B cell targeted therapies

Iguratimod: Novel Molecular Insights and a New csDMARD for Rheumatoid Arthritis, from Japan to the World

Iguratimod (IGU) is a conventional synthetic disease-modifying anti-rheumatic drug (csDMARD) routinely prescribed in Japan since 2012 to patients with rheumatoid arthritis (RA). Iguratimod acts directly on B cells by inhibiting the production of inflammatory cytokines (tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-8, IL-17), thereby suppressing the production of immunoglobulin and inhibiting the activity of nuclear factor kappa-light chain enhancer of activated B cells. In Japan, it is one of the most used csDMARDs in daily practice, but it is not recommended as a treatment for RA due to the lack of large-scale evidence established overseas. However, recent reports on the novel pharmacological effects of IGU on lymphocytes and synovial fibroblasts, as well as its efficacy in daily practice, have increased its importance as a drug for the treatment of RA. In this review, we highlighted the basic and clinical studies in IGU and discuss its potential as a new therapeutic agent for the treatment of RA.

Early restoration of immune and vascular phenotypes in systemic lupus erythematosus and rheumatoid arthritis patients after B cell depletion

This translational multi‐centre study explored early changes in serologic variables following B lymphocyte depletion by rituximab (RTX) treatment in systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) patients and investigated in vitro effects on the activity of other immune cells and the vascular endothelium. Eighty‐five SLE patients, seventy‐five RA patients and ninety healthy donors were enrolled. Two additional cohorts of selected SLE and RA patients were treated with RTX for 3 months. Changes in circulating levels of inflammatory mediators, oxidative stress markers and NETosis‐derived bioproducts were evaluated. Serum miRNomes were identified by next‐generation sequencing, and RTX‐induced changes were delineated. Mechanistic in vitro studies were performed to assess activity profiles. Altered inflammatory, oxidative and NETosis‐derived biomolecules were found in SLE and RA patients, closely interconnected and associated to specific miRNA profiles. RTX treatment reduced SLE and RA patients' disease activity, linked to a prominent alteration in those biomolecules and the reversal of altered regulating miRNAs. In vitro studies showed inhibition of NETosis and decline of pro‐inflammatory profiles of leucocytes and human umbilical vein endothelial cells (HUVECs) after B cell depletion. This study provides evidence supporting an early RTX‐induced re‐setting of the pro‐inflammatory status in SLE and RA, involving a re‐establishment of the homeostatic equilibrium in immune system and the vascular wall.

Inhibition of the catalytic function of activation-induced cytidine deaminase promotes apoptosis of germinal center B cells in BXD2 mice

OBJECTIVE

To determine whether functional suppression of the catalytic domain of activation-induced cytidine deaminase (AID) can suppress the hyperreactive germinal center (GC) responses in BXD2 mice.

METHODS

We generated transgenic BXD2 mice expressing a dominant-negative (DN) form of Aicda at the somatic hypermutation site (BXD2-Aicda-DN-transgenic mice). Real-time quantitative reverse transcriptase-polymerase chain reaction was used to determine the expression of Aicda and DNA damage/repair genes. Enzyme-linked immunosorbent assay was used to measure serum levels of autoantibodies and immune complexes (ICs). Development of GCs and antibody-containing ICs as well as numbers of proliferative and apoptotic cells were determined using flow cytometry and/or immunohistochemical analyses. Development of arthritis and kidney disease was evaluated histologically in 6-8-month-old mice.

RESULTS

Suppression of the somatic hypermutation function of AID resulted in a significant decrease in autoantibody production without affecting the expression of DNA damage-related genes in GC B cells of BXD2-Aicda-DN-transgenic mice. There was decreased proliferation, increased apoptosis, increased expression of caspase 9 messenger RNA in GC B cells, and lower numbers of GCs in the spleens of BXD2-Aicda-DN-transgenic mice. Decreased GC response was associated with lower levels of IgG-containing ICs. Anti-IgM- and anti-CD40 plus anti-Ig-induced B cell proliferative responses were decreased in BXD2-Aicda-DN-transgenic mice.

CONCLUSION

Inhibition of the AID somatic hypermutation function in BXD2 mice suppressed development of spontaneous GCs, generation of autoantibody-producing B cells, and autoimmunity in BXD2 mice. Suppression of AID catalytic function to limit selection-based survival of GC B cells could become a novel therapy for the treatment of autoimmune disease.

Modulation of molecular imprints in the antigen-experienced B cell repertoire by rituximab

OBJECTIVE

Transient B cell depletion by rituximab has recently gained more importance in the treatment of rheumatic disorders. Nevertheless, little is known about the reemerging B cells. We analyzed dynamic changes in the repopulating B cells, particularly the postswitch B cells, and studied the mutational patterns of Ig genes in antigen-experienced B cells.

METHODS

Five patients with active rheumatoid arthritis (RA) were treated with rituximab. In 3 patients, B cell receptor (BCR) gene analysis was performed before treatment and during B cell recovery using genomic DNA. In 2 patients, B cell subsets were studied during the early recovery phase using single-cell technology. For comparison, immunophenotyping of B cell subsets was performed.

RESULTS

Early B cell recovery was marked by a relatively expanded population of highly mutated B cells, which were correlated with B cells with a plasmablast phenotype on comparative immunophenotyping. Analysis of the mutational pattern in these cells revealed increased RGYW/WRCY (where R = A/G, Y = C/T, and W = A/T) hotspot targeting (44% before rituximab versus 59% after) and elevated ratios of replacement to silent mutations within the complementarity-determining regions in Ig genes (1.87 before rituximab versus 2.67 after; P < or = 0.0025).

CONCLUSION

Our findings show that rituximab leads to qualitative changes in the imprints of highly mutated, antigen-experienced BCRs, representing the result of selection, whereas molecular processes such as Ig V rearrangements are not affected by this treatment.

Identification of intra-group, inter-individual, and gene-specific variances in mRNA expression profiles in the rheumatoid arthritis synovial membrane

Introduction

Rheumatoid arthritis (RA) is a chronic inflammatory and destructive joint disease characterized by overexpression of pro-inflammatory/pro-destructive genes and other activating genes (for example, proto-oncogenes) in the synovial membrane (SM). The gene expression in disease is often characterized by significant inter-individual variances via specific synchronization/desynchronization of gene expression. To elucidate the contribution of the variance to the pathogenesis of disease, expression variances were tested in SM samples of RA patients, osteoarthritis (OA) patients, and normal controls (NCs).

Method

Analysis of gene expression in RA, OA, and NC samples was carried out using Affymetrix U133A/B oligonucleotide arrays, and the results were validated by real-time reverse transcription-polymerase chain reaction. For the comparison between RA and NC, 568 genes with significantly different variances in the two groups (P ≤ 0.05; Bonferroni/Holm corrected Brown-Forsythe version of the Levene test) were selected. For the comparison between RA and OA, 333 genes were selected. By means of the Kyoto Encyclopedia of Genes and Genomes, the pathways/complexes significantly affected by higher gene expression variances were identified in each group.

Results

Ten pathways/complexes significantly affected by higher gene expression variances were identified in RA compared with NC, including cytokine–cytokine receptor interactions, the transforming growth factor-beta pathway, and anti-apoptosis. Compared with OA, three pathways with significantly higher variances were identified in RA (for example, B-cell receptor signaling and vascular endothelial growth factor signaling). Functionally, the majority of the identified pathways are involved in the regulation of inflammation, proliferation, cell survival, and angiogenesis.

Conclusion

In RA, a number of disease-relevant or even disease-specific pathways/complexes are characterized by broad intra-group inter-individual expression variances. Thus, RA pathogenesis in different individuals may depend to a lesser extent on common alterations of the expression of specific key genes, and rather on individual-specific alterations of different genes resulting in common disturbances of key pathways.

[Indications and options of new immune modulatory therapies for Sjögren's syndrome]

Sjögren's syndrome is a systemic inflammatory rheumatic disorder of unknown origin with so far inadequate therapy options. Management of Sjögren's syndrome is still primarily palliative using local symptomatic measures, and if appropriate glucocorticoids, NSAIDs and immunosuppressive drugs. New clues to the pathogenesis of this disorder pave the way for new therapeutic strategies. In particular targeting B-cells offers promising results and emphasizes the role of B-cells in the pathogenesis of this complex disorder. Rituximab was introduced into the standard treatment of different forms of low-grade and high-grade B-cell non-Hodgkins lymphomas, and is also an option for some lymphomas associated with Sjögren's syndrome. Whether interference with T-cell function is also a safe and effective strategy in Sjögren's syndrome, has to be shown in controlled clinical trials. However, there is no clear evidence to suggest that treatment with TNF-alpha blockers is efficacious in Sjögren's syndrome. Standardization of disease activity and outcome measurements are critical for further clinical trials for Sjögren's syndrome.

Quantitative determination of humanized monoclonal antibody rhuMAb2H7 in cynomolgus monkey serum using a Generic Immunoglobulin Pharmacokinetic (GRIP) assay

Preclinical pharmacokinetic (PK) assays are important to help evaluate the safety and efficacy of a potential biotherapeutic before clinical studies. The assay typically requires a biotherapeutic-specific reagent to minimize matrix effects especially when the host species are non-human primates such as cynomolgus monkeys and the biotherapeutic is a humanized monoclonal antibody (MAb). Recombinant humanized mAb 2H7 (rhuMAb2H7) binds to the extracellular domain of CD20 that is expressed on B cells and results in B cell depletion. It is currently being evaluated for its therapeutic potential in rheumatoid arthritis (RA) in clinical studies. During the early development of rhuMAb2H7, a cynomolgus monkey PK assay was needed to help assess the pharmacokinetic parameters of rhuMAb2H7 in a pilot cynomolgus monkey study. However, development of a cynomolgus monkey PK assay was challenging due to lack of rhuMAb2H7-specific reagents. Here we describe an alternative method for detection of rhuMAb2H7 in cynomolgus monkey serum using polyclonal antibodies against human IgGs. This assay quantifies rhuMAb2H7 in 10% cynomolgus monkey serum with high sensitivity, accuracy, and precision. This assay successfully supported the rhuMAb2H7 development, and has the potential to be used to quantify other humanized MAb biotherapeutics in serum from a variety of non-human species.

Developments in the synovial biology field 2006

Synovial pathophysiology is a complex and synergistic interplay of different cell populations with tissue components, mediated by a variety of signaling mechanisms. All of these mechanisms drive the affected joint into inflammation and drive the subsequent destruction of cartilage and bone. Each cell type contributes significantly to the initiation and perpetuation of this deleterious concert, especially in rheumatoid arthritis. Rheumatoid arthritis synovial fibroblasts and macrophages, both cell types with pivotal roles in inflammation and destruction, but also T cells and B cells are crucial for complex network in the inflamed synovium. An even more complex cellular crosstalk between these key players maintains a process of chronic inflammation. As outlined in the present review, in the past year substantial progress has been made to elucidate further details of the rich pathophysiology of rheumatoid arthritis, which may also facilitate the identification of novel targets for future therapeutic strategies.

Targeting CD22 as a strategy for treating systemic autoimmune diseases

B-cells play an important role in the diagnosis and to some extent the pathogenesis of many autoimmune diseases. Specific B-cell directed antibodies are now gaining an increasing role in the management of these diseases. The first antibody target in this regard was CD20, with the development and introduction of rituximab in the management of B-cell malignancies as well as rheumatoid arthritis. A second candidate target is CD22, and the first antagonistic antibody to this B-cell marker is epratuzumab, which appears to function, in contrast to CD20 antibodies, more by modulation of B-cells than by their depletion capacity. Originally developed for the treatment of non-Hodgkin lymphoma, epratuzumab has now been reported to be effective, with a very good safety profile, in two prototype autoimmune diseases, systemic lupus erythematosus and primary Sjögren's syndrome. As such, this new investigational antibody may provide distinct therapeutic effects and may be complementary to the known effects and role of CD20 antibodies.

New treatments for acute humoral rejection of kidney allografts

Acute antibody-mediated rejection (acute humoral rejection; AHR) of organ allografts usually presents as severe dysfunction with a high risk of allograft loss. Peritubular capillary complement C4d deposition with renal dysfunction, associated with circulating donor-specific anti-human leukocyte antigen alloantibodies, is diagnostic of AHR in kidney allografts. Removal of alloantibodies with suppression of antibody production and rejection reversal is now possible. Therapeutic strategies that include combinations of plasmapheresis (or immunoadsorption), tacrolimus, mycophenolate mofetil and/or intravenous immunoglobulins, as well as rituximab or splenectomy, have been recently used to successfully treat AHR. However, the optimal protocol to treat AHR still remains to be defined. Anti-CD20+ monoclonal antibody therapy (rituximab) aiming at depleting B cells and suppressing antibody production has been used as rescue therapy in some episodes of steroid- and antilymphocyte-resistant humoral rejection. Plasmapheresis and/or intravenous polyclonal immunoglobulin, as well as rituximab, have also been used to successfully desensitize selected high-immunological risk patients in anticipation of a previously cross-match positive (or ABO incompatible) kidney transplantation. In the near future, the possible role of new specific anti-B-cell approaches or, possibly, of new anti-T-cell activation approaches using selective agents such as belatacept should be assessed to further refine the present treatment of humoral rejection.

Epratuzumab in the therapy of oncological and immunological diseases

B cells play an important role in the pathogenesis of certain lymphomas and leukemias, as well as many autoimmune diseases. Antagonistic B-cell antibodies are thus gaining an increasing role in the management of these diseases. The first antibody target in this regard was CD20, with the development and introduction of rituximab in the management of B-cell malignancies, as well as rheumatoid arthritis. A second candidate target is CD22. The first antagonistic antibody to this B-cell marker, epratuzumab, appears to function, in contrast to CD20 antibodies, more by modulation of B cells rather than by their high depletion in circulation. Originally developed for the treatment of non-Hodgkin's lymphoma, epratuzumab has now been found to be effective, with a very good safety profile, in two prototype autoimmune diseases: systemic lupus erythematosus and primary Sjögren's syndrome. Recent studies have demonstrated the activity and safety of epratuzumab in non-Hodgkin's lymphoma patients who have relapsed or are refractive to conventional therapy, including rituximab, and has also shown good activity in follicular and diffuse large B-cell lymphoma in combination with rituximab. As such, this new investigative antibody may have a significant market potential owing to the multitude of diseases and patients who may benefit from a CD22, B-cell antibody immunotherapy that is complementary to the known effects and role of CD20 antibodies, but can usually be administered within 1 h and depletes approximately 50% of circulating B cells.

Non-fucosylated therapeutic antibodies as next-generation therapeutic antibodies

Most of the existing therapeutic antibodies that have been licensed and developed as medical agents are of the human IgG1 isotype, the molecular weight of which is approximately 150 kDa. Human IgG1 is a glycoprotein bearing two N-linked biantennary complex-type oligosaccharides bound to the antibody constant region (Fc), in which the majority of the oligosaccharides are core fucosylated, and it exercises the effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity through the interaction of the Fc with either leukocyte receptors (FcgammaRs) or complement. Recently, therapeutic antibodies have been shown to improve overall survival as well as time to disease progression in a variety of human malignancies, such as breast, colon and haematological cancers, and genetic analysis of FcgammaR polymorphisms of cancer patients has demonstrated that ADCC is a major antineoplasm mechanism responsible for clinical efficacy. However, the ADCC of existing licensed therapeutic antibodies has been found to be strongly inhibited by serum due to nonnpecific IgG competing for binding of the therapeutics to FcgammaRIIIa on natural killer cells, which leads to the requirement of a significant amount of drug and very high costs associated with such therapies. Moreover, enhanced ADCC of non-fucosylated forms of therapeutic antibodies through improved FcgammaRIIIa binding is shown to be inhibited by the fucosylated counterparts. In fact, non-fucosylated therapeutic antibodies, not including the fucosylated forms, exhibit the strongest and most saturable in vitro and ex vivo ADCC among such antibody variants with improved FcgammaRIIIa binding as those bearing naturally occurring oligosaccharide heterogeneities and artificial amino acid mutations, even in the presence of plasma IgG. Robust stable production of completely non-fucosylated therapeutic antibodies in a fixed quality has been achieved by the generation of a unique host cell line, in which the endogenous alpha-1,6-fucosyltransferase (FUT8) gene is knocked out. Thus, the application of non-fucosylated antibodies is expected to be a promising approach as next-generation therapeutic antibodies with improved efficacy, even when administrated at low doses in humans in vivo. Clinical trials using non-fucosylated antibody therapeutics are underway at present.

B lymphocytes as therapeutic targets in systemic lupus erythematosus

In recent years, experimental evidence supporting a major role of B cells in the pathogenesis of autoimmune diseases has grown. This includes the discovery of novel mechanisms of autoantibody pathogenicity and the potential of B cells to mediate inflammation and tissue injury. In some instances, engagement of the B cell receptor and other surface receptors is sufficient to stimulate B cells to produce antibody. As a result, B cells have become targets for immunointervention. In lupus, targeting B cell activation factor (BAFF, BLys) indicates that specific blockade of this longevity factor might be sufficient to suppress systemic autoimmunity. Targeting CD20 represents another promising avenue for the treatment of refractory lupus in both adults and children. Although the clinical data add weight to the importance of B cells in the pathogenesis of lupus, new targets for B cell depletion therapy are being investigated. In experimental models, combining CD19 and CD20 antibodies was more effective than either treatment alone.

B-cell targeted therapies in rheumatoid arthritis and systemic lupus erythematosus

B cells appear to have a central role in the immunopathogenesis of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE); both autoantibody production and B-cell anomalies are characteristic of these diseases. With the recent availability of biologic agents that can deplete B cells or block their function in vivo, it has become possible to target B cells therapeutically. Evidence strongly suggests that novel B-cell targeting agents are effective. In addition, the mechanistic specificity of B-cell targeted approaches, combined with the ability to test them in large randomized controlled trials, will provide an unprecedented opportunity to study the precise roles of B cells in the immunopathogenesis of RA and SLE. The largest volume of information is available for rituximab, a chimeric monoclonal antibody that depletes B cells by binding to the CD20 cell-surface antigen. Information from multiple investigator-sponsored trials and from off-label use suggests efficacy of this antibody in RA, SLE, and other autoimmune syndromes. Randomized controlled trials have also provided solid evidence for the efficacy of rituximab in RA and are ongoing in SLE. Other therapeutic agents supported by controlled data include cytotoxic T-lymphocyte-associated protein 4 immunoglobulin and antibodies against the interleukin-6 receptor and the B-cell survival molecule BLyS. Additional agents and targets are in earlier stages of development. The concerns about infectious complications have so far not proven to be justified. We can reasonably expect important advances in the understanding and treatment of RA and SLE in the next 5-10 years, as B-cell targeting methods become more widespread and sophisticated.

Biological therapies directed against cells in autoimmune disease

Among the cells of the immune system involved in the pathogenesis of autoimmune disease, T cells have received the most attention. The central role of these cells in several animal models of autoimmune diseases and in human disease counterparts has provided the rationale for specific therapeutic targeting of T cell subsets, especially CD4 T cells. So far, the applicability of this approach has not been clearly evident in clinical trials, which was also the case when nondepleting "coating" anti-CD4 monoclonal antibodies was used. In the past several years, experimental evidence supporting a major role of B cells in systemic autoimmune disease has grown. This includes the pathogenicity of certain autoantibodies, the potential of B cells to present antigen in the context of MHC Class II and to signal via costimulatory molecules, and to secrete proinflammatory cytokines. In some instances, engagement of the B cell receptor and other surface receptors is sufficient to stimulate B cells to produce antibodies. The depletion of B cells by targeting the surface marker CD20 has been shown to be effective in treating rheumatoid arthritis with a good side effect profile. Series of cases with other systemic autoimmune diseases indicate that this strategy may be effective in these conditions too. The clinical data add weight to the importance of B cells in the pathogenesis of autoimmune diseases.

Targeting Toll-like receptor signaling in plasmacytoid dendritic cells and autoreactive B cells as a therapy for lupus

This review focuses on the role of Toll-like receptors (TLRs) in lupus and on possibilities to treat lupus using TLR modulating inhibitory oligodeoxynucleotides (INH-ODNs). TLRs bridge innate and adaptive immune responses and may play an important role in the pathogenesis of systemic lupus erythematosus. Of particular interest are TLR3, -7, -8, and -9, which are localized intracellularly. These TLRs recognize single-stranded or double-stranded RNA or hypomethylated CpG-DNA. Exposure to higher order CpG-DNA ligands or to immune complexed self-RNA triggers activation of autoreactive B cells and plasmacytoid dendritic cells. INH-ODNs were recently developed that block all downstream signaling events in TLR9-responsive cells. Some of these INH-ODNs can also target TLR7 signaling pathways. Based on their preferential cell reactivity, we classify INH-ODNs into class B and class R. Class B ('broadly reactive') INH-ODNs target a broad range of TLR-expressing cells. Class R ('restricted') INH-ODNs easily form DNA duplexes or higher order structures, and are preferentially recognized by autoreactive B cells and plasmacytoid dendritic cells, rather than by non-DNA specific follicular B cells. Both classes of INH-ODNs can block animal lupus. Hence, therapeutic application of these novel INH-ODNs in human lupus, particularly class R INH-ODNs, may result in more selective and disease-specific immunosuppression.

The therapeutic potential of anti-CD20 "what do B-cells do?"

B-cells play a major role in the immunopathogenesis of autoimmune diseases. Not only do they produce autoantibodies, but they regulate other cell types, secrete cytokines, and present antigens. They are thus potential targets for therapeutic intervention. CD20 is a B-cell specific cell surface molecule of uncertain function. An anti-CD20 chimeric mAb (rituximab) has been FDA approved for treatment of B-cell lymphomas since 1997. Rituximab also depletes normal B-cells by several mechanisms, including ADCC. Over the past seven years, it has shown promise in a number of autoimmune diseases in phase I trials and anecdotal reports. Efficacy in rheumatoid arthritis has already been demonstrated in randomized control trials (RCTs), and RCTs in SLE, inflammatory myositis, and ANCA associated vasculitis are under way. Safety does not appear to be a major problem, but continued vigilance is warranted. The increased use of rituximab, other anti-CD20 agents, and other B-cell targeting therapies holds great promise for substantial clinical benefits, as well as providing special opportunities to understand better disease pathogenesis.