BAFF-neutralizing interaction of belimumab related to its therapeutic efficacy for treating systemic lupus erythematosus

Therapeutic tactics for targeting B lymphocytes in autoimmunity and cancer

B lymphocytes have become a very popular therapeutic target in a number of autoimmune indications due to their newly appreciated roles, and approachability, in these diseases. Many of the therapies now applied in autoimmunity were initially developed to deplete malignant B cells. These strategies have also been found to benefit patients suffering from such autoimmune diseases as multiple sclerosis, type I diabetes, systemic lupus erythematosus, and rheumatoid arthritis, to name a few. These observations have supported the expansion of research addressing the mechanistic contributions of B cells in these diseases, as well as blossoming of therapeutics that target them. This review seeks to summarize cutting-edge modalities for targeting B cells, including monoclonal antibodies, bispecific antibodies, antibody-drug conjugates, chimeric antigen receptor-T cells, and small molecule inhibitors. Efforts to refine B-cell targeted therapy to eliminate only pathogenic autoreactive cells will be addressed as well as the potential for future B-cell-based cellular therapeutics. Finally, we also address approaches that seek to silence B-cell function without depletion.

High-dimensional analysis of T-cell profiling variations following belimumab treatment in systemic lupus erythematosus

OBJECTIVE

This study sought to elucidate the molecular impacts of belimumab (BEL) treatment on T-cell immune profiling in SLE.

METHODS

We used mass cytometry with 25 marker panels for T-cell immune profiling in peripheral blood T cells (CD3+) from 22 patients with BEL-treated SLE and 20 controls with non-BEL-treated SLE. An unsupervised machine-learning clustering, FlowSOM, was used to identify 39 T-cell clusters (TCLs; TCL01-TCL39). TCLs (% of CD3+) showing significant (p<0.05) associations with BEL treatment (BEL-TCL) were selected by a linear mixed-effects model for comparing groups of time-series data. Furthermore, we analysed the association between BEL treatment and variations in regulatory T-cell (Treg) phenotypes, and the ratio of other T-cell subsets to Treg as secondary analysis.

RESULTS

Clinical outcomes: BEL treatment was associated with a decrease in daily prednisolone use (coef=-0.1769, p=0.00074), and an increase in serum CH50 (coef=0.4653, p=0.003), C3 (coef=1.1047, p=0.00001) and C4 (coef=0.2990, p=0.00157) levels. Molecular effects: five distinct BEL-TCLs (TCL 04, 07, 11, 12 and 27) were identified. Among these, BEL-treated patients exhibited increased proportions in the Treg-like cluster TCL11 (coef=0.404, p=0.037) and two naïve TCLs (TCL04 and TCL07). TCL27 showed increased levels (coef=0.222, p=0.037) inversely correlating with baseline C3 levels. Secondary analyses revealed associations between BEL treatment and an increase in Tregs (coef=1.749, p=0.0044), elevated proportions of the fraction of Tregs with inhibitory function (fTregs, coef=0.7294, p=0.0178) and changes in peripheral helper T cells/fTreg (coef=-4.475, p=0.0319) and T helper 17/fTreg ratios (coef=-6.7868, p=0.0327). Additionally, BEL was linked to variations in T-cell immunoglobulin and mucin domain-containing protein-3 expression (coef=0.2422, p=0.039).

CONCLUSIONS

The study suggests an association between BEL treatment and variations in T cells, particularly Tregs, in SLE pathologies involving various immune cells.

Construction of a two-gene prognostic model related to ferroptosis in renal cell carcinoma

BACKGROUND

Renal cell carcinoma (RCC) is a common and aggressive tumor. A newly discovered form of programmed cell death, ferroptosis, plays an important role in tumor development and progression. However, a clear prognostic correlation between Ferroptosis-related genes (FRGs) and RCC has not yet been established. In this study, prognostic markers associated with FRGs were investigated to improve the therapeutic, diagnostic, and preventive strategies available to patients with renal cancer.

METHODS

The present study analyzed the predictive value of 23 FRGs in RCC through bioinformatics techniques, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) tools, Kaplan-Meier survival analysis, Cox regression modeling, tumor mutational burden (TMB), CIBERSORT, and half maximal inhibitory concentration (IC50) difference analysis.

RESULTS

We screened FRGs by differentially expressed genes (DEGs) and overall survival (OS). Four candidate genes were obtained by hybridization. Then, we constructed a two-gene prognostic signature (NCOA4 and CDKN1A) via univariate Cox regression and multivariate stepwise Cox regression, which classified RCC patients into high- and low-risk groups, and patients in the high-risk group were found to have worse OS and progression-free survival (PFS). We also found that patients with higher TNM stage, T stage, and M stage had higher risk scores than those with lower TNM stage, T stage, and M stage (P<0.05). Males had higher risk scores than females. This signature was identified as an independent prognostic indicator for RCC. These results were validated in both the test cohort and the entire cohort. In addition, we also constructed a nomogram that predicted the OS in RCC patients, the consistency index (C-index) of the nomogram was 0.731 [95% confidence interval (CI): 0.672-0.790], the areas under the receiver operating characteristic (ROC) curves (AUCs) were 0.728, 0.704, and 0.898 at 1-, 3-, and 5-year, respectively, which shows that nomogram has good prediction ability. and we also analyzed the immune status and drug sensitivity between the high- and low-risk groups.

CONCLUSIONS

We constructed a prognostic model associated with ferroptosis, which may provide clinicians with a reliable predictive assessment tool and offer new perspectives for the future clinical management of RCC.

B cell-activating factor (BAFF) from dendritic cells, monocytes and neutrophils is required for B cell maturation and autoantibody production in SLE-like autoimmune disease

Purpose and methods

B cell-activating factor (BAFF) contributes to the pathogenesis of autoimmune diseases including systemic lupus erythematosus (SLE). Although several anti-BAFF Abs and derivatives have been developed for the treatment of SLE, the specific sources of BAFF that sustain autoantibody (auto-Ab) producing cells have not been definitively identified. Using BAFF-RFP reporter mice, we identified major changes in BAFF-producing cells in two mouse spontaneous lupus models (Tlr7 Tg mice and Sle1), and in a pristane-induced lupus (PIL) model.

Results

First, we confirmed that similar to their wildtype Tlr7 Tg and Sle1 mice counterparts, BAFF-RFP Tlr7 Tg mice and BAFF-RFP Sle1 mice had increased BAFF serum levels, which correlated with increases in plasma cells and auto-Ab production. Next, using the RFP reporter, we defined which cells had dysregulated BAFF production. BAFF-producing neutrophils (Nphs), monocytes (MOs), cDCs, T cells and B cells were all expanded in the spleens of BAFF-RFP Tlr7 Tg mice and BAFF-RFP Sle1 mice compared to controls. Furthermore, Ly6C^hi inflammatory MOs and T cells had significantly increased BAFF expression per cell in both spontaneous lupus models, while CD8^- DCs up-regulated BAFF expression only in the Tlr7 Tg mice. Similarly, pristane injection of BAFF-RFP mice induced increases in serum BAFF levels, auto-Abs, and the expansion of BAFF-producing Nphs, MOs, and DCs in both the spleen and peritoneal cavity. BAFF expression in MOs and DCs, in contrast to BAFF from Nphs, was required to maintain homeostatic and pristane-induced systemic BAFF levels and to sustain mature B cell pools in spleens and BMs. Although acting through different mechanisms, Nph, MO and DC sources of BAFF were each required for the development of auto-Abs in PIL mice.

Conclusions

Our findings underscore the importance of considering the relative roles of specific myeloid BAFF sources and B cell niches when developing treatments for SLE and other BAFF-associated autoimmune diseases.

Dual B-cell targeting therapy ameliorates autoimmune cholangitis

OBJECTIVE

The ability to regulate B cell development has long been recognized to have therapeutic potential in a variety of autoimmune diseases. However, despite the presence of a classic autoantibody in primary biliary cholangitis (PBC), B cell depleting therapy and indeed therapy with other biologic agents has been disappointing. Unsuccessful treatment using Rituximab is associated with elevation of B-cell activating factor (BAFF) level. Indeed, therapies for PBC remain directed at modulating bile salt biology, rather than targeting effector pathways. With these data in mind, we proposed that targeting two major stages of B cell development, namely long-lived memory B cells and short-lived peripheral autoreactive plasma cells would have therapeutic potential.

METHODS

To address this thesis, we administrated anti-BAFF and anti-CD20 monoclonal antibody to ARE-Del mice, a well-characterized murine model of human PBC. We evaluated and compared the therapeutic efficacy of the two agents individually and the combination of anti-BAFF and anti-CD20 in female mice with well-established disease.

RESULTS

Our data demonstrate that there was an increased level of B cell depletion that resulted in a significantly more effective clinical and serologic response using the combination of agents as compared with the use of the individual agents. The combination of anti-BAFF and anti-CD20 treatment was more effective in reducing serum levels of antimitochondrial antibody (AMA), total IgM and IgG compared to mice treated with the 2 individual agents. Combination treatment efficiently depleted B cells in the peripheral blood, peritoneal cavity and spleen. Importantly, we identified a unique IgM+ FCRL5+ B cell subset which was sensitive to dual B-cell targeting therapy and depletion of this unique population was associated with reduced portal infiltration and bile duct damage. Taken together, our data indicate that dual B cell targeting therapy with anti-BAFF and anti-CD20 not only led to the efficient depletion of B cells both in the peripheral blood and tissues, but also led to significant clinical improvement. These findings highlight the potential application of combination of anti-BAFF and anti-CD20 in treating patients with PBC. However, additional studies in other animal models of PBC should be undertaken before considering human trials in those PBC patients who have incomplete responses to conventional therapy.

BAFF antagonism via the BAFF receptor 3 binding site attenuates BAFF 60-mer-induced classical NF-κB signaling and metabolic reprogramming of B cells

Human recombinant B cell activating factor (BAFF) is secreted as 3-mers, which can associate to form 60-mers in culture supernatants. However, the presence of BAFF multimers in humans is still debated and it is incompletely understood how BAFF multimers activate the B cells. Here, we demonstrate that BAFF can exist as 60-mers or higher order multimers in human plasma. In vitro, BAFF 60-mer strongly induced the transcriptome of B cells which was partly attenuated by antagonism using a soluble fragment of BAFF receptor 3. Furthermore, compared to BAFF 3-mer, BAFF 60-mer strongly induced a transient classical and prolonged alternate NF-κB signaling, glucose oxidation by both aerobic glycolysis and oxidative phosphorylation, and succinate utilization by mitochondria. BAFF antagonism selectively attenuated classical NF-κB signaling and glucose oxidation. Altogether, our results suggest critical roles of BAFF 60-mer and its BAFF receptor 3 binding site in hyperactivation of B cells.

Developing high-affinity decoy receptors to treat multiple myeloma and diffuse large B cell lymphoma

Disease relapse and treatment-induced immunotoxicity pose significant clinical challenges for patients with hematological cancers. Here, we reveal distinctive requirements for neutralizing TNF receptor ligands APRIL and BAFF and their receptor activity in MM and DLBCL, impacting protein translation and production in MM cells and modulating the translation efficiency of the ATM interactor (ATMIN/ACSIZ). Therapeutically, we investigated the use of BCMA decoy receptor (sBCMA-Fc) as an inhibitor of APRIL and BAFF. While wild-type sBCMA-Fc effectively blocked APRIL signaling in MM, it lacked activity in DLBCL due to its weak BAFF binding. To expand the therapeutic utility of sBCMA-Fc, we engineered an affinity-enhanced mutant sBCMA-Fc fusion molecule (sBCMA-Fc V3) 4- and 500-fold stronger in binding to APRIL and BAFF, respectively. The mutant sBCMA-Fc V3 clone significantly enhanced antitumor activity against both MM and DLBCL. Importantly, we also demonstrated an adequate toxicity profile and on-target mechanism of action in nonhuman primate studies.

Distinct binding mode of BAFF antagonist antibodies belimumab and tabalumab, analyzed by computer simulation

B cell-activating factor (BAFF) can bind with specific receptors to activate signalling pathways associated with the B cell activation. Belimumab and tabalumab are anti-BAFF (B cell depleting) monoclonal antibodies, with therapeutic efficacy demonstrated for the treatment of autoimmune disorders, while belimumab was approved by FDA in 2011 as a targeted therapy for systemic lupus erythematosus (SLE) and exhibited better clinical outcome than tabalumab. In this investigation, the combination modes of BAFF-belimumab and BAFF-tabalumab complexes were simulated in silico to better understand the reason for the comparative inhibitory difference between belimumab and tabalumab. The structures of belimumab and tabalumab were constructed through homology modelling. The combination mode of BAFF-belimumab complex was analyzed by molecular dynamics simulation, while that of BAFF-tabalumab complex was analyzed by protein-protein docking following the molecular dynamics simulation. Both belimumab and tabalumab were bound with BAFF at the same hydrophobic center to which the natural receptors of BAFF bind as well. Belimumab heavy chain components I51, F54, K58, D100, D101, L102, L103, and P105 and R27, Y30, K49, and S65 of belimumab light chain contribute to the BAFF-belimumab interaction mainly via hydrogen bonds, salt bridges, and hydrophobic interactions. More importantly, belimumab could bind to L83 of BAFF and produce steric hindrance with the adjacent BAFF trimers, while tabalumab could not. Therefore, our results indicated that belimumab has a better clinical outcome compared with tabalumab mainly because belimumab could bind to L83 of BAFF and interfere the formation of a BAFF 60-mer, besides mediating inhibition of the interaction of BAFF with its receptors.

Protein and functional isoform levels and genetic variants of the BAFF and APRIL pathway components in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is the prototype of an autoimmune disease. Belimumab, a monoclonal antibody targets BAFF, is the only biologic approved for SLE and active lupus nephritis. BAFF is a cytokine with a key-regulatory role in the B cell homeostasis, which acts by binding to three receptors: BAFF-R, TACI and BCMA. TACI and BCMA also bind APRIL. Many studies reported elevated soluble BAFF and APRIL levels in the sera of SLE patients, but other questions about the role of this system in the disease remain open. The study aimed to investigate the utility of the cytokine levels in serum and urine as biomarkers, the role of non-functional isoforms, and the association of gene variants with the disease. This case–control study includes a cohort (women, 18–60 years old) of 100 patients (48% with nephritis) and 100 healthy controls. We used ELISA assays to measure the cytokine concentrations in serum (sBAFF and sAPRIL) and urine (uBAFF and uAPRIL); TaqMan Gene Expression Assays to quantify the relative mRNA expression of ΔBAFF, βAPRIL, and εAPRIL, and next-generation sequencing to genotype the cytokine (TNFSF13 and TNFSF13B) and receptor (TNFRSF13B, TNFRSF17 and TNFRSF13C) genes. The statistical tests used were: Kruskal–Wallis (qualitative variables), the Spearman Rho coefficient (correlations), the Chi-square and SKAT (association of common and rare genetic variants, respectively). As expected, sBAFF and sAPRIL levels were higher in patients than in controls (p ≤ 0.001) but found differences between patient subgroups. sBAFF and sAPRIL significantly correlated only in patients with nephritis (r_s = 0.67, p ≤ 0.001) and βAPRIL levels were lower in patients with nephritis (p = 0.04), and ΔBAFF levels were lower in patients with dsDNA antibodies (p = 0.04). Rare variants of TNFSF13 and TNFRSF13B and TNFSF13 p.Gly67Arg and TNFRSF13B p.Val220Ala were associated with SLE. Our study supports differences among SLE patient subgroups with diverse clinical features in the BAFF/APRIL pathway. In addition, it suggests the involvement of genetic variants in the susceptibility to the disease.

Recent advances in the intracellular delivery of macromolecule therapeutics

This review summarizes the uptake pathway of intracellular delivery vehicles for macromolecule therapeutics, and provides in-depth discussions and prospects about intracellular delivery of macromolecule therapeutics.

Immunosuppression in Rheumatologic and Auto-immune Disease

Many rheumatologic diseases are thought to originate in dysregulation of the immune system; lupus nephritis, for example, involves humoral immunity, while autoinflammatory diseases such as familial Mediterranean fever are caused by defects in innate immunity. Of note, this dysregulation may involve both upregulation of immune system components and aspects of immunodeficiency. Treatment of rheumatologic diseases thus requires a familiarity with a variety of immunosuppressive medications and their effects on immune system function.In many rheumatologic conditions, due to an incompletely elucidated mechanism of disease, immunosuppression is relatively broad in contrast to agents used, for example, in treatment of transplant rejection. Multiple immunosuppressive drugs may also be used in succession or in combination. As such, an understanding of the mechanisms and targets of immunosuppressive drugs is essential to appreciating their utility and potential adverse effects. Because of the overlap between therapies used in rheumatologic as well as other inflammatory disorders, some of these medications are discussed in other disease processes (e.g., Immunosuppression for inflammatory bowel disease) or in greater detail in other chapters of this textbook (corticosteroids, mTOR inhibitors, antiproliferative agents).

Interplay of immune and kidney resident cells in the formation of tertiary lymphoid structures in lupus nephritis

Kidney involvement confers significant morbidity and mortality in patients with systemic lupus erythematosus (SLE). The pathogenesis of lupus nephritis (LN) involves diverse mechanisms instigated by elements of the autoimmune response which alter the biology of kidney resident cells. Processes in the glomeruli and in the interstitium may proceed independently albeit crosstalk between the two is inevitable. Podocytes, mesangial cells, tubular epithelial cells, kidney resident macrophages and stromal cells with input from cytokines and autoantibodies present in the circulation alter the expression of enzymes, produce cytokines and chemokines which lead to their injury and damage of the kidney. Several of these molecules can be targeted independently to prevent and reverse kidney failure. Tertiary lymphoid structures with true germinal centers are present in the kidneys of patients with lupus nephritis and have been increasingly recognized to associate with poorer renal outcomes. Stromal cells, tubular epithelial cells, high endothelial vessel and lymphatic venule cells produce chemokines which enable the formation of structures composed of a T-cell-rich zone with mature dendritic cells next to a B-cell follicle with the characteristics of a germinal center surrounded by plasma cells. Following an overview on the interaction of the immune cells with kidney resident cells, we discuss the cellular and molecular events which lead to the formation of tertiary lymphoid structures in the interstitium of the kidneys of mice and patients with lupus nephritis. In parallel, molecules and processes that can be targeted therapeutically are presented.

Prediction of Belimumab Pharmacokinetics in Chinese Pediatric Patients with Systemic Lupus Erythematosus

Background and Objective

Intravenous (IV) belimumab is the first treatment approved for children ≥5 years of age with active autoantibody-positive systemic lupus erythematosus (SLE) in the USA, Europe, and Japan. Pharmacokinetic data for belimumab were collected from several clinical trials in Chinese and non-Chinese adults and non-Chinese pediatric patients with SLE. This study aimed to predict the belimumab dose-exposure relationship to Chinese pediatric patients with SLE, as part of the belimumab registration process for this population in China, using a population PK modeling approach.

Methods

An initial linear two-compartment population pharmacokinetic model was built using data from adults only, and considering and adjusting for the covariates age, body weight, body mass index, fat-free mass, race, baseline albumin and immunoglobulin G levels. The model was used to study possible ethnic differences between Chinese and non-Chinese adults and to predict pediatric pharmacokinetic data in a study of non-Chinese pediatric patients (PLUTO study; NCT01649765). The predicted data were compared with the observed data from PLUTO. The model was then updated with pediatric data from PLUTO to predict steady-state belimumab exposure in Chinese pediatric patients with SLE receiving belimumab 10 mg/kg IV every 4 weeks.

Results

The dataset comprised 9650 sampled concentration values from 1783 patients. The pharmacokinetics of belimumab were adequately described by the final model using all adult and pediatric data with the estimated typical clearance of 238 ml/day in adult and pediatric patients and steady-state volume of distribution of 4915 ml in adults. Between-patient variability was modest (coefficients of variation: 26.1% for clearance; 8.9% and 28.5%, respectively, for volumes of distribution of the central and peripheral compartments). Six covariates were identified that influenced pharmacokinetics: age, fat-free mass, an indicator of North East Asian race, baseline albumin, immunoglobulin G, and an early study indicator (two early phase I and phase II belimumab studies: LBSL01 and LBSL02). The analysis showed no apparent difference in steady-state exposure between Chinese and non-Chinese populations and between pediatric and adult populations receiving belimumab 10 mg/kg IV.

Conclusions

In Chinese pediatric patients with SLE, belimumab 10 mg/kg IV every 4 weeks is expected to have exposure similar to that in Chinese adults and non-Chinese pediatric patients with SLE, supporting the use of this regimen in Chinese pediatric patients with SLE.

Clinical Trial Registration Numbers

NCT01649765, NCT00657007, NCT00071487, NCT01345253, NCT01516450, NCT00410384, NCT00424476, NCT02880852, NCT01583530.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40268-021-00363-2.

Function, occurrence and inhibition of different forms of BAFF

B cell activating factor (BAFF or BLyS), an important cytokine for B cell survival and humoral immune responses, is targeted in the clinic for the treatment of systemic lupus erythematosus. This review focuses on the structure, function and inhibition profiles of membrane-bound BAFF, soluble BAFF 3-mer and soluble BAFF 60-mer, all of which have distinct properties. BAFF contains a loop region not required for receptor binding but essential for receptor activation via promotion of BAFF-to-BAFF contacts. This loop region additionally allows formation of BAFF 60-mer, in which epitopes of the BAFF inhibitor belimumab are inaccessible. If 60-mer forms in humans, it is predicted to be short-lived and to act locally because adult serum contains a BAFF 60-mer dissociating activity. Cord blood contains elevated levels of BAFF, part of which displays attributes of 60-mer, suggesting a role for this form of BAFF in the development of foetal or neonate B cells.

TriBAFF-CAR-T cells eliminate B-cell malignancies with BAFFR-expression and CD19 antigen loss

Background

To investigate the effect of TriBAFF-CAR-T cells on hematological tumor cells.

Methods

TriBAFF-CAR-T and CD19-CAR-T cells were co-cultured with BAFFR-bearing B-cell malignancies at different effector/target ratios to evaluate the anti-tumor effects. In vivo, TriBAFF-CAR-T and CD19-CAR-T cells were intravenously injected into Raji-luciferase xenograft mice. CD19 antigens losing lymphoblasts was simulated by Raji knocking out CD19 (CD19^KO) to investigate the effect of TriBAFF-CAR-T cells on CD19^KO Raji.

Results

Both TriBAFF-CAR-T and CD19-CAR-T cells significantly induced the lysis of Raji, BALL-1, and Jeko-1. Moreover, when CD19-CAR-T cells specifically caused the lysis of K562 with overexpressed CD19, the lethal effect of TriBAFF-CAR-T cells was also specific for BAFFR-bearing K562 with increasing levels of interleukin-2 and INF-γ. The TriBAFF-CAR-T have the same effect with CD19-CAR-T cells in treating Raji xenofraft mice. TriBAFF-CAR-T cells also have great effect in CD19^KO Raji cells.

Conclusions

In this study, we successfully constructed novel TriBAFF-CAR-T cells to eliminate BAFFR-bearing and CD19 antigen loss in hematological tumor cells.

The gene silencing of IRF5 and BLYSS effectively modulates the outcome of experimental lupus nephritis

Systemic lupus erythematosus is a highly complex and heterogeneous autoimmune disease mostly mediated by B cells. It is characterized by circulating self-reactive antibodies that deposit and form immune complexes in kidney, leading to irreparable tissue damage and resulting in lupus nephritis. In a New Zealand Black X New Zealand White F1 mouse model, we tested two different small interfering RNA (siRNA) silencing treatments against interferon regulatory factor 5 (IRF5) and B cell-activating factor (BLYSS) expression and their combination in a second set of animals. The administration of these two siRNAs separately prevented the progression of proteinuria and albuminuria at similar levels to that in cyclophosphamide animals. These treatments effectively resulted in a reduction of serum anti-double-stranded DNA (dsDNA) antibodies and histopathological renal score compared with non-treated group. Treated groups showed macrophage, T cell, and B cell infiltrate reduction in renal tissue. Moreover, kidney gene expression analysis revealed that siRNA treatments modulated very few pathways in contrast to cyclophosphamide, despite showing similar therapeutic effects. Additionally, the combined therapy tested in a second set of animals, in which the disease appeared more virulent, exhibited better results than monotherapies in the disease progression, delaying the disease onset and ameliorating the disease outcome. Herein, we provide the potential therapeutic effect of both selective IRF5 and BLYSS silencing as an effective and potential treatment, particularly in early phases of the disease.

Targeting B cells for inflammatory bowel disease treatment: back to the future

B cells are critical to immune homeostasis at mucosal surfaces including those of the gastrointestinal tract. B cell-related abnormalities, comprising of a lympho-plasmacytic infiltrate, as well as anti-microbial antibodies, are well reported in patients with inflammatory bowel disease (IBD). However, B cell-targeting is not part of the therapeutic armamentarium in IBD. Recently, driven by the identification of genetic associations between IgG Fc receptors and IBD susceptibility, there has been renewed interest in defining the immunobiology of B cells during mucosal inflammation. Functional studies have demonstrated mechanisms of IgG-mediated disease pathogenesis and deep mucosal immunophenotyping using single cell RNA sequencing has elaborated a significant remodelling of the B cell compartment in IBD. In light of these novel data, here we discuss potential strategies to target B cell immunity in IBD. Finally, we discuss potential risks and pitfalls of these approaches and emphasize on distinguishing between homeostatic and pathological B cell signatures, allowing for a data-based, prudent therapeutic approach.

BAFF 60-mer, and Differential BAFF 60-mer Dissociating Activities in Human Serum, Cord Blood and Cerebrospinal Fluid

B cell activation factor of the TNF family (BAFF/BLyS), an essential B cell survival factor of which circulating levels are elevated in several autoimmune disorders, is targeted in the clinic for the treatment of systemic lupus erythematosus (SLE). The soluble form of BAFF can exist as 3-mer, or as 60-mer that results from the ordered assembly of twenty 3-mers and that can be obtained from naturally cleaved membrane-bound BAFF or made as a recombinant protein. However, which forms of soluble BAFF exist and act in humans is unclear. In this study, BAFF 3-mer and 60-mer in biological fluids were characterized for size, activity and response to specific stimulators or inhibitors of BAFF. Human cerebrospinal fluids (CSF) from patients with multiple sclerosis and adult human sera contained exclusively BAFF 3-mer in these assays, also when BAFF concentrations were moderately SLE or highly (BAFFR-deficient individual) increased. Human sera, but not CSF, contained a high molecular weight, saturable activity that dissociated preformed recombinant BAFF 60-mer into 3-mer. This activity was lower in cord blood. Cord blood displayed BAFF levels 10-fold higher than in adults and consistently contained a fair proportion of active high molecular weight BAFF able to dissociate into 3-mer but not endowed with all properties of recombinant BAFF 60-mer. If BAFF 60-mer is produced in humans, it is dissociated, or at least attenuated in the circulation.

Etanercept Inhibits B Cell Differentiation by Regulating TNFRII/TRAF2/NF-κB Signaling Pathway in Rheumatoid Arthritis

Objective

To explore the role of B cells in rheumatoid arthritis (RA) and the potential effects and mechanisms of etanercept on B cells.

Methods

In RA patients, the levels of tumor necrosis factor-α (TNF-α) and B cell activating factor (BAFF) were detected by ELISA. The percentage of B cell subsets was measured by flow cytometry. Laboratory indicators (rheumatoid factor, C-reactive protein, erythrocyte sedimentation rate) and clinical indicators (disease activity score in 28 joints, health assessment questionnaire score, swollen joint counts, tender joint counts) were measured. The correlation between B cell subsets and laboratory indicators or clinical indicators was analyzed. In mice, B cells proliferation was detected by CCK-8 kit. The expression of TNFRII and the percentage of B cell subsets in spleen were detected by flow cytometry. The expressions of TRAF2, p38, P-p38, p65, P-p65 in B cells were detected by WB.

Results

The percentage of CD19⁻CD27⁺CD138⁺ plasma B cells was positively correlated with ESR or RF. Etanercept could decrease the percentage of CD19⁺ total B cells, CD19⁺CD27⁺ memory B cells and CD19⁻CD27⁺CD138⁺ plasma B cells, reduce the levels of TNF-α, BAFF, relieve clinical and laboratory indicators in RA patients. In addition, etanercept could inhibit the proliferation of B cells, bate the differentiation of transitional B cells to mature B cells, down-regulate the expression of TNFRII, TRAF2, P-p38, P-p65 in B cells.

Conclusion

B cells act a key role in the pathogenesis of RA. Etanercept inhibits B cells differentiation by down-regulating TNFRII/TRAF2/NF-κB signaling pathway.

Abnormal expression of BAFF and its receptors in peripheral blood and skin lesions from systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by abnormal T and B cells. B-cell activating factor (BAFF) has been suggested to play a crucial role in lupus by promoting the proliferation, differentiation, and survival of B cells. Increased serum levels of BAFF have been found in patients with lupus. However, the expression of BAFF and its receptors on immune cells and in skin has not been systematically reported before. Here, we report that SLE patients showed increased levels of BAFF on circulating CD3⁺ T cells and B-cell maturation antigen (BCMA) on CD14⁺ monocytes and dramatically increased expression of BAFF in lupus skin lesions compared with those of healthy controls. TACI was undetectable on circulating immune cells. An increased serum level of BAFF was also confirmed in lupus patients in this study. Our findings may provide a better understanding of the pathogenesis and predictors of BAFF antibody treatment response, as well as potential targets for skin therapies.

The pathological role of B cells in systemic lupus erythematosus: From basic research to clinical

Systemic lupus erythematosus (SLE) is an autoimmune disease that often occurs in females of child-bearing age. It involves multiple systems and severely threatens human life. One of the typical characteristics of SLE is the formation of immune complexes with autoantibodies produced by B cells that target various autoantigens, thus indicating the pivotal role of B cells in the pathogenesis of SLE. Increasing evidence has shown abnormal expression of B cells in the peripheral blood of SLE patients. Moreover, numerous studies have shown that B cells in SLE patients are abnormally activated, as well as aberrantly differentiated, and are involved in the inflammatory cytokine milieu, abnormal transcription factor activity, and signalling pathways. Several biological therapies targeting B cells, such as anti-CD20 antibodies, have been intensively studied in preclinical and clinical trials. However, the results have not met expectations. Therefore, new therapies targeting B cells are in great need. This review will summarize the latest progress in basic research on B cells to better understand the pathogenesis of SLE and will discuss the outcomes of B-cell-targeting treatments that provide potential therapeutic targets and strategies for SLE. Studies have clarified high levels of IL-21 in serum from SLE patients and animal models. IL-21 promotes B cell differentiation, which results in antibodies accumulation leads to SLE. Therefore, further studies on IL-21 will give new perspectives on SLE treatments. In addition, the application of drugs targeting plasma cell depletion in SLE patients may also achieve satisfied results in treatment.

BAFF inhibition in SLE-Is tolerance restored?

The B cell activating factor (BAFF) inhibitor, belimumab, is the first biologic drug approved for the treatment of SLE, and exhibits modest, but durable, efficacy in decreasing disease flares and organ damage. BAFF and its homolog APRIL are TNF-like cytokines that support the survival and differentiation of B cells at distinct developmental stages. BAFF is a crucial survival factor for transitional and mature B cells that acts as rheostat for the maturation of low-affinity autoreactive cells. In addition, BAFF augments innate B cell responses via complex interactions with the B cell receptor (BCR) and Toll like receptor (TLR) pathways. In this manner, BAFF impacts autoreactive B cell activation via extrafollicular pathways and fine tunes affinity selection within germinal centers (GC). Finally, BAFF and APRIL support plasma cell survival, with differential impacts on IgM- and IgG-producing populations. Therapeutically, BAFF and combined BAFF/APRIL inhibition delays disease onset in diverse murine lupus strains, although responsiveness to BAFF inhibition is model dependent, in keeping with heterogeneity in clinical responses to belimumab treatment in humans. In this review, we discuss the mechanisms whereby BAFF/APRIL signals promote autoreactive B cell activation, discuss whether altered selection accounts for therapeutic benefits of BAFF inhibition, and address whether new insights into BAFF/APRIL family complexity can be exploited to improve human lupus treatments.

A novel human anti-BAFF neutralizing monoclonal antibody derived from in vitro immunization

B-cell activating factor (BAFF) plays a key role in the normal regulation of B cell development and immune response. Its abnormal expression level is accompanied by the occurrence of various autoimmune diseases. Therefore, BAFF is an effective target for the treatment of such diseases. Here, we report a new anti-BAFF monoclonal antibody. Based on improved in vitro immunization method, we used a recombinant BAFF containing unnatural amino acid p-nitro-phenylalanine (pNO₂Phe) as an antigen to trigger immune response in vitro. The plasma cells were sorted by flow cytometry (FACS), and the antibody library was constructed based on the sorted plasma cells. The high affinity antigen-binding fragments were panned by phage display technology, and finally the anti-BAFF human IgG was obtained. The antibody demonstrated its ability to neutralize BAFF effectively both in vitro and in vivo. We propose that this novel full-length human anti-BAFF monoclonal antibody is a promising therapeutic candidate for the treatment of autoimmune diseases.

Inhibition of Membrane-Bound BAFF by the Anti-BAFF Antibody Belimumab

B cell activating factor of the TNF family (BAFF, also known as BLyS), a cytokine that regulates homeostasis of peripheral B cells, is elevated in the circulation of patients with autoimmune diseases such as systemic lupus erythematosus (SLE). BAFF is synthetized as a membrane-bound protein that can be processed to a soluble form after cleavage at a furin consensus sequence, a site that in principle can be recognized by any of the several proteases of the pro-protein convertase family. Belimumab is a human antibody approved for the treatment of SLE, often cited as specific for the soluble form of BAFF. Here we show in different experimental systems, including in a monocytic cell line (U937) that naturally expresses BAFF, that belimumab binds to membrane-bound BAFF with similar EC50 as the positive control atacicept, which is a decoy receptor for both BAFF and the related cytokine APRIL (a proliferation inducing ligand). In U937 cells, binding of both reagents was only detectable in furin-deficient U937 cells, showing that furin is the main BAFF processing protease in these cells. In CHO cells expressing membrane-bound BAFF lacking the stalk region, belimumab inhibited the activity of membrane-bound BAFF less efficiently than atacicept, while in furin-deficient U937 cells, belimumab inhibited membrane-bound BAFF and residual soluble BAFF as efficiently as atacicept. These reagents did not activate complement or antibody-dependent cell cytotoxicity upon binding to membrane-bound BAFF in vitro. In conclusion, our data show that belimumab can inhibit membrane-bound BAFF, and that BAFF in U937 cells is processed by furin.

Improvement of pharmacokinetic properties of therapeutic antibodies by antibody engineering

Monoclonal antibodies (mAbs) have become an important therapeutic option for several diseases. Since several mAbs have shown promising efficacy in clinic, the competition to develop mAbs has become severe. In efforts to gain a competitive advantage over other mAbs and provide significant benefits to patients, innovations in antibody engineering have aimed at improving the pharmacokinetic properties of mAbs. Because engineering can provide therapeutics that are more convenient, safer, and more efficacious for patients in several disease areas, it is an attractive approach to provide significant benefits to patients. Further advances in engineering mAbs to modulate their pharmacokinetics were driven by the increase of total soluble target antigen concentration that is often observed after injecting a mAb, which then requires a high dosage to antagonize. To decrease the required dosage, several antibody engineering techniques have been invented that reduce the total concentration of soluble target antigen. Here, we review the various ways that antibody engineering can improve the pharmacokinetic properties of mAbs.