The role of B lymphocyte stimulator in B cell biology: implications for the treatment of lupus

Circulating and skin biopsy-present cytokines related to the pathogenesis of cutaneous lupus erythematosus

Cutaneous lupus erythematosus (CLE) is a common disease that may appear as a separate entity from systemic lupus erythematosus (SLE), precede SLE development, or occur as a manifestation of this systemic disease. It has a complex pathophysiology that involves genetic, environmental, and immune-mediated factors creating a self-amplification pro-inflammatory cycle. CLE is characterized by prominent type I interferons (IFNs) inflammation which are considered as the first precursors of the inflammatory cascade generated within the pathophysiology of CLE. TNF-α enhances the production of antibodies through the activation of B cells, and favors the expression of surface nuclear antigens on keratinocytes. UV light exposure favors keratinocyte apoptosis or necroptosis, which results in the release of multiple proinflammatory cytokines, including IL-6, IL-1α, IL-1β, TNF-α, IFNs, and CXCL10. Serum levels of IL-17 are elevated in patients with ACLE, SCLE, and DLE. Evidence suggests IL-22 plays a role primarily in tissue repair rather than in inflammation. High expression of BAFF and its receptors have been found in lesioned keratinocytes of patients with CLE, and patients with CLE have lower serum levels of the regulatory cytokines TGF-β and IL-10. The chemokines CXCL9 and CXCL10 (CXCR3 ligands) have an increased expression among these patients, and their expression is correlated with IFNs levels. CXCR3 ligands recruit cytotoxic type I cells through this receptor, further supporting the death of keratinocytes via necroptosis with the subsequent release of eNAs perpetuating the inflammatory cycle. Interface dermatitis is characterized by the presence of CXCR3-positive lymphocytes. This review describes the leading cytokines and chemokines present in the circulation and skin that play a fundamental role in the pathogenesis of CLE.

Mechanism of action of baricitinib and identification of biomarkers and key immune pathways in patients with active systemic lupus erythematosus

OBJECTIVES

To elucidate the mechanism of action of baricitinib, a Janus kinase (JAK) 1/2 inhibitor, and describe immunological pathways related to disease activity in adults with systemic lupus erythematosus (SLE) receiving standard background therapy in a phase II trial.

METHODS

Patients with SLE were treated with baricitinib 2 mg or 4 mg in a phase II randomised, placebo-controlled study. Sera from 239 patients (baricitinib 2 mg: n=88; baricitinib 4 mg: n=82; placebo: n=69) and 49 healthy controls (HCs) were collected at baseline and week 12 and analysed using a proximity extension assay (Target 96 Inflammation Panel (Olink)). Interferon (IFN) scores were determined using an mRNA panel. Analytes were compared in patients with SLE versus HCs and in changes from baseline at week 12 between baricitinib 2 mg, 4 mg and placebo groups using a restricted maximum likelihood-based mixed models for repeated measures. Spearman correlations were computed for analytes and clinical measurements.

RESULTS

At baseline, SLE sera had strong cytokine dysregulation relative to HC sera. C-C motif chemokine ligand (CCL) 19, C-X-C motif chemokine ligand (CXCL) 10, tumour necrosis factor alpha (TNF-α), TNF receptor superfamily member (TNFRSF)9/CD137, PD-L1, IL-6 and IL-12β were significantly reduced in patients treated with baricitinib 4 mg versus placebo at week 12. Inflammatory biomarkers indicated correlations/associations with type I IFN (CCL19, CXCL10, TNF-α and PD-L1), anti-double stranded DNA (dsDNA) (TNF-α, CXCL10) and Systemic Lupus Erythematosus Disease Activity Index-2000, tender and swollen joint count and worst joint pain (CCL19, IL-6 and TNFRSF9/CD137).

CONCLUSION

These results suggest that baricitinib 4 mg downregulated key cytokines that are upregulated in patients with SLE and may play a role in a multitargeted mechanism beyond the IFN signature although clinical relevance remains to be further delineated.

TRIAL REGISTRATION NUMBER

NCT02708095.

Abrogated AID Function Prolongs Survival and Diminishes Renal Pathology in the BXSB Mouse Model of Systemic Lupus Erythematosus

Almost a decade has passed since the approval of belimumab, an mAb directed against B lymphocyte stimulation and the first targeted therapy approved for systemic lupus erythematous (SLE) in over 50 y. Although well tolerated, the efficacy of belimumab remains limited and is not labeled for patients suffering from nephritis, the leading cause of patient mortality. We sought to explore alternative targets of autoreactive B lymphocytes through manipulation of affinity maturation. The BXSB/MpJ mouse, a well-established model of human SLE, develops elevated antinuclear Abs and immune complex-mediated nephritis along with other manifestations of SLE-like disease. To limit interfering with critical background genetics, we used CRISPR-Cas9 to disrupt activation-induced cytidine deaminase (AID; Aicda) directly in BXSB zygotes. Homozygous null mice demonstrated significantly prolonged survival compared with wild-type. Although mice continued to develop plasma cells, splenic follicular structure was restored, and renal pathology was reduced. Mice developed expanded germinal center B lymphocyte populations as in other models of AID deficiency as well as increased populations of CD73⁺ B lymphocytes. Treatment with the small molecule inhibitor of RAD51, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid, resulted in minimal changes in disease markers in BXSB mice. The prolonged survival in AID-deficient BXSB mice appears attributed primarily to the reduced renal pathology, warranting further exploration, as current therapeutics targeting lupus nephritis are limited and, thus, in great demand.

Autoreactive B cells in SLE, villains or innocent bystanders?

The current concepts for development of autoreactive B cells in SLE (systemic lupus erythematosus) focus on extrinsic stimuli and factors that provoke B cells into tolerance loss. Traditionally, major tolerance loss pathways are thought to be regulated by factors outside the B cell including autoantigen engagement of the B-cell receptor (BCR) with simultaneous type I interferon (IFN) produced by dendritic cells, especially plasmacytoid dendritic cells (pDCs). Later, in autoreactive follicles, B-cells encounter T-follicular helper cells (Tfh) that produce interleukin (IL)-21, IL-4 and pathogenic cytokines, IL-17 and IFN gamma (IFNɣ). This review discusses these mechanisms and also highlights recent advances pointing to the peripheral transitional B-cell stage as a major juncture where transient autocrine IFNβ expression by developing B-cells imprints a heightened susceptibility to external factors favoring differentiation into autoantibody-producing plasmablasts. Recent studies highlight transitional B-cell heterogeneity as a determinant of intrinsic resistance or susceptibility to tolerance loss through the shaping of B-cell responsiveness to cytokines and other environment factors.

Belimumab alters transitional B-cell subset proportions in patients with stable systemic lupus erythematosus

OBJECTIVE

We evaluated the effects of the B-cell activating factor (BAFF)-targeting antibody Belimumab on human nonmemory B-cell pools. Human B-cell pools were identified using surface markers adapted from mouse studies that specifically assessed reductions in immature B cells due to BAFF depletion. Patients with systemic lupus erythematosus (SLE) have high levels of both BAFF and immature B cells. Mechanistic mouse studies provide a framework for understanding human responses to therapies that target B cells.

METHODS

Peripheral blood mononuclear cells were isolated from healthy donors and SLE patients on Belimumab or standard-of-care therapy (SCT). Cells were stained for flow cytometry to identify B-cell subsets based on CD21/CD24. Differences in subset proportions were determined by one-way ANOVA and Tukey's post hoc test.

RESULTS

Patients treated with Belimumab show alterations in the nonmemory B-cell pool characterized by a decrease in the Transitional 2 (T2) subset (p = 0.002), and an increase in the proportion of Transitional 1 (T1) cells (p = 0.005) as compared with healthy donors and SCT patients. The naïve B-cell compartment showed no significant differences between the groups (p = 0.293).

CONCLUSION

Using a translational approach, we show that Belimumab-mediated BAFF depletion reduces the T2 subset in patients, similar to observations in mouse models with BAFF depletion.

Belimumab promotes negative selection of activated autoreactive B cells in systemic lupus erythematosus patients

Belimumab has therapeutic benefit in active systemic lupus erythematosus (SLE), especially in patients with high-titer anti-dsDNA antibodies. We asked whether the profound B cell loss in belimumab-treated SLE patients is accompanied by shifts in the immunoglobulin repertoire. We enrolled 15 patients who had been continuously treated with belimumab for more than 7 years, 17 matched controls, and 5 patients who were studied before and after drug initiation. VH genes of sort-purified mature B cells and plasmablasts were subjected to next-generation sequencing. We found that B cell-activating factor (BAFF) regulates the transitional B cell checkpoint, with conservation of transitional 1 (T1) cells and approximately 90% loss of T3 and naive B cells after chronic belimumab treatment. Class-switched memory B cells, B1 B cells, and plasmablasts were also substantially depleted. Next-generation sequencing revealed no redistribution of VH, DH, or JH family usage and no effect of belimumab on representation of the autoreactive VH4-34 gene or CDR3 composition in unmutated IgM sequences, suggesting a minimal effect on selection of the naive B cell repertoire. Interestingly, a significantly greater loss of VH4-34 was observed among mutated IgM and plasmablast sequences in chronic belimumab-treated subjects than in controls, suggesting that belimumab promotes negative selection of activated autoreactive B cells.

Toll-like receptor-9 is involved in the development of B cell stimulating factor-induced systemic lupus erythematosus

The objective of the present study was to investigate the role of Toll-like receptor (TLR)-9 in B lymphocyte stimulating factor (BLyS)-induced systemic lupus erythematosus (SLE) in mice. The anti-double stranded (ds)DNA antibody titer, levels of complement proteins (C3 and C4), interleukin (IL)-10 and the disease activity [assessed by the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level] were measured. A total of 21 transgenic female mice (aged 8-10 weeks and weighing 30-40 g) expressing the Epstein-Barr virus membrane antigen, BLLF1, were studied. Mice were randomly divided into the control, the BLyS inhibition and the TLR-9 inhibition groups, with 7 mice in each group. Mice in the blank control group received intraperitoneal injections of normal saline, mice in the BLyS inhibition group received intraperitoneal injections of anti-BR3 monoclonal antibody (5,000 ng/day) and mice in the TLR-9 inhibition group received intraperitoneal injections of anti-human TLR-9 antibody (250 ng/day). The treatment regimens continued for 10 days, followed by the collection of peripheral venous blood. The relative levels of TLR-9 mRNA were measured by reverse transcription-quantitative polymerase chain reaction. Furthermore, the BLyS protein concentration and IL-10 levels were measured by ELISA. TLR-9 mRNA, BLyS, IL-10, anti-dsDNA antibody titer, C3, C4, ESR and CRP levels of the blank control group were significantly higher than those of the other two groups (P<0.05). The differences in comparison of these indexes between the BLyS inhibition and TLR-9 inhibition groups were not statistically significant (P>0.05), with the exception of TLR-9 mRNA and BLyS. In conclusion, the TLR-9 signaling pathway may be important for BLyS-induced SLE, and regulation of the inflammatory immune level.

BAFF Induces Tertiary Lymphoid Structures and Positions T Cells within the Glomeruli during Lupus Nephritis

Tissue-specific immune responses play an important role in the pathology of autoimmune diseases. In systemic lupus erythematosus, deposits of IgG-immune complexes and the activation of complement in the kidney have long been thought to promote inflammation and lupus nephritis. However, the events that localize cells in non-lymphoid tertiary organs and sustain tissue-specific immune responses remain undefined. In this manuscript, we show that BAFF promotes events leading to lupus nephritis. Using an inducible model of systemic lupus erythematosus, we found that passive transfer of antinucleosome IgG into AID^-/-MRL/lpr mice elevated autoantibody levels and promoted lupus nephritis by inducing BAFF production in the kidneys, and the formation of renal tertiary lymphoid structures (TLSs). Reducing BAFF in vivo prevented the formation of TLSs and lupus nephritis; however, it did not reduce immune cell infiltrates, or the deposits of IgG and complement in the kidney. Mechanistically, lowering BAFF levels also diminished the number of T cells positioned inside the glomeruli and reduced inflammation. Thus, BAFF plays a previously unappreciated role in lupus nephritis by inducing renal TLSs and regulating the position of T cells within the glomeruli.

Vibration Induces BAFF Overexpression and Aberrant O-Glycosylation of IgA1 in Cultured Human Tonsillar Mononuclear Cells in IgA Nephropathy

Objective. To investigate the influence of in vitro vibratory stimulation of human tonsillar mononuclear cells (TMCs). Methods. Fourteen IgA nephropathy (IgAN) patients with chronic tonsillitis (CT) and 12 CT patients with no renal pathology were enrolled. Group A TMCs were collected after 24 hours of culture and used to determine baseline levels. TMCs in groups B, C, D, E, and F were exposed to vibratory stimulation (60 Hz) for 0 (as the control group), 1, 3, 5, and 10 minutes, respectively. Results. Baseline concentrations of B-cell-activation factor (BAFF) and IgA1, BAFF mRNA expression, and aberrant O-glycosylation IgA1 level were higher in the IgAN group as compared to that in the CT group, and all increased after vibratory stimulation. Baseline mRNA expressions of core β1,3-galactosyltransferase (C1GALT1) and core β1,3GalT-specific molecular chaperone (Cosmc) were lower in the IgAN group; the levels decreased further after vibratory stimulation. Conclusion. In patients with IgAN, vibratory stimulation of TMCs appears to induce IgA1 secretion through activation of BAFF release and to aberrant O-glycosylation IgA1 by suppressing C1GALT1 and Cosmc expression. In vitro vibratory stimulation of human TMCs mimics the vibratory simulation of palatine tonsils produced by vocal cords during phonation.

Impact of population admixture on the distribution of immune response co-stimulatory genes polymorphisms in a Brazilian population

Co-stimulatory molecules are essential in the orchestration of immune response and polymorphisms in their genes are associated with various diseases. However, in the case of variable allele frequencies among continental populations, this variation can lead to biases in genetic studies conducted in admixed populations such as those from Brazil. The aim of this study was to evaluate the influence of genomic ancestry on distributions of co-stimulatory genes polymorphisms in an admixed Brazilian population. A total of 273 individuals from the north of Brazil participated in this study. Nine single nucleotide polymorphisms in 7 genes (CD28, CTLA4, ICOS, CD86, CD40, CD40L and BLYS) were determined by polymerase chain reaction-restriction fragment length polymorphism. We also investigated 48 insertion/deletion ancestry markers to characterize individual African, European and Amerindian ancestry proportions in the samples. The analysis showed that the main contribution was European (43.9%) but also a significant contribution of African (31.6%) and Amerindian (24.5%) ancestry. ICOS, CD40L and CD86 polymorphisms were associated with genomic ancestry. However there were no significant differences in the proportions of ancestry for the other SNPs and haplotypes studied. Our findings reinforce the need to apply AIMs in genetic association studies involving these polymorphisms in the Brazilian population.

New treatments for inflammatory rheumatic disease

As our understanding of the pathogenesis of autoimmune diseases is growing, new therapies are being developed to target disease-specific pathways. Since the introduction of etanercept in 1998, several biotechnological agents have been developed, most of them indicated in the treatment of rheumatoid arthritis, but also psoriatic arthritis. Most currently available molecules target TNF-alfa with different strategies (i.e., etanercept, infliximab, adalimumab, golimumab, and certolizumab pegol), IL-6 (tocilizumab), CTLA-4 (abatacept), and B cells (rituximab, belimumab) as they are key mediators in the cascade of inflammation. Further, small molecules have been recently developed to target intracellular signaling, such as Janus Kinases for tofacitinib, the first FDA-approved small molecule for rheumatoid arthritis. Most novel treatments are being developed for arthritis with specific differences between rheumatoid and psoriatic arthritis, as well as for systemic lupus erythematosus, following the approval of belimumab. Finally, biologic therapies are effective also in gout, mainly targeting interleukin-1 to block the inflammasome. This review article describes the new and upcoming treatment options for rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, and gout to dissect what we should be aware of when discussing these new and promising molecules.

Violation of an evolutionarily conserved immunoglobulin diversity gene sequence preference promotes production of dsDNA-specific IgG antibodies

Variability in the developing antibody repertoire is focused on the third complementarity determining region of the H chain (CDR-H3), which lies at the center of the antigen binding site where it often plays a decisive role in antigen binding. The power of VDJ recombination and N nucleotide addition has led to the common conception that the sequence of CDR-H3 is unrestricted in its variability and random in its composition. Under this view, the immune response is solely controlled by somatic positive and negative clonal selection mechanisms that act on individual B cells to promote production of protective antibodies and prevent the production of self-reactive antibodies. This concept of a repertoire of random antigen binding sites is inconsistent with the observation that diversity (D_H) gene segment sequence content by reading frame (RF) is evolutionarily conserved, creating biases in the prevalence and distribution of individual amino acids in CDR-H3. For example, arginine, which is often found in the CDR-H3 of dsDNA binding autoantibodies, is under-represented in the commonly used D_H RFs rearranged by deletion, but is a frequent component of rarely used inverted RF1 (iRF1), which is rearranged by inversion. To determine the effect of altering this germline bias in D_H gene segment sequence on autoantibody production, we generated mice that by genetic manipulation are forced to utilize an iRF1 sequence encoding two arginines. Over a one year period we collected serial serum samples from these unimmunized, specific pathogen-free mice and found that more than one-fifth of them contained elevated levels of dsDNA-binding IgG, but not IgM; whereas mice with a wild type D_H sequence did not. Thus, germline bias against the use of arginine enriched D_H sequence helps to reduce the likelihood of producing self-reactive antibodies.

DNA vaccine molecular adjuvants SP-D-BAFF and SP-D-APRIL enhance anti-gp120 immune response and increase HIV-1 neutralizing antibody titers

Broadly neutralizing antibodies (bNAbs) specific for conserved epitopes on the HIV-1 envelope (Env) are believed to be essential for protection against multiple HIV-1 clades. However, vaccines capable of stimulating the production of bNAbs remain a major challenge. Given that polyreactivity and autoreactivity are considered important characteristics of anti-HIV bNAbs, we designed an HIV vaccine incorporating the molecular adjuvants BAFF (B cell activating factor) and APRIL (a proliferation-inducing ligand) with the potential to facilitate the maturation of polyreactive and autoreactive B cells as well as to enhance the affinity and/or avidity of Env-specific antibodies. We designed recombinant DNA plasmids encoding soluble multitrimers of BAFF and APRIL using surfactant protein D as a scaffold, and we vaccinated mice with these molecular adjuvants using DNA and DNA-protein vaccination strategies. We found that immunization of mice with a DNA vaccine encoding BAFF or APRIL multitrimers, together with interleukin 12 (IL-12) and membrane-bound HIV-1 Env gp140, induced neutralizing antibodies against tier 1 and tier 2 (vaccine strain) viruses. The APRIL-containing vaccine was particularly effective at generating tier 2 neutralizing antibodies following a protein boost. These BAFF and APRIL effects coincided with an enhanced germinal center (GC) reaction, increased anti-gp120 antibody-secreting cells, and increased anti-gp120 functional avidity. Notably, BAFF and APRIL did not cause indiscriminate B cell expansion or an increase in total IgG. We propose that BAFF and APRIL multitrimers are promising molecular adjuvants for vaccines designed to induce bNAbs against HIV-1.

IMPORTANCE

Recent identification of antibodies that neutralize most HIV-1 strains has revived hopes and efforts to create novel vaccines that can effectively stimulate HIV-1 neutralizing antibodies. However, the multiple immune evasion properties of HIV have hampered these efforts. These include the instability of the gp120 trimer, the inaccessibility of the conserved sequences, highly variable protein sequences, and the loss of HIV-1-specific antibody-producing cells during development. We have shown previously that tumor necrosis factor (TNF) superfamily ligands, including BAFF and APRIL, can be multitrimerized using the lung protein SP-D (surfactant protein D), enhancing immune responses. Here we show that DNA or DNA-protein vaccines encoding BAFF or APRIL multitrimers, IL-12p70, and membrane-bound HIV-1 Env gp140 induced tier 1 and tier 2 neutralizing antibodies in a mouse model. BAFF and APRIL enhanced the immune reaction, improved antibody binding, and increased the numbers of anti-HIV-1 antibody-secreting cells. Adaptation of this vaccine design may prove useful in designing preventive HIV-1 vaccines for humans.

Dedicator of cytokinesis 8-deficient patients have a breakdown in peripheral B-cell tolerance and defective regulatory T cells

BACKGROUND

Dedicator of cytokinesis 8 (DOCK8) deficiency is typified by recurrent infections, increased serum IgE levels, eosinophilia, and a high incidence of allergic and autoimmune manifestations.

OBJECTIVE

We sought to determine the role of DOCK8 in the establishment and maintenance of human B-cell tolerance.

METHODS

Autoantibodies were measured in the plasma of DOCK8-deficient patients. The antibody-coding genes from new emigrant/transitional and mature naive B cells were cloned and assessed for their ability to bind self-antigens. Regulatory T (Treg) cells in the blood were analyzed by means of flow cytometry, and their function was tested by examining their capacity to inhibit the proliferation of CD4(+)CD25(-) effector T cells.

RESULTS

DOCK8-deficient patients had increased levels of autoantibodies in their plasma. We determined that central B-cell tolerance did not require DOCK8, as evidenced by the normally low frequency of polyreactive new emigrant/transitional B cells in DOCK8-deficient patients. In contrast, autoreactive B cells were enriched in the mature naive B-cell compartment, revealing a defective peripheral B-cell tolerance checkpoint. In addition, we found that Treg cells were decreased and exhibited impaired suppressive activity in DOCK8-deficient patients.

CONCLUSIONS

Our data support a critical role for DOCK8 in Treg cell homeostasis and function and the enforcement of peripheral B-cell tolerance.

Rationale for B cell targeting in SLE

B cells are central pathogenic players in systemic lupus erythematosus and multiple other autoimmune diseases through antibody production as well as antibody independent function. At the same time, B cells are known to play important regulatory functions that may protect against autoimmune manifestations. Yet, the functional role of different B cell populations and their contribution to disease remain to be understood. The advent of agents that specifically target B cells, in particular anti-CD20 and ant-BLyS antibodies, have demonstrated the efficacy of this approach for the treatment of human autoimmunity. The analysis of patients treated with these and other B cell agents provides a unique opportunity to understand the correlates of clinical response and the significance of different B cell subsets. Here, we discuss this information and how it could be used to better understand SLE and improve the rational design of B cell-directed therapies in this disease.

Association of signaling transducers and activators of transcription 1 and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is complex autoimmune disease which involves various facets of the immune system. Signaling transducers and activators of transcription 1 (STAT1) belongs to the family of STAT transcription factors that mediate various biological responses. Recently, studies in both experimental animal models of lupus and patients with SLE have revealed expression and activation of STAT1 is closely associated with the pathogenesis of SLE. Moreover, increased production of interferons (IFNs) and aberrant activation of IFNs signaling, which is mechanistically linked to increased level of STAT1, are crucial for the development of SLE. Therefore, we will focus on the association of STAT1 and SLE based on recent understandings to render more information about the mechanisms of STAT1 might perform in. Hopefully, the information obtained will lead to a better understanding of the development and pathogenesis of systemic autoimmune diseases, as well as its clinical implications and therapeutic potential.