Human regulatory B cells in health and disease: therapeutic potential

Regulatory B cells (Bregs) modulate immune responses predominantly, although not exclusively, via the release of IL-10. The importance of human Bregs in the maintenance of immune homeostasis comes from a variety of immune-related pathologies, such as autoimmune diseases, cancers, and chronic infections that are often associated with abnormalities in Breg numbers or function. A continuous effort toward understanding Breg biology in healthy individuals will provide new opportunities to develop Breg immunotherapy that could prove beneficial in treating various immune-mediated pathologies. In this Review, we discuss findings regarding human Bregs, including their mechanisms of suppression and role in different disease settings. We also propose several therapeutic strategies targeting Bregs for better management of immune disorders.

TIM-1 defines a human regulatory B cell population that is altered in frequency and function in systemic sclerosis patients

BACKGROUND

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by excessive production of extracellular matrix by fibroblasts on skin and internal organs. Although Th2 cells have been involved in fibroblast stimulation, hyperactivated B cells may also play an important role. Regulatory B cells (Bregs) are cells capable of inhibiting inflammatory responses and controlling autoimmune diseases. Although many Breg populations have in common the ability to produce high amounts of IL-10, a unique surface marker defining most human Bregs is lacking. It has been described in mice that T cell Ig and mucin domain protein 1 (TIM-1) is an inclusive marker for Bregs, and that TIM-1+ B cells are able to prevent the development of autoimmunity. The aim of this work was to evaluate TIM-1 as a marker for human IL-10⁺ Bregs, and to determine whether TIM-1+ B cells are defective in SSc patients.

METHODS

SSc patients (n = 39) and 53 healthy subjects were recruited. TIM-1 and IL-10 expression was assessed in resting or activated peripheral blood CD19⁺ B cells by flow cytometry. The regulatory function of TIM-1⁺ or activated B cells from SSc patients and healthy subjects was assessed in autologous and allogenic co-cultures with CD4⁺ T cells, where T cell proliferation and IFN-γ, IL-17, TNF-α and IL-4 production by T cells was measured by flow cytometry.

RESULTS

TIM-1 and IL-10 were preferentially expressed in transitional B cells, but were upregulated in naïve and memory B cells upon stimulation. The frequency of transitional TIM-1⁺ IL-10⁺ B cells was significantly decreased in SSc patients compared to healthy controls. In addition, activated B cells from SSc patients induced stronger allogenic Th1 and Th2 responses than activated B cells from healthy controls. Finally, TIM-1⁺ B cells, including transitional and non-transitional cells, exhibited a higher CD4⁺ T cell suppressive ability than TIM-1^- B cells in healthy controls, but not in SSc patients.

CONCLUSIONS

TIM-1 is a unique marker for the identification of a human IL-10⁺ Breg subpopulation which is partially superimposed with transitional B cells. Alterations in TIM-1⁺ B cells could contribute to the development of autoimmune diseases such as SSc.

A clinical update on the significance of the gut microbiota in systemic autoimmunity

Systemic lupus erythematosus (SLE) is a complex autoimmune disease where a loss of tolerance to nuclear antigens leads to inflammation in multiple organ systems. The cause of SLE remains ill defined, although it is known that a complex interplay between genes and environment is necessary for disease development. In recent years, case studies have reported that the incidence of SLE in the USA, for example, has increased by approximately 3 fold. Although the reason for this is likely to be multifactorial, it has been hypothesized that the increasing incidence of autoimmune disease is due to considerable shifts in the bacterial communities resident the gut, collectively known as the gut microbiota, following a change in diet and the widespread introduction of antibiotics. Furthermore, a growing body of evidence suggests that the gut microbiota plays a role in the development of a range of autoimmune diseases including inflammatory bowel disease, multiple sclerosis, type one diabetes and rheumatoid arthritis. In this review, we summarize how advances in DNA-based sequencing technologies have been critical in providing baseline information concerning the gut microbiota in health and how variation amongst individuals in controlled by multiples factors including age, genetics, environment and the diet. We also discuss the importance of the gut microbiota in the development of a healthy immune system and how changes in particular bacterial phyla have been associated with immune abnormalities in animal models of autoimmune disease. Finally, in order to place the data in a clinical context, we highlight recent findings showing that abnormalities in the gut microbiota can be detected in patients with SLE, which provides the rationale for greater investigation into whether microbiota-targeted therapies could be used for the treatment/prevention of disease.

A Regulatory Feedback between Plasmacytoid Dendritic Cells and Regulatory B Cells Is Aberrant in Systemic Lupus Erythematosus

Signals controlling the generation of regulatory B (Breg) cells remain ill-defined. Here we report an “auto”-regulatory feedback mechanism between plasmacytoid dendritic cells (pDCs) and Breg cells. In healthy individuals, pDCs drive the differentiation of CD19⁺CD24^hiCD38^hi (immature) B cells into IL-10-producing CD24⁺CD38^hi Breg cells and plasmablasts, via the release of IFN-α and CD40 engagement. CD24⁺CD38^hi Breg cells conversely restrained IFN-α production by pDCs via IL-10 release. In systemic lupus erythematosus (SLE), this cross-talk was compromised; pDCs promoted plasmablast differentiation but failed to induce Breg cells. This defect was recapitulated in healthy B cells upon exposure to a high concentration of IFN-α. Defective pDC-mediated expansion of CD24⁺CD38^hi Breg cell numbers in SLE was associated with altered STAT1 and STAT3 activation. Both altered pDC-CD24⁺CD38^hi Breg cell interactions and STAT1-STAT3 activation were normalized in SLE patients responding to rituximab. We propose that alteration in pDC-CD24⁺CD38^hi Breg cell interaction contributes to the pathogenesis of SLE.

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pDCs induce the differentiation of Breg cells in an IFN-α-dependent manner

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Breg cells limit pDC-derived IFN-α in an IL-10-dependent mechanism

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pDCs are hyperactivated in SLE and fail to induce Breg cells

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Patients responding to rituximab display a normalized pDC-Breg cell interaction

Standardizing terms, definitions and concepts for describing and interpreting unwanted immunogenicity of biopharmaceuticals: recommendations of the Innovative Medicines Initiative ABIRISK consortium

Biopharmaceuticals (BPs) represent a rapidly growing class of approved and investigational drug therapies that is contributing significantly to advancing treatment in multiple disease areas, including inflammatory and autoimmune diseases, genetic deficiencies and cancer. Unfortunately, unwanted immunogenic responses to BPs, in particular those affecting clinical safety or efficacy, remain among the most common negative effects associated with this important class of drugs. To manage and reduce risk of unwanted immunogenicity, diverse communities of clinicians, pharmaceutical industry and academic scientists are involved in: interpretation and management of clinical and biological outcomes of BP immunogenicity, improvement of methods for describing, predicting and mitigating immunogenicity risk and elucidation of underlying causes. Collaboration and alignment of efforts across these communities is made difficult due to lack of agreement on concepts, practices and standardized terms and definitions related to immunogenicity. The Innovative Medicines Initiative (IMI; http://www.imi-europe.org), ABIRISK consortium [Anti-Biopharmaceutical (BP) Immunization Prediction and Clinical Relevance to Reduce the Risk; http://www.abirisk.eu] was formed by leading clinicians, academic scientists and EFPIA (European Federation of Pharmaceutical Industries and Associations) members to elucidate underlying causes, improve methods for immunogenicity prediction and mitigation and establish common definitions around terms and concepts related to immunogenicity. These efforts are expected to facilitate broader collaborations and lead to new guidelines for managing immunogenicity. To support alignment, an overview of concepts behind the set of key terms and definitions adopted to date by ABIRISK is provided herein along with a link to access and download the ABIRISK terms and definitions and provide comments (http://www.abirisk.eu/index_t_and_d.asp).

The many faces of type I interferon in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with a broad spectrum of clinical presentations involving multiple organ systems. An abnormal response to self-antigens is thought to drive the development of SLE; however, the factors that underlie this dysfunction are not clear. In this issue of the JCI, Li and colleagues present compelling evidence to show that type I interferons (IFNs) produced by plasmacytoid dendritic cells inhibit the clearance of apoptotic cells (ACs) by marginal zone macrophages. Specifically, type I IFNs increase the translocation of marginal zone (MZ) B cells to the follicular region of the spleen, thereby disrupting interactions between these B cells and MZ macrophages (MZMs), which in turn disrupts megakaryoblastic leukemia 1-mediated (MKL1-mediated) mechanosensing and inhibits AC phagocytosis by MZMs. The results of this study provide important insight into factors that inhibit AC clearance and promote the development of SLE.

The expanding family of regulatory B cells

Over the last decade it has become evident that in addition to producing antibody, B cells activate the immune system by producing cytokines and via antigen presentation. In addition, B cells also exhibit immunosuppressive functions via diverse regulatory mechanisms. This subset of B cells, known as regulatory B cells (Bregs), contributes to the maintenance of tolerance, primarily via the production of IL-10. Studies in experimental animal models, as well as in patients with autoimmune diseases, have identified multiple Breg subsets exhibiting diverse mechanisms of immune suppression. In this review, we describe the different Breg subsets identified in mice and humans, and their diverse mechanisms of suppression in different disease settings.

The quest for personalized B-cell depletion therapy in rheumatic disease

Although B cell depletion therapy (BCDT) is now a well-accepted therapeutic option in autoimmune rheumatic disease, a significant proportion of patients remain resistant to therapy. .19pt?>A more challenging clinical problem is the high rate of relapse after B cell reconstitution, as well as the difficulty in predicting the exact timing of that relapse. In this article, we consider the immunological mechanisms that may account for the heterogeneity of clinical response to BCDT. Understanding how BCDT alters the balance between different B cell subsets, some pathogenic and some regulatory, may help us correctly target BCDT to the right patients, and thereby improve treatment responses in rheumatic disease.

The incognito journey of a regulatory B cell

Regulatory B cells have largely been reported as B cells at a developmental stage before plasma cell differentiation. Matsumoto et al. (2014) report that IL-10(+) plasmablasts restrain autoimmune inflammation and suggest an ontological connection between immature B cells and regulatory plasmablasts.

Cellular targets of regulatory B cell-mediated suppression

Regulatory B cells (Bregs) are defined by their ability to restrain inflammatory responses both in vivo and in vitro. Interleukin 10 (IL-10) production by Bregs is thought to be central to their ability to regulate inflammation, largely due to IL-10s' ability to suppress pro-inflammatory cytokine production by effector lymphocytes and to maintain the differentiation of regulatory T cells (Tregs). However, with an increase in available published data, it has become evident that Bregs utilize a number of suppressive mechanisms in order to alter the activation of a variety of different lymphocytes. Here, we summarize the multiplicity of cellular targets of Breg-mediated suppression and describe the mechanisms employed by Bregs to suppress chronic inflammatory responses.

Regulatory B cells are induced by gut microbiota-driven interleukin-1β and interleukin-6 production

Regulatory B cells (Breg cells) differentiate in response to inflammation and subsequently restrain excessive immune responses via the release of interleukin-10 (IL-10). However, the precise inflammatory signals governing their differentiation remain to be elucidated. Here we show that the gut microbiota promotes the differentiation of Breg cells in the spleen as well as in the mesenteric lymph nodes. Perturbation of the gut microbiome imposed either by antibiotic treatment or by changes in the sterility of housing conditions reduces the number and function of Breg cells. Following the induction of arthritis, IL-1β and IL-6 are produced only in conventionally housed mice and both cytokines directly promote Breg cell differentiation and IL-10 production. Mice lacking IL-6 receptor (IL-6R) or IL-1 receptor 1 (IL-1R1) specifically on B cells have a reduced number of IL-10-producing B cells and develop exacerbated arthritis compared to control animals. Thus, in response to inflammatory signals induced by both the gut flora and arthritis, Breg cells increase in number and restrain excessive inflammation.

Exacerbated experimental arthritis in Wiskott-Aldrich syndrome protein deficiency: modulatory role of regulatory B cells

Patients deficient in the cytoskeletal regulator Wiskott–Aldrich syndrome protein (WASp) are predisposed to varied autoimmunity, suggesting it has an important controlling role in participating cells. IL-10-producing regulatory B (Breg) cells are emerging as important mediators of immunosuppressive activity. In experimental, antigen-induced arthritis WASp-deficient (WASp knockout [WAS KO]) mice developed exacerbated disease associated with decreased Breg cells and regulatory T (Treg) cells, but increased Th17 cells in knee-draining LNs. Arthritic WAS KO mice showed increased serum levels of B-cell-activating factor, while their B cells were unresponsive in terms of B-cell-activating factor induced survival and IL-10 production. Adoptive transfer of WT Breg cells ameliorated arthritis in WAS KO recipients and restored a normal balance of Treg and Th17 cells. Mice with B-cell-restricted WASp deficiency, however, did not develop exacerbated arthritis, despite exhibiting reduced Breg- and Treg-cell numbers during active disease, and Th17 cells were not increased over equivalent WT levels. These findings support a contributory role for defective Breg cells in the development of WAS-related autoimmunity, but demonstrate that functional competence in other regulatory populations can be compensatory. A properly regulated cytoskeleton is therefore important for normal Breg-cell activity and complementation of defects in this lineage is likely to have important therapeutic benefits.

Regulatory B cells are numerically but not functionally deficient in anti-neutrophil cytoplasm antibody-associated vasculitis

OBJECTIVES

B cells are central to the pathology of ANCA-associated vasculitis (AAV), a disease characterized by autoantibodies and effectively treated by rituximab. In addition to promoting inflammation, a subset of B cells act to suppress harmful autoimmune responses (Breg). The balance of effector and regulatory B cell subsets in AAV is not known. This study was conducted to assess the relative frequency of these subsets during different states of disease activity.

METHODS

B memory (Bmem), naive (Bnaive) and regulatory (Breg) subsets were defined by their relative expression of CD24 and CD38. Function was assessed by cytokine production and suppressive action on CD4(+) Th1 activation evaluated in a co-culture system.

RESULTS

Compared with healthy controls, the frequency of Breg (CD24(hi)CD38(hi)) was significantly reduced during disease remission in both proteinase 3 (PR3)- and MPO-ANCA patients and during acute disease in PR3-ANCA patients, while the frequency of memory cells (CD24(hi)CD38(lo)) was reduced during active disease and restored during remission. Breg cell frequency showed a positive correlation, while Bmem had an inverse correlation with IL-10 production in vitro. B and T cell co-cultures revealed that memory and naive B cell subsets augmented Th1 activation in vitro, which was prevented by Breg, and this pattern did not differ between remission AAV patients and controls.

CONCLUSION

In remission there is a numerical, but not functional, deficiency in Breg and preservation of Bmem associated with reduced IL-10 production and increased Th1 activation in vitro. This imbalance may contribute to the high rate of relapse observed in AAV, especially in PR3-ANCA patients.