Regulation of dendritic cell maturation and function by Bruton's tyrosine kinase via IL-10 and Stat3

The Immunomodulatory Mechanisms of BTK Inhibition in CLL and Beyond

Bruton's tyrosine kinase (BTK), a cytoplasmic tyrosine kinase, plays a pivotal role in B cell biology and function. As an essential component of the B cell receptor (BCR) signaling pathway, BTK is expressed not only in B cells but also in myeloid cells, including monocytes/macrophages, dendritic cells, neutrophils, and mast cells. BTK inhibitors (BTKis) have revolutionized the treatment of chronic lymphocytic leukemia (CLL) and other B cell malignancies. Besides their well-characterized role in inhibiting BCR signaling, BTKis also exert significant immunological influences outside the tumor cell that extend their therapeutic potential and impact on the immune system in different ways. This work elucidates the immunomodulatory mechanisms associated with BTK inhibition, focusing on CLL and other clinical contexts. We discuss how BTK inhibition affects various immune cells, including B cells, T cells, and macrophages. The effects of BTKis on the profiles of cytokines, also fundamental parts of the tumor microenvironment (TME), are summarized here as well. This review also appraises the implications of these immunomodulatory actions in the management of autoimmune diseases and infections. Summarizing the dual role of BTK inhibition in modulating malignant lymphocyte and immune cell functions, this paper highlights the broader potential clinical use of compounds targeting BTK.

Targeting BCL9/BCL9L enhances antigen presentation by promoting conventional type 1 dendritic cell (cDC1) activation and tumor infiltration

Conventional type 1 dendritic cells (cDC1) are the essential antigen-presenting DC subset in antitumor immunity. Suppressing B-cell lymphoma 9 and B-cell lymphoma 9-like (BCL9/BCL9L) inhibits tumor growth and boosts immune responses against cancer. However, whether oncogenic BCL9/BCL9L impairs antigen presentation in tumors is still not completely understood. Here, we show that targeting BCL9/BCL9L enhanced antigen presentation by stimulating cDC1 activation and infiltration into tumor. Pharmacological inhibition of BCL9/BCL9L with a novel inhibitor hsBCL9z96 or Bcl9/Bcl9l knockout mice markedly delayed tumor growth and promoted antitumor CD8+ T cell responses. Mechanistically, targeting BCL9/BCL9L promoted antigen presentation in tumors. This is due to the increase of cDC1 activation and tumor infiltration by the XCL1-XCR1 axis. Importantly, using single-cell transcriptomics analysis, we found that Bcl9/Bcl9l deficient cDC1 were superior to wild-type (WT) cDC1 at activation and antigen presentation via NF-κB/IRF1 signaling. Together, we demonstrate that targeting BCL9/BCL9L plays a crucial role in cDC1-modulated antigen presentation of tumor-derived antigens, as well as CD8+ T cell activation and tumor infiltration. Targeting BCL9/BCL9L to regulate cDC1 function and directly orchestrate a positive feedback loop necessary for optimal antitumor immunity could serve as a potential strategy to counter immune suppression and enhance cancer immunotherapy.

Bruton's tyrosine kinase inhibition limits endotoxic shock by suppressing IL-6 production by marginal zone B cells in mice

Sepsis is a systemic inflammatory response to a severe, life-threatening infection with organ dysfunction. Although there is no effective treatment for this fatal illness, a deeper understanding of the pathophysiological basis of sepsis and its underlying mechanisms could lead to the development of new treatment approaches. Here, we demonstrate that the selective Bruton's tyrosine kinase (Btk) inhibitor acalabrutinib augments survival rates in a lipopolysaccharide (LPS)-induced septic model. Our in vitro and in vivo findings both indicate that acalabrutinib reduces IL-6 production specifically in marginal zone B (MZ B) cells rather than in macrophages. Furthermore, Btk-deficient MZ B cells exhibited suppressed LPS-induced IL-6 production in vitro. Nuclear factor-kappa B (NF-κB) signaling, which is the downstream signaling cascade of Toll-like receptor 4 (TLR4), was also severely attenuated in Btk-deficient MZ B cells. These findings suggest that Btk blockade may prevent sepsis by inhibiting IL-6 production in MZ B cells. In addition, although Btk inhibition may adversely affect B cell maturation and humoral immunity, antibody responses were not impaired when acalabrutinib was administered for a short period after immunization with T-cell-independent (TI) and T-cell-dependent (TD) antigens. In contrast, long-term administration of acalabrutinib slightly impaired humoral immunity. Therefore, these findings suggest that Btk inhibitors may be a potential option for alleviating endotoxic shock without compromising humoral immunity and emphasize the importance of maintaining a delicate balance between immunomodulation and inflammation suppression.

Clinical advances in immunotherapy for immune-mediated glomerular diseases

BACKGROUND AND OBJECTIVE

Due to the suboptimal therapeutic efficacy and potential adverse effects associated with traditional immunosuppressive medications, there has been an increasing emphasis on the development and utilization of immunotherapies. This paper aims to provide clinicians with valuable insights for selecting appropriate therapeutic approaches and contribute to the development of novel immunotherapeutic drugs.

MAIN BODY

This paper categorizes the immunotherapeutic drugs that are used for the treatment of immune-mediated glomerular diseases into three groups: immunotherapies targeting antigen-presenting cells (anti-CD80), immunotherapies targeting T/B cells (anti-CD20, anti-CD22, BAFF and APRIL inhibitors, CD40-CD40L inhibitors, proteasome inhibitors, Syk inhibitors, and Btk inhibitors), and immunotherapies targeting the complement system (C5 inhibitors, C5a/C5aR inhibitors, C3 inhibitors, MASP2 inhibitors, factor B inhibitors, and factor D inhibitors). The article then provides a comprehensive overview of advances related to these immunotherapeutic drugs in clinical research.

CONCLUSION

Certain immunotherapeutic drugs, such as rituximab, belimumab, and eculizumab, have exhibited notable efficacy in treating specific immune-mediated glomerular diseases, thereby providing novel therapeutic approaches for patients. Nonetheless, the efficacy of numerous immunotherapeutic drugs remains to be substantiated.

Amino acid metabolism in immune cells: essential regulators of the effector functions, and promising opportunities to enhance cancer immunotherapy

Amino acids are basic nutrients for immune cells during organ development, tissue homeostasis, and the immune response. Regarding metabolic reprogramming in the tumor microenvironment, dysregulation of amino acid consumption in immune cells is an important underlying mechanism leading to impaired anti-tumor immunity. Emerging studies have revealed that altered amino acid metabolism is tightly linked to tumor outgrowth, metastasis, and therapeutic resistance through governing the fate of various immune cells. During these processes, the concentration of free amino acids, their membrane bound transporters, key metabolic enzymes, and sensors such as mTOR and GCN2 play critical roles in controlling immune cell differentiation and function. As such, anti-cancer immune responses could be enhanced by supplement of specific essential amino acids, or targeting the metabolic enzymes or their sensors, thereby developing novel adjuvant immune therapeutic modalities. To further dissect metabolic regulation of anti-tumor immunity, this review summarizes the regulatory mechanisms governing reprogramming of amino acid metabolism and their effects on the phenotypes and functions of tumor-infiltrating immune cells to propose novel approaches that could be exploited to rewire amino acid metabolism and enhance cancer immunotherapy.

Current Perspectives: Evidence to Date on BTK Inhibitors in the Management of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system leading to demyelination and neurodegeneration. Basic and translational studies have shown that B cells and myeloid cells are critical players for the development and course of the disease. Bruton's tyrosine kinase (BTK) is essential for B cell receptor-mediated B cell activation and for normal B cell development and maturation. In addition to its role in B cells, BTK is also involved in several functions of myeloid cells. Although significant number of disease-modifying treatments (DMTs) have been approved for clinical use in MS patients, novel targeted therapies should be studied in refractory patients and patients with progressive forms of the disease. On the basis of its role in B cells and myeloid cells, BTK inhibitors can provide attractive therapeutic benefits for MS. In this article, we review the main effects of BTK inhibitors on different cell types involved in the pathogenesis of MS and summarise recent advances in the development of BTK inhibitors as novel therapeutic approaches in different MS clinical trials. Available data regarding the efficacy and safety of these drugs are described.

The role of BTK inhibitors on the tumor microenvironment in CLL

The CLL disease course is heterogeneous with many patients never requiring treatment and some having very aggressive rapid onset disease.Innate and adaptive immune compensatory mechanisms driven by malignant cells often lead to clonal proliferation, migration and resistance to treatment in CLL. Cell-to-cell interactions occurring within the tumor Micro-environment (TME) can impact greatly on the course of the disease as well as contribute to the variable spread of CLL cells, known as spatial heterogeneity. Following evidence showing the expression of BTK on many hematopoietic cells (an exception beting T lymphocytes) has given rise to the idea that inhibition of BTK with BTK inhibitors (BTKi) such as ibrutinib can help treat CLL.As BTK has a wide variation of expression among cells the use of BTKi has been shown to not only control CLL clones but also redistribute the balance of humoral immunity back toward those of healthy control. n this review article we look at role of BTK in the pathogenesis of CLL, the use of BTKi and their effect on humoral immunity.

Leishmania donovani Impedes Antileishmanial Immunity by Suppressing Dendritic Cells via the TIM-3 Receptor

An immunological hallmark of visceral leishmaniasis (VL), caused by Leishmania donovani, is profound immunosuppression. However, the molecular basis for this immune dysfunction has remained ill defined. Since dendritic cells (DCs) normally initiate antileishmanial immune responses, we investigated whether DCs are dysregulated during L. donovani infection and assessed its role in immunosuppression. Accordingly, we determined the regulatory effect of L. donovani on DCs. Notably, it is still unclear whether L. donovani activates or suppresses DCs. In addition, the molecular mechanism and the relevant receptor (or receptors) mediating the immunoregulatory effect of L. donovani on DCs are largely undefined. Here, we report that L. donovani inhibited DC activation/maturation by transmitting inhibitory signals through the T cell immunoglobulin and mucin protein-3 (TIM-3) receptor and thereby suppressed antileishmanial immune responses. L. donovani in fact triggered TIM-3 phosphorylation in DCs, which in turn recruited and activated a nonreceptor tyrosine kinase, Btk. Btk then inhibited DC activation/maturation by suppressing the NF-κB pathway in an interleukin-10 (IL-10)-dependent manner. Treatment with TIM-3-specific blocking antibody or suppressed expression of TIM-3 or downstream effector Btk made DCs resistant to the inhibitory effects of L. donovani. Adoptive transfer experiments further demonstrated that TIM-3-mediated L. donovani-induced inhibition of DCs plays a crucial role in the suppression of the antileishmanial immune response in vivo. These findings identify TIM-3 as a new regulator of the antileishmanial immune response and demonstrate a unique mechanism for host immunosuppression associated with L. donovani infection. IMPORTANCE Visceral leishmaniasis (VL), a poverty-related disease caused by Leishmania donovani, is ranked by the World Health Organization as the second largest killer parasitic disease in the world. The protective immune response against VL is primarily regulated by dendritic cells (DCs), which upon activation/maturation initiate an antileishmanial immune response. However, it remains obscure whether L. donovani promotes or inhibits DC activation. In addition, the receptor through which L. donovani exerts immunoregulatory effect on DCs is ill defined. Here, we for the first time report that L. donovani inhibits DC activation and maturation via the T cell immunoglobulin and mucin protein-3 (TIM-3) receptor and thereby attenuates the capacity of DCs to trigger antileishmanial immune responses in vivo. In fact, we demonstrate here that suppression of TIM-3 expression in DCs augments antileishmanial immunity. Our study uncovers a unique mechanism by which L. donovani subverts host immune responses and suggests TIM-3 as a potential new target for immunotherapy against VL.

BTK Inhibitors Impair Humoral and Cellular Responses to Recombinant Zoster Vaccine in CLL

Vaccinations effectively prevent infections; however, patients with chronic lymphocytic leukemia (CLL) have reduced antibody responses following vaccinations. Combined humoral and cellular immune responses to novel adjuvanted vaccines are not well characterized in CLL. In an open-label, single-arm clinical trial, we measured the humoral and cellular immunogenicity of the recombinant zoster vaccine (RZV) in CLL patients who were treatment naïve (TN) or receiving Bruton tyrosine kinase inhibitor (BTKi) therapy. The primary endpoint was antibody response to RZV (≥4-fold increase in anti glycoprotein E [gE]). Cellular response of gE-specific CD4+ T cells was assessed by flow cytometry for upregulation of ≥ 2 effector molecules. The antibody response rate was significantly higher in the TN cohort (76.8% [95% confidence interval 65.7-87.8]) compared to patients receiving a BTKi (40.0% [26.4-53.6]; P = .0002). The cellular response rate was also significantly higher in the TN cohort (70.0% [57.3-82.7]) compared to the BTKi group (41.3% [27.1-55.5]; P = .0072). A concordant positive humoral and cellular immune response was observed in 69.1% [56.9-81.3] of subjects with a humoral response, whereas 39.0% [24.1-54.0] of subjects without a humoral response attained a cellular immune response (P = .0033). Antibody titers and T cell responses were not correlated with age, absolute B and T cell counts, or serum immunoglobulin levels (all P > 0.05). RZV induced both humoral and cellular immune responses in treated and untreated CLL patients, albeit with lower response rates in patients on BTKi therapy compared to TN patients. Registered at www.clinicaltrials.gov as #NCT03702231.

Clinical Trials of the BTK Inhibitors Ibrutinib and Acalabrutinib in Human Diseases Beyond B Cell Malignancies

The BTK inhibitors ibrutinib and acalabrutinib are FDA-approved drugs for the treatment of B cell malignances. Both drugs have demonstrated clinical efficacy and safety profiles superior to chemoimmunotherapy regimens in patients with chronic lymphocytic leukemia. Mounting preclinical and clinical evidence indicates that both ibrutinib and acalabrutinib are versatile and have direct effects on many immune cell subsets as well as other cell types beyond B cells. The versatility and immunomodulatory effects of both drugs have been exploited to expand their therapeutic potential in a wide variety of human diseases. Over 470 clinical trials are currently registered at ClinicalTrials.gov to test the efficacy of ibrutinib or acalabrutinib not only in almost every type of B cell malignancies, but also in hematological malignancies of myeloid cells and T cells, solid tumors, chronic graft versus host disease (cGHVD), autoimmune diseases, allergy and COVID-19 (http:www.clinicaltrials.gov). In this review, we present brief discussions of the clinical trials and relevant key preclinical evidence of ibrutinib and acalabrutinib as monotherapies or as part of combination therapies for the treatment of human diseases beyond B cell malignancies. Adding to the proven efficacy of ibrutinib for cGVHD, preliminary results of clinical trials have shown promising efficacy of ibrutinib or acalabrutinib for certain T cell malignancies, allergies and severe COVID-19. However, both BTK inhibitors have no or limited efficacy for refractory or recurrent solid tumors. These clinical data together with additional pending results from ongoing trials will provide valuable information to guide the design and improvement of future trials, including optimization of combination regimens and dosing sequences as well as better patient stratification and more efficient delivery strategies. Such information will further advance the precise implementation of BTK inhibitors into the clinical toolbox for the treatment of different human diseases.

Inhibition of the BTK-IDO-mTOR axis promotes differentiation of monocyte-lineage dendritic cells and enhances anti-tumor T cell immunity

Monocytic-lineage inflammatory Ly6c+CD103+ dendritic cells (DCs) promote antitumor immunity, but these DCs are infrequent in tumors, even upon chemotherapy. Here, we examined how targeting pathways that inhibit the differentiation of inflammatory myeloid cells affect antitumor immunity. Pharmacologic inhibition of Bruton's tyrosine kinase (BTK) and the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) or deletion of Btk or Ido1 allowed robust differentiation of inflammatory Ly6c+CD103+ DCs during chemotherapy, promoting antitumor T cell responses and inhibiting tumor growth. Immature Ly6c+c-kit+ precursor cells had epigenetic profiles similar to conventional DC precursors; deletion of Btk or Ido1 promoted differentiation of these cells. Mechanistically, a BTK-IDO axis inhibited a tryptophan-sensitive differentiation pathway driven by GATOR2 and mTORC1, and disruption of the GATOR2 in monocyte-lineage precursors prevented differentiation into inflammatory DCs in vivo. IDO-expressing DCs and monocytic cells were present across a range of human tumors. Thus, a BTK-IDO axis represses differentiation of inflammatory DCs during chemotherapy, with implications for targeted therapies.

Multifaceted Immunomodulatory Effects of the BTK Inhibitors Ibrutinib and Acalabrutinib on Different Immune Cell Subsets - Beyond B Lymphocytes

The clinical success of the two BTK inhibitors, ibrutinib and acalabrutinib, represents a major breakthrough in the treatment of chronic lymphocytic leukemia (CLL) and has also revolutionized the treatment options for other B cell malignancies. Increasing evidence indicates that in addition to their direct effects on B lymphocytes, both BTK inhibitors also directly impact the homeostasis, phenotype and function of many other cell subsets of the immune system, which contribute to their high efficacy as well as adverse effects observed in CLL patients. In this review, we attempt to provide an overview on the overlapping and differential effects of ibrutinib and acalabrutinib on specific receptor signaling pathways in different immune cell subsets other than B cells, including T cells, NK cells, monocytes, macrophages, granulocytes, myeloid-derived suppressor cells, dendritic cells, osteoclasts, mast cells and platelets. The shared and distinct effects of ibrutinib versus acalabrutinib are mediated through BTK-dependent and BTK-independent mechanisms, respectively. Such immunomodulatory effects of the two drugs have fueled myriad explorations of their repurposing opportunities for the treatment of a wide variety of other human diseases involving immune dysregulation.

Bruton's Tyrosine Kinase Inhibition as an Emerging Therapy in Systemic Autoimmune Disease

Systemic autoimmune disorders are complex heterogeneous chronic diseases involving many different immune cells. A significant proportion of patients respond poorly to therapy. In addition, the high burden of adverse effects caused by "classical" anti-rheumatic or immune modulatory drugs provides a need to develop more specific therapies that are better tolerated. Bruton's tyrosine kinase (BTK) is a crucial signaling protein that directly links B-cell receptor (BCR) signals to B-cell activation, proliferation, and survival. BTK is not only expressed in B cells but also in myeloid cells, and is involved in many different signaling pathways that drive autoimmunity. This makes BTK an interesting therapeutic target in the treatment of autoimmune diseases. The past decade has seen the emergence of first-line BTK small-molecule inhibitors with great efficacy in the treatment of B-cell malignancies, but with unfavorable safety profiles for use in autoimmunity due to off-target effects. The development of second-generation BTK inhibitors with superior BTK specificity has facilitated the investigation of their efficacy in clinical trials with autoimmune patients. In this review, we discuss the role of BTK in key signaling pathways involved in autoimmunity and provide an overview of the different inhibitors that are currently being investigated in clinical trials of systemic autoimmune diseases, including rheumatoid arthritis and systemic lupus erythematosus, as well as available results from completed trials.

Bruton's tyrosine kinase (BTK) mediates resistance to EGFR inhibition in non-small-cell lung carcinoma

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are current standard of care for patients with EGFR mutation and metastatic non-small-cell lung carcinoma (NSCLC), but most patients using EGFR TKIs acquire resistance later. So, overcoming resistance of EGFR TKIs has become an important issue in the treatment of NSCLC. Previously, therapeutics targeting Bruton's tyrosine kinase (BTK) have been successful in treating several hematologic malignancies. However, the role of BTK in NSCLC is still unknown. In this study, by examining surgical specimens from 80 NSCLC patients and their clinicopathologic parameters, we found significant correlation between high BTK expression and tumor differentiation, p-stage, lymph node metastatic status, maximum tumor size, and poor prognosis of patients. Using two NSCLC cell lines A540 and PC9, we demonstrated that BTK^pos cells exhibited more stemness (OCT4, SOX2) and EMT (E-Cadherin, Slug) markers than BTK^neg cells. Knockdown of BTK sensitized the NSCLC cells to Gefitinib. Meanwhile, the second-generation BTK inhibitor Acalabrutinib effectively suppressed SOX2, STAT3/JAK2/Akt axis and potentiated the anti-proliferative effect of Gefitinib and Osimertinib in NSCLC cells, including the T790M H1975 cells. Furthermore, Acalabrutinib and Osimertinib combination exhibited significant tumor growth inhibition of H1975-derived tumors in vivo. Our findings suggested that BTK mediates stemness and EMT properties, and inhibition of BTK potentiates the effect of Gefitinib and Osimertinib in NSCLC cells resistant to TKI. This implies a new approach to treat the NSCLC patients with resistance to previous TKI treatment.

Targeting Bruton's Tyrosine Kinase in Inflammatory and Autoimmune Pathologies

Bruton's tyrosine kinase (BTK) was discovered due to its importance in B cell development, and it has a critical role in signal transduction downstream of the B cell receptor (BCR). Targeting of BTK with small molecule inhibitors has proven to be efficacious in several B cell malignancies. Interestingly, recent studies reveal increased BTK protein expression in circulating resting B cells of patients with systemic autoimmune disease (AID) compared with healthy controls. Moreover, BTK phosphorylation following BCR stimulation in vitro was enhanced. In addition to its role in BCR signaling, BTK is involved in many other pathways, including pattern recognition, Fc, and chemokine receptor signaling in B cells and myeloid cells. This broad involvement in several immunological pathways provides a rationale for the targeting of BTK in the context of inflammatory and systemic AID. Accordingly, numerous in vitro and in vivo preclinical studies support the potential of BTK targeting in these conditions. Efficacy of BTK inhibitors in various inflammatory and AID has been demonstrated or is currently evaluated in clinical trials. In addition, very recent reports suggest that BTK inhibition may be effective as immunosuppressive therapy to diminish pulmonary hyperinflammation in coronavirus disease 2019 (COVID-19). Here, we review BTK's function in key signaling pathways in B cells and myeloid cells. Further, we discuss recent advances in targeting BTK in inflammatory and autoimmune pathologies.

Targeting BTK Signaling in the Microenvironment of Solid Tumors as a Feasible Cancer Therapy Option

Simple Summary

Protein tyrosine kinase BTK is essential for B cell maturation and proliferation. Dysregulation of BTK signaling in B cells leads to B cell lymphoma. In addition to B cells, BTK is also expressed in other types of immune cells including MDSC, dendritic cells, mast cells and macrophages, all of which comprise the tumor microenvironment in solid cancers. Although BTK inhibitors have been FDA-approved as the front-line treatment for B cell malignancy CLL/SLL, studies have been reluctant to report on BTKs role within the tumor microenvironment during solid cancer development limiting the possibility of using these BTK inhibitors as an adjuvant treatment option for solid cancers. Here, we review BTK signaling within the cells found in the tumor microenvironment as well as summarizing clinical trials using BTK inhibitors which target the tumor microenvironment in an attempt to combat solid tumors.

Abstract

The cell environment plays a pivotal role in determining cellular outcome, as well as cancer initiation, progression, and dissemination. Within this environment, in addition to the structural components, such as the extracellular matrix, there are various types of cells surrounding the tumor cells. Communication among these cells and the tumor cells via signaling pathways is important for tumor growth. Originally discovered in patients with immunodeficiency X-linked gammaglobulinemia, the Bruton’s tyrosine kinase (BTK) signaling pathway, known for its role in B cell maturation, is critical to cancer cell proliferation, metastasis and evasion of cancer eliminating cells. Given that BTK inhibitors have been FDA approved for chronic lymphocytic leukemia/small lymphocytic lymphoma and that the majority of BTK studies have been focused on B cells, the use of BTK inhibitors as a future treatment strategy of solid tumors has yet to be evaluated. In this review, we summarize studies analyzing BTK signaling within the cells found in the tumor microenvironment, as well as clinical trial where BTK inhibitors are currently being used to target the tumor microenvironment as a way to combat solid tumors.

MicroRNA155 Plays a Critical Role in the Pathogenesis of Cutaneous Leishmania major Infection by Promoting a Th2 Response and Attenuating Dendritic Cell Activity

Interferon (IFN)-γ is indispensable in the resolution of cutaneous leishmaniasis (CL), while the Th2 cytokines IL-4, IL-10, and IL-13 mediate susceptibility. A recent study found that miR155, which promotes CD4⁺ Th1 response and IFN-γ production, is dispensable in the control of Leishmania donovani infection. Here, the role of miR155 in CL caused by L. major was investigated using miR155-deficient (miR155^-/-) mice. Infection was controlled significantly quicker in the miR155^-/- mice than in their wild-type (WT) counterparts, indicating that miR155 contributes to the pathogenesis of CL. Faster resolution of infection in miR155^-/- mice was associated with increased levels of Th1-associated IL-12 and IFN-γ and reduced production of Th2- associated IL-4, IL-10, and IL-13. Concentrations of IFN-γ⁺CD8⁺ T cells and natural killer cells in draining lymph nodes were significantly higher in the L. major-infected miR155^-/- mice than in the infected WT mice, as indicated by flow-cytometry. After in vitro IFN-γ stimulation, nitric oxide and IL-12 production were increased, IL-10 production was decreased, and parasite clearance was enhanced in L. major-infected miR155^-/- DCs compared to those in WT DCs. Furthermore, IFN-γ production from activated miR155^-/- T cells was significantly enhanced in L. major-infected miR155^-/- DCs. Together, these findings demonstrate that miR155 promotes susceptibility to CL caused by L. major by promoting Th2 response and inhibiting DC function.

Bruton's tyrosine kinase regulates gut immune homeostasis through attenuating Th1 response

Inflammatory bowel disease (IBD) is driven by multiple genetic and environmental risk factors. Patients with mutations in Bruton’s tyrosine kinase (BTK) is known to manifest high prevalence of intestinal disorders including IBD. Although BTK mediates the signaling of various immune receptors, little is known how BTK maintains the homeostasis of the gut immune system. Here, we show that BTK-deficiency promotes IBD progression in a mouse model of colitis. Interestingly, the increased colitis susceptibility of BTK-deficient mice is not caused by gut microbiota changes but rather arises from enhanced pro-inflammatory Th1 response. More importantly, we find the heightened Th1 response in BTK-deficient mice to result from both T cell-extrinsic and -intrinsic mechanisms. BTK-deficient dendritic cells secret elevated levels of the Th1-polarizing cytokine IL-12 and BTK-deficient T cells are inherently more prone to Th1 differentiation. Thus, BTK plays critical roles in maintaining gut immune homeostasis and preventing inflammation via regulating T-cell polarization.

Bruton's tyrosine kinase: an emerging targeted therapy in myeloid cells within the tumor microenvironment

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase belonging to the Tec family of kinases. The role of BTK in B cell receptor signaling is well defined and is known to play a key role in the proliferation and survival of malignant B cells. Moreover, BTK has been found to be expressed in cells of the myeloid lineage. BTK has been shown to contribute to a variety of cellular pathways in myeloid cells including signaling in the NLRP3 inflammasome, receptor activation of nuclear factor-κβ and inflammation, chemokine receptor activation affecting migration, and phagocytosis. Myeloid cells are crucial components of the tumor microenvironment and suppressive myeloid cells contribute to cancer progression, highlighting a potential role for BTK inhibition in the treatment of malignancy. The increased interest in BTK inhibition in cancer has resulted in many preclinical studies that are testing the efficacy of using single-agent BTK inhibitors. Moreover, the ability of tumor cells to develop resistance to single-agent checkpoint inhibitors has resulted in clinical studies utilizing BTK inhibitors in combination with these agents to improve clinical responses. Furthermore, BTK regulates the immune response in microbial and viral infections through B cells and myeloid cells such as monocytes and macrophages. In this review, we describe the role that BTK plays in supporting suppressive myeloid cells, including myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM), while also discussing the anticancer effects of BTK inhibition and briefly describe the role of BTK signaling and BTK inhibition in microbial and viral infections.

BTK inhibition modulates multiple immune cell populations involved in the pathogenesis of immune mediated nephritis

Lupus nephritis (LN) is a serious end organ complication of systemic lupus erythematosus. Nephrotoxic serum nephritis (NTN) is an inducible model of LN, which utilizes passive transfer of pre-formed nephrotoxic antibodies to initiate disease. In previous studies, we demonstrated that the Bruton's tyrosine kinase inhibitor, BI-BTK-1, prevents the development of nephritis in NTN when treatment was started prior to nephrotoxic serum transfer, and reverses established proteinuria as well. We manipulated the initiation and duration of BI-BTK-1 therapy in NTN to study its delayed therapeutic effects when treatment is given later in the disease course, as well as to further understand what effect BI-BTK-1 is having to prevent initiation of nephritis with early treatment. Early treatment and remission induction each correlated with decreased inflammatory macrophages, CD4+ and CD8+ T cells, and decreased B220+ B cells. Additionally, an increased proportion of resident macrophages within the CD45+ population favored a delay of disease onset and remission induction. We also studied the cellular processes involved in reactivation of nephritis by withdrawing BI-BTK-1 treatment at different time points. Treatment cessation led to either early or later onset of renal flares inversely dependent on the initial duration of BTK inhibition, as assessed by increased proteinuria and BUN levels and worse renal pathology. These flares were associated with an increase in kidney CD45+ infiltrates, including myeloid cell populations. IL-6, CD14, and CCL2 were also increased in mice developing late flares. These analyses point to the role of macrophages as an important contributor to the pathogenesis of immune mediated nephritis, and further support the therapeutic potential of BTK inhibition in this disease and related conditions.

Rheumatoid arthritis synovial microenvironment induces metabolic and functional adaptations in dendritic cells

Rheumatoid arthritis (RA) is a chronic autoimmune disease which causes degradation of cartilage and bone. It is well appreciated that the pathogenic hallmark of RA is the mass influx of inflammatory cells into the joint. However, the role that dendritic cells (DC) may play in this inflammatory milieu is still relatively unexplored. Moreover, the contribution this unique synovial microenvironment has on DC maturation is still unknown. Using monocyte-derived DC (MoDC), we established an in-vitro model to recapitulate the synovial microenvironment to explore DC maturation. MoDC treated with conditioned media from ex-vivo synovial tissue biopsy cultures [explant-conditioned media (ECM)] have increased expression of proinflammatory cytokines, chemokines and adhesion molecules. ECM DC have increased expression of CD83 and CC-chemokine receptor (CCR)7 and decreased expression of CCR5 and phagocytic capacity, suggestive of heightened DC maturation. ECM-induced maturation is concomitant with altered cellular bioenergetics, whereby increased expression of glycolytic genes and increased glucose uptake are observed in ECM DC. Collectively, this results in a metabolic shift in DC metabolism in favour of glycolysis. These adaptations are in-part mediated via signal transducer and activator of transcription-3 (STAT-3), as demonstrated by decreased expression of proinflammatory cytokines and glycolytic genes in ECM DC in response to STAT-3 inhibition. Finally, to translate these data to a more in-vivo clinically relevant setting, RNA-seq was performed on RA synovial fluid and peripheral blood. We identified enhanced expression of a number of glycolytic genes in synovial CD1c+ DC compared to CD1c+ DC in circulation. Collectively, our data suggest that the synovial microenvironment in RA contributes to DC maturation and metabolic reprogramming.

Ibrutinib treatment inhibits breast cancer progression and metastasis by inducing conversion of myeloid-derived suppressor cells to dendritic cells

BACKGROUND

Ibrutinib is a Bruton's tyrosine kinase (BTK) and interleukin-2-inducible kinase (ITK) inhibitor used for treating chronic lymphocytic leukaemia (CLL) and other cancers. Although ibrutinib is known to inhibit the growth of breast cancer cell growth in vitro, its impact on the treatment and metastasis of breast cancer is unclear.

METHODS

Using an orthotopic mouse breast cancer model, we show that ibrutinib inhibits the progression and metastasis of breast cancer.

RESULTS

Ibrutinib inhibited proliferation of cancer cells in vitro, and Ibrutinib-treated mice displayed significantly lower tumour burdens and metastasis compared to controls. Furthermore, the spleens and tumours from Ibrutinib-treated mice contained more mature DCs and lower numbers of myeloid-derived suppressor cells (MDSCs), which promote disease progression and are linked to poor prognosis. We also confirmed that ex vivo treatment of MDSCs with ibrutinib switched their phenotype to mature DCs and significantly enhanced MHCII expression. Further, ibrutinib treatment promoted T cell proliferation and effector functions leading to the induction of antitumour T_H1 and CTL immune responses.

CONCLUSIONS

Ibrutinib inhibits tumour development and metastasis in breast cancer by promoting the development of mature DCs from MDSCs and hence could be a novel therapeutic agent for the treatment of breast cancer.

Immunomodulatory effect of ibrutinib: Reducing the barrier against fungal infections

The Bruton tyrosine kinase (BTK) inhibitor ibrutinib is increasingly used in the treatment of chronic lymphocytic leukemia (CLL). Moreover, very promising results have been reported in other B-cell malignancies, including primary central nervous system lymphoma (PCNSL). Although well-tolerated in the majority of patients, ibrutinib demonstrates in some cases troublesome toxicities, including invasive fungal infections (IFIs). In the present review, we summarize clinical manifestations of IFIs in patients treated with ibrutinib, generally characterized by an early onset, mild clinical manifestations, asymptomatic/low symptomatic pulmonary localization and high incidence of central nervous system (CNS) involvement. IFI risk appears particularly increased in patients receiving ibrutinib associated with other immune modulator agents, especially with steroids or immune-chemotherapy. Moreover, the immunomodulatory effect of ibrutinib is described, pointing the attention on the involvement of specific molecules targeted by ibrutinib in innate and adaptive response to fungal infection. Overall, the findings indicate the ibrutinib may rapidly impair innate immune cell functions, while concomitantly restoring an effective protective potential of adaptive immune compartment. A correct awareness, especially when other predisposing factors are present, is warranted about the potential risk of IFIs in ibrutinib-treated patients.

The novel Isatin analog KS99 targets stemness markers in acute myeloid leukemia

Leukemic stem cells are multipotent, self-renewing, highly proliferative cells that can withstand drug treatments. Although currently available treatments potentially destroy blast cells, they fail to eradicate leukemic progenitor cells completely. Aldehyde dehydrogenase and STAT3 are frequently up-regulated in pre-leukemic stem cells as well as in acute myeloid leukemia (AML) expressing the CD34⁺CD38⁻ phenotype. The Isatin analog, KS99 has shown anticancer activity against multiple myeloma which may, in part, be mediated by inhibition of Bruton’s tyrosine kinase activation. Here we demonstrate that KS99 selectively targets leukemic stem cells with high aldehyde dehydrogenase activity and inhibits phosphorylation of STAT3. KS99 targeted cells co-expressing CD34, CD38, CD123, TIM-3, or CD96 immunophenotypes in AML, alone or in combination with the standard therapeutic agent cytarabine. AML with myelodysplastic-related changes was more sensitive than de novo AML with or without NPM1 mutation. KS99 treatment reduced the clonogenicity of primary human AML cells as compared to normal cord blood mononuclear cells. Downregulation of phosphorylated Bruton’s tyrosine kinase, STAT3, and aldehyde dehydrogenase was observed, suggesting interaction with KS99 as predicted through docking. KS99 with or without cytarabine showed in vivo preclinical efficacy in human and mouse AML animal models and prolonged survival. KS99 was well tolerated with overall negligible adverse effects. In conclusion, KS99 inhibits aldehyde dehydrogenase and STAT3 activities and causes cell death of leukemic stem cells, but not normal hematopoietic stem and progenitor cells.

mKLRL1 regulates the maturation of dendritic cells and plays important roles in immune tolerance

KLRL1 is a member of C-type lectin-like receptors (CLEC) and preferentially expressed on the surface of immune cells. We have previously illustrated its inhibitory role in Natural killer (NK) cells. Though cloned from dendritic cells (DCs), its role in DCs has not been fully identified. Here, we found that mKLRL1 markedly decreased during DC maturation; mKLRL1-modifed DCs showed enhanced phagocytic capability and reduced ability to induce T cell proliferation, which mimics immature DCs. Further investigation revealed that IL-10 was indispensable for mKLRL1 to suppress DC maturation. And p38 activation was responsible for preferential IL-10 production. Pretreatment with mKLRL1-modified DCs protected mice from subsequently EAE induction, indicating a role in immune tolerance. Taken together, our results have revealed an inhibitory role of KLRL1 in mouse DCs.

Bruton's Tyrosine Kinase, a Component of B Cell Signaling Pathways, Has Multiple Roles in the Pathogenesis of Lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the loss of adaptive immune tolerance to nucleic acid-containing antigens. The resulting autoantibodies form immune complexes that promote inflammation and tissue damage. Defining the signals that drive pathogenic autoantibody production is an important step in the development of more targeted therapeutic approaches for lupus, which is currently treated primarily with non-specific immunosuppression. Here, we review the contribution of Bruton’s tyrosine kinase (Btk), a component of B and myeloid cell signaling pathways, to disease in murine lupus models. Both gain- and loss-of-function genetic studies have revealed that Btk plays multiple roles in the production of autoantibodies. These include promoting the activation, plasma cell differentiation, and class switching of autoreactive B cells. Small molecule inhibitors of Btk are effective at reducing autoantibody levels, B cell activation, and kidney damage in several lupus models. These studies suggest that Btk may promote end-organ damage both by facilitating the production of autoantibodies and by mediating the inflammatory response of myeloid cells to these immune complexes. While Btk has not been associated with SLE in GWAS studies, SLE B cells display signaling defects in components both upstream and downstream of Btk consistent with enhanced activation of Btk signaling pathways. Taken together, these observations indicate that limiting Btk activity is critical for maintaining B cell tolerance and preventing the development of autoimmune disease. Btk inhibitors, generally well-tolerated and approved to treat B cell malignancy, may thus be a useful therapeutic approach for SLE.

A Patient with Non-Hodgkin Lymphoma and Nonspecific Interstitial Pneumonia during Ibrutinib Therapy

We present a 74-year-old male with nonspecific interstitial pneumonia (NSIP) during treatment with ibrutinib for mantle cell lymphoma. Previously, the patient had received six cycles of bendamustine and rituximab and six cycles of R-CHOP, followed by rituximab maintenance therapy. Respiratory tract complications of ibrutinib other than infectious pneumonia have not been mentioned in larger trials, but individual case reports hinted to a possible association with the development of pneumonitis. In our patient, the onset of alveolitis that progressed towards NSIP together with the onset of ibrutinib treatment suggests causality. One week after ibrutinib was discontinued, nasal symptoms resolved first. A follow-up CT showed a reduction in the reticular hyperdensities and ground-glass opacities, suggestive of restitution of the lung disease. To our knowledge, this is the first case showing a strong link between ibrutinib and interstitial lung disease, strengthening a previous report on subacute pneumonitis. Our findings have clinical implications because pulmonary side effects were reversible at this early stage. We, therefore, suggest close monitoring for respiratory side effects in patients receiving ibrutinib.

The role of STAT3 in leading the crosstalk between human cancers and the immune system

The development and progression of human cancers are continuously and dynamically regulated by intrinsic and extrinsic factors. As a converging point of multiple oncogenic pathways, signal transducer and activator of transcription 3 (STAT3) is constitutively activated both in tumor cells and tumor-infiltrated immune cells. Activated STAT3 persistently triggers tumor progression through direct regulation of oncogenic gene expression. Apart from its oncogenic role in regulating gene expression in tumor cells, STAT3 also paves the way for human cancer growth through immunosuppression. Activated STAT3 in immune cells results in inhibition of immune mediators and promotion of immunosuppressive factors. Therefore, STAT3 modulates the interaction between tumor cells and host immunity. Accumulating evidence suggests that targeting STAT3 may enhance anti-cancer immune responses and rescue the suppressed immunologic microenvironment in tumors. Taken together, STAT3 has emerged as a promising target in cancer immunotherapy.

Bruton's Tyrosine Kinase: An Emerging Key Player in Innate Immunity

Bruton’s tyrosine kinase (BTK) was initially discovered as a critical mediator of B cell receptor signaling in the development and functioning of adaptive immunity. Growing evidence also suggests multiple roles for BTK in mononuclear cells of the innate immune system, especially in dendritic cells and macrophages. For example, BTK has been shown to function in Toll-like receptor-mediated recognition of infectious agents, cellular maturation and recruitment processes, and Fc receptor signaling. Most recently, BTK was additionally identified as a direct regulator of a key innate inflammatory machinery, the NLRP3 inflammasome. BTK has thus attracted interest not only for gaining a more thorough basic understanding of the human innate immune system but also as a target to therapeutically modulate innate immunity. We here review the latest developments on the role of BTK in mononuclear innate immune cells in mouse versus man, with specific emphasis on the sensing of infectious agents and the induction of inflammation. Therapeutic implications for modulating innate immunity and critical open questions are also discussed.

Oxidized Hemoglobin Is Antigenic and Immunogenic in Lupus

Hemolysis-associated anemia is characteristic of diseases such as atherosclerosis, lupus, malaria, and leishmaniasis; the toxic effects of free hemoglobin (Hb) have been extensively described. This study was based on the premise that release of this sequestered, inflammatory molecule can result in deleterious immunological consequences, particularly in the context of pre-existing lupus. IgG anti-Hb responses were detected in the sera of lupus patients. Lupus-prone mice exhibited heightened plasma Hb levels, and ferric (Fe³⁺) Hb triggered preferential release of lupus-associated cytokines from splenocytes derived from aging lupus-prone mice. Anti-Hb B cell precursor frequencies were heightened in such mice, which also expressed increased titers of anti-Hb antibodies in serum and in kidney eluates. Fe³⁺ Hb preferentially increased the functional maturation of bone marrow-derived dendritic cells (BMDCs) from lupus-prone mice, effects abrogated upon the inhibition of Stat3. Hb interacted with lupus-associated autoantigens extruded during apoptosis and coincubation of Hb and apoptotic blebs had additional maturation-inducing effects on lupus BMDCs. Immunization with Hb in lupus-prone mice induced antigen spreading to lupus-associated moieties; Hb-interacting autoantigens were preferentially targeted and increased complement deposition and glomerulosclerosis were observed. Hb therefore demonstrates both antigenicity and immunogenicity and triggers specific immuno-pathological effects in a lupus milieu.

Regulation of B cell fate by chronic activity of the IgE B cell receptor

IgE can trigger potent allergic responses, yet the mechanisms regulating IgE production are poorly understood. Here we reveal that IgE⁺ B cells are constrained by chronic activity of the IgE B cell receptor (BCR). In the absence of cognate antigen, the IgE BCR promoted terminal differentiation of B cells into plasma cells (PCs) under cell culture conditions mimicking T cell help. This antigen-independent PC differentiation involved multiple IgE domains and Syk, CD19, BLNK, Btk, and IRF4. Disruption of BCR signaling in mice led to consistently exaggerated IgE⁺ germinal center (GC) B cell but variably increased PC responses. We were unable to confirm reports that the IgE BCR directly promoted intrinsic apoptosis. Instead, IgE⁺ GC B cells exhibited poor antigen presentation and prolonged cell cycles, suggesting reduced competition for T cell help. We propose that chronic BCR activity and access to T cell help play critical roles in regulating IgE responses.

DOI:http://dx.doi.org/10.7554/eLife.21238.001

Antibodies are proteins that recognize and bind to specific molecules, and so help the immune system to defend the body against foreign substances that are potentially harmful. In some cases, harmless substances – such as pollen, dust or food – can trigger this response and lead to an allergic reaction. A type of antibody called immunoglobulin E (IgE) is particularly likely to trigger an allergic response.

In general, immune cells called plasma cells produce antibodies and release them into the body. However, in B cells – the cells from which plasma cells develop – the antibodies remain on the surface of the cells. Here, the antibody acts as a “receptor” that allows the B cell to tell when its antibody has bound to a specific substance.

Generally, B cells only activate when their B cell receptors bind to a specific substance. This binding triggers signals inside the cell that determine its fate – such as whether it will develop into a plasma cell. Recent studies have shown that B cells that have IgE on their surface (IgE⁺ B cells) are predisposed to develop rapidly into plasma cells.

To investigate why this is the case, Yang et al. have now studied B cells both in cell culture and in mice. The results show that the IgE B cell receptor autonomously signals to the cell even when it is not bound to a specific substance, in a manner that differs from other types of B cell receptors. This increases the likelihood that the IgE⁺ B cell will develop into a plasma cell and limits the competitive fitness of IgE⁺ B cells. These findings provide new insights into how IgE responses are regulated by the B cell receptor.

The next step will be to determine, at a molecular level, the basis for the autonomous signaling produced by the IgE B cell receptor when it is not bound to a specific substance. It will then be possible to investigate how this mechanism compares with the way that signals are normally transmitted when a B cell receptor binds to a specific substance.

DOI:http://dx.doi.org/10.7554/eLife.21238.002

Bruton's Tyrosine Kinase Deficiency Inhibits Autoimmune Arthritis in Mice but Fails to Block Immune Complex-Mediated Inflammatory Arthritis

OBJECTIVE

Bruton's tyrosine kinase (BTK) is a B cell signaling protein that also contributes to innate immunity. BTK inhibitors prevent autoimmune arthritis but have off-target effects, and the mechanisms of protection remain unknown. We undertook these studies using genetic deletion to investigate the role of BTK in adaptive and innate immune responses that drive inflammatory arthritis.

METHODS

BTK-deficient K/BxN mice were generated to study the role of BTK in a spontaneous model that requires both adaptive and innate immunity. The K/BxN serum-transfer model was used to bypass the adaptive system and elucidate the role of BTK in innate immune contributions to arthritis.

RESULTS

BTK deficiency conferred disease protection to K/BxN mice, confirming outcomes of BTK inhibitors. B lymphocytes were profoundly reduced, more than in other models of BTK deficiency. Subset analysis revealed loss of B cells at all developmental stages. Germinal center B cells were also decreased, with downstream effects on numbers of follicular helper T cells and greatly reduced autoantibodies. In contrast, total IgG was only mildly decreased. Strikingly, and in contrast to small molecule inhibitors, BTK deficiency had no effect in the serum-transfer model of arthritis.

CONCLUSION

BTK contributes to autoimmune arthritis primarily through its role in B cell signaling and not through innate immune components.

c-Src Suppresses Dendritic Cell Antitumor Activity via T Cell Ig and Mucin Protein-3 Receptor

The enhanced expression of T cell Ig and mucin protein-3 (TIM-3) on tumor-associated dendritic cells (DCs) attenuates antitumor effects of DNA vaccines. To identify a potential target (or targets) for reducing TIM-3 expression on tumor-associated DCs, we explored the molecular mechanisms regulating TIM-3 expression. In this study, we have identified a novel signaling pathway (c-Src→Bruton's tyrosine kinase→transcription factors Ets1, Ets2, USF1, and USF2) necessary for TIM-3 upregulation on DCs. Both IL-10 and TGF-β, which are produced in the tumor microenvironment, upregulated TIM-3 expression on DCs via this pathway. Suppressed expression of c-Src or downstream Bruton's tyrosine kinase, Ets1, Ets2, USF1, or USF2 blocked IL-10- and TGF-β-induced TIM-3 upregulation on DCs. Notably, in vivo knockdown of c-Src in mice reduced TIM-3 expression on tumor-associated DCs. Furthermore, adoptive transfer of c-Src-silenced DCs in mouse tumors enhanced the in vivo antitumor effects of immunostimulatory CpG DNA; however, TIM-3 overexpression in c-Src-silenced DCs blocked this effect. Collectively, our data reveal the molecular mechanism regulating TIM-3 expression in DCs and identify c-Src as a target for improving the efficacy of nucleic acid-mediated anticancer therapy.

A Tec kinase BTK inhibitor ibrutinib promotes maturation and activation of dendritic cells

Ibrutinib, a BTK inhibitor, is currently used to treat various hematological malignancies. We evaluated whether ibrutinib treatment during development of murine bone marrow-derived dendritic cells (DCs) modulates their maturation and activation. Ibrutinib treatment increased the proportion of CD11c⁺ DCs, upregulated the expression of MHC-II and CD80 and downregulated Ly6C expression by DCs. Additionally, ibrutinib treatment led to an increase in MHC-II⁺, CD80⁺ and CCR7⁺ DCs but a decrease in CD86⁺ DCs upon LPS stimulation. LPS/ibrutinib-treated DCs displayed increased IFNβ and IL-10 synthesis and decreased IL-6, IL-12 and NO production compared to DCs stimulated with LPS alone. Finally, LPS/ibrutinib-treated DCs promoted higher rates of CD4⁺ T cell proliferation and cytokine production compared to LPS only stimulated DCs. Taken together, our results indicate that ibrutinib enhances the maturation and activation of DCs to promote CD4⁺ T cell activation which could be exploited for the development of DC-based cancer therapies.

The role of Bruton's tyrosine kinase in autoimmunity and implications for therapy

Bruton's tyrosine kinase (BTK) mediates B cell signaling and is also present in innate immune cells but not T cells. BTK propagates B cell receptor (BCR) responses to antigen-engagement as well as to stimulation via CD40, toll-like receptors (TLRs), Fc receptors (FCRs) and chemokine receptors. Importantly, BTK can modulate signaling, acting as a "rheostat" rather than an "on-off" switch; thus, overexpression leads to autoimmunity while decreased levels improve autoimmune disease outcomes. Autoreactive B cells depend upon BTK for survival to a greater degree than normal B cells, reflected as loss of autoantibodies with maintenance of total antibody levels when BTK is absent. This review describes contributions of BTK to immune tolerance, including studies testing BTK-inhibitors for treatment of autoimmune diseases.

Myeloid-Derived Suppressor Cells Express Bruton's Tyrosine Kinase and Can Be Depleted in Tumor-Bearing Hosts by Ibrutinib Treatment

Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of immature myeloid cells that expand in tumor-bearing hosts in response to soluble factors produced by tumor and stromal cells. MDSC expansion has been linked to loss of immune effector cell function and reduced efficacy of immune-based cancer therapies, highlighting the MDSC population as an attractive therapeutic target. Ibrutinib, an irreversible inhibitor of Bruton's tyrosine kinase (BTK) and IL2-inducible T-cell kinase (ITK), is in clinical use for the treatment of B-cell malignancies. Here, we report that BTK is expressed by murine and human MDSCs, and that ibrutinib is able to inhibit BTK phosphorylation in these cells. Treatment of MDSCs with ibrutinib significantly impaired nitric oxide production and cell migration. In addition, ibrutinib inhibited in vitro generation of human MDSCs and reduced mRNA expression of indolamine 2,3-dioxygenase, an immunosuppressive factor. Treatment of mice bearing EMT6 mammary tumors with ibrutinib resulted in reduced frequency of MDSCs in both the spleen and tumor. Ibrutinib treatment also resulted in a significant reduction of MDSCs in wild-type mice bearing B16F10 melanoma tumors, but not in X-linked immunodeficiency mice (XID) harboring a BTK mutation, suggesting that BTK inhibition plays an important role in the observed reduction of MDSCs in vivo Finally, ibrutinib significantly enhanced the efficacy of anti-PD-L1 (CD274) therapy in a murine breast cancer model. Together, these results demonstrate that ibrutinib modulates MDSC function and generation, revealing a potential strategy for enhancing immune-based therapies in solid malignancies. Cancer Res; 76(8); 2125-36. ©2016 AACR.

Immunological Effects of Conventional Chemotherapy and Targeted Anticancer Agents

The tremendous clinical success of checkpoint blockers illustrates the potential of reestablishing latent immunosurveillance for cancer therapy. Although largely neglected in the clinical practice, accumulating evidence indicates that the efficacy of conventional and targeted anticancer agents does not only involve direct cytostatic/cytotoxic effects, but also relies on the (re)activation of tumor-targeting immune responses. Chemotherapy can promote such responses by increasing the immunogenicity of malignant cells, or by inhibiting immunosuppressive circuitries that are established by developing neoplasms. These immunological "side" effects of chemotherapy are desirable, and their in-depth comprehension will facilitate the design of novel combinatorial regimens with improved clinical efficacy.

Ibrutinib enhances IL-17 response by modulating the function of bone marrow derived dendritic cells

Ibrutinib (PCI-32765) is an irreversible dual Btk/Itk inhibitor shown to be effective in treating several B cell malignancies. However, limited studies have been conducted to study the effect of this drug on myeloid cell function. Hence, we studied the effect of ibrutinib treatment on TLR-4 mediated activation of bone marrow derived dendritic cell culture (DCs). Upon ibrutinib treatment, LPS-treated DCs displayed lower synthesis of TNF-α and nitric oxide (NO) and higher induction of IL-6, TGF-β, IL-10 and IL-18. While ibrutinib dampened MHC-II and CD86 expression on DCs, CD80 expression was upregulated. Further, ibrutinib-treated DCs promoted T cell proliferation and enhanced IL-17 production upon co-culture with nylon wool enriched T cells. Taken together, our results indicate that ibrutinib modulates TLR-4 mediated DC activation to promote an IL-17 response. We describe a novel mode of action for ibrutinib on DCs which should be explored to treat other forms of cancer besides B cell malignancies.

Ibrutinib enhances the antitumor immune response induced by intratumoral injection of a TLR9 ligand in mouse lymphoma

We have designed a novel therapeutic approach for lymphoma that combines targeted kinase inhibition with in situ vaccination. Intratumoral injection of an unmethylated cytosine guanine dinucleotide (CpG)-enriched oligodeoxynucleotide, an agonist for the toll-like receptor 9 (TLR9), induces the activation of natural killer cells, macrophages, and antigen presenting cells that control tumor growth at the local site. Ibrutinib, an irreversible inhibitor of Bruton's tyrosine kinase, a key enzyme in the signaling pathway downstream of B-cell receptor, is an effective treatment against many types of B-cell lymphomas. The combination of intratumoral injection of CpG with systemic treatment by ibrutinib resulted in eradication of the tumors not only in the injected site, but also at distant sites. Surprisingly, this combinatorial antitumor effect required an intact T-cell immune system since it did not occur in nude, severe combined immunodeficiency, or T-cell depleted mice. Moreover, T cells from animals treated with intratumoral CpG and ibrutinib prevented the outgrowth of newly injected tumors. This result suggests that ibrutinib can induce immunogenic cell death of lymphoma cells and that concomitant stimulation of antigen-presenting cells in the tumor microenvironment by toll-like receptor ligands can lead to a powerful systemic antitumor immune response.

Immunoregulation of dendritic cells by the receptor T cell Ig and mucin protein-3 via Bruton's tyrosine kinase and c-Src

The receptor T cell Ig and mucin protein-3 (TIM-3) has emerged as an important regulator of innate immune responses. However, whether TIM-3-induced signaling promotes or inhibits the activation and maturation of dendritic cells (DCs) still remains uncertain. In addition, the TIM-3 signaling events involved in this immunoregulatory function are yet to be established. In this article, we report that TIM-3 crosslinking by anti-TIM-3 Ab inhibited DC activation and maturation by blocking the NF-κB pathway. After Ab-mediated crosslinking, TIM-3 became tyrosine phosphorylated, which then sequentially bound and activated the nonreceptor tyrosine kinases Bruton's tyrosine kinase (Btk) and c-Src. Activation of Btk-c-Src signaling in turn triggered the secretion of some inhibitory factor (or factors) from DCs that inhibited the NF-κB pathway and subsequent activation and maturation of DCs. Silencing of Btk or c-Src abrogated the inhibitory effects of TIM-3 on DCs. These results demonstrate an essential role for Btk-c-Src signaling in TIM-3-induced DC suppression. Thus, in addition to demonstrating an inhibitory role for TIM-3 signaling in DC activation, we define the molecular mechanism by which TIM-3 mediates this effect.

Bruton's tyrosine kinase and protein kinase C µ are required for TLR7/9-induced IKKα and IRF-1 activation and interferon-β production in conventional dendritic cells

Stimulation of TLR7/9 by their respective ligands leads to the activation of IκB kinase α (IKKα) and Interferon Regulatory Factor 1 (IRF-1) and results in interferon (IFN)-β production in conventional dendritic cells (cDC). However, which other signaling molecules are involved in IKKα and IRF-1 activation during TLR7/9 signaling pathway are not known. We and others have shown that Bruton's Tyrosine Kinase (BTK) played a part in TLR9-mediated cytokine production in B cells and macrophages. However, it is unclear if BTK participates in TLR7/9-induced IFN-β production in cDC. In this study, we show that BTK is required for IFN-β synthesis in cDC upon TLR7/9 stimulation and that stimulated BTK-deficient cDC are defective in the induction of IKKα/β phosphorylation and IRF-1 activation. In addition, we demonstrate that Protein Kinase C µ (PKCµ) is also required for TLR7/9-induced IRF-1 activation and IFN-β upregulation in cDC and acts downstream of BTK. Taken together, we have uncovered two new molecules, BTK and PKCµ, that are involved in TLR7/9-triggered IFN-β production in cDC.

Identification of Bruton's tyrosine kinase as a therapeutic target in acute myeloid leukemia

Bruton's tyrosine kinase (BTK) is a cytoplasmic protein found in all hematopoietic cell lineages except for T cells. BTK mediates signaling downstream of a number of receptors. Pharmacologic targeting of BTK using ibrutinib (previously PCI-32765) has recently shown encouraging clinical activity in a range of lymphoid malignancies. This study reports for the first time that ibrutinib inhibits blast proliferation from human acute myeloid leukemia (AML) and that treatment with ibrutinib significantly augmented cytotoxic activities of standard AML chemotherapy cytarabine or daunorubicin. Here we describe that BTK is constitutively phosphorylated in the majority of AML samples tested, with BTK phosphorylation correlating highly with the cell's cytotoxic sensitivity toward ibrutinib. BTK-targeted RNAi knockdown reduced colony-forming capacity of primary AML blasts and proliferation of AML cell lines. We showed that ibrutinib binds at nanomolar range to BTK. Furthermore, we showed ibrutinib's antiproliferative effects in AML are mediated via an inhibitory effect on downstream nuclear factor-κB survival pathways. Moreover, ibrutinib inhibited AML cell adhesion to bone marrow stroma. Furthermore, these effects of ibrutinib in AML were seen at comparable concentrations efficacious in chronic lymphocytic leukemia. These results provide a biological rationale for clinical evaluation of BTK inhibition in AML patients.

Btk regulates macrophage polarization in response to lipopolysaccharide

Bacterial Lipopolysaccharide (LPS) is a strong inducer of inflammation and does so by inducing polarization of macrophages to the classic inflammatory M1 population. Given the role of Btk as a critical signal transducer downstream of TLR4, we investigated its role in M1/M2 induction. In Btk deficient (Btk^−\−) mice we observed markedly reduced recruitment of M1 macrophages following intraperitoneal administration of LPS. Ex vivo analysis demonstrated an impaired ability of Btk^−/− macrophages to polarize into M1 macrophages, instead showing enhanced induction of immunosuppressive M2-associated markers in response to M1 polarizing stimuli, a finding accompanied by reduced phosphorylation of STAT1 and enhanced STAT6 phosphorylation. In addition to STAT activation, M1 and M2 polarizing signals modulate the expression of inflammatory genes via differential activation of transcription factors and regulatory proteins, including NF-κB and SHIP1. In keeping with a critical role for Btk in macrophage polarization, we observed reduced levels of NF-κB p65 and Akt phosphorylation, as well as reduced induction of the M1 associated marker iNOS in Btk^−/− macrophages in response to M1 polarizing stimuli. Additionally enhanced expression of SHIP1, a key negative regulator of macrophage polarisation, was observed in Btk^−/− macrophages in response to M2 polarizing stimuli. Employing classic models of allergic M2 inflammation, treatment of Btk^−/− mice with either Schistosoma mansoni eggs or chitin resulted in increased recruitment of M2 macrophages and induction of M2-associated genes. This demonstrates an enhanced M2 skew in the absence of Btk, thus promoting the development of allergic inflammation.

Suppression of glomerulonephritis in lupus-prone NZB × NZW mice by RN486, a selective inhibitor of Bruton's tyrosine kinase

OBJECTIVE

Bruton's tyrosine kinase (BTK) plays a critical role in B cell development and function. We recently described a selective BTK inhibitor, RN486, that blocks B cell receptor (BCR) and Fcγ receptor signaling and is efficacious in animal models of arthritis. The aim of this study was to examine the potential efficacy of BTK in systemic lupus erythematosus (SLE), using an NZB × NZW mouse model of spontaneous SLE.

METHODS

Mice received RN486 or its vehicle (administered in chow) at a final concentration of 30 mg/kg for 8 weeks, starting at 32 weeks of age.

RESULTS

The administration of RN486 completely stopped disease progression, as determined by histologic and functional analyses of glomerular nephritis. The efficacy was associated with striking inhibition of B cell activation, as demonstrated by a significant reduction in CD69 expression in response to BCR crosslinking. RN486 markedly reduced the secretion of IgG anti-double-stranded DNA (anti-dsDNA) secretion, as determined by enzyme-linked immunosorbent and enzyme-linked immunospot assays. Flow cytometric analysis demonstrated depletion of CD138(high) B220(low) plasma cells in the spleen. RN486 inhibited secretion of IgG anti-dsDNA but not IgM anti-dsDNA, suggesting that pharmacologic blockade of BTK resembles the reported transgenic expression of low levels of endogenous BTK in B cells. In addition, RN486 may also impact the effector function of autoantibodies, as evidenced by a significant reduction in immune complex-mediated activation of human monocytes in vitro and down-regulation of the expression of macrophage-related and interferon-inducible genes in both the kidneys and spleens of treated mice.

CONCLUSION

Collectively, our data suggest that BTK inhibitors may simultaneously target autoantibody-producing and effector cells in SLE, thus constituting a promising therapeutic alternative for this disease.

Bruton's tyrosine kinase--an integral protein of B cell development that also has an essential role in the innate immune system

Btk is the protein affected in XLA, a disease identified as a B cell differentiation defect. Btk is crucial for B cell differentiation and activation, but its role in other cells is not fully understood. This review focuses on the function of Btk in monocytes, neutrophils, and platelets and the receptors and signaling cascades in such cells with which Btk is associated.

Ibrutinib is an irreversible molecular inhibitor of ITK driving a Th1-selective pressure in T lymphocytes

Given its critical role in T-cell signaling, interleukin-2-inducible kinase (ITK) is an appealing therapeutic target that can contribute to the pathogenesis of certain infectious, autoimmune, and neoplastic diseases. Ablation of ITK subverts Th2 immunity, thereby potentiating Th1-based immune responses. While small-molecule ITK inhibitors have been identified, none have demonstrated clinical utility. Ibrutinib is a confirmed irreversible inhibitor of Bruton tyrosine kinase (BTK) with outstanding clinical activity and tolerability in B-cell malignancies. Significant homology between BTK and ITK alongside in silico docking studies support ibrutinib as an immunomodulatory inhibitor of both ITK and BTK. Our comprehensive molecular and phenotypic analysis confirms ITK as an irreversible T-cell target of ibrutinib. Using ibrutinib clinical trial samples along with well-characterized neoplastic (chronic lymphocytic leukemia), parasitic infection (Leishmania major), and infectious disease (Listeria monocytogenes) models, we establish ibrutinib as a clinically relevant and physiologically potent ITK inhibitor with broad therapeutic utility. This trial was registered at www.clinicaltrials.gov as #NCT01105247 and #NCT01217749.

MyD88 is involved in myeloid as well as lymphoid hematopoiesis independent of the presence of a pathogen

MyD88 was originally described as a primary response gene up-regulated during myeloid differentiation after IL-6 induction. Later, MyD88 was shown to be a key molecule necessary for IL1, IL18 and Toll-like receptor signaling. Since these receptors recognize abundantly produced cytokines during infection or molecular patterns of pathogens, MyD88 itself was suggested to be an important regulator of the first line of defense against invading pathogens, including the differentiation and maturation of myeloid cells. Here we describe that MyD88 is important for early and late hematopoietic events that occur independently of antigen under steady-state conditions. In MyD88-deficient mice the earliest alteration in hematopoiesis was found at the level of long-term hematopoietic stem cells. Moreover, we found that MyD88 influences not only the development of the myeloid lineage but also the differentiation of B cells. The B cell defect observed in Btk-deficient mice is further enhanced when both molecules, Btk and MyD88, are not expressed. Therefore, MyD88 affects myeloid as well as lymphoid hematopoiesis. Since Btk and MyD88 deficiencies influence differentially myeloid and lymphoid development, both molecules seem to act in different signaling pathways important for appropriate developmental events during myelo- and lymphopoiesis.