TLR9 stimulation drives naïve B cells to proliferate and to attain enhanced antigen presenting function

Toll-like receptor agonists as cancer vaccine adjuvants

Cancer immunotherapy has emerged as a promising strategy to treat cancer patients. Among the wide range of immunological approaches, cancer vaccines have been investigated to activate and expand tumor-reactive T cells. However, most cancer vaccines have not shown significant clinical benefit as monotherapies. This is likely due to the antigen targets of vaccines, "self" proteins to which there is tolerance, as well as to the immunosuppressive tumor microenvironment. To help circumvent immune tolerance and generate effective immune responses, adjuvants for cancer vaccines are necessary. One representative adjuvant family is Toll-Like receptor (TLR) agonists, synthetic molecules that stimulate TLRs. TLRs are the largest family of pattern recognition receptors (PRRs) that serve as the sensors of pathogens or cellular damage. They recognize conserved foreign molecules from pathogens or internal molecules from cellular damage and propel innate immune responses. When used with vaccines, activation of TLRs signals an innate damage response that can facilitate the development of a strong adaptive immune response against the target antigen. The ability of TLR agonists to modulate innate immune responses has positioned them to serve as adjuvants for vaccines targeting infectious diseases and cancers. This review provides a summary of various TLRs, including their expression patterns, their functions in the immune system, as well as their ligands and synthetic molecules developed as TLR agonists. In addition, it presents a comprehensive overview of recent strategies employing different TLR agonists as adjuvants in cancer vaccine development, both in pre-clinical models and ongoing clinical trials.

Enhancing vaccine effectiveness in the elderly to counter antibiotic resistance: The potential of adjuvants via pattern recognition receptors

Vaccines are an effective way to prevent the emergence and spread of antibiotic resistance by preventing diseases and establishing herd immunity. However, the reduced effectiveness of vaccines in the elderly due to immunosenescence is one of the significant contributors to the increasing antibiotic resistance. To counteract this decline and enhance vaccine effectiveness in the elderly, adjuvants play a pivotal role. Adjuvants are designed to augment the effectiveness of vaccines by activating the innate immune system, particularly through pattern recognition receptors on antigen-presenting cells. To improve vaccine effectiveness in the elderly using adjuvants, it is imperative to select the appropriate adjuvants based on an understanding of immunosenescence and the mechanisms of adjuvant functions. This review demonstrates the phenomenon of immunosenescence and explores various types of adjuvants, including their mechanisms and their potential in improving vaccine effectiveness for the elderly, thereby contributing to developing more effective vaccines for this vulnerable demographic.

In vivo analysis of CRISPR-edited germinal center murine B cells

The germinal center (GC) reaction is crucial for somatic hypermutation, affinity maturation, and the selection of high-affinity B cells, all of which are hallmarks of the humoral immune response. Understanding the distinct roles of various B cell genes is essential for elucidating the selection mechanisms within the GC reaction. Traditionally, studying B cell gene function in the GC reaction involved generating knock-out mice, a highly time-consuming method that necessitates complex vectors. The advent of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology has simplified the creation of knock-out mice. However, even with CRISPR, the generation of knock-out mice still faces challenges, including being time-consuming, costly, having low knock-out efficiency, and raising ethical concerns regarding animal use. To address these challenges, we developed an alternative method to traditional knock-out mouse generation. Our approach entails the ex vivo CRISPR editing of B cells from transgenic donor mice with different B cell receptor affinities followed by their adoptive transfer into recipient mice. We present a cost-effective, rapid, versatile, and adaptable CRISPR-Cas9 method for in vivo loss-of-function studies of individual murine B cell genes within the context of the GC reaction. This method provides a valuable tool for investigating the complex roles of different B cell genes in the GC selection process. As proof of concept, we validated our approach by examining the role of the pro-apoptotic gene Fas in the GC selection process. We adoptively transferred a mix of Fas knock-out (FasKO) low-affinity B cells, Fas wild-type (FasWT) low-affinity B cells, and FasWT high-affinity B cells into recipient mice. From our results, FasKO low-affinity B cells were still outcompeted by the FasWT high-affinity B cells for selection in the GC. An important observation was the accumulation of FasKO low-affinity GC B cells when compared to the FasWT low-affinity B cells, which suggested a role of Fas in the GC selection process.

Site-specific regulation of Th2 differentiation within lymph node microenvironments

T helper 2 (Th2) responses protect against pathogens while also driving allergic inflammation, yet how large-scale Th2 responses are generated in tissue context remains unclear. Here, we used quantitative imaging to investigate early Th2 differentiation within lymph nodes (LNs) following cutaneous allergen administration. Contrary to current models, we observed extensive activation and "macro-clustering" of early Th2 cells with migratory type-2 dendritic cells (cDC2s), generating specialized Th2-promoting microenvironments. Macro-clustering was integrin-mediated and promoted localized cytokine exchange among T cells to reinforce differentiation, which contrasted the behavior during Th1 responses. Unexpectedly, formation of Th2 macro-clusters was dependent on the site of skin sensitization. Differences between sites were driven by divergent activation states of migratory cDC2 from different dermal tissues, with enhanced costimulatory molecule expression by cDC2 in Th2-generating LNs promoting prolonged T cell activation, macro-clustering, and cytokine sensing. Thus, the generation of dedicated Th2 priming microenvironments through enhanced costimulatory molecule signaling initiates Th2 responses in vivo and occurs in a skin site-specific manner.

Application of toll-like receptors (TLRs) and their agonists in cancer vaccines and immunotherapy

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) expressed in various immune cell types and perform multiple purposes and duties involved in the induction of innate and adaptive immunity. Their capability to propagate immunity makes them attractive targets for the expansion of numerous immunotherapeutic approaches targeting cancer. These immunotherapeutic strategies include using TLR ligands/agonists as monotherapy or combined therapeutic strategies. Several TLR agonists have demonstrated significant efficacy in advanced clinical trials. In recent years, multiple reports established the applicability of TLR agonists as adjuvants to chemotherapeutic drugs, radiation, and immunotherapies, including cancer vaccines. Cancer vaccines are a relatively novel approach in the field of cancer immunotherapy and are currently under extensive evaluation for treating different cancers. In the present review, we tried to deliver an inclusive discussion of the significant TLR agonists and discussed their application and challenges to their incorporation into cancer immunotherapy approaches, particularly highlighting the usage of TLR agonists as functional adjuvants to cancer vaccines. Finally, we present the translational potential of rWTC-MBTA vaccination [irradiated whole tumor cells (rWTC) pulsed with phagocytic agonists Mannan-BAM, TLR ligands, and anti-CD40 agonisticAntibody], an autologous cancer vaccine leveraging membrane-bound Mannan-BAM, and the immune-inducing prowess of TLR agonists as a probable immunotherapy in multiple cancer types.

Toll-like receptors 7 and 9 regulate the proliferation and differentiation of B cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune illness marked by the loss of immune tolerance and the production of autoantibodies against nucleic acids and other nuclear antigens (Ags). B lymphocytes are important in the immunopathogenesis of SLE. Multiple receptors control abnormal B-cell activation in SLE patients, including intrinsic Toll-like receptors (TLRs), B-cell receptors (BCRs), and cytokine receptors. The role of TLRs, notably TLR7 and TLR9, in the pathophysiology of SLE has been extensively explored in recent years. When endogenous or exogenous nucleic acid ligands are recognized by BCRs and internalized into B cells, they bind TLR7 or TLR9 to activate related signalling pathways and thus govern the proliferation and differentiation of B cells. Surprisingly, TLR7 and TLR9 appear to play opposing roles in SLE B cells, and the interaction between them is still poorly understood. In addition, other cells can enhance TLR signalling in B cells of SLE patients by releasing cytokines that accelerate the differentiation of B cells into plasma cells. Therefore, the delineation of how TLR7 and TLR9 regulate the abnormal activation of B cells in SLE may aid the understanding of the mechanisms of SLE and provide directions for TLR-targeted therapies for SLE.

Challenges and opportunities in gene editing of B cells

B cells have long been an underutilized target in immune cell engineering, despite a number of unique attributes that could address longstanding challenges in medicine. Notably, B cells evolved to secrete large quantities of antibodies for prolonged periods, making them suitable platforms for long-term protein delivery. Recent advances in gene editing technologies, such as CRISPR-Cas, have improved the precision and efficiency of engineering and expanded potential applications of engineered B cells. While most work on B cell editing has focused on ex vivo modification, a body of recent work has also advanced the possibility of in vivo editing applications. In this review, we will discuss both past and current approaches to B cell engineering, and its promising applications in immunology research and therapeutic gene editing.

Contribution of T- and B-cell intrinsic toll-like receptors to the adaptive immune response in viral infectious diseases

Toll-like receptors (TLRs) comprise a class of highly conserved molecules that recognize pathogen-associated molecular patterns and play a vital role in host defense against multiple viral infectious diseases. Although TLRs are highly expressed on innate immune cells and play indirect roles in regulating antiviral adaptive immune responses, intrinsic expression of TLRs in adaptive immune cells, including T cells and B cells, cannot be ignored. TLRs expressed in CD4 + and CD8 + T cells play roles in enhancing TCR signal-induced T-cell activation, proliferation, function, and survival, serving as costimulatory molecules. Gene knockout of TLR signaling molecules has been shown to diminish antiviral adaptive immune responses and affect viral clearance in multiple viral infectious animal models. These results have highlighted the critical role of TLRs in the long-term immunological control of viral infection. This review summarizes the expression and function of TLR signaling pathways in T and B cells, focusing on the in vitro and vivo mechanisms and effects of intrinsic TLR signaling in regulating T- and B-cell responses during viral infection. The potential clinical use of TLR-based immune regulatory drugs for viral infectious diseases is also explored.

Role of B cells as antigen presenting cells

B cells have been long studied for their role and function in the humoral immune system. Apart from generating antibodies and an antibody-mediated memory response against pathogens, B cells are also capable of generating cell-mediated immunity. It has been demonstrated by several groups that B cells can activate antigen-specific CD4 and CD8 T cells, and can have regulatory and cytotoxic effects. The function of B cells as professional antigen presenting cells (APCs) to activate T cells has been largely understudied. This, however, requires attention as several recent reports have demonstrated the importance of B cells within the tumor microenvironment, and B cells are increasingly being evaluated as cellular therapies. Antigen presentation through B cells can be through antigen-specific (B cell receptor (BCR) dependent) or antigen non-specific (BCR independent) mechanisms and can be modulated by a variety of intrinsic and external factors. This review will discuss the pathways and mechanisms by which B cells present antigens, and how B cells differ from other professional APCs.

Pattern recognition receptor ligand-induced differentiation of human transitional B cells

B cells represent a critical component of the adaptive immune response whose development and differentiation are determined by antigen-dependent and antigen-independent interactions. In this study, we explored the effects of IL-4 and pattern-recognition receptor (PRR) ligands on B cell development and differentiation by investigating their capacity to drive the in vitro maturation of human transitional B cells. In the presence of IL-4, ligands for TLR7/8, TLR9, and NOD1 were effective in driving the in vitro maturation of cord blood transitional B cells into mature, naïve B cells as measured by CD23 expression, ABCB1 transporter activation and upregulation of sIgM and sIgD. In addition, several stimulation conditions, including TLR9 ligand alone, favored an expansion of CD27⁺ IgM memory B cells. Transitional B cells stimulated with TLR7/8 ligand + IL-4 or TLR9 ligand, with or without IL-4, induced a significant subpopulation of CD23⁺CD27⁺ B cells expressing high levels of sIgM and sIgD, a minor B cell subpopulation found in human peripheral blood. These studies illustrate the heterogeneity of the B cell populations induced by cytokine and PRR ligand stimulation. A comparison of transitional and mature, naïve B cells transcriptomes to identify novel genes involved in B cell maturation revealed that mature, naïve B cells were less transcriptionally active than transitional B cells. Nevertheless, a subset of differentially expressed genes in mature, naïve B cells was identified including genes associated with the IL-4 signaling pathway, PI3K signaling in B lymphocytes, the NF-κB signaling pathway, and the TNFR superfamily. When transitional B cells were stimulated in vitro with IL-4 and PRR ligands, gene expression was found to be dependent on the nature of the stimulants, suggesting that exposure to these stimulants may alter the developmental fate of transitional B cells. The influence of IL-4 and PRR signaling on transitional B cell maturation illustrates the potential synergy that may be achieved when certain PRR ligands are incorporated as adjuvants in vaccine formulations and presented to developing B cells in the context of an inflammatory cytokine environment. These studies demonstrate the potential of the PRR ligands to drive transitional B cell differentiation in the periphery during infection or vaccination independently of antigen mediated BCR signaling.

Tilsotolimod: an investigational synthetic toll-like receptor 9 (TLR9) agonist for the treatment of refractory solid tumors and melanoma

INTRODUCTION

Cancer immunotherapy has seen tremendous strides in the past 15 years, with the introduction of several novel immunotherapeutic agents. Nevertheless, as clinical practice has shown, significant challenges remain with a considerable number of patients responding sub-optimally to available therapeutic options. Research has demonstrated the important immunoregulatory role of the tumor microenvironment (TME), with the potential to either hinder or promote an effective anti-tumor immune response. As such, scientific efforts have focused on investigating novel candidate immunomodulatory agents with the potential to alter the TME toward a more immunopotentiating composition.

AREAS COVERED

Herein, we discuss the novel investigational toll-like receptor 9 agonist tilsotolimod currently undergoing phase II and III clinical trials for advanced refractory cancer, highlighting its mode of action, efficacy, tolerability, and potential future applications in the treatment of cancer. To this effect, we conducted an exhaustive Web of Science and PubMed search to evaluate available research on tilsotolimod as of August 2021.

EXPERT OPINION

With encouraging early clinical results demonstrating extensive TME immunomodulation and abscopal effects on distant tumor lesions, tilsotolimod has emerged as a potential candidate immunomodulatory agent with the possibility to augment currently available immunotherapy and provide novel avenues of treatment for patients with advanced refectory cancer.

Anti-viral and pro-inflammatory functions of Toll-like receptors during gamma-herpesvirus infections

Toll-like receptors (TLRs) control anti-viral responses both directly in infected cells and in responding cells of the immune systems. Therefore, they are crucial for responses against the oncogenic γ-herpesviruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus and the related murine virus MHV68, which directly infect immune system cells. However, since these viruses also cause lifelong persistent infections, TLRs may also be involved in modulation of inflammation during latent infection and contribute to virus-driven tumorigenesis. This review summarizes work on both of these aspects of TLR/γ-herpesvirus interactions, as well as results showing that TLR activity can drive these viruses' re-entry into the replicative lytic cycle.

Toll-Like Receptors in Adaptive Immunity

The immune (innate and adaptive) system has evolved to protect the host from any danger present in the surrounding outer environment (microbes and associated MAMPs or PAMPs, xenobiotics, and allergens) and dangers originated within the host called danger or damage-associated molecular patterns (DAMPs) and recognizing and clearing the cells dying due to apoptosis. It also helps to lower the tissue damage during trauma and initiates the healing process. The pattern recognition receptors (PRRs) play a crucial role in recognizing different PAMPs or MAMPs and DAMPs to initiate the pro-inflammatory immune response to clear them. Toll-like receptors (TLRs) are first recognized PRRs and their discovery proved milestone in the field of immunology as it filled the gap between the first recognition of the pathogen by the immune system and the initiation of the appropriate immune response required to clear the infection by innate immune cells (macrophages, neutrophils, dendritic cells or DCs, and mast cells). However, in addition to their expression by innate immune cells and controlling their function, TLRs are also expressed by adaptive immune cells. We have identified 10 TLRs (TLR1-TLR10) in humans and 12 TLRs (TLR1-TLR13) in laboratory mice till date as TLR10 in mice is present only as a defective pseudogene. The present chapter starts with the introduction of innate immunity, timing of TLR evolution, and the evolution of adaptive immune system and its receptors (T cell receptors or TCRs and B cell receptors or BCRs). The next section describes the role of TLRs in the innate immune function and signaling involved in the generation of inflammation. The subsequent sections describe the expression and function of different TLRs in murine and human adaptive immune cells (B cells and different types of T cells, including CD4⁺T cells, CD8⁺T cells, CD4⁺CD25⁺T_regs, and CD8⁺CD25⁺T_regs, etc.). The modulation of TLRs expressed on T and B cells has a great potential to develop different vaccine candidates, adjuvants, immunotherapies to target various microbial infections, including current COVID-19 pandemic, cancers, and autoimmune and autoinflammatory diseases.

Antibody-independent functions of B cells during viral infections

The humoral immune response and antibody-mediated functions of B cells during viral infections are well described. However, we have limited understanding of antibody-independent B cell functions, such as cytokine production and antigen presentation, in acute and chronic viral infections and their role in protection and/or immunopathogenesis. Here, we summarize the current literature on these antibody-independent B cell functions and identify remaining knowledge gaps. B cell subsets produce anti- and pro-inflammatory cytokines, which can have both beneficial and detrimental effects during viral clearance. As professional antigen presenting cells, B cells also play an important role in immune regulation/shaping of the developing adaptive immune responses. Since B cells primarily express TLR7 and TLR9, we specifically discuss the role of Toll-like receptor (TLR)-mediated B cell responses to viral infections and their role in augmenting adaptive immunity through enhanced cytokine production and antigen presentation. However, viruses have evolved strategies to subvert TLR signaling and additional stimulation via B cell receptor (BCR) may be required to overcome the defective TLR response in B cells. To conclude, antibody-independent B cell functions seem to have an important role in regulating both acute and chronic viral infections and may form the basis for novel therapeutic approaches in treatment of viral infections in the future.

Toll-Like Receptor-Based Strategies for Cancer Immunotherapy

Toll-like receptors (TLRs) are expressed and play multiple functional roles in a variety of immune cell types involved in tumor immunity. There are plenty of data on the pharmacological targeting of TLR signaling using agonist molecules that boost the antitumor immune response. A recent body of research has also demonstrated promising strategies for improving the cell-based immunotherapy methods by inducing TLR signaling. These strategies include systemic administration of TLR antagonist along with immune cell transfer and also genetic engineering of the immune cells using TLR signaling components to improve the function of genetically engineered immune cells such as chimeric antigen receptor-modified T cells. Here, we explore the current status of the cancer immunotherapy approaches based on manipulation of TLR signaling to provide a perspective of the underlying rationales and potential clinical applications. Altogether, reviewed publications suggest that TLRs make a potential target for the immunotherapy of cancer.

CpG ODN as an adjuvant arouses the vigor of B cells by relieving the negative regulation of surface TLR9 to enhance the antibody response to vaccine

The surface Toll-like receptor 9 (sTLR9) has been identified on the surface of the B cells and was presumed to be a negative regulator of B cell responses. CpG ODN, a TLR9 agonist, has been successfully used as an adjuvant of hepatitis B vaccine to enhance antibody responses. However, it is unknown whether the sTLR9 is involved in regulating the activation and maturation of B cells in the antibody responses induced by CpG ODN-adjuvanted vaccines. In this study, we immunized mice with hepatitis B vaccine adjuvanted by CpG ODN (CpG 5805) and found that CpG 5805 enhanced the antibody response to vaccine and meanwhile down-regulated the sTLR9 levels on B cells. With antibody feeding assay and flow cytometry analysis, we further found that CpG 5805 induced a movement of the sTLR9 in B cells, internalized first and then mobilized to endosomes. Accompanied with the movement, CD80, CD86, CD40, and MHC II molecules were significantly up-regulated on the B cells. Interestingly, the B cells with internalized sTLR9 enlarged morphologically, and the sTLR9 levels were obviously lower and CD40 levels were obviously higher on the enlarged B cells. Together, the data presented here uncover that CpG ODN can induce the mobilization and relocation of sTLR9 in B cells, thereby triggering the B cell vigor by relieving the negative regulatory effect of sTLR9 on B cells, which may be one of the mechanisms for CpG ODN acting as a vaccine adjuvant to enhance the antibody response.Key points• CpG ODN-enhanced antibody response positively associates with B cell sTLR9 reduction.• CpG ODN reduces the sTLR9 levels by relocating it from B cell surface to endosomes.• sTLR9 reduction arouses B cell vigor via promoting B cell maturation and activation. Graphical Abstract.

CpG Oligonucleotides as Vaccine Adjuvants

CpG Oligonucleotides (ODN) are immunomodulatory synthetic oligonucleotides specifically designed to stimulate Toll-like receptor 9. TLR9 is expressed on human plasmacytoid dendritic cells and B cells and triggers an innate immune response characterized by the production of Th1 and pro-inflammatory cytokines. This chapter reviews recent progress in understanding the mechanism of action of CpG ODN and provides an overview of human clinical trial results using CpG ODN to improve vaccines for the prevention/treatment of cancer, allergy, and infectious disease.

Defective Toll-Like Receptors Driven B Cell Response in Hyper IgE Syndrome Patients With STAT3 Mutations

Autosomal dominant hyper-IgE syndrome (AD-HIES) is a rare inherited primary immunodeficient disease (PIDs), which is caused by STAT3 gene mutations. Previous studies indicated a defective Toll-like receptor (TLR) 9-induced B cell response in AD-HIES patients, including proliferation, and IgG production. However, the other TLRs-mediated B cell responses in AD-HIES patients were not fully elucidated. In this study, we systematically studied the B cell response to TLRs signaling pathways in AD-HIES patients, including proliferation, activation, apoptosis, cytokine, and immunoglobulin production. Our results showed that the TLRs-induced B cell proliferation and activation was significantly impaired in AD-HIES patients. Besides, AD-HIES patients had defects in TLRs-induced B cell class switch, as well as IgG/IgM secretion and IL-10 production in B cells. Taken together, we first systematically reported the deficiency of TLRs driven B cell response in AD-HIES patients, which help to have a better understanding of the pathology of AD-HIES.

Use of Toll-Like Receptor (TLR) Ligation to Characterize Human Regulatory B-Cells Subsets

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs), which constitute key components in the recognition of pathogens, thereby initiating innate immune responses and promoting adaptive immune responses. In B cells, TLR ligation is important for their activation and, together with CD40, for their differentiation. TLR ligands are also strong promoters of regulatory B (Breg)-cell development, by enhancing the production of IL-10 and their capacity to induce tolerance. In inflammatory diseases, such as autoimmunity or allergies, Breg-cell function is often impaired, while in chronic infections, such as with helminths, or cancer, Breg-cell function is boosted. Following pathogen exposure, B cells can respond directly by producing cytokines and/or IgM (innate response) and develop into various memory B (Bmem)-cell subsets with class-switched immunoglobulin receptors. Depending on the disease state or chronic infection conditions, various Breg subsets can be recognized as well. Currently, a large array of surface markers is known to distinguish between these large range of B-cell subsets. In recent years, the development of mass cytometers and spectral flow cytometry has allowed for high-dimensional detection of up to 48 markers, including both surface and intracellular/intranuclear markers. Therefore, this novel technology is highly suitable to provide a comprehensive overview of Bmem/Breg-cell subsets in different disease states and/or in clinical intervention trials. Here, we provide detailed instructions of the steps necessary to obtain high-quality data for high-dimensional analysis of multiple human Breg-cell subsets using various TLR ligands.

Toll-like receptor signalling in B cells during systemic lupus erythematosus

B lymphocytes have a central role in autoimmune diseases, which are often defined by specific autoantibody patterns and feature a loss of B cell tolerance. A prototypic disease associated with B cell hyperactivity is systemic lupus erythematosus (SLE). In patients with SLE, the loss of B cell tolerance to autoantigens is controlled in a cell-intrinsic manner by Toll-like receptors (TLRs), which sense nucleic acids in endosomes. TLR7 drives the extrafollicular B cell response and the germinal centre reaction that are involved in autoantibody production and disease pathogenesis. Surprisingly, TLR9 seems to protect against SLE, even though it is required for the production of autoantibodies recognizing double-stranded DNA-associated antigens, which are abundant in SLE and are a hallmark of this disease. The protective function of TLR9 is at least partly mediated by its capacity to limit the stimulatory activity of TLR7. The roles of TLR7 and TLR9 in the effector function of B cells in lupus-like disease and in patients with SLE, and the unique features of TLR signalling in B cells, suggest that targeting TLR signalling in SLE might be therapeutically beneficial.

Loss of B cell tolerance to autoantigens in systemic lupus erythematosus (SLE) is driven by TLR7, whereas TLR9 appears to protect against SLE by limiting the stimulatory activity of TLR7. The unique features of Toll-like receptor signalling in B cells implicate it as a therapeutic target in SLE.

Intrinsic TLR7 and TLR9 signalling in B cells plays an important role in the development and pathogenesis of systemic lupus erythematosus (SLE).

In patients with SLE, effector plasma cells are generated via the extrafollicular response and via the formation of spontaneous germinal centres.

TLR7 plays key roles in the extrafollicular response and the response mediated by germinal centres.

Some plasma cells produce IL-10 and can have protective roles in lupus-like disease.

Innate Immune Sensing by Cells of the Adaptive Immune System

Sensing of microbes or of danger signals has mainly been attributed to myeloid innate immune cells. However, T and B cells also express functional pattern recognition receptors (PRRs). In these cells, PRRs mediate signaling cascades that result in different functions depending on the cell's activation and/or differentiation status, on the environment, and on the ligand/agonist. Some of these functions are beneficial for the host; however, some are detrimental and are exploited by pathogens to establish persistent infections. In this review, we summarize the available literature on innate immune sensing by cells of the adaptive immune system and discuss possible implications for chronic infections.

Underlying Immune Disorder May Predispose Some Transthyretin Amyloidosis Subjects to Inotersen-Mediated Thrombocytopenia

Inotersen, a 2'-O-methoxyethyl (2'-MOE) phosphorothioate antisense oligonucleotide, reduced disease progression and improved quality of life in patients with hereditary transthyretin amyloidosis with polyneuropathy (hATTR-PN) in the NEURO-TTR and NEURO-TTR open-label extension (OLE) trials. However, 300 mg/week inotersen treatment was associated with platelet count reductions in several patients. Mean platelet counts in patients in the NEURO-TTR-inotersen group remained ≥140 × 10⁹/L in 50% and ≥100 × 10⁹/L in 80% of the subjects. However, grade 4 thrombocytopenia (<25 × 10⁹/L) occurred in three subjects in NEURO-TTR trial, and one of these suffered a fatal intracranial hemorrhage. The two others were treated successfully with corticosteroids and discontinuation of inotersen. Investigations in a subset of subjects in NEURO-TTR (n = 17 placebo; n = 31 inotersen) and OLE (n = 33) trials ruled out direct myelotoxicity, consumptive coagulopathy, and heparin-induced thrombocytopenia. Antiplatelet immunoglobulin G (IgG) antibodies were detected at baseline in 5 of 31 (16%) inotersen-treated subjects in NEURO-TTR, 4 of whom eventually developed grade 1 or 2 thrombocytopenia while on the drug. In addition, 24 subjects in the same group developed treatment-emergent antiplatelet IgG antibodies, of which 2 developed grade 2, and 3 developed grade 4 thrombocytopenia. Antiplatelet IgG antibodies in two of the three grade 4 thrombocytopenia subjects targeted GPIIb/IIIa. Plasma cytokines previously implicated in immune dysregulation, such as interleukin (IL)-23 and a proliferation-inducing ligand (APRIL) were often above the normal range at baseline. Collectively, these findings suggest an underlying immunologic dysregulation predisposing some individuals to immune-mediated thrombocytopenia during inotersen treatment.

Effect of high mobility group box 1 on Toll-like receptor 9 in B cells in myeloperoxidase-ANCA-associated vasculitis

High mobility group box 1 (HMGB1) played pathogenic role in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Recent findings demonstrated that Toll-like receptor 9 (TLR9) was involved in B cell tolerance breaking of autoimmune disease, including AAV. Here, we investigated the effect of HMGB1 on TLR9 in B cells of AAV. In the present work, patients with myeloperoxidase (MPO)-AAV in active stage were recruited. Intracellular TLR9 expression in various B cell subpopulations of the whole blood was detected by flow cytometry and the correlation with clinical data was analysed. Our results showed that intracellular TLR9 expression in B cells, memory B cells and plasmablasts correlated with erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). In particular, TLR9 expression in plasma cells correlated with ESR, CRP, serum creatinine, eGFR, and Birmingham Vasculitis Activity Score. To further explore the effect of HMGB1 on B cell, peripheral blood mononuclear cells (PBMCs) from AAV patients were isolated. After stimulated with HMGB1, TLR9 expression in various B cell subpopulations and proliferation ratio of live B cells were analysed by flow cytometry. We found that TLR9 expression in plasma cells and the proliferation ratio of live B cells by HMGB1 stimulation were significantly upregulated compared with the control group. Therefore, TLR9 expression in plasma cells was associated with disease activity of MPO-AAV. HMGB1 could enhance TLR9 expression in plasma cells and B cell proliferation. These indicated a role of HMGB1 on TLR9 in B cells in MPO-AAV, which would provide potential clues for intervention strategies.

Distinguishing naive- from memory-derived human B cells during acute responses

Objectives

A fundamental question in influenza research is whether antibody titre decline upon successive exposure to variant strains is consequent to recall of cross‐reactive memory B cells that competitively inhibit naive B‐cell responses. In connection, it is not clear whether naive and memory B cells remain phenotypically distinct acutely after activation such that they may be distinguished ex vivo.

Methods

Here, we first compared the capacity of anti‐Ig and Toll‐like‐receptor (TLR) 7/8 and TLR9 agonists (R848 and CpG) to augment human B‐cell differentiation induced by IL‐21 and sCD40L. The conditions that induced optimal differentiation were then used to compare the post‐activation phenotype of sort‐purified naive and memory B‐cell subsets by FACS and antibody‐secreting cell (ASC) ELISPOT.

Results

Sort‐purified naive and memory B cells underwent robust plasmablast and ASC formation when stimulated with R848, but not CpG, and co‐cultured with monocytes. This coincided with increased IL‐1β and IL‐6 production when B cells were co‐cultured with monocytes and stimulated with R848, but not CpG. Naive B cells underwent equivalent ASC generation, but exhibited less class‐switch and modulation of CD27, CD38 and CD20 expression than memory B cells after stimulation with R848 and monocytes for 6 days.

Conclusion

Stimulation with R848, IL‐21 and sCD40L in the presence of monocytes induces robust differentiation and ASC generation from both naive and memory B‐cells. However, naive and memory B cells retain key phenotypic differences after activation that may facilitate ex vivo discrimination and better characterisation of acute responses to variant antigens.

TLR9 agonist MGN1703 enhances B cell differentiation and function in lymph nodes

Background

TLR9 agonists are being developed as immunotherapy against malignancies and infections. TLR9 is primarily expressed in B cells and plasmacytoid dendritic cells (pDCs). TLR9 signalling may be critically important for B cell activity in lymph nodes but little is known about the in vivo impact of TLR9 agonism on human lymph node B cells. As a pre-defined sub-study within our clinical trial investigating TLR9 agonist MGN1703 (lefitolimod) treatment in the context of developing HIV cure strategies (NCT02443935), we assessed TLR9 agonist-mediated effects in lymph nodes.

Methods

Participants received MGN1703 for 24 weeks concurrent with antiretroviral therapy. Seven participants completed the sub-study including lymph node resection at baseline and after 24 weeks of treatment. A variety of tissue-based immunologic and virologic parameters were assessed.

Findings

MGN1703 dosing increased B cell differentiation; activated pDCs, NK cells, and T cells; and induced a robust interferon response in lymph nodes. Expression of Activation-Induced cytidine Deaminase, an essential regulator of B cell diversification and somatic hypermutation, was highly elevated. During MGN1703 treatment IgG production increased and antibody glycosylation patterns were changed.

Interpretation

Our data present novel evidence that the TLR9 agonist MGN1703 modulates human lymph node B cells in vivo. These findings warrant further considerations in the development of TLR9 agonists as immunotherapy against cancers and infectious diseases.

Fund

This work was supported by Aarhus University Research Foundation, the Danish Council for Independent Research and the NovoNordisk Foundation. Mologen AG provided study drug free of charge.

Neisserial PorB immune enhancing activity and use as a vaccine adjuvant

Our laboratory has focused on Porin B (PorB), an outer membrane protein from Neisseria meningitidis and TLR2 ligand-based adjuvant, to characterize specific molecular and cellular pathways involved in improved immune responses induced by vaccine adjuvants. PorB’s ability to form micellar nanoparticular multi-molecular organized structures and its interaction with Toll-like receptor 2/1 complexes likely accounts for its potent adjuvant activity. Downstream from this stimulation, we have observed enhanced antigen uptake in antigen presenting cells (APC), greater antigen deposition in secondary lymphoid organs, and promotion of germinal center reactions. In mice, antigen-specific IgGs were increased after PorB adjuvanted vaccination using the model antigen ovalbumin (OVA). Likewise, this formulation resulted in more IL-4 and IFN-γ positive T cells. Mice that received PorB adjuvanted vaccinations benefitted from lower bacterial burdens when challenged with recombinant Listeria monocytogenes expressing OVA. Mouse models lacking MyD88 signaling in various APC types helped identify macrophages as an essential cell type for the adjuvant activity of PorB. We believe the work presented here provides examples of the mechanistic studies required to understand how vaccine adjuvants are contributing to the establishment of protective immunity.

Expression of Toll-like receptors and costimulatory molecules in splenic B cells in a normal and abortion-prone murine pregnancy model

PROBLEM

The regulatory role of B lymphocytes in the pregnancy-induced maternal immune response is not well recognized. B lymphocytes function as antigen-presenting cells (APCs) and regulate Toll-like receptors and costimulatory molecule expression in response to intrinsic and extrinsic signals. Therefore, the aim of this study was to determine the expression of TLR2, TLR4, TLR9, and MHC class II and the costimulatory molecules CD80, CD86, and CD40 in splenic B cells in a normal and abortion-prone murine pregnancy model.

METHODS OF STUDY

The expression level of these molecules on female splenic B cells was investigated using real-time PCR and flow cytometry. The analysis was performed on the 3rd and 14th day of normal (CBA/JxBALB/c) and abortion-prone (CBA/JxDBA/2J) murine pregnancy.

RESULTS

The expression of Tlr9, Cd86, and H2-Ab1 in splenic B cells on the 3rd day after mating was upregulated, whereas Tlr2 was downregulated in abortion-prone females. On day 14, we observed lower expression levels of Tlr4 and Cd80 and higher expression levels of Cd86 in CBA/J females mated with DBA/2J males. At the protein level, the differences were observed only on day 3 of pregnancy. TLR4 and CD40 molecules were upregulated in splenic B cells, while TLR9 and CD86 were downregulated in abortion-prone mice.

CONCLUSION

Differential expression of TLRs and costimulatory molecules in splenic B cells in abortion-prone and normal pregnancies suggests the involvement of these cells in the regulation of the immune response at the periphery in pregnant females.

CpG enhances the immunogenicity of heterologous DNA-prime/protein-boost vaccination with the heavy chain myosin of Brugia malayi in BALB/c mice

The recombinant heavy chain myosin of Brugia malayi (Bm-Myo) has earlier been reported as a potent vaccine candidate in our lab. Subsequently, we further enhanced its efficacy employing heterologous DNA prime/protein boost (Myo-pcD+Bm-Myo) immunization approach that produced superior immune-protection than protein or DNA vaccination. In the present study, we evaluated the efficacy of heterologous prime boost vaccination in combination with CpG, synthetic oligodeoxynucleotides (ODN) adjuvant in BALB/c mice. The results showed that CpG/Myo-pcD+Bm-Myo conferred 84.5 ± 0.62% protection against B. malayi infective larval challenge which was considerably higher than Myo-pcD+Bm-Myo (75.6 ± 1.10%) following immunization. Although, both the formulations of immunization elicited robust production of specific IgG antibody and their isotypes (IgG1, IgG2a, IgG2b, and IgG3); however, CpG/Myo-pcD+Bm-Myo predominantly enhanced the level of IgG2a suggesting Th1 biased immune response in presence of CpG. Furthermore, spleen isolated from mice that immunized with CpG/Myo-pcD+Bm-Myo had greater accumulation of CD4+, CD8+, and CD19+ B cells and there was an augmented expression of co-stimulatory molecules CD40, CD86 on host dendritic cells (DCs). In contrast to Myo-pcD+Bm-Myo group, the splenocytes of CpG/Myo-pcD+Bm-Myo immunized mice developed comparatively higher pro-inflammatory cytokines IL-2 and IFN-γ leaving anti-inflammatory cytokine levels unchanged. Moreover, CpG formulation also upregulated the RNA expression of IL-12 and TNF-α in spleenocytes. The current findings suggest that the use of CpG would be more advantageous as an adjuvant predominantly in DNA/protein prime boost vaccine against Bm-Myo and presumably also for filarial infection.

IL1R8 Deficiency Drives Autoimmunity-Associated Lymphoma Development

Chronic inflammation, including that driven by autoimmunity, is associated with the development of B-cell lymphomas. IL1R8 is a regulatory receptor belonging to the IL1R family, which negatively regulates NF-κB activation following stimulation of IL1R or Toll-like receptor family members. IL1R8 deficiency is associated with the development of severe autoimmune lupus-like disease in lpr mice. We herein investigated whether concomitant exacerbated inflammation and autoimmunity caused by the deficiency of IL1R8 could recapitulate autoimmunity-associated lymphomagenesis. We thus monitored B-cell lymphoma development during the aging of IL1R8-deficient lpr mice, observing an increased lymphoid cell expansion that evolved to diffuse large B-cell lymphoma (DLBCL). Molecular and gene-expression analyses showed that the NF-κB pathway was constitutively activated in Il1r8 ^-/-/lpr B splenocytes. In human DLBCL, IL1R8 had reduced expression compared with normal B cells, and higher IL1R8 expression was associated with a better outcome. Thus, IL1R8 silencing is associated with increased lymphoproliferation and transformation in the pathogenesis of B-cell lymphomas associated with autoimmunity.

CpG Oligodeoxynucleotides Modulate Innate and Adaptive Functions of IgM+ B Cells in Rainbow Trout

Oligodeoxynucleotides (ODN) containing unmethylated CpG motifs have been widely postulated as vaccine adjuvants both in mammals and teleost fish. However, to date, the effects that CpGs provoke on cells of the adaptive immune system remain mostly unexplored in fish. Given that rainbow trout (Oncorhynchus mykiss) IgM⁺ B cells from spleen and blood transcribe high levels of toll like receptor 9 (TLR9), the receptor responsible for CpG detection in mammals, in the current work, we have investigated the effects of CpGs on both spleen and blood IgM⁺ B cells from this species. CpGs were shown to exert strong proliferative effects on both spleen and blood IgM⁺ B cells, also increasing their survival. The fact that CpGs increase the size of IgM⁺ B cells, reduce the expression of surface IgM and IgD and up-regulate the number of IgM-secreting cells strongly suggest that IgM⁺ B cells differentiate to plasmablasts/plasma cells in response to CpG stimulation. Additionally, CpGs were shown to modulate the antigen presenting capacities of trout IgM⁺ B cells through an increased surface MHC II expression and transcriptional up-regulation of co-stimulatory molecules, although in this case, significant differences were observed between the effects exerted on spleen and blood cells. Similarly, differences were observed between spleen and blood IgM⁺ B cells when CpG stimulation was combined with B cell receptor (BCR) cross-linking. Finally, CpGs were also shown to affect innate functions of teleost IgM⁺ B cells such as their phagocytic capacity. These results demonstrate that CpGs regulate many adaptive and innate functions of teleost B cells, supporting their inclusion as adjuvants in novel vaccine formulations.

Leukemia-derived exosomes and cytokines pave the way for entry into the brain

Infiltration of acute lymphoblastic leukemia (ALL) blasts into the CNS remains as a major clinical problem, with high risk for chemotherapy-resistant relapse and treatment-related morbidity. Despite the common inclusion of CNS prophylaxis treatments in therapy regimens, there are significant gaps in understanding the mechanisms that mediate leukemia cell entry into the CNS as well as roles for resident cells in the brain. In this study, we employ a xenograft model of human B cell precursor (BCP)-ALL in immunocompromised mice. This model system recapitulates key pathological characteristics of leptomeningeal involvement seen in patients and provides insights into rare cases that involve parenchymal invasion. We examine the infiltration of engrafted leukemia blasts into brains of recipient mice and provide evidence that the interaction between blasts and brain resident cells causes aberrant activation of host cells in the brain microenvironment. BCP-ALL blasts also release multiple cytokines and exosomes containing IL-15 that bind and are internalized by astrocytes and brain vessel endothelial cells. Leukemic invasion is linked to production of VEGF-AA by astrocytes and disruption of the blood-brain-barrier (BBB) integrity. Knockdown of either IL-15 or IL-15Rα in the NALM6 cell line decreases CNS infiltration in engrafted mice. These results provide important insights into the multiple mechanisms by which lymphoblasts modulate the brain microenvironment to breach the BBB for metastatic invasion.

Activation of Innate Immune Responses by a CpG Oligonucleotide Sequence Composed Entirely of Threose Nucleic Acid

Recent advances in synthetic biology have led to the development of nucleic acid polymers with backbone structures distinct from those found in nature, termed xeno-nucleic acids (XNAs). Several unique properties of XNAs make them attractive as nucleic acid therapeutics, most notably their high resistance to serum nucleases and ability to form Watson-Crick base pairing with DNA and RNA. The ability of XNAs to induce immune responses has not been investigated. Threose nucleic acid (TNA), a type of XNA, is recalcitrant to nuclease digestion and capable of undergoing Darwinian evolution to produce high affinity aptamers; thus, TNA is an attractive candidate for diverse applications, including nucleic acid therapeutics. In this study, we evaluated a TNA oligonucleotide derived from a cytosine-phosphate-guanine oligonucleotide sequence known to activate toll-like receptor 9-dependent immune signaling in B cell lines. We observed a slight induction of relevant mRNA signals, robust B cell line activation, and negligible effects on cellular proliferation.

Preclinical development of the TLR9 agonist DV281 as an inhaled aerosolized immunotherapeutic for lung cancer: Pharmacological profile in mice, non-human primates, and human primary cells

CpG-motif-containing oligodeoxynucleotides (CpG-ODN) activate innate immunity through Toll-Like Receptor (TLR) 9 signaling and generate local immune responses when delivered directly to the lung. Herein we describe pharmacological studies in mice, cynomolgus monkeys, and in human primary cells which support the development of DV281, a C-class CpG-ODN, as an inhaled aerosolized immunotherapeutic for lung cancer to be combined with an inhibitor of the anti-programmed cell death protein 1 (PD‑1) immune checkpoint. In vitro, DV281 potently induced Interferon (IFN)‑α from monkey and human peripheral blood mononuclear cells (PBMCs), stimulated interleukin‑6 production and proliferation in human B cells, and induced TLR9-dependent cytokine responses from mouse splenocytes. Intranasal delivery of DV281 to mice led to substantial but transient cytokine and chemokine responses in the lung. Lung responses to repeated intranasal DV281 were partially to fully reversible 2 weeks after the final dose and were absent in TLR9-deficient mice. Single escalating doses of aerosolized DV281 in monkeys induced dose-dependent induction of IFN-regulated genes in bronchoalveolar lavage cells and blood. In a repeat-dose safety study in monkeys, inhaled DV281 was well-tolerated, and findings were mechanism of action-related and non-adverse. Co-culture of human PBMC with DV281 and anti-PD‑1 antibody did not augment cytokine or cellular proliferation responses compared to DV281 alone, indicating that the combination did not lead to dysregulated cytokine responses. These studies support clinical development of inhaled aerosolized DV281 as a combination therapy with anti-PD‑1 antibody for lung cancer immunotherapy.

A Comparison of Toll-Like Receptor 5 and 21 Ligands as Adjuvants for a Formaldehyde Inactivated H9N2 Avian Influenza Virus Vaccine in Chickens

Low pathogenic avian influenza virus (AIV) infection in chickens can result in economic losses and has impacts on human health. Poultry vaccination is a tool that can be used to decrease infection and transmission of AIVs. Prior research has demonstrated that Toll-like receptor (TLR) ligands can act as vaccine adjuvants and their addition to inactivated AIV vaccines can enhance immune responses elicited in chickens. The objective of this study was to compare the adjuvant capabilities of TLR5 ligand (flagellin) and TLR21 ligand (CpG ODN 2007) administered either alone or in combination with an intramuscular formaldehyde inactivated H9N2 whole virus vaccine in chickens. Along with the inactivated virus, chickens were administered either a single dose of CpG ODN 2007 (2 or 10 μg), flagellin (0.4 or 2 μg), or a combination of both ligands. An additional group received AddaVax™, an oil emulsion style adjuvant. Chickens were vaccinated twice and serum and lachrymal samples were collected weekly following the primary vaccination, and antibody-mediated immune responses were quantified. Results showed that vaccines containing CpG ODN 2007 induce significantly greater systemic and lachrymal antibody responses than vaccines containing flagellin or AddaVax. Combinations of flagellin and CpG ODN 2007 did not demonstrate inhibitory, additive, or synergistic effects on systemic or lachrymal antibody-mediated immune responses. Additionally, for both flagellin and CpG ODN 2007, a fivefold higher dose of each did not induce significantly higher antibody-mediated immune responses compared with the lesser dose. Future studies should examine the induction of cell-mediated immune responses when flagellin, CpG ODN 2007, or other TLR ligands are administered either alone or combined as adjuvants for inactivated H9N2 AIV vaccines.

Mast cells in early rheumatoid arthritis associate with disease severity and support B cell autoantibody production

OBJECTIVES

Mast cells (MCs) are involved in the pathogenesis of rheumatoid arthritis (RA). However, their contribution remains controversial. To establish their role in RA, we analysed their presence in the synovium of treatment-naïve patients with early RA and their association and functional relationship with histological features of synovitis.

METHODS

Synovial tissue was obtained by ultrasound-guided biopsy from treatment-naïve patients with early RA (n=99). Immune cells (CD3/CD20/CD138/CD68) and their relationship with CD117⁺MCs in synovial tissue were analysed by immunohistochemistry (IHC) and immunofluorescence (IF). The functional involvement of MCs in ectopic lymphoid structures (ELS) was investigated in vitro, by coculturing MCs with naïve B cells and anticitrullinated protein antibodies (ACPA)-producing B cell clones, and in vivo in interleukin-27 receptor alpha (IL27ra)-deficient and control mice during antigen-induced arthritis (AIA).

RESULTS

High synovial MC counts are associated with local and systemic inflammation, autoantibody positivity and high disease activity. IHC/IF showed that MCs reside at the outer border of lymphoid aggregates. Furthermore, human MCs promote the activation and differentiation of naïve B cells and induce the production of ACPA, mainly via contact-dependent interactions. In AIA, synovial MC numbers increase in IL27ra deficient mice, in association with ELS and worse disease activity.

CONCLUSIONS

Synovial MCs identify early RA patients with a severe clinical form of synovitis characterised by the presence of ELS.

Chronic Lymphocytic Leukemia B-Cell Normal Cellular Counterpart: Clues From a Functional Perspective

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of small mature-looking CD19+ CD23+ CD5+ B-cells that accumulate in the blood, bone marrow, and lymphoid organs. To date, no consensus has been reached concerning the normal cellular counterpart of CLL B-cells and several B-cell types have been proposed. CLL B-cells have remarkable phenotypic and gene expression profile homogeneity. In recent years, the molecular and cellular biology of CLL has been enriched by seminal insights that are leading to a better understanding of the natural history of the disease. Immunophenotypic and molecular approaches (including immunoglobulin heavy-chain variable gene mutational status, transcriptional and epigenetic profiling) comparing the normal B-cell subset and CLL B-cells provide some new insights into the normal cellular counterpart. Functional characteristics (including activation requirements and propensity for plasma cell differentiation) of CLL B-cells have now been investigated for 50 years. B-cell subsets differ substantially in terms of their functional features. Analysis of shared functional characteristics may reveal similarities between normal B-cell subsets and CLL B-cells, allowing speculative assignment of a normal cellular counterpart for CLL B-cells. In this review, we summarize current data regarding peripheral B-cell differentiation and human B-cell subsets and suggest possibilities for a normal cellular counterpart based on the functional characteristics of CLL B-cells. However, a definitive normal cellular counterpart cannot be attributed on the basis of the available data. We discuss the functional characteristics required for a cell to be logically considered to be the normal counterpart of CLL B-cells.

Profiling Atlantic salmon B cell populations: CpG-mediated TLR-ligation enhances IgM secretion and modulates immune gene expression

While TLR-activated pathways are key regulators of B cell responses in mammals, their impact on teleost B cells are scarcely addressed. Here, the potential of Atlantic salmon B cells to respond to TLR ligands was shown by demonstrating a constitutive expression of nucleic-acid sensing TLRs in magnetic sorted IgM+ cells. Of the two receptors recognizing CpG in teleosts, tlr9 was the dominating receptor with over ten-fold higher expression than tlr21. Upon CpG-stimulation, IgM secretion increased for head kidney (HK) and splenic IgM+ cells, while blood B cells were marginally affected. The results suggest that CpG directly affects salmon B cells to differentiate into antibody secreting cells (ASCs). IgM secretion was also detected in the non-treated controls, again with the highest levels in the HK derived population, signifying that persisting ASCs are present in this tissue. In all tissues, the IgM+ cells expressed high MHCII levels, suggesting antigen-presenting functions. Upon CpG-treatment the co-stimulatory molecules cd83 and cd40 were upregulated, while cd86 was down-regulated under the same conditions. Finally, ifna1 was upregulated upon CpG-stimulation in all tissues, while a restricted upregulation was evident for ifnb, proposing that salmon IgM+ B cells exhibit a type I IFN-response.

Engineering Protein-Secreting Plasma Cells by Homology-Directed Repair in Primary Human B Cells

The ability to engineer primary human B cells to differentiate into long-lived plasma cells and secrete a de novo protein may allow the creation of novel plasma cell therapies for protein deficiency diseases and other clinical applications. We initially developed methods for efficient genome editing of primary B cells isolated from peripheral blood. By delivering CRISPR/CRISPR-associated protein 9 (Cas9) ribonucleoprotein (RNP) complexes under conditions of rapid B cell expansion, we achieved site-specific gene disruption at multiple loci in primary human B cells (with editing rates of up to 94%). We used this method to alter ex vivo plasma cell differentiation by disrupting developmental regulatory genes. Next, we co-delivered RNPs with either a single-stranded DNA oligonucleotide or adeno-associated viruses containing homologous repair templates. Using either delivery method, we achieved targeted sequence integration at high efficiency (up to 40%) via homology-directed repair. This method enabled us to engineer plasma cells to secrete factor IX (FIX) or B cell activating factor (BAFF) at high levels. Finally, we show that introduction of BAFF into plasma cells promotes their engraftment into immunodeficient mice. Our results highlight the utility of genome editing in studying human B cell biology and demonstrate a novel strategy for modifying human plasma cells to secrete therapeutic proteins.

Rapid de novo generation of antigen specific human B cells with expression of Blimp-1 and AID by in vitro immunization

In vitro immunization with antigens and cytokines triggers specific human B-cell response in short periods and is therefore superior to conventional in vivo immunization for antibody development. However, this new technology is limited by low efficiency, poor reproducibility, and requirement of pre-immunized lymphocytes. In this study, we demonstrate a novel method for de novo inducing antigen-specific human B cells in vitro. Unlike previous in vitro immunization of unfractionated PBMCs, we firstly optimized the conditions for inducing monocyte-derived dendritic cells (DCs) to efficiently capture, process, and present antigens. Instead of using the conventional method to activate Th2 cells for in vitro immunization, we succeeded to differentiate naïve CD4⁺ T cells into T follicular helper (Tfh) cells using antigen-sensitized DCs and cytokine cocktail. We discovered the differentiated T cells expressed ICOS, PD-1, BCL-6, and IL-21 at high levels. After 12 days of T-B co-culture, we observed induced T cells efficiently promoted naïve B cells to differentiate into plasmablasts secreting antigen-specific antibodies, with expression of Blimp-1 and AID related to affinity maturation and class switching. Thus, we established a new co-culture system with naïve lymphocyte populations for de novo acquisition of specifically in vitro immunized B cells potentially for development of therapeutic antibodies, which also provides novel insights into understanding the complex interactions among immune cells in lymph nodes.

Heterogeneity of Toll-like receptor 9 signaling in B cell malignancies and its potential therapeutic application

Toll-like receptor 9 (TLR9) is expressed in a variety of B-cell malignancies and works as a bridge between innate and adaptive immunity. CpG oligodeoxynucleotides (CpG ODNs), TLR9 agonists, are able to induce anticancer immune responses and exert direct effects against cancer cells, serving as cancer therapeutic agents. Therefore, TLR9 might be a potential therapeutic target for drug development. However, several new evidences have revealed that direct effects of TLR9 agonists on B-cell malignancies is controversial. For example, CpG ODNs can induce apoptosis in certain type of chronic lymphocytic leukemia and lymphoma cells, while induce proliferation in multiple myeloma and other types of lymphoma cells. In this review, we summarize current understanding of the heterogeneity in responses of normal and malignant B cells to TLR9 agonists, due to differences in TLR9 expression levels, genetic alterations (such as MyD88 mutation), and signaling pathway activation. Especially, the downstream molecules of NF-κB signaling pathway play an important role in the heterogeneous response. In order to provide possibilities for therapeutic manipulation of TLR9 agonists in the treatment of these disorders, the preclinical and clinical advances in using CpG ODNs alone and in combination therapies are also summarized in this review.

Effect of Antiretroviral Therapy on the Memory and Activation Profiles of B Cells in HIV-Infected African Women

Human immunodeficiency virus infection induces a wide range of effects in B cells, including skewed memory cell differentiation, compromised B cell function, and hypergammaglobulinemia. However, data on the extent to which these B cell abnormalities can be reversed by antiretroviral therapy (ART) are limited. To investigate the effect of ART on B cells, the activation (CD86) and differentiation (IgD, CD27, and CD38) profiles of B cells were measured longitudinally in 19 HIV-infected individuals before (median, 2 mo) and after ART initiation (median, 12 mo) and compared with 19 age-matched HIV-uninfected individuals using flow cytometry. Twelve months of ART restored the typical distribution of B cell subsets, increasing the proportion of naive B cells (CD27^-IgD⁺CD38^-) and concomitantly decreasing the immature transitional (CD27^-IgD⁺CD38⁺), unswitched memory (CD27⁺IgD⁺CD38^-), switched memory (CD27⁺IgD^-CD38^- or CD27^-IgD^-CD38^-), and plasmablast (CD27⁺IgD^-CD38^high) subsets. However, B cell activation was only partially normalized post-ART, with the frequency of activated B cells (CD86⁺CD40⁺) reduced compared with pre-ART levels (p = 0.0001), but remaining significantly higher compared with HIV-uninfected individuals (p = 0.0001). Interestingly, unlike for T cell activation profiles, the extent of B cell activation prior to ART did not correlate with HIV plasma viral load, but positively associated with plasma sCD14 levels (p = 0.01, r = 0.58). Overall, ART partially normalizes the skewed B cell profiles induced by HIV, with some activation persisting. Understanding the effects of HIV on B cell dysfunction and restoration following ART may provide important insights into the mechanisms of HIV pathogenesis.

B-cell activation with CD40L or CpG measures the function of B-cell subsets and identifies specific defects in immunodeficient patients

Around 65% of primary immunodeficiencies are antibody deficiencies. Functional tests are useful tools to study B-cell functions in vitro. However, no accepted guidelines for performing and evaluating functional tests have been issued yet. Here, we report our experience on the study of B-cell functions in infancy and throughout childhood. We show that T-independent stimulation with CpG measures proliferation and differentiation potential of memory B cells. Switched memory B cells respond better than IgM memory B cells. On the other hand, CD40L, a T-dependent stimulus, does not induce plasma cell differentiation, but causes proliferation of naïve and memory B cells. During childhood, the production of plasmablasts in response to CpG increases with age mirroring the development of memory B cells. The response to CD40L does not change with age. In patients with selective IgA deficiency (SIgAD), we observed that switched memory B cells are reduced due to the absence of IgA memory B cells. In agreement, IgA plasma cells are not generated in response to CpG. Unexpectedly, B cells from SIgAD patients show a reduced proliferative response to CD40L. Our results demonstrate that functional tests are an important tool to assess the functions of the humoral immune system.

Reconstituted B cell receptor signaling reveals carbohydrate-dependent mode of activation

Activation of immune cells (but not B cells) with lectins is widely known. We used the structurally defined interaction between influenza hemagglutinin (HA) and its cell surface receptor sialic acid (SA) to identify a B cell receptor (BCR) activation modality that proceeded through non-cognate interactions with antigen. Using a new approach to reconstitute antigen-receptor interactions in a human reporter B cell line, we found that sequence-defined BCRs from the human germline repertoire could be triggered by both complementarity to influenza HA and a separate mode of signaling that relied on multivalent ligation of BCR sialyl-oligosaccharide. The latter suggested a new mechanism for priming naïve B cell responses and manifested as the induction of SA-dependent pan-activation by peripheral blood B cells. BCR crosslinking in the absence of complementarity is a superantigen effect induced by some microbial products to subvert production of antigen-specific immune responses. B cell superantigen activity through affinity for BCR carbohydrate is discussed.

Toll-like receptor 9 expression and activation in acute coronary syndrome patients on dual anti-platelet therapy

INTRODUCTION

The Toll-like receptor 9 (TLR9) pathway can activate platelets but its role in acute coronary syndromes (ACS) is unknown. This study examined TLR9 expression and platelet activation in response to ODN2006, a TLR9 agonist, in healthy subjects and in ACS subjects treated with dual anti-platelet therapy (DAPT).

MATERIALS AND METHODS

TLR9 expression was examined in both resting and thrombin receptor activator peptide (TRAP)-activated platelets (1 and 10μM) from healthy and ACS subjects by flow cytometry. In both cohorts, ODN2006-mediated platelet activation (5μM) was examined in whole blood (WB) and platelet-rich plasma (PRP) using cell-surface CD62p and CD63 expression by flow cytometry.

RESULTS

Baseline TLR9 expression was significantly greater in ACS subjects compared to healthy subjects (p<0.01). Following TRAP activation, TLR9 expression increased dose-dependently in healthy subjects. However, no difference in TLR9 expression was seen in ACS platelets following TRAP activation. ODN2006 treatment resulted in significant increases in cell-surface expression of CD62p and CD63 in both WB (all p<0.001) and PRP (all p<0.001) in comparison to unstimulated platelets in healthy subjects. Despite DAPT, ODN2006 treatment produced significant increases in both activation markers in the ACS cohort across WB and PRP (all p<0.0001). Elevated baseline expression of TLR9 in ACS platelets may indicate increased sensitivity to TLR9 agonists and contribute to increased platelet activation in these patients. Furthermore, ODN2006 stimulation can activate platelets in ACS subjects despite treatment with DAPT.

CONCLUSION

This study demonstrates TLR9 expression and activation to be of potential therapeutic importance in ASC patients.

Efficient Culture of Human Naive and Memory B Cells for Use as APCs

The ability to culture and expand B cells in vitro has become a useful tool for studying human immunity. A limitation of current methods for human B cell culture is the capacity to support mature B cell proliferation. We developed a culture method to support the efficient activation and proliferation of naive and memory human B cells. This culture supports extensive B cell proliferation, with ∼10³-fold increases following 8 d in culture and 10⁶-fold increases when cultures are split and cultured for 8 more days. In culture, a significant fraction of naive B cells undergo isotype switching and differentiate into plasmacytes. Culture-derived (CD) B cells are readily cryopreserved and, when recovered, retain their ability to proliferate and differentiate. Significantly, proliferating CD B cells express high levels of MHC class II, CD80, and CD86. CD B cells act as APCs and present alloantigens and microbial Ags to T cells. We are able to activate and expand Ag-specific memory B cells; these cultured cells are highly effective in presenting Ag to T cells. We characterized the TCR repertoire of rare Ag-specific CD4⁺ T cells that proliferated in response to tetanus toxoid (TT) presented by autologous CD B cells. TCR Vβ usage by TT-activated CD4⁺ T cells differs from resting and unspecifically activated CD4⁺ T cells. Moreover, we found that TT-specific TCR Vβ usage by CD4⁺ T cells was substantially different between donors. This culture method provides a platform for studying the BCR and TCR repertoires within a single individual.

TNFRSF14 aberrations in follicular lymphoma increase clinically significant allogeneic T-cell responses

Donor T-cell immune responses can eradicate lymphomas after allogeneic hematopoietic stem cell transplantation (AHSCT), but can also damage healthy tissues resulting in harmful graft-versus-host disease (GVHD). Next-generation sequencing has recently identified many new genetic lesions in follicular lymphoma (FL). One such gene, tumor necrosis factor receptor superfamily 14 (TNFRSF14), abnormal in 40% of FL patients, encodes the herpes virus entry mediator (HVEM) which limits T-cell activation via ligation of the B- and T-lymphocyte attenuator. As lymphoma B cells can act as antigen-presenting cells, we hypothesized that TNFRSF14 aberrations that reduce HVEM expression could alter the capacity of FL B cells to stimulate allogeneic T-cell responses and impact the outcome of AHSCT. In an in vitro model of alloreactivity, human lymphoma B cells with TNFRSF14 aberrations had reduced HVEM expression and greater alloantigen-presenting capacity than wild-type lymphoma B cells. The increased immune-stimulatory capacity of lymphoma B cells with TNFRSF14 aberrations had clinical relevance, associating with higher incidence of acute GVHD in patients undergoing AHSCT. FL patients with TNFRSF14 aberrations may benefit from more aggressive immunosuppression to reduce harmful GVHD after transplantation. Importantly, this study is the first to demonstrate the impact of an acquired genetic lesion on the capacity of tumor cells to stimulate allogeneic T-cell immune responses which may have wider consequences for adoptive immunotherapy strategies.

Regulatory and effector B cell cytokine production in patients with relapsing granulomatosis with polyangiitis

Background

B cells are capable of producing regulatory and effector cytokines. In patients with granulomatosis with polyangiitis (GPA), skewing of the pro- and anti-inflammatory cytokine balance may affect the risk of relapse. This study aimed to investigate differences in B cell cytokine production in patients with relapsing GPA and in controls, and determine whether this can aid in relapse prediction.

Methods

Thirteen GPA patients with an upcoming relapse were matched with non-relapsing patients and healthy controls in a retrospective design. The B cell subset distribution was determined from peripheral blood. Cryopreserved peripheral blood mononuclear cells were cultured and intracellular B cell production of regulatory (IL10) and effector (TNFα, IFNγ, IL2, IL6) cytokines was assessed. Finally, serum markers associated with B cell activation (sCD27) and migration (CCL19) were determined.

Results

GPA patient samples exhibited significantly lower percentages of TNFα+ B cells than controls, an effect that was most pronounced in patients about to relapse. B cell capacity for IL10 production was similar in patients and controls. No significant differences were observed for cytokine production in relapsing and non-relapsing GPA patients. TNFα production correlated strongly with IL2, IFNγ and the percentage of memory B cells. No change in effector cytokines occurred before relapse, while the percentage of IL10+ B cells significantly decreased. GPA patients in remission had increased serum levels of CCL19 and sCD27, and sCD27 levels increased upon active disease.

Conclusions

While differences in effector B cell cytokine production were observed between patients and controls, monitoring this in GPA did not clearly distinguish patients about to relapse. Prospective measurements of the regulatory cytokine IL10 may have potential for relapse prediction. Memory B cells appear mainly responsible for effector cytokine production. Increased migration of these cells could explain the decreased presence of TNFα+ B cells in the circulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-0978-1) contains supplementary material, which is available to authorized users.