents, Plasmapheresis and Long-term Steroid Despite Serologically Persistent Cryoglobulinemia

Novel treatments with rituximab or direct-acting antiviral agents (DAAs) were expected to improve the clinical outcomes of hepatitis C virus (HCV)-associated cryoglobulinemia in the last decade. Recently, however, persistent cases of cryoglobulinemia have been reported, and the ideal approach to treating such cases has not been established. We herein report a case of the successful treatment of HCV-associated cryoglobulinemic glomerulonephritis with rituximab, DAAs, occasional plasmapheresis and long-term steroid, with the patient's renal function and proteinuria improving over the long term despite serologically persistent cryoglobulinemia. This case suggests the efficacy of combination treatment with rituximab, DAAs, occasional plasmapheresis and long-term steroid for persistent cryoglobulinemia.

P2Y2 receptor antagonism resolves sialadenitis and improves salivary flow in a Sjögren's syndrome mouse model

OBJECTIVE

Sjögren's syndrome (SS) is a chronic autoimmune exocrinopathy characterized by lymphocytic infiltration of the salivary and lacrimal glands and decreased saliva and tear production. Previous studies indicate that the G protein-coupled P2Y₂ nucleotide receptor (P2Y₂R) is upregulated in numerous models of salivary gland inflammation (i.e., sialadenitis), where it has been implicated as a key mediator of chronic inflammation. Here, we evaluate both systemic and localized P2Y₂R antagonism as a means to resolve sialadenitis in the NOD.H-2^h4,IFNγ^-/-,CD28^-/- (NOD.H-2^h4 DKO) mouse model of SS.

DESIGN

Female 4.5 month old NOD.H-2^h4 DKO mice received daily intraperitoneal injections for 10 days of the selective P2Y₂R antagonist, AR-C118925, or vehicle-only control. Single-dose localized intraglandular antagonist delivery into the Wharton's duct was also evaluated. Carbachol-induced saliva was measured and then submandibular glands (SMGs) were isolated and either fixed and paraffin-embedded for H&E staining, homogenized for RNA isolation or dissociated for flow cytometry analysis.

RESULTS

Intraperitoneal injection, but not localized intraglandular administration, of AR-C118925 significantly enhanced carbachol-induced salivation and reduced lymphocytic foci and immune cell markers in SMGs of 5 month old NOD.H-2^h4 DKO mice, compared to vehicle-injected control mice. We found that B cells represent the primary immune cell population in inflamed SMGs of NOD.H-2^h4 DKO mice that express elevated levels of P2Y₂R compared to C57BL/6 control mice. We further demonstrate a role for P2Y₂Rs in mediating B cell migration and the release of IgM.

CONCLUSION

Our findings suggest that the P2Y₂R represents a novel therapeutic target for the treatment of Sjögren's syndrome.

Escape from X chromosome inactivation and female bias of autoimmune diseases

Generally, autoimmune diseases are more prevalent in females than males. Various predisposing factors, including female sex hormones, X chromosome genes, and the microbiome have been implicated in the female bias of autoimmune diseases. During embryogenesis, one of the X chromosomes in the females is transcriptionally inactivated, in a process called X chromosome inactivation (XCI). This equalizes the impact of two X chromosomes in the females. However, some genes escape from XCI, providing a basis for the dual expression dosage of the given gene in the females. In the present review, the contribution of the escape genes to the female bias of autoimmune diseases will be discussed.

Skin-Associated B Cells in the Pathogenesis of Cutaneous Autoimmune Diseases-Implications for Therapeutic Approaches

B lymphocytes are crucial mediators of systemic immune responses and are known to be substantial in the pathogenesis of autoimmune diseases with cutaneous manifestations. Amongst them are lupus erythematosus, dermatomyositis, systemic sclerosis and psoriasis, and particularly those driven by autoantibodies such as pemphigus and pemphigoid. However, the concept of autoreactive skin-associated B cells, which may reside in the skin and locally contribute to chronic inflammation, is gradually evolving. These cells are believed to differ from B cells of primary and secondary lymphoid organs and may provide additional features besides autoantibody production, including cytokine expression and crosstalk to autoreactive T cells in an antigen-presenting manner. In chronically inflamed skin, B cells may appear in tertiary lymphoid structures. Those abnormal lymph node-like structures comprise a network of immune and stromal cells possibly enriched by vascular structures and thus constitute an ideal niche for local autoimmune responses. In this review, we describe current considerations of different B cell subsets and their assumed role in skin autoimmunity. Moreover, we discuss traditional and B cell-associated approaches for the treatment of autoimmune skin diseases, including drugs targeting B cells (e.g., CD19- and CD20-antibodies), plasma cells (e.g., proteasome inhibitors, CXCR4 antagonists), activated pathways (such as BTK- and PI3K-inhibitors) and associated activator molecules (BLyS, APRIL).

IL-17 sustains the plasma cell response via p38-mediated Bcl-xL RNA stability in lupus pathogenesis

Recent studies have demonstrated a central role for plasma cells in the development of autoimmune diseases, such as systemic lupus erythematosus (SLE). Currently, both the phenotypic features and functional regulation of autoreactive plasma cells during SLE pathogenesis remain largely unclear. In this study, we first found that a major subset of IL-17 receptor-expressing plasma cells potently produced anti-dsDNA IgG upon IL-17A (IL-17) stimulation in SLE patients and lupus mice. Using a humanized lupus mouse model, we showed that the transfer of Th17 cell-depleted PBMCs from lupus patients resulted in a significantly reduced plasma cell response and attenuated renal damage in recipient mice compared to the transfer of total SLE PBMCs. Moreover, long-term BrdU incorporation in lupus mice detected highly enriched long-lived BrdU⁺ subsets among IL-17 receptor-expressing plasma cells. Lupus mice deficient in IL-17 or IL-17 receptor C (IL-17RC) exhibited a diminished plasma cell response and reduced autoantibody production with attenuated renal damage, while the adoptive transfer of Th17 cells triggered the plasma cell response and renal damage in IL-17-deficient lupus mice. In reconstituted chimeric mice, IL-17RC deficiency resulted in severely impaired plasma cell generation but showed no obvious effect on germinal center B cells. Further mechanistic studies revealed that IL-17 significantly promoted plasma cell survival via p38-mediated Bcl-xL transcript stabilization. Together, our findings identified a novel function of IL-17 in enhancing plasma cell survival for autoantibody production in lupus pathogenesis, which may provide new therapeutic strategies for the treatment of SLE.

Treatment of chronic hepatitis C-associated cryoglobulinemia vasculitis at the era of direct-acting antivirals

Hepatitis C virus (HCV) infection is responsible for both hepatic and extrahepatic manifestations. Before the era of direct-acting antivirals (DAA), cryoglobulinemia was related to HCV infection in 70-90% of cases. Observed in 30% to 40% of patients with hepatitis C, mixed cryoglobulinemia is mainly asymptomatic. Conversely, symptomatic cryoglobulinemia vasculitis (CV) can occur in 5-10% of patients with HCV-associated cryoglobulinemia. CV is a small-vessel systemic vasculitis, and organ damage results from circulation and precipitation of cryoglobulins and complement activation. A wide range of clinical symptoms can be observed during CV, and manifestations are potentially life-threatening. The most frequent manifestations occurring in CV are cutaneous, with recurrent purpura, articular with joint pains, neurologic with peripheric neuropathy, and renal with membranoproliferative glomerulonephritis. DAA have drastically changed chronic HCV therapy. DAA induce sustained virological response (SVR) rates greater than 95%, and also improve extrahepatic manifestations such as CV. We review recent studies investigating the clinical and immune effects of DAA therapy on HCV-CV.

Emerging drugs for primary Sjögren's syndrome

Introduction: Primary Sjögren's syndrome (pSS) is an autoimmune systemic disease characterized by a complex and not yet completely elucidated etiopathogenesis, where autoimmune manifestations coexist with different degree of lymphoproliferation, resulting in multiple possible scenarios extremely heterogeneous from patient to patient. Although considerable progress has been made in the identifications of potential novel therapeutic targets in recent years, the biological complexity of pSS, combined to such heterogeneous clinical manifestations, makes the treatment of pSS, even today, a great challenge. Areas covered: A therapy specifically approved for pSS is still lacking. In recent years, several novel promising agents are being tested in pSS. Based on a deep revision of drugs evaluated for pSS therapy, it is striking that several clinical trials, some of them testing very promising agents, failed. Expert opinion: a renewal of clinical trial design, including the definition of novel inclusion criteria and outcome measures, together with the development of a stratification model of pSS patients and the advance in the definition of pathogenetic mechanisms underlying peculiar pSS subsets, represent preliminary and crucial steps to overcome the current therapeutic impasse in pSS.

Hspa13 Promotes Plasma Cell Production and Antibody Secretion

The generation of large numbers of plasma cells (PCs) is a main factor in systemic lupus erythematosus (SLE). We hypothesize that Hspa13, a member of the heat shock protein family, plays a critical role in the control of PC differentiation. To test the hypothesis, we used lipopolysaccharide (LPS)-activated B cells and a newly established mouse line with a CD19^cre-mediated, B cell–specific deletion of Hspa13: Hspa13 cKO mice. We found that Hspa13 mRNA was increased in PCs from atacicept-treated lupus-prone mice and in LPS-stimulated plasmablasts (PBs) and PCs. A critical finding was that PBs and PCs [but not naïve B cells and germinal center (GC) B cells] expressed high levels of Hspa13. In contrast, the Hspa13 cKO mice had a reduction in BPs, PCs, and antibodies induced in vitro by LPS and in vivo by sheep red blood cells (SRCs)- or 4-hydroxy-3-nitrophenylacetyl (NP)-immunization. Accordingly, the Hspa13 cKO mice had reduced class-switched and somatically hypermutated antibodies with defective affinity maturation. Our work also showed that Hspa13 interacts with proteins (e.g., Bcap31) in the endoplasmic reticulum (ER) to positively regulate protein transport from the ER to the cytosol. Importantly, Hspa13 mRNA was increased in B220⁺ cells from patients with multiple myeloma (MM) or SLE, whereas Hspa13 cKO led to reduced autoantibodies and proteinuria in both pristane-induced lupus and lupus-prone MRL/lpr mouse models. Collectively, our data suggest that Hspa13 is critical for PC development and may be a new target for eliminating pathologic PCs.

Sustained B cell depletion by CD19-targeted CAR T cells is a highly effective treatment for murine lupus

The failure of anti-CD20 antibody (Rituximab) as therapy for lupus may be attributed to the transient and incomplete B cell depletion achieved in clinical trials. Here, using an alternative approach, we report that complete and sustained CD19⁺ B cell depletion is a highly effective therapy in lupus models. CD8⁺ T cells expressing CD19-targeted chimeric antigen receptors (CARs) persistently depleted CD19⁺ B cells, eliminated autoantibody production, reversed disease manifestations in target organs, and extended life spans well beyond normal in the (NZB × NZW) F₁ and MRL ^fas/fas mouse models of lupus. CAR T cells were active for 1 year in vivo and were enriched in the CD44⁺CD62L⁺ T cell subset. Adoptively transferred splenic T cells from CAR T cell-treated mice depleted CD19⁺ B cells and reduced disease in naive autoimmune mice, indicating that disease control was cell-mediated. Sustained B cell depletion with CD19-targeted CAR T cell immunotherapy is a stable and effective strategy to treat murine lupus, and its effectiveness should be explored in clinical trials for lupus.

Is There a Future for Anti-CD38 Antibody Therapy in Systemic Autoimmune Diseases?

CD38 is a type II glycoprotein highly expressed on plasmablasts, short-lived and long-lived plasma cells, but weakly expressed on other lymphoid cells, myeloid cells and non-hematopoietic cells. This expression pattern makes CD38 an interesting target for a targeted therapy aiming to deplete antibody-producing plasma cells. We present data suggesting that anti-CD38 therapy may be effective for the prevention at the preclinical stage and for the treatment of established autoimmune diseases, such as systemic lupus erythematosus, systemic sclerosis, Sjögren’s syndrome and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Given the high unmet need for efficacious disease-modifying treatment in these diseases, studies are warranted to determine if anti-CD38 antibody-based therapies may delay or prevent the disease progression of systemic autoimmune diseases.

Multiple Functions of B Cells in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by excessive autoantibody production and multi-organ involvement. Although the etiology of SLE still remains unclear, recent studies have characterized several pathogenic B cell subsets and regulatory B cell subsets involved in the pathogenesis of SLE. Among pathogenic B cell subsets, age-associated B cells (ABCs) are a newly identified subset of autoreactive B cells with T-bet-dependent transcriptional programs and unique functional features in SLE. Accumulation of T-bet+ CD11c+ ABCs has been observed in SLE patients and lupus mouse models. In addition, innate-like B cells with the autoreactive B cell receptor (BCR) expression and long-lived plasma cells with persistent autoantibody production contribute to the development of SLE. Moreover, several regulatory B cell subsets with immune suppressive functions have been identified, while the impaired inhibitory effects of regulatory B cells have been indicated in SLE. Thus, further elucidation on the functional features of B cell subsets will provide new insights in understanding lupus pathogenesis and lead to novel therapeutic interventions in the treatment of SLE.

High-throughput compound screen reveals mTOR inhibitors as potential therapeutics to reduce (auto)antibody production by human plasma cells

Antibody production by the B cell compartment is a crucial part of the adaptive immune response. Dysregulated antibody production in the form of autoantibodies can cause autoimmune disease. To date, B‐cell depletion with anti‐CD20 antibodies is commonly applied in autoimmunity, but pre‐existing plasma cells are not eliminated in this way. Alternative ways of more selective inhibition of antibody production would add to the treatment of these autoimmune diseases. To explore novel therapeutic targets in signaling pathways essential for plasmablast formation and/or immunoglobulin production, we performed a compound screen of almost 200 protein kinase inhibitors in a robust B‐cell differentiation culture system. This study yielded 35 small cell‐permeable compounds with a reproducible inhibitory effect on B‐cell activation and plasmablast formation, among which was the clinically applied mammalian target of rapamycin (mTOR) inhibitor rapamycin. Two additional compounds targeting the phosphoinositide 3‐kinase‐AKT‐mTOR pathway (BKM120 and WYE‐354) did not affect proliferation and plasmablast formation, but specifically reduced the immunoglobulin production. With this compound screen we successfully applied a method to investigate therapeutic targets for B‐cell differentiation and identified compounds in the phosphoinositide 3‐kinase‐AKT‐mTOR pathway that could specifically inhibit immunoglobulin production only. These drugs may well be explored to be of value in current B‐cell‐depleting treatment regimens in autoimmune disorders.

Bcl2 like protein-12 suppresses Foxp3+ regulatory T cells in patients with rheumatoid arthritis

Immune dysregulation plays an important role in the pathogenesis of rheumatoid arthritis (RA). Bcl2 like protein 12 (Bcl2L12) has the ability of immune regulation. This study aims to investigate the role of Bcl2L12 in interfering with Foxp3⁺ regulatory T cell (Treg) development and function in RA patients. In this study, RA patients were recruited in RA clinic. The peripheral blood samples were collected from RA patients and healthy (HA) subjects. Treg status was analyzed by a variety of immune assessing approaches. We observed that the frequency of Tregs in RA patients was significantly lower than that in HA subjects. The expression of Bcl2L12 was detected in CD4⁺ T cells, which was markedly higher in the RA group than that in HA group. Naive CD4⁺ T cells from RA patients were refractory to develop as Tregs. Inhibition of Bcl2L12 in CD4⁺ T cells from RA patients promoted Treg generation. Tregs isolated from RA patients showed functional defects, which could be restored by knocking down of Bcl2L12. In conclusion, Bcl2L12 plays a role in suppressing Treg development and function in RA patients. Inhibition of Bcl2L12 may have therapeutic potential in the treatment of RA.

Protein-engineered molecules carrying GAD65 epitopes and targeting CD35 selectively down-modulate disease-associated human B lymphocytes

Type 1 diabetes mellitus is an autoimmune metabolic disorder characterized by chronic hyperglycemia, the presence of autoreactive T and B cells and autoantibodies against self-antigens. A membrane-bound enzyme on the pancreatic beta-cells, glutamic acid decarboxylase 65 (GAD65), is one of the main autoantigens in type 1 diabetes. Autoantibodies against GAD65 are potentially involved in beta-cell destruction and decline of pancreatic functions. The human complement receptor type 1 (CD35) on B and T lymphocytes has a suppressive activity on these cells. We hypothesized that it may be possible to eliminate GAD65-specific B cells from type 1 diabetes patients by using chimeric molecules, containing an anti-CD35 antibody, coupled to peptides resembling GAD65 B/T epitopes. These molecules are expected to selectively bind the anti-GAD65 specific B cells by the co-cross-linking of the immunoglobulin receptor and CD35 and to deliver a suppressive signal. Two synthetic peptides derived from GAD65 protein (GAD65 epitopes) and anti-CD35 monoclonal antibody were used for the construction of two chimeras. The immunomodulatory activity of the engineered antibodies was tested in vitro using peripheral blood mononuclear cells (PBMCs) from type 1 diabetes patients. A reduction in the number of anti-GAD65 IgG antibody-secreting plasma cells and increased percentage of apoptotic B lymphocytes was observed after treatment of these PBMCs with the engineered antibodies. The constructed chimeric molecules are able to selectively modulate the activity of GAD65-specific B lymphocytes and the production of anti-GAD65 IgG autoantibodies by co-cross-linking of the inhibitory CD35 and the B cell antigen receptor (BCR). This treatment presents a possible way to alter the autoimmune nature of these cells.

Biological therapy of autoimmune blistering diseases

INTRODUCTION

Autoimmune blistering skin diseases are a group of disorders subdivided according to the location of blister formation: intraepidermal blistering in the pemphigus group and subepidermal in the pemphigoid group. These conditions are clinically heterogeneous and are treated with systemic corticosteroids and/or other forms of immunosuppression on the basis of clinical subtype and disease severity. These approaches may not be effective for the induction and maintenance of clinical response or need to be stopped because of intolerable side effects.

AREAS COVERED

Biological therapies can represent a valid alternative strategy in various autoimmune blistering disorders and this review article will address this issue with a special focus on pemphigus vulgaris and bullous pemphigoid. These biological approaches are designed to target B cells, autoantibodies, complement proteins, and several cytokines.

EXPERT OPINION

Innovative strategies for the treatment of autoimmune blistering conditions primarily depend on the use of drugs with a high degree of specificity targeting crucial steps in the immunopathology of these disorders. Novel biological agents offer treatment alternatives to patients with autoimmune blistering conditions by targeting B cells, pathogenic autoantibodies, complement and cytokines.

Prevention of the anti-factor VIII memory B-cell response by inhibition of Bruton tyrosine kinase in experimental hemophilia A

Hemophilia A is a rare hemorrhagic disorder caused by the lack of functional pro-coagulant factor VIII. Factor VIII replacement therapy in patients with severe hemophilia A results in the development of inhibitory anti-factor VIII IgG in up to 30% of cases. To date, immune tolerance induction, with daily injection of large amounts of factor VIII, is the only strategy to eradicate factor VIII inhibitors. This strategy is, however, efficient in only 60-80% of patients. We investigated whether blocking B-cell receptor signaling upon inhibition of Bruton tyrosine kinase prevents anti-factor VIII immune responses in a mouse model of severe hemophilia A. Factor VIII-naïve and factor VIII-sensitized factor VIII-deficient mice were fed with the selective inhibitor of Bruton tyrosine kinase, (R)-5-amino-1-(1-cyanopiperidin-3-yl)-3-(4-[2,4-difluorophenoxyl] phenyl)-1H pyrazole-4-carboxamide (PF-06250112), to inhibit B-cell receptor signaling prior to challenge with exogenous factor VIII. The consequences on the anti-factor VIII immune response were studied. Inhibition of Bruton tyrosine kinase during the primary anti-factor VIII immune response in factor VIII-naïve mice did not prevent the development of inhibitory anti-factor VIII IgG. In contrast, the anti-factor VIII memory B-cell response was consistently reduced upon treatment of factor VIII-sensitized mice with the Bruton tyrosine kinase inhibitor. The Bruton tyrosine kinase inhibitor reduced the differentiation of memory B cells ex vivo and in vivo following adoptive transfer to factor VIII-naïve animals. Taken together, our data identify inhibition of Bruton tyrosine kinase using PF-06250112 as a strategy to limit the reactivation of factor VIII-specific memory B cells upon re-challenge with therapeutic factor VIII.

The long and the short of it: insights into the cellular source of autoantibodies as revealed by B cell depletion therapy

High titers of pathogenic autoantibodies are a hallmark of many autoimmune diseases. However, much remains unknown about the self-reactive plasma cells that are key mediators of disease. We propose a model in which the varying efficacy of precursor B cell depletion for the treatment of humoral autoimmunity can be explained by differences in the relative contributions of pathogenic antibodies by short-lived versus long-lived plasma cells. Beyond therapeutic considerations, this model suggests that we can infer the cellular source of disease-associated autoantibodies by the durability of serum titers following B cell depletion. Data from clinical trials and animal models across different autoimmune diseases may provide useful insights into the lifespan, lifestyle and fate of autoreactive plasma cells.

Reversing Autoimmunity Combination of Rituximab and Intravenous Immunoglobulin

In this concept paper, the authors present a unique and novel protocol to treat autoimmune diseases that may have the potential to reverse autoimmunity. It uses a combination of B cell depletion therapy (BDT), specifically rituximab (RTX) and intravenous immunoglobulin (IVIg), based on a specifically designed protocol (Ahmed Protocol). Twelve infusions of RTX are given in 6–14 months. Once the CD20⁺ B cells are depleted from the peripheral blood, IVIg is given monthly until B cells repopulation occurs. Six additional cycles are given to end the protocol. During the stages of B cell depletion, repopulation and after clinical recovery, IVIg is continued. Along with clinical recovery, significant reduction and eventual disappearance of pathogenic autoantibody occurs. Administration of IVIg in the post-clinical period is a crucial part of this protocol. This combination reduces and may eventually significantly eliminates inflammation in the microenvironment and facilitates restoring immune balance. Consequently, the process of autoimmunity and the phenomenon that lead to autoimmune disease are arrested, and a sustained and prolonged disease and drug-free remission is achieved. Data from seven published studies, in which this combination protocol was used, are presented. It is known that BDT does not affect check points. IVIg has functions that mimic checkpoints. Hence, when inflammation is reduced and the microenvironment is favorable, IVIg may restore tolerance. The authors provide relevant information, molecular mechanism of action of BDT, IVIg, autoimmunity, and autoimmune diseases. The focus of the manuscript is providing an explanation, using the current literature, to demonstrate possible pathways, used by the combination of BDT and IVIg in providing sustained, long-term, drug-free remissions of autoimmune diseases, and thus reversing autoimmunity, albeit for the duration of the observation.

Identification of a new subset of lymph node stromal cells involved in regulating plasma cell homeostasis

Antibody-secreting plasma cells (PCs) arise rapidly during adaptive immunity to control infections. The early PCs are retained within the reactive lymphoid organ where their localization and homeostasis rely on extrinsic factors, presumably produced by local niche cells. While myeloid cells have been proposed to form those niches, the contribution by colocalizing stromal cells has remained unclear. Here, we characterized a subset of fibroblastic reticular cells (FRCs) that forms a dense meshwork throughout medullary cords of lymph nodes (LNs) where PCs reside. This medullary FRC type is shown to be anatomically, phenotypically, and functionally distinct from T zone FRCs, both in mice and humans. By using static and dynamic imaging approaches, we provide evidence that medullary FRCs are the main cell type in contact with PCs guiding them in their migration. Medullary FRCs also represent a major local source of the PC survival factors IL-6, BAFF, and CXCL12, besides also producing APRIL. In vitro, medullary FRCs alone or in combination with macrophages promote PC survival while other LN cell types do not have this property. Thus, we propose that this FRC subset, together with medullary macrophages, forms PC survival niches within the LN medulla, and thereby helps in promoting the rapid development of humoral immunity, which is critical in limiting early pathogen spread.

TACI deletion protects against progressive murine lupus nephritis induced by BAFF overexpression

B cells are known to promote the pathogenesis of systemic lupus erythematosus (SLE) via the production of pathogenic anti-nuclear antibodies. However, the signals required for autoreactive B cell activation and the immune mechanisms whereby B cells impact lupus nephritis pathology remain poorly understood. The B cell survival cytokine B cell activating factor of the TNF Family (BAFF) has been implicated in the pathogenesis of SLE and lupus nephritis in both animal models and human clinical studies. Although the BAFF receptor has been predicted to be the primary BAFF family receptor responsible for BAFF-driven humoral autoimmunity, in the current study we identify a critical role for signals downstream of Transmembrane Activator and CAML Interactor (TACI) in BAFF-dependent lupus nephritis. Whereas transgenic mice overexpressing BAFF develop progressive membranoproliferative glomerulonephritis, albuminuria and renal dysfunction, TACI deletion in BAFF-transgenic mice provided long-term (about 1 year) protection from renal disease. Surprisingly, disease protection in this context was not explained by complete loss of glomerular immune complex deposits. Rather, TACI deletion specifically reduced endocapillary, but not mesangial, immune deposits. Notably, although excess BAFF promoted widespread breaks in B cell tolerance, BAFF-transgenic antibodies were enriched for RNA- relative to DNA-associated autoantigen reactivity. These RNA-associated autoantibody specificities were specifically reduced by TACI or Toll-like receptor 7 deletion. Thus, our study provides important insights into the autoantibody specificities driving proliferative lupus nephritis, and suggests that TACI inhibition may be novel and effective treatment strategy in lupus nephritis.

BAFF and CD4+ T cells are major survival factors for long-lived splenic plasma cells in a B-cell–depletion context

Modification of the splenic microenvironment induced by B-cell depletion creates a dependence of PCs on BAFF and CD4+ T cells. Combining anti-CD20 and anti-BAFF reduces the number of splenic PCs, opening therapeutic perspectives for antibody-mediated cytopenia.

Dual immuno-renal targeting of 7-benzylidenenaltrexone alleviates lupus nephritis via FcγRIIB and HO-1

Known as a selective δ1 opioid receptor (DOR1) antagonist, the 7-benzylidenenaltrexone (BNTX) is also a DOR1-independent immunosuppressant with unknown mechanisms. Here we investigated if BNTX could be beneficial for diseased MRL/lpr lupus mice. We treated mice with 0.5, 2, 5 or 10 mg/kg/day of BNTX for 2 weeks. At as low as 2 mg/kg/day, BNTX significantly improved splenomegaly and lymphadenopathy. Notably, B cell numbers, particularly autoreactive plasma cells, were preferentially reduced; moreover, BNTX enhanced surface expression of FcγRIIB, an immune complex (IC)-dependent apoptotic trigger of B cells. Consequently, serum autoantibody concentrations were significantly decreased, leading to diminished glomerular IC deposition and renal fibrosis, thereby improving proteinuria. Microarray and pathway analyses revealed heme oxygenase-1 (HO-1) and p38 MAPK as key mediators of BNTX-induced upregulation of FcγRIIB. Moreover, HO-1 expression was also induced by BNTX via p38 MAPK at renal proximal tubules to further cytoprotection. Taken together, we demonstrate that BNTX can alleviate lupus nephritis by reducing autoreactive B cells via FcγRIIB and by augmenting renal protection via HO-1. Accordingly, we propose a new strategy to treat lupus nephritis via such a dual immuno-renal targeting using either a single agent or combined agents to simultaneously deplete B cells and enhance renal protection.

KEY MESSAGES

7-Benzylidenenaltrexone (BNTX) alleviates lupus nephritis in diseased MRL/lpr mice. BNTX reduces autoreactive plasma cell numbers and serum autoantibody titers. BNTX upregulates FcγRIIB levels via p38 MAPK and HO-1 to reduce B cell numbers. Reduction of immune complex deposition and fibrosis by BNTX improves proteinuria. BNTX induces HO-1 via p38 MAPK to enhance protection of renal proximal tubules.

Plasma Cell Differentiation Pathways in Systemic Lupus Erythematosus

Plasma cells (PCs) are responsible for the production of protective antibodies against infectious agents but they also produce pathogenic antibodies in autoimmune diseases, such as systemic lupus erythematosus (SLE). Traditionally, high affinity IgG autoantibodies are thought to arise through germinal center (GC) responses. However, class switching and somatic hypermutation can occur in extrafollicular (EF) locations, and this pathway has also been implicated in SLE. The pathway from which PCs originate may determine several characteristics, such as PC lifespan and sensitivity to therapeutics. Although both GC and EF responses have been implicated in SLE, we hypothesize that one of these pathways dominates in each individual patient and genetic risk factors may drive this predominance. While it will be important to distinguish polymorphisms that contribute to a GC-driven or EF B cell response to develop targeted treatments, the challenge will be not only to identify the differentiation pathway but the molecular mechanisms involved. In B cells, this task is complicated by the cross-talk between the B cell receptor, toll-like receptors (TLR), and cytokine signaling molecules, which contribute to both GC and EF responses. While risk variants that affect the function of dendritic cells and T follicular helper cells are likely to primarily influence GC responses, it will be important to discover whether some risk variants in the interferon and TLR pathways preferentially influence EF responses. Identifying the pathways of autoreactive PC differentiation in SLE may help us to understand patient heterogeneity and thereby guide precision therapy.

Upregulation of FcγRIIB by resveratrol via NF-κB activation reduces B-cell numbers and ameliorates lupus

Resveratrol, an anti-inflammatory agent, can inhibit pro-inflammatory mediators by activating Sirt1, which is a class III histone deacetylase. However, whether resveratrol can regulate inhibitory or anti-inflammatory molecules has been less studied. FcγRIIB, a receptor for IgG, is an essential inhibitory receptor of B cells for blocking B-cell receptor-mediated activation and for directly inducing apoptosis of B cells. Because mice deficient in either Sirt1 or FcγRIIB develop lupus-like diseases, we investigated whether resveratrol can alleviate lupus through FcγRIIB. We found that resveratrol enhanced the expression of FcγRIIB in B cells, resulting in a marked depletion of plasma cells in the spleen and notably in the bone marrow, thereby decreasing serum autoantibody titers in MRL/lpr mice. The upregulation of FcγRIIB by resveratrol involved an increase of Sirt1 protein and deacetylation of p65 NF-κB (K310). Moreover, increased binding of phosphor-p65 NF-κB (S536) but decreased association of acetylated p65 NF-κB (K310) and phosphor-p65 NF-κB (S468) to the −480 promoter region of Fcgr2b gene was responsible for the resveratrol-mediated enhancement of FcγRIIB gene transcription. Consequently, B cells, especially plasma cells, were considerably reduced in MRL/lpr mice, leading to improvement of nephritis and prolonged survival. Taken together, we provide evidence that pharmacological upregulation of FcγRIIB expression in B cells via resveratrol can selectively reduce B cells, decrease serum autoantibodies and ameliorate lupus nephritis. Our findings lead us to propose FcγRIIB as a new target for therapeutic exploitation, particularly for lupus patients whose FcγRIIB expression levels in B cells are downregulated.

Altered B cell signalling in autoimmunity

Recent work has provided new insights into how altered B cell-intrinsic signals - through the B cell receptor (BCR) and key co-receptors - function together to promote the pathogenesis of autoimmunity. These combined signals affect B cells at two distinct stages: first, in the selection of the naive repertoire; and second, during extrafollicular or germinal centre activation responses. Thus, dysregulated signalling can lead to both an altered naive BCR repertoire and the generation of autoantibody-producing B cells. Strikingly, high-affinity autoantibodies predate and predict disease in several autoimmune disorders, including type 1 diabetes and systemic lupus erythematosus. This Review summarizes how, rather than being a downstream consequence of autoreactive T cell activation, dysregulated B cell signalling can function as a primary driver of many human autoimmune diseases.

Pre-symptomatic autoimmunity in rheumatoid arthritis: when does the disease start?

It is well recognised that a state of autoimmunity, in which immunological tolerance is broken, precedes the development of symptoms in the majority of patients with rheumatoid arthritis (RA). For individuals who will later develop seropositive disease, this manifests as autoantibodies directed against proteins that have undergone specific post-translational modifications. There is evidence that the induction of this autoantibody response occurs at peripheral extra-articular mucosal sites, such as the periodontium and lung. In addition to their utility as diagnostic markers, these autoantibodies may have a pathogenic role that helps localise disease to the synovium. Alongside the development of autoantibodies, other factors contributing to pre-symptomatic autoimmunity may include dysbiosis of the gastrointestinal tract, abnormal development of lymphoid tissue, and dysregulated autonomic and lipid-mediated anti-inflammatory signalling. These factors combine to skew the balance between pro-inflammatory and anti-inflammatory signalling in a manner that is permissive for the development of clinical arthritis. We present data to support the concept that the transitions from at-risk states to systemic autoimmunity and then to classifiable RA depend on multiple “switches”. However, further prospective studies are necessary to define the molecular basis of these switches and the specific features of pre-symptomatic autoimmunity, so that preventative treatments can be targeted to individuals at high risk for RA. In this review, we analyse mechanisms that may contribute to the development of autoimmunity in at-risk individuals and discuss the relationship between this pre-symptomatic state and subsequent development of RA.

Inebilizumab, a B Cell-Depleting Anti-CD19 Antibody for the Treatment of Autoimmune Neurological Diseases: Insights from Preclinical Studies

Exaggerated or inappropriate responses by B cells are an important feature in many types of autoimmune neurological diseases. The recent success of B-cell depletion in the treatment of multiple sclerosis (MS) has stimulated the development of novel B-cell-targeting therapies with the potential for improved efficacy. CD19 has emerged as a promising target for the depletion of B cells as well as CD19-positive plasmablasts and plasma cells. Inebilizumab (MEDI-551), an anti-CD19 antibody with enhanced antibody-dependent cell-mediated cytotoxicity against B cells, is currently being evaluated in MS and neuromyelitis optica. This review discusses the role of B cells in autoimmune neurological disorders, summarizes the development of inebilizumab, and analyzes the recent results for inebilizumab treatment in an autoimmune encephalitis mouse model. The novel insights obtained from these preclinical studies can potentially guide future investigation of inebilizumab in patients.

Safety and tolerability of an anti-CD19 monoclonal antibody, MEDI-551, in subjects with systemic sclerosis: a phase I, randomized, placebo-controlled, escalating single-dose study

Background

Systemic sclerosis (SSc) is a clinically heterogeneous, life-threatening disease characterized by fibrosis, microvasculopathy, and autoimmunity. Extensive nonclinical and clinical data implicate B cells in the pathogenesis of SSc. MEDI-551 is an investigational humanized monoclonal antibody that targets the B cell surface antigen CD19 and mediates antibody-dependent, cell-mediated cytotoxicity of B cells. This clinical study evaluated the safety and tolerability, pharmacokinetics, and pharmacodynamics of MEDI-551 in subjects with SSc.

Methods

This phase I multicenter, randomized, double-blind, placebo-controlled, single escalating dose study enrolled adult subjects with either limited or diffuse cutaneous SSc. A single intravenous dose of MEDI-551 was administered, and safety and tolerability were evaluated. MEDI-551 pharmacokinetics (PK), pharmacodynamics, and immunogenicity were also assessed. Safety assessments included the incidence of adverse events and changes in clinical and laboratory results. MEDI-551 serum concentrations, effects on circulating and tissue B cells and plasma cells (PCs), and antidrug antibodies were analyzed. Modified Rodnan skin score (MRSS) and pulmonary function tests were used to explore the clinical effect of MEDI-551.

Results

The study enrolled 28 subjects with SSc (mean age, 47.3 years; 67.9 % female). Twenty-four received a single dose of MEDI-551 (0.1–10.0 mg/kg) and four received placebo. Treatment-emergent adverse events (TEAEs) occurred in 95.8 % of subjects in the MEDI-551 group and in 75.0 % of subjects in the placebo group; the majority of TEAEs were mild or moderate in severity. Two serious adverse events were considered possibly related to the study drug. One death, deemed not related to the study drug, occurred in a MEDI-551-treated subject. MEDI-551 exhibited linear PK in the dose range of 1.0 to 10.0 mg/kg, and more rapid clearance at lower doses. Dose-dependent depletion of circulating B cells and plasma cells was observed. MRSS assessments suggest a possible clinical effect of MEDI-551 on affected skin.

Conclusions

A single escalating dose of MEDI-551 was tolerable and safe in this subject population. B cell depletion was achieved and was dose dependent. A signal of clinical effect was observed. Based on these results, further investigation of MEDI-551 as a disease-modifying treatment for SSc is warranted.

Trial registration

www.clinicaltrials.gov identifier, NCT00946699; registered 23 July 2009.

Disruption of Splenic Lymphoid Tissue and Plasmacytosis in Canine Visceral Leishmaniasis: Changes in Homing and Survival of Plasma Cells

Visceral leishmaniasis (VL) is a disease caused by Leishmania infantum, which is transmitted by phlebotomine sandflies. Dogs are the main urban reservoir of this parasite and the disease presents similar characteristics in both humans and dogs. In this paper, we investigated the potential pathways involved in plasma cell replacement of normal cell populations in the spleen, with respect to disease severity in dogs from an endemic area for visceral leishmaniasis. To this end, canine spleen samples were grouped into three categories: TYPE1SC- (non-infected dogs or without active infection with organized white pulp), TYPE1SC+ (infected dogs with organized white pulp) or TYPE3SC+ (infected animals with disorganized white pulp). We analyzed the distribution of different plasma cell isotypes (IgA, IgG and IgM) in the spleen. The expression of cytokines and chemokines involved in plasma cell homing and survival were assessed by real time RT-PCR. Polyclonal B cell activation and hypergammaglobulinemia were also evaluated. The proportion of animals with moderate or intense plasmacytosis was higher in the TYPE3SC+ group than in the other groups (Fisher test, P<0.05). This was mainly due to a higher density of IgG+ plasma cells in the red pulp of this group. The albumin/globulin ratio was lower in the TYPE3SC+ animals than in the TYPE1SC- or TYPE1SC+ animals, which evidences VL-associated dysproteinemia. Interestingly, TYPE3SC+ animals showed increased expression of the BAFF and APRIL cytokines, as well as chemokine CXCL12. Aberrant expression of BAFF, APRIL and CXCL12, together with amplified extrafollicular B cell activation, lead to plasma cell homing and the extended survival of these cells in the splenic red pulp compartment. These changes in the distribution of immunocompetent cells in the spleen may contribute to the progression of VL, and impair the spleen's ability to protect against blood borne pathogens.