TACI and BCMA are receptors for a TNF homologue implicated in B-cell autoimmune disease

Nogo-receptors NgR1 and NgR2 do not mediate regulation of CD4 T helper responses and CNS repair in experimental autoimmune encephalomyelitis

Myelin-associated inhibition of axonal regrowth after injury is considered one important factor that contributes to regeneration failure in the adult central nervous system (CNS). Blocking strategies targeting this pathway have been successfully applied in several nerve injury models, including experimental autoimmune encephalomyelitis (EAE), suggesting myelin-associated inhibitors (MAIs) and functionally related molecules as targets to enhance regeneration in multiple sclerosis. NgR1 and NgR2 were identified as interaction partners for the myelin proteins Nogo-A, MAG and OMgp and are probably mediating their growth-inhibitory effects on axons, although the in vivo relevance of this pathway is currently under debate. Recently, alternative functions of MAIs and NgRs in the regulation of immune cell migration and T cell differentiation have been described. Whether and to what extent NgR1 and NgR2 are contributing to Nogo and MAG-related inhibition of neuroregeneration or immunomodulation during EAE is currently unknown. Here we show that genetic deletion of both receptors does not promote functional recovery during EAE and that NgR1 and NgR2-mediated signals play a minor role in the development of CNS inflammation. Induction of EAE in Ngr1/2-double mutant mice resulted in indifferent disease course and tissue damage when compared to WT controls. Further, the development of encephalitogenic CD4⁺ Th1 and Th17 responses was unchanged. However, we observed a slightly increased leukocyte infiltration into the CNS in the absence of NgR1 and NgR2, indicating that NgRs might be involved in the regulation of immune cell migration in the CNS. Our study demonstrates the urgent need for a more detailed knowledge on the multifunctional roles of ligands and receptors involved in CNS regeneration failure.

Molecular cloning, expression and functional analysis of TNF13b (BAFF) in Japanese sea perch, Lateolabrax japonicus

Members of the tumor necrosis factor (TNF) family play key roles in the regulation of inflammation, immune responses and tissue homeostasis. Here we describe the identification of the Japanese sea perch (Lateolabrax japonicus) homologue of mammalian B cell activating factor of the TNF family (BAFF/BLyS) (designated LjBAFF). The cDNA contains an open reading frame (ORF) of 783 nucleotides that are translated into a predicted 260 amino acid protein. Like most known BAFFs, Japanese sea perch BAFF contains three cysteine residues (Cys(123), Cys(218) and Cys(232)) which are conserved in the aligned BAFF sequences and a furin protease cleavage site (R-K-K-R). Real-time quantitative PCR (qPCR) analysis revealed that LjBAFF could be detected in various tissues and predominantly expressed in lymphoid tissue spleen. The soluble BAFF (LjsBAFF) had been cloned into a pET28a vector to express the recombinant protein. The His-LjsBAFF was efficiently expressed in Escherichia coli BL21 (DE3) and its expression was confirmed by SDS-PAGE and Western blotting analysis. After purification, MTT assays and flow cytometric analysis revealed that LjsBAFF could promote the survival/proliferation of splenic B cells in vitro. Furthermore, bacterially expressed LjsBAFF induced the selective expansion of B cells in the spleen when administered to young mice. Our results suggest that like its mammalian counterparts, LjsBAFF plays an important role in the survival and/or proliferation of B cells.

Biodistribution, pharmacokinetics, and nuclear imaging studies of 111In-labeled rGel/BLyS fusion toxin in SCID mice bearing B cell lymphoma

PURPOSE

We examined the biodistribution and pharmacokinetics of (111)In-labeled rGel/BLyS, a gelonin toxin (rGel)-B lymphocyte stimulator (BLyS) fusion protein.

MATERIALS AND METHODS

rGel/BLyS was labeled with In-111 through DTPA with a labeling efficiency >95%. Biodistribution/imaging studies were obtained in severe-combined immunodeficiency mice bearing diffuse large B cell lymphoma OCI-Ly10. Pharmacokinetic studies were performed in BALB/c mice.

RESULTS

In vitro, DTPA-conjugated rGel/BLyS displayed selective cytotoxicity against OCI-Ly10 cells and mantle cell lymphoma JeKo cells. In vivo, rGel/BLyS exhibited a tri-exponential disposition with a rapid initial mean distribution followed by an extensive mean distribution and a long terminal elimination phase. At 48 h after injection, uptake of the radiotracer in tumors was 1.25 %ID/g, with a tumor-to-blood ratio of 13. Tumors were clearly visualized at 24-72 h post-injection. Micro-SPECT-CT images and ex vivo analyses confirmed the accumulation of rGel/BLyS in OCI-Ly10 tumors.

CONCLUSIONS

(111)In-DTPA-rGel/BLyS are distributed to B cell tumors and induce apoptosis in tumors. Preclinical antitumor studies using rGel/BLyS should use a twice-per-week treatment schedule.

Regulatory mechanisms for the production of BAFF and IL-6 are impaired in monocytes of patients of primary Sjögren's syndrome

INTRODUCTION

In this study, we investigated possible aberrations of monocytes from patients with primary Sjögren's syndrome (pSS). We focused on B-cell-activating factor of the TNF family (BAFF) and IL-6 because they are both produced by monocytes and are known to be involved in the pathogenesis of pSS.

METHODS

Peripheral monocytes were prepared from both pSS patients and normal individuals. The cells were stimulated in vitro with IFN-γ, and the amounts of IL-6 and soluble BAFF (sBAFF) produced by the cells were quantitated. The effect of sBAFF itself on the production of IL-6 was also studied. To investigate the response of pSS monocytes to these stimuli, the expression levels of the genes encoding BAFF receptors and IL-6-regulating transcription factors were quantitated.

RESULTS

Peripheral pSS monocytes produced significantly higher amounts of sBAFF and IL-6 than normal monocytes did, even in the absence of stimulation. The production of these cytokines was significantly increased upon stimulation with IFN-γ. The elevated production of IL-6 was significantly suppressed by an anti-BAFF antibody. In addition, stimulation of pSS monocytes with sBAFF induced a significant increase in IL-6 production. Moreover, the expression levels of a BAFF receptor and transcription factors regulating IL-6 were significantly elevated in pSS monocytes compared to normal monocytes.

CONCLUSIONS

The results of the present study suggest that the mechanisms underlying the production of sBAFF and IL-6 are impaired in pSS monocytes. Our research implies that this impairment is due to abnormally overexpressed IL-6-regulating transcription factors and a BAFF receptor. These abnormalities may cause the development of pSS.

Effects of APRIL (TNFSF13) polymorphisms and splicing isoforms on the secretion of soluble APRIL

Functional APRIL (TNFSF13) is a secreted trimer generated by furin protease cleavage. We previously reported the association of APRIL haplotypes formed by two nonsynonymous polymorphisms, Gly67Arg and Asn96Ser, with systemic lupus erythematosus. Here, we tested the hypothesis that polymorphisms and/or alternative splicing may influence the generation of soluble APRIL (sAPRIL). HEK 293T cells were transfected with plasmids containing one of the six combinations of splicing isoforms (α or β) and haplotypes (susceptible, neutral, or protective). APRIL concentrations were quantitated in the cell lysates and supernatants using an enzyme-linked immunosorbent assay (ELISA). The association between splicing efficiency and polymorphisms was analyzed using quantitative reverse transcription polymerase chain reaction (RT-PCR). The efficiency of cleavage by furin protease was analyzed using western blotting. Although both splicing isoforms were cleaved by furin protease, sAPRIL was not detected in the supernatant of the cells transfected with the β isoform, regardless of the haplotype. This suggested that, similarly to B-cell activating factor (BAFF), one of the major APRIL splicing isoforms may not be secreted as a functional molecule. Furthermore, the secretion of sAPRIL was decreased in the transfectants expressing the protective haplotype. An association between the polymorphisms and splicing efficiency or furin cleavage efficiency was not detected. In conclusion, these observations suggested that both alternative splicing and polymorphisms may affect the generation of functional sAPRIL.

Differential expression of the adaptor protein HSH2 controls the quantitative and qualitative nature of the humoral response

Endogenous expression of the adaptor protein hematopoietic Src homology 2-containing adaptor protein (HSH2) is regulated in a dynamic manner during B cell maturation and differentiation. Developing B cells lack detectable HSH2, whereas transitional 1 and 2 B cells in the periphery exhibit increasing levels of expression. Mature follicular B cells exhibit decreased expression of HSH2 compared with transitional 2 B cells, and expression is further downregulated in germinal center B cells. In contrast, marginal zone B cells and B1a/b B cells exhibit high-level HSH2 expression. Regulation of HSH2 expression plays a critical role in determining the outcome of the humoral immune response as demonstrated using HSH2 transgenic (Tg) mice. Constitutive expression of HSH2 in the B lineage at levels comparable to B1a/b B cells results in decreased serum Ig titers for all subclasses with the exception of IgA. HSH2 Tg mice immunized with T-dependent or T-independent Ags exhibit a moderate decrease in the production of Ag-specific IgM, whereas class-switched isotypes are decreased by ∼80-90% compared with control mice. Analysis of HSH2 Tg B cell activation in vitro demonstrated that HSH2 selectively regulates the B cell response to TNF family receptors (i.e., CD40 and BAFF-R), but not BCR- or TLR-dependent signals. These data demonstrate that changes in HSH2 expression have profound effects on the humoral immune response.

Cellular and molecular pathogenesis of systemic lupus erythematosus: lessons from animal models

Systemic lupus erythematosus (SLE) is a complex disease characterized by the appearance of autoantibodies against nuclear antigens and the involvement of multiple organ systems, including the kidneys. The precise immunological events that trigger the onset of clinical manifestations of SLE are not yet well understood. However, research using various mouse strains of spontaneous and inducible lupus in the last two decades has provided insights into the role of the immune system in the pathogenesis of this disease. According to our present understanding, the immunological defects resulting in the development of SLE can be categorized into two phases: (a) systemic autoimmunity resulting in increased serum antinuclear and antiglomerular autoantibodies and (b) immunological events that occur within the target organ and result in end organ damage. Aberrations in the innate as well as adaptive arms of the immune system both play an important role in the genesis and progression of lupus. Here, we will review the present understanding - as garnered from studying mouse models - about the roles of various immune cells in lupus pathogenesis.

Temporal changes in salivary glands of non-obese diabetic mice as a model for Sjögren's syndrome

OBJECTIVE

Non-obese diabetic (NOD) mice develop an autoimmune exocrinopathy that shows similarities with Sjögren's syndrome. They provide an experimental model to study the pathoetiogenesis of this disease.

MATERIALS AND METHODS

Salivary gland (SG) function and salivary sodium content were measured in 8-, 12-, 16- and 20-week-old NOD and age-matched CB6 mice. In NOD mice, SG expression of phenotypic cell markers, B cell-stimulating and costimulatory molecules were evaluated. Cytokine levels were measured in serum and SG homogenates.

RESULTS

  Microscopically evident SG inflammation in NOD mice was preceded by expression of intercellular adhesion molecule 1 on epithelial cells in the presence of macrophages and relatively high levels of cytokines. Next, an influx consisting of mainly T, B, natural killer, plasma and dendritic cells was seen. Most cytokines, except for interleukin (IL)12/IL23p40 and B cell-activating factor, decreased or remained stable over time, while glandular function deteriorated from 16 weeks of age onward compared with CB6 mice.

CONCLUSION

Sjögren's syndrome-like disease in NOD mice occurs in multiple stages; immunological and physiological abnormalities can be detected before focal inflammation appears and salivary output declines. Extrapolating this knowledge to human subjects could help in understanding the pathogenesis and aid the identification of potential therapeutic targets.

Protective antiviral antibody responses in a mouse model of influenza virus infection require TACI

Antiviral Abs, for example those produced in response to influenza virus infection, are critical for virus neutralization and defense against secondary infection. While the half-life of Abs is short, Ab titers can last a lifetime due to a subset of the Ab-secreting cells (ASCs) that is long lived. However, the mechanisms governing ASC longevity are poorly understood. Here, we have identified a critical role for extrinsic cytokine signals in the survival of respiratory tract ASCs in a mouse model of influenza infection. Irradiation of mice at various time points after influenza virus infection markedly diminished numbers of lung ASCs, suggesting that they are short-lived and require extrinsic factors in order to persist. Neutralization of the TNF superfamily cytokines B lymphocyte stimulator (BLyS; also known as BAFF) and a proliferation-inducing ligand (APRIL) reduced numbers of antiviral ASCs in the lungs and bone marrow, whereas ASCs in the spleen and lung-draining lymph node were surprisingly unaffected. Mice deficient in transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), a receptor for BLyS and APRIL, mounted an initial antiviral B cell response similar to that generated in WT mice but failed to sustain protective Ab titers in the airways and serum, leading to increased susceptibility to secondary viral challenge. These studies highlight the importance of TACI signaling for the maintenance of ASCs and protection against influenza virus infection.

BAFF promotes Th17 cells and aggravates experimental autoimmune encephalomyelitis

Background

BAFF, in addition to promoting B cell survival and differentiation, may affect T cells. The objective of this study was to determine the effect of BAFF on Th17 cell generation and its ramifications for the Th17 cell-driven disease, EAE.

Methodology/Principal Findings

Th17 cells were increased in BAFF-Tg B6 (B6.BTg) mice and decreased in B6.Baff^−/− mice. Th17 cells in B6.Baff^−/− mice bearing a BAFF Tg (B6.Baff^−/−.BTg mice) were identical to those in B6.BTg mice, indicating that membrane BAFF is dispensable for Th17 cell generation as long as soluble BAFF is plentiful. In T + non-T cell criss-cross co-cultures, Th17 cell generation was greatest in cultures containing B6.BTg T cells and lowest in cultures containing B6.Baff^−/− T cells, regardless of the source of non-T cells. In cultures containing only T cells, Th17 cell generation followed an identical pattern. CD4⁺ cell expression of CD126 (IL-6R α chain) was increased in B6.BTg mice and decreased in B6.Baff^−/− mice, and activation of STAT3 following stimulation with IL-6 + TGF-β was also greatest in B6.BTg cells and lowest in B6.Baff^−/− cells. EAE was clinically and pathologically most severe in B6.BTg mice and least severe in B6.Baff^−/− mice and correlated with MOG_35–55 peptide-induced Th17 cell responses.

Conclusions/Significance

Collectively, these findings document a contribution of BAFF to pathogenic Th17 cell responses and suggest that BAFF antagonism may be efficacious in Th17 cell-driven diseases.

KR33426, [2-(2,5-dichlorophenyl)-5-methyloxazol-4yl]carbonylguanidine, is a novel compound to be effective on mouse systemic lupus erythematosus

B cell-activating factor (BAFF) is a key regulator of B lymphocyte development. Signals from BAFF are transmitted through binding to a specific BAFF receptor (BAFF-R). Here, we established screening method to find a specific inhibitor for the interference of BAFF-BAFF-R interactions. We screened oxazole-4-carbonylguanidine derivatives and selected KR33426, [2-(2,5-dichlorophenyl)-5-methyloxazol-4yl]carbonylguanidine, as a candidate to interfere BAFF-BAFF-R interactions. KR33426 inhibited BAFF-mediated anti-apoptotic effect on splenocytes as judged by hypodiploid cell formation. KR33426 also increased the degradation of procaspase-3 that was inhibited by BAFF protein. In addition, we examined whether KR33426 was effective on the treatment of systemic lupus erythematosus-like symptom in MRL(lpr/lpr) mouse. When 5 or 10mg/kg KR33426 was intraperitoneally administered to MRL(lpr/lpr) mice for 4 weeks, histopathological changes were ameliorated in the narrowed space between renal glomerulus and glomerulus capsule. KR33426 reduced B220(+) B cell population and B cell mitogen, lipopolysaccharide-stimulated lymphocyte proliferation in splenocytes. KR33426 attenuated an increase in CD43(-)IgM(+) immature pro-B and a decrease in CD21(+) IgM(+) T2-B and IgD(+) IgM(-)recirculating-B cells on B cell development. Data show that KR33426 inhibits BAFF-BAFF-R interactions and it is effective on the treatment of systemic lupus erythematosus-like symptom in MRL(lpr/lpr) mice. Thus, it suggests that KR33426 is a novel candidate to develop anti-autoimmune therapeutics by the interference of BAFF-BAFF-R interactions, specifically.

Clinical significance of B cell-activating factor in autoimmune pancreatitis

OBJECTIVES

Overexpression of B Cell-activating factor (BAFF) is involved in autoimmunity, but little is known about its role in autoimmune pancreatitis (AIP). The aim of this study was to investigate the role of BAFF in the diagnosis and pathogenesis of AIP.

METHODS

Patients with AIP (n = 19) were compared with 2 disease control groups (chronic pancreatitis [n = 17] and pancreatic cancer [n = 15]) and a healthy subject group (n = 19). Serum BAFF levels were assessed using an enzyme-linked immunosorbent assay. The expressions of BAFF and BAFF receptor in the pancreatic tissue of patients with AIP were estimated using immunohistochemistry.

RESULTS

Mean serum BAFF levels were higher in the patients with AIP than in the patients with chronic pancreatitis, the patients with pancreatic cancer, and the healthy subjects (P < 0.0001 for all groups). Using the cutoff value of 1389 pg/mL, the sensitivity and specificity to differentiate AIP from disease and healthy controls were 89.5% and 92.2%, respectively. Glucocorticoid therapy decreased serum BAFF levels below 1389 pg/mL in all patients with AIP (P < 0.0001). B Cell-activating factor and BAFF receptor were expressed on cells infiltrating the pancreas of patients with AIP.

CONCLUSIONS

B Cell-activating factor could be a novel marker for diagnosis and treatment response in AIP and may contribute to its pathogenesis.

Atacicept: targeting B cells in multiple sclerosis

Multiple sclerosis (MS) has traditionally been considered to be a T-cell-mediated disease. However, there is an increasing body of evidence for the involvement of B cells and autoantibodies in the pathology of this disease, providing a rationale for treatments directed against B cells. In this paper we summarize evidence for the key role of B cells in the immunopathology of MS and review data supporting the use of a novel B-cell targeted therapy, atacicept, in this condition. Atacicept is a human recombinant fusion protein that comprises the binding portion of a receptor for both BLyS (B-Lymphocyte Stimulator) and APRIL (A PRoliferation-Inducing Ligand), two cytokines that have been identified as important regulators of B-cell maturation, function and survival. Atacicept has shown selective effects on cells of the B-cell lineage, acting on mature B cells and blocking plasma cells and late stages of B-cell development while sparing B-cell progenitors and memory cells. The efficacy of atacicept in animal models of autoimmune disease and the biological activity of atacicept in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) has been demonstrated. Clinical studies were initiated to investigate the safety, tolerability and efficacy of atacicept in patients with MS. An unexpected increase in inflammatory activity in one of the trials, however, led to suspension of all atacicept trials in MS.

Elevated BAFF (BLyS) and APRIL in Juvenile idiopathic arthritis patients: relation to clinical manifestations and disease activity

OBJECTIVE

To assess the level of B-cell activating factor belonging to the tumor necrosis factor family (BAFF) also known as B-lymphocyte stimulator (BLyS) and A proliferation-inducing ligand (APRIL) in the serum of Juvenile idiopathic arthritis (JIA) patients and to detect their relation to the clinical manifestations and disease activity in the different subtypes of the disease.

METHODS

Seventy-four consecutively recruited JIA patients were clinically examined, the Juvenile arthritis disease activity score in 27 joints (JADAS-27) calculated and Childhood Health Assessment Questionnaire (CHAQ) used to measure the functional status. Thirty-four healthy matched children served as controls. Routine laboratory examinations were recorded and serum BAFF and April were determined.

RESULTS

The JIA patients were 20 systemic-onset, 31 oligoarticular and 23 polyarticular. Serum BAFF and APRIL were elevated in JIA patients being higher in systemic onset and both significantly correlated. APRIL significantly correlated with both JADAS-27 and CHAQ scores while BAFF correlated only with JADAS-27. The APRIL serum levels were significantly associated with the presence of RF and ANA. The BAFF serum levels were significantly higher in oligoarticular onset JIA patients with uveitis compared to those without.

CONCLUSION

Our results suggest increased BAFF and APRIL serum levels in JIA patients denoting their possible role in the disease and calling for additional research to elucidate the intrinsic mechanisms explaining APRIL and BAFF over expression.

Disease causing mutations in the TNF and TNFR superfamilies: Focus on molecular mechanisms driving disease

The tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies comprise multidomain proteins with diverse roles in cell activation, proliferation and cell death. These proteins play pivotal roles in the initiation, maintenance and termination of immune responses and have vital roles outside the immune system. The discovery and analysis of diseases associated with mutations in these families has revealed crucial mechanistic details of their normal functions. This review focuses on mutations causing four different diseases, which represent distinct pathological mechanisms that can exist within these superfamilies: autoimmune lymphoproliferative syndrome (ALPS; FAS mutations), common variable immunodeficiency (CVID; TACI mutations), tumor necrosis factor receptor associated periodic syndrome (TRAPS; TNFR1 mutations) and hypohidrotic ectodermal dysplasia (HED; EDA1/EDAR mutations). In particular, we highlight how mutations have revealed information about normal receptor-ligand function and how such studies might direct new therapeutic approaches.

B-cell activating factor (BAFF) promotes CpG ODN-induced B cell activation and proliferation

It is controversial whether naïve B cells are directly activated in response to TLR9 ligand, CpG ODN. Although bovine blood-derived CD21(+) B cells express TLR9 and proliferate in response to CpG in mixed-cell populations, purified bovine B cells do not proliferate significantly in response to CpG ODN, even when the B cell receptor is engaged. When co-cultured with CD14(+) myeloid cells and/or B-cell activating factor (BAFF), a cytokine produced by activated myeloid cells, there was a significant increase in CpG-specific B cell proliferation, and the number of large B cells in general or positive for CD25, all of which are markers for B cell activation. These data suggest that activated myeloid cells and BAFF prime B cells for significant CpG-specific activation. Understanding the signals required to mediate efficient CpG-induced, antigen-independent and T-cell independent activation of B cells has implications for polyclonal B cell activation and the development of autoimmune diseases.

Sjögren's syndrome: studying the disease in mice

Sjögren's syndrome (SS), a systemic autoimmune disease, is characterized by inflammation of exocrine tissues accompanied by a significant loss of their secretory function. Clinical symptoms develop late and there are no diagnostic tests enabling early diagnosis of SS. Thus, particularly to study these covert stages, researchers turn to studying animal models where mice provide great freedom for genetic manipulation and testing the effect of experimental intervention. The present review summarizes current literature pertaining to both spontaneous and extrinsic-factor induced SS-like diseases in mouse models, discussing advantages and disadvantages related to the use of murine models in SS research.

Aberrant expression of functional BAFF-system receptors by malignant B-cell precursors impacts leukemia cell survival

Despite exhibiting oncogenic events, patient's leukemia cells are responsive and dependent on signals from their malignant bone marrow (BM) microenvironment, which modulate their survival, cell cycle progression, trafficking and resistance to chemotherapy. Identification of the signaling pathways mediating this leukemia/microenvironment interplay is critical for the development of novel molecular targeted therapies.

We observed that primary leukemia B-cell precursors aberrantly express receptors of the BAFF-system, BAFF-R, BCMA, and TACI. These receptors are functional as their ligation triggers activation of NF-κB, MAPK/JNK, and Akt signaling. Leukemia cells express surface BAFF and APRIL ligands, and soluble BAFF is significantly higher in leukemia patients in comparison to age-matched controls. Interestingly, leukemia cells also express surface APRIL, which seems to be encoded by APRIL-δ, a novel isoform that lacks the furin convertase domain. Importantly, we observed BM microenvironmental cells express the ligands BAFF and APRIL, including surface and secreted BAFF by BM endothelial cells. Functional studies showed that signals through BAFF-system receptors impact the survival and basal proliferation of leukemia B-cell precursors, and support the involvement of both homotypic and heterotypic mechanisms.

This study shows an unforeseen role for the BAFF-system in the biology of precursor B-cell leukemia, and suggests that the target disruption of BAFF signals may constitute a valid strategy for the treatment of this cancer.

Molecular structure, expression and bioactivity characterization of TNF13B (BAFF) gene in mefugu, Takifugu obscurus

B-cell activating factor of the TNF family (BAFF) induces B-cell survival, proliferation, immunoglobulin secretion and plays a role in enhancing immune responses. In the present study, a BAFF homolog has been identified in mefugu Takifugu obscurus, and its biological activities have been characterized. The mefugu BAFF (fBAFF) cDNA is 789 bp in length and translates into a 262-aa protein. The fBAFF genomic sequence consists of six exons and five introns, is approximately 1.8 kb in size. Amino acid sequence comparison indicated that fBAFF possessed the TNF signatures, a transmembrane domain, a putative furin protease cleavage site and three cysteine residues, which were the typical characteristics of TNF gene in mammals and birds. The predicted three-dimensional (3D) structure of the fsBAFF monomer analyzed by comparative protein modeling revealed that it was very similar to its human counterpart. Real-time quantitative PCR (qPCR) analysis revealed that fBAFF was predominantly expressed in mefugu lymphoid tissue spleen. The SUMO-fsBAFF and GFP/fsBAFF efficiently expressed in Escherichia coli Rosetta (DE3) were confirmed by SDS-PAGE and Western blotting analysis. After purification, the GFP/fsBAFF fusion protein obtained similar fluorescence spectrum to those of GFP. Laser scanning confocal microscopy analysis showed GFP/fsBAFF could bind to its receptors. In vitro, the MTT assays and flow cytometric analysis indicated that SUMO-fsBAFF could promote the proliferation of mefugu splenocytes or mouse splenic B cells together with/without anti-mouse IgM. These findings indicate that SUMO-fsBAFF plays an important role in proliferation of mefugu B cells and has functional cross-reactivity among mefugu and other mammalians. Therefore, BAFF may be a potential immunologic factor for enhancing immunological efficacy in fish.

B cell maturation antigen deficiency exacerbates lymphoproliferation and autoimmunity in murine lupus

Systemic lupus erythematosus and its preclinical lupus-prone mouse models are autoimmune disorders involving the production of pathogenic autoantibodies. Genetic predisposition to systemic lupus erythematosus results in B cell hyperactivity, survival of self-reactive B cells, and differentiation to autoantibody-secreting plasma cells (PCs). These corrupt B cell responses are, in part, controlled by excess levels of the cytokine BAFF that normally maintains B cell homeostasis and self-tolerance through limited production. B cell maturation Ag (BCMA) is a receptor for BAFF that, under nonautoimmune conditions, is important for sustaining enduring Ab protection by mediating survival of long-lived PCs but is not required for B cell maturation and homeostasis. Through analysis of two different lupus-prone mouse models deficient in BCMA, we identify BCMA as an important factor in regulating peripheral B cell expansion, differentiation, and survival. We demonstrate that a BCMA deficiency combined with the lpr mutation or the murine lupus susceptibility locus Nba2 causes dramatic B cell and PC lymphoproliferation, accelerated autoantibody production, and early lethality. This study unexpectedly reveals that BCMA works to control B cell homeostasis and self-tolerance in systemic autoimmunity.

An increase in B cell apoptosis by interfering BAFF-BAFF-R interaction with small synthetic molecules

B cell-activating factor (BAFF) transmitted signals through binding to specific BAFF receptors (BAFF-R) to regulate B cell survival and development. We used MTT assay to examine the cytotoxicity of chemicals, flow cytometry analysis to measure BAFF-BAFF-R interactions, and western blotting to detect BAFF protein. Here, we established screening method to find specific compounds to interfere with BAFF-BAFF-R interactions in WIL2-NS B lymphoblast cells. According to screening (imidazol-4-ylcarbonyl)guanidine or (oxazol-4-ylcarbonyl)guanidine derivatives, we selected KR32592, KR32673, KR33232, KR33341 and KR33426 as candidates to interfere with BAFF-BAFF-R interaction. No cytotoxicity was detected by KR32592, KR33232, and KR33426 at the concentration of 5 μM, and by KR32673, and KR33341 at the concentration of 0.5 μM. Cell population with BAFF-BAFF-R interactions was reduced by the pre-incubation of chemicals with human BAFF-murine CD8 (BAFF-muCD8). Cell population with BAFF-BAFF-R interactions was also decreased by pre-exposure of WIL2-NS cells to chemicals prior to the incubation with BAFF-muCD8. Chemicals also inhibited LPS-stimulated BAFF production from splenocytes. All these effects of chemicals may contribute to the inhibition of BAFF-mediated anti-apoptosis. These data demonstrate that chemicals interfering with BAFF-BAFF-R interaction may be screened with our experimental condition. It suggests that BAFF-BAFF-R interaction could be a chemical target to develop therapeutics for BAFF-mediated autoimmune diseases.

A role of both NF-κB pathways in expression and transcription regulation of BAFF-R gene in multiple myeloma cells

B-lymphocyte stimulator (BAFF) is a recently recognized member of the tumor necrosis factor ligand family (TNF) and a potent cell-survival factor expressed in many hematopoietic cells. BAFF regulates B-cell survival, differentiation, and proliferation by binding to three TNF receptors: TACI, BCMA, and BAFF-R. The mechanism involved in BAFF-R gene expression and regulation remains elusive. In this study, we examined BAFF-R gene expression, function, and regulation in multiple myeloma (KM3) cells. It was found that BAFF-BAFF-R induced cell survival by activating NF-κB1 pathway and NF-κB2 pathway. It was also found that NF-κB was an important transcription factor involved in regulating BAFF-R expression through one NF-κB binding site in the BAFF-R promoter, suggesting that inhibiting NF-κB could decrease the expression of BAFF-R mRNA and protein, and promote activity of BAFF-R gene. Our findings indicate that both NF-κB pathways are involved in the regulation of BAFF-R gene and the NF-κB-binding site of BAFF-R may be a new therapeutic target in this disease.

BAFF inhibition: a new class of drugs for the treatment of autoimmunity

BAFF (BLyS) and APRIL are TNF-like cytokines that support survival and differentiation of B cells. Recent studies have discovered a role for BAFF in augmenting both innate and adaptive immune responses as well as in collaborating with other inflammatory cytokines to promote the activation and differentiation of effector immune cells. BAFF is an important pathogenic factor in lupus mouse models and BAFF inhibition successfully delays disease onset in these mice, although the responsiveness to BAFF inhibition varies among different strains. These results have led to the development of inhibitors targeting BAFF and APRIL in humans. An anti-BAFF antibody has shown significant but modest efficacy in two Phase III clinical trials for moderately active SLE and other inhibitors are being developed or at early stages of clinical testing.

Transient increases in anti-aquaporin-4 antibody titers following rituximab treatment in neuromyelitis optica, in association with elevated serum BAFF levels

Rituximab is increasingly used for prevention of relapses of neuromyelitis optica (NMO), a condition that is highly associated with serum anti-aquaporin-4 (AQP4) antibodies. However, B-cell depletion also induces systemic B-cell activating factor (BAFF), which may promote antibody production. We collected serial serum samples from a total of seven patients with NMO prior to, and following, treatment with rituximab. The samples were analyzed for anti-AQP4 antibody titer using a cell-based assay and serum BAFF levels were measured on available samples by standard enzyme-linked immunosorbent assay. Anti-AQP4 antibody levels decreased after 4 weeks to 12 weeks from the first injection of rituximab, but they increased transiently in several patients at 2 weeks after the first injection, in association with a parallel increase in serum BAFF levels. Although anti-AQP4 antibodies appear to decrease overall following rituximab treatment, our findings raise concern over the potential for an early BAFF-mediated worsening of patients with NMO receiving rituximab.

Accelerated central nervous system autoimmunity in BAFF-receptor-deficient mice

B cell activating factor (BAFF) is critical for B cell survival, a function that is mediated by BAFF receptor, (BAFF-R). The role of BAFF (or BAFF-R) in the multiple sclerosis model, experimental autoimmune encephalomyelitis (EAE), was examined using BAFF-R-deficient mice. BAFF-R deficiency resulted in paradoxically increased severity of EAE induced by myelin-oligodendrocyte glycoprotein (MOG) peptide 35-55. Inflammatory foci in BAFF-R-deficient mice comprised increased numbers of activated macrophages expressing BAFF and correlated with increased BAFF secretion. Thus, BAFF-R may be important in EAE pathogenesis, possibly by influencing macrophage function through a mechanism that involves modulation of BAFF expression.

Targeting BLyS in rheumatic disease: the sometimes-bumpy road from bench to bedside

PURPOSE OF REVIEW

BLyS family ligands and receptors are key players in the selection and survival of most mature B lymphocytes. The fundamental role of BLyS in transitional B cell selection, coupled with the relative BLyS-independence of memory B cells and plasma cells, suggests that BLyS may be a useful therapeutic target in strategies directed against preimmune B cell pools. Several agents that target BLyS are in clinical trials now, and we summarize recent results here, with a focus on systemic lupus erythematosus (SLE).

RECENT FINDINGS

Belimumab, a human neutralizing anti-BLyS monoclonal antibody, has delivered moderate but positive results in two separate phase III clinical trials for SLE, and was recently recommended for approval by an FDA advisory panel. Additional agents targeting BLyS or other members of this cytokine receptor family are also being tested in clinical trials.

SUMMARY

Together, these trials should yield novel therapies for a debilitating and often intractable illness and offer insights that in turn should foster subsequent generations of personalized, targeted therapies for rheumatic diseases.

New therapies in the management of rheumatoid arthritis

PURPOSE OF REVIEW

The therapeutic landscape in the management of rheumatoid arthritis (RA) has witnessed significant changes over the past decade. The ambition to improve outcomes further, minimize safety concerns and provide more convenient means of administration are all factors that continue to drive continued drug development. This review summarizes novel therapies that have been most recently under investigation.

RECENT FINDINGS

More refined drug technology has seen the development of subcutaneous forms of existing therapies (abatacept, tocilizumab), as well as newer-generation monoclonal antibodies (e.g. B-cell-depleting agents, ocrelizumab and ofatumumab and the TNF-inhibitors certolizumab and golimumab). Alternative methods of targeting critical pathways, for example Blys inhibition (atacicept) and IL-6 as opposed to IL-6 receptor antagonism, have also been evaluated. Finally, small molecules are receiving increasing attention, with some of the protein kinases inhibitors particularly promising.

SUMMARY

The new emerging therapies for the management of RA illustrate much diversity, in terms of both drug technology as well as the immunological target. Although not all may succeed in reaching the market, important insights can still be gained. Challenging and exciting times lie ahead as these new technologies are embraced and efforts are made to determine how best to implement in practice.

Examination of candidate genes for hypoadrenocorticism in Nova Scotia Duck Tolling Retrievers

Inherited hypoadrenocorticism occurs in some dog breeds including the Nova Scotia Duck Tolling Retriever (NSDTR) and is thought to be due to an immune attack on the adrenal glands. The genetic cause of this disorder in dogs has not been identified; however, many genes have been associated with hypoadrenocorticism and other immune-mediated conditions in humans including AIRE, BAFF, Casp10, CD28, CTLA-4, FASL, PTPN22, and TNFRSF6B. Microsatellite marker loci were analysed for linkage with the disease phenotype in a pedigree of NSDTRs and excluded all genes examined, the exception being CTLA-4, which was neither excluded nor shown to be associated by this analysis. Thus, genes associated with hypoadrenocorticism in humans were not linked with the condition in the dog. Further examination is necessary to identify the genetic cause of inherited hypoadrenocorticism in dogs and this may reveal a novel gene not yet implicated with immune-mediated disease.

B Cell and BAFF dependence of IFN-α-exaggerated disease in systemic lupus erythematosus-prone NZM 2328 mice

IFN-α is a potent activator of innate and adaptive immunity, and its administration to preautoimmune (NZB×NZW)F1 mice promotes virulent systemic lupus erythematosus (SLE) disease. Given the known contributions of B cells and BAFF to SLE, we evaluated the ability of IFN-α administration to induce disease in wild-type (WT), B cell-deficient, and BAFF-deficient NZM 2328 mice. Whereas WT mice rapidly developed proliferative glomerulonephritis, marked proteinuria, and increased mortality in response to IFN-α administration, B cell-deficient mice developed neither renal pathology nor clinical disease. Moreover, BAFF-deficient mice, despite developing limited glomerular IgG and C3 deposition, also remained free of histological glomerulonephritis and clinical disease. Strikingly, similar T cell expansion and serum IgG responses were observed in adenovirus (Adv)-IFN-treated WT and BAFF-deficient mice despite their disparate pathological and clinical responses, whereas numbers of activated B cells increased in WT mice but not in BAFF-deficient mice. Nonetheless, B cell, plasma cell, and T cell infiltration of the kidneys in Adv-IFN-treated WT mice was similar to that in WT mice treated with Adv-control. Its ability to promote SLE disease in WT mice notwithstanding, IFN-α administration failed to drive the preferential expansion of CD4(+) memory T cells that occurs during the natural course of disease, and glomerular infiltration of macrophages failed to associate with development of disease. These results collectively suggest that therapeutic targeting in SLE of BAFF and/or B cells in SLE could be successful even in states of IFN-α overexpression. Moreover, our results document important biological differences between IFN-α-driven and spontaneous natural SLE disease.

Vstm3 is a member of the CD28 family and an important modulator of T-cell function

Members of the CD28 family play important roles in regulating T-cell functions and share a common gene structure profile. We have identified VSTM3 as a protein whose gene structure matches that of the other CD28 family members. This protein (also known as TIGIT and WUCAM) has been previously shown to affect immune responses and is expressed on NK cells, activated and memory T cells, and Tregs. The nectin-family proteins CD155 and CD112 serve as counter-structures for VSTM3, and CD155 and CD112 also bind to the activating receptor CD226 on T cells and NK cells. Hence, this group of interacting proteins forms a network of molecules similar to the well-characterized CD28-CTLA-4-CD80-CD86 network. In the same way that soluble CTLA-4 can be used to block T-cell responses, we show that soluble Vstm3 attenuates T-cell responses in vitro and in vivo. Moreover, animals deficient in Vstm3 are more sensitive to autoimmune challenges indicating that this new member of the CD28 family is an important regulator of T-cell responses.

Murine models of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disorder. The study of diverse mouse models of lupus has provided clues to the etiology of SLE. Spontaneous mouse models of lupus have led to identification of numerous susceptibility loci from which several candidate genes have emerged. Meanwhile, induced models of lupus have provided insight into the role of environmental factors in lupus pathogenesis as well as provided a better understanding of cellular mechanisms involved in the onset and progression of disease. The SLE-like phenotypes present in these models have also served to screen numerous potential SLE therapies. Due to the complex nature of SLE, it is necessary to understand the effect specific targeted therapies have on immune homeostasis. Furthermore, knowledge gained from mouse models will provide novel therapy targets for the treatment of SLE.

Enhanced immunogenicity of pneumococcal surface adhesin A (PsaA) in mice via fusion to recombinant human B lymphocyte stimulator (BLyS)

Background

B lymphocyte stimulator (BLyS) is a member of the tumor necrosis factor superfamily of ligands that mediates its action through three known receptors. BLyS has been shown to enhance the production of antibodies against heterologous antigens when present at elevated concentrations, supporting an immunostimulatory role for BLyS in vivo.

Methods

We constructed a fusion protein consisting of human BLyS and Pneumococcal Surface Adhesin A (PsaA) and used this molecule to immunize mice. The immunostimulatory attributes mediated by BLyS in vivo were evaluated by characterizing immune responses directed against PsaA.

Results

The PsaA-BLyS fusion protein was able to act as a co-stimulant for murine spleen cell proliferation induced with F(ab')₂ fragments of anti-IgM in vitro in a fashion similar to recombinant BLyS, and immunization of mice with the PsaA-BLyS fusion protein resulted in dramatically elevated serum antibodies specific for PsaA. Mice immunized with PsaA admixed with recombinant BLyS exhibited only modest elevations in PsaA-specific responses following two immunizations, while mice immunized twice with PsaA alone exhibited undetectable PsaA-specific serum antibody responses. Sera obtained from PsaA-BLyS immunized mice exhibited high titers of IgG1, IgG2a, IgG2b, and IgG3, but no IgA, while mice immunized with PsaA admixed with BLyS exhibited only elevated titers of IgG1 following two immunizations. Splenocytes from PsaA-BLyS immunized mice exhibited elevated levels of secretion of IL-2, IL-4 and IL-5, and a very modest but consistent elevation of IFN-γ following in vitro stimulation with PsaA. In contrast, mice immunized with either PsaA admixed with BLyS or PsaA alone exhibited modestly elevated to absent PsaA-specific recall responses for the same cytokines. Mice deficient for one of the three receptors for BLyS designated Transmembrane activator, calcium modulator, and cyclophilin ligand [CAML] interactor (TACI) exhibited attenuated PsaA-specific serum antibody responses following immunization with PsaA-BLyS relative to wild-type littermates. TACI-deficient mice also exhibited decreased responsiveness to a standard pneumococcal conjugate vaccine.

Conclusion

This study identifies covalent attachment of BLyS as a highly effective adjuvant strategy that may yield improved vaccines. In addition, this is the first report demonstrating an unexpected role for TACI in the elicitation of antibodies by the PsaA-BLyS fusion protein.

Reviewers

This article was reviewed by Jonathan Yewdell, Rachel Gerstein, and Michael Cancro (nominated by Andy Caton).

Expressions of BAFF/BAFF receptors and their correlation with disease activity in Chinese SLE patients

B-cell activating factor belonging to tumour necrosis factor family (BAFF) is essential for B-cell survival and function through interaction with its receptors BAFF receptor 3 (BR3), B-cell maturation antigen (BCMA) and/or transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), though BCMA and/or TACI can also bind to a proliferation-inducing ligand (APRIL). We evaluate the correlation of the expressions of these ligands/receptors with different clinical manifestations of systemic lupus erythematosus (SLE). Levels of BAFF and APRIL in plasma from 73 SLE patients were determined by enzyme-linked immunosorbent assay. Expressions of BR3, TACI and BCMA on CD19+ B cells were detected by flow cytometry. Clinical data were collected and disease activity was evaluated using SLEDAI-2000. SLE patients had elevated BAFF and APRIL levels in their plasma. BAFF levels correlated positively with SLEDAI while negatively with the BR3 protein expression on CD19+ B cells (p < .05). The detected BR3 protein expression in SLE patients was reduced on CD19+IgD+CD27-, CD19+IgD+CD27+ as well as CD19+IgD-CD27+ B cells compared to the counterparts of healthy controls (p < .001), whereas SLE patients did not differ from healthy controls in BR3 mRNA levels. In untreated new-onset patients, the expression rate of BR3 on CD19+ B cells correlated negatively with SLEDAI (p < .05). Elevation of BAFF and reduction of BR3 on CD19+ B cells were more obvious in those with lupus nephritis (LN, p < .05). TACI expression on CD19+ B cells was up-regulated only in those subjects with LN (p < .05). Elevated plasma BAFF and reduced BR3 protein expression on peripheral B cells could act as biomarkers for active disease in SLE patients. High expression of TACI may indicate the occurrence of LN.

Development of autoimmune nephritis in genetically asplenic and splenectomized BAFF transgenic mice

B cell activating factor belonging to the TNF family (BAFF or BLyS) is a critical B cell survival factor essential for B cell maturation. BAFF transgenic (Tg) mice develop autoimmunity resembling Systemic Lupus Erythematosus (SLE) in a T cell-independent but toll-like receptor (TLR) signalling-dependent manner, requiring TLR-induced innate B cell-derived pro-inflammatory autoantibody deposition in the kidneys. Importantly, neutralizing BAFF in the clinic shows efficacy in patients with SLE, confirming its critical role in the progression of this disease in both humans and mouse models. The specific B cell types that produce autoantibodies in BAFF Tg mice are TLR-activated innate marginal zone (MZ) B cells and B1 cells, but not follicular B cells. Interestingly, in BAFF Tg mice MZ-like B cells infiltrate salivary glands whereas B1 B cells infiltrate the kidneys. To ascertain the relevance of B1 and MZ-like B cells in the development of nephritis in BAFF Tg mice, we generated genetically asplenic as well as splenectomized BAFF Tg animals. BAFF Tg mice born without a spleen lack MZ B cells, have very reduced B1a B cell numbers but a normal B1b B cell compartment. Loss of these B cell subsets failed to protect BAFF Tg mice against nephritis indicating that B1b B cells are an important subset for the development of autoimmune nephritis in BAFF Tg mice. Thus the spleen is dispensable for the development of autoimmune nephritis in BAFF Tg mice and points toward a pathogenic role for innate B1 B cells. Identifying similar innate B cells in humans may offer the possibility of more targeted B cell therapies.

Intrarenal production of B-cell survival factors in human lupus nephritis

The B-cell survival factors APRIL and BLyS are important for B-cell maturation and activation and contribute to human autoimmune diseases. Interference with B-cell function by targeting these molecules is currently being investigated in large clinical trials for systemic lupus erythematosus. The local expression patterns of APRIL and BLyS have not been investigated in detail in kidneys with lupus nephritis. We studied the mRNA expression of APRIL, BLyS, and the corresponding receptors BCMA, TACI, and BAFF-R in microdissected human biopsies with proliferative lupus nephritis (n=25) and compared it with pretransplant biopsies of living donors (n=9). APRIL and BLyS mRNA levels were significantly higher in glomeruli of patients with proliferative lupus nephritis (12- and 30-fold, respectively). Tubulointerstitial expression of APRIL, BLyS, BCMA, and TACI was also significantly elevated. To localize the respective proteins in the kidney, APRIL, BLyS, and BAFF-R were studied by immunohistochemistry in renal biopsies with proliferative (n=21) or membranous (n=8) lupus nephritis. APRIL was prominently expressed in glomeruli with proliferative, but not membranous, lupus nephritis. The staining pattern was consistent with mesangial cells. A prominent accumulation of CD68-positive cells was present in glomeruli in association with APRIL expression. APRIL, BLyS, and BAFF-R were also expressed in interstitial inflammatory cell accumulation. This is the first study, which details local expression of APRIL and BLyS in glomeruli and tubulointerstitium of human proliferative lupus nephritis. This information might help define intrarenal effects of APRIL and BLyS inhibition in human lupus nephritis.

B cell immunotherapy in autoimmunity--2010 update

B cells play important roles in normal immunity and human disease. While much has been learned from elegant studies utilizing genetically modified mice or with immunotherapy in normal and in autoimmune mice, we are merely at the start of learning about the mechanism(s) by which B cells contribute to human autoimmune disease. Here, I will review the most recent insights obtained with immunomodulatory therapies in human disease highlighting the clinical and immunological lessons we have learned with B cell depleting (e.g., rituximab) and immunomodulatory (e.g., BAFF/BLys neutralization through belimumab) therapies.

Therapeutic effects of TACI-Ig on rat with adjuvant arthritis

Transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin (TACI-Ig) is a human fusion protein that binds and neutralizes both B lymphocyte stimulator (BLyS), a cytokine shown to be a key regulator of B cell maturation, proliferation and survival, and a proliferation-inducing ligand (APRIL). Rat adjuvant arthritis (AA) is an experimental animal model of rheumatoid arthritis (RA), which is mainly dependent on T cells and neutrophil-mediated cytokine production. The purpose of the present study was to investigate the effects of TACI-Ig on rat AA. Rat AA was induced by intradermal injection of 0·1 ml complete Freund's adjuvant (CFA). TACI-Ig (0·7, 2·1 and 6·3 mg/kg), recombinant human tumour necrosis factor-α receptor (rhTNFR) : Fc (2·8 mg/kg) and IgG-Fc (6·3 mg/kg) were administered subcutaneously every other day from days 16 to 34 after immunization. Arthritis was evaluated by arthritis global assessment and swollen joint count (SJC). The ankle joint and spleen were harvested for histopathological examination. Spleen index and thymus index were calculated. The levels of BLyS, interleukin (IL)-17, interferon (IFN)-γ, IgG1, IgG2a and IgM in AA rat spleen were measured by enzyme-linked immunosorbent assay. Administration of TACI-Ig significantly reduced the arthritis global assessment and SJC, decreased spleen index and ameliorated histopathological manifestations of rat AA. Suppressing the levels of BLyS, IL-17, IFN-γ and Ig in AA rat spleen were observed after administration of TACI-Ig. These results showed that TACI-Ig significantly inhibited the degree of rat AA, and the inhibitory effects might be associated with its ability to reduce BLyS, proinflammatory cytokines and Ig levels in spleen.

Pharmacokinetics and immunoglobulin response of subcutaneous and intravenous atacicept in patients with systemic lupus erythematosus

Atacicept, a recombinant fusion protein of the TACI receptor and human IgG, is an inhibitor of B-Lymphocyte Stimulator (BLyS) and APRIL, potent stimulators of B cell maturation, proliferation, and survival. Pharmacokinetics (PKs) and biological activity of intravenous (iv) and subcutaneous (sc) atacicept are described here for patients with systemic lupus erythematosus in two randomized, double-blind, placebo-controlled, Phase Ib studies. Study 1: Six cohorts of eight patients received sc atacicept (single dose: 0.3, 1, 3, or 9 mg/kg; four weekly doses: 1 or 3 mg/kg), or placebo (3:1 ratio). Study 2: Four cohorts of six patients received iv atacicept (single dose: 3, 9, or 18 mg/kg; multiple dose: 2 x 9 mg/kg), or matching placebo (5:1 ratio). PK profiles were determined through serum atacicept and atacicept-BLyS complex, and biological activity through IgA, IgG, and IgM levels. PK profiles of atacicept were influenced by saturable binding between atacicept and its ligands, and were consistent and predictable across doses and regimens. Atacicept's biological activity was compatible with its presumed mechanism of action. Bioavailability was approximately 30-40% following sc or iv administration and similar doses yielded similar biological activity irrespective of administration route. This observation may have a mechanistic foundation and may inform dosing regimen design for future studies.

A BAFF-R mutation associated with non-Hodgkin lymphoma alters TRAF recruitment and reveals new insights into BAFF-R signaling

The cytokine B cell activating factor (BAFF) and its receptor, BAFF receptor (BAFF-R), modulate signaling cascades critical for B cell development and survival. We identified a novel mutation in TNFRSF13C, the gene encoding human BAFF-R, that is present in both tumor and germline tissue from a subset of patients with non-Hodgkin lymphoma. This mutation encodes a His159Tyr substitution in the cytoplasmic tail of BAFF-R adjacent to the TRAF3 binding motif. Signaling through this mutant BAFF-R results in increased NF-κB1 and NF-κB2 activity and increased immunoglobulin production compared with the wild-type (WT) BAFF-R. This correlates with increased TRAF2, TRAF3, and TRAF6 recruitment to His159Tyr BAFF-R. In addition, we document a requirement for TRAF6 in WT BAFF-R signaling. Together, these data identify a novel lymphoma-associated mutation in human BAFF-R that results in NF-κB activation and reveals TRAF6 as a necessary component of normal BAFF-R signaling.