BTK Signaling in B Cell Differentiation and Autoimmunity

Scedosporium Brain Abscess: A Rare and Fatal Drawback of Bruton Tyrosine Kinase Inhibitor Therapy

The patient described in this case report was admitted to the San Luigi Hospital in Turin for confusion, drowsiness, and buccal and eye deviation. An acute neurological disease was suspected. He was affected by chronic lymphocytic leukemia (CLL) on active treatment with the novel Bruton tyrosine kinase inhibitor (BTKi) acalabrutinib. Other comorbidities included type II diabetes mellitus, arterial hypertension, and nonalcoholic steatohepatitis. Imaging exams showed multiple brain lesions, which appeared to be of infectious-inflammatory origin. Consequently, therapy with acalabrutinib was withheld. The patient was later transferred to the intensive care unit, because of worsening neurological conditions. The definite diagnosis of fungal abscess was obtained through a stereotactic biopsy of the widest brain lesion. Microbiological tests confirmed Scedosporium spp. as the etiological agent. Once a detailed antibiogram had been obtained, voriconazole therapy was started. However, the patient's clinical conditions decayed rapidly and he later died of neurological complications. BTKis represent a milestone in the treatment of CLL; however, little is known about how these molecules act on the immune system. Fungal brain abscesses are rare conditions more commonly seen in heavily immunocompromised patients, such as those affected by acquired immune deficiency syndrome, after bone marrow transplant or treatment for acute leukemia. Whether or not therapy with BTKis can favor opportunistic fungal infections is still a matter of debate. Various reports of Aspergillosis infections developing after therapy with ibrutinib exist. Evidence does suggest that an iatrogenic impairment in the innate immune system could favor these infections. In addition, the patient's comorbidities, such as diabetes mellitus and advancing hematological disease, might create the ideal breeding ground for these microorganisms.

Bioactive atropisomers: Unraveling design strategies and synthetic routes for drug discovery

Atropisomerism, an expression of axial chirality caused by limited bond rotation, is a prominent aspect within the field of medicinal chemistry. It has been shown that atropisomers of a wide range of compounds, including established FDA-approved drugs and experimental molecules, display markedly different biological activities. The time-dependent reversal of chirality in atropisomers poses complexity and obstacles in the process of drug discovery and development. Nonetheless, recent progress in understanding atropisomerism and enhanced characterization methods have greatly assisted medicinal chemists in the effective development of atropisomeric drug molecules. This article provides a comprehensive review of their special design thoughts, synthetic routes, and biological activities, serving as a reference for the synthesis and biological evaluation of bioactive atropisomers in the future.

Zanubrutinib in Mantle Cell Lymphoma Management: A Comprehensive Review

Purpose

The pharmacology, pharmacokinetics, pharmacodynamics, clinical efficacy, and safety of zanbrutinib are described.

Summary

Mantle cell lymphoma (MCL) is a mature B-cell lymphoma that is typically associated with unfavorable outcomes, and virtually all patients with MCL have refractory or relapsed disease despite aggressive treatment. The treatment paradigm for MCL has transformed dramatically over the past decade owing to rapid advancements in immunotherapy and molecular-targeted therapies. Zanubrutinib, a second-generation Bruton's tyrosine kinase inhibitor (BTKI) designated for mature B-cell non-Hodgkin's lymphoma (NHL), has drastically improved the survival outcomes in relapsed/refractory (R/R) MCL patients. This selective BTKI is a small molecule that functions by forming a covalent bond in the active site of BTK. The inhibition of BTK activity is essential for the signaling of B-cell antigen receptor (BCR) and cytokine receptor pathways. In a preclinical study, zanubrutinib inhibited malignant B-cell proliferation and reduced tumor growth. Zanubrutinib was granted FDA-accelerated approval based on the results of Phase I and II trials. The investigator-assessed overall response rate was 83.7%, of which 78% of patients achieved complete response. The median duration of response was 19.5 months, and the median progression-free survival was 22.1 months. The most common (≥20%) all-grade adverse events were low neutrophil count (46.5%), upper respiratory tract infection (38.4%), rash (36.0%), low white blood cell count (33.7%), and low platelet count (32.6%).

Conclusion

Zanubrutinib is a selective, next-generation, orally active, irreversible BTK inhibitor. The selectivity of zanubrutinib and its superior efficacy, with a well-tolerated safety profile, have proven to be attractive options for other malignancies.

Overexpression of Bruton Tyrosine Kinase Inhibits the Proliferation, Migration, and Invasion of Non-Small Cell Lung Cancer Cells

Lung cancer is one of the most lethal malignant tumors in the world. Non-small cell lung cancer (NSCLC) is the most common pathological subtype. However, the molecular mechanism of NSCLC progress is still unclear. We extracted the expression data of the Bruton's tyrosine kinase (BTK) gene in NSCLC tissues from the TCGA database. The results of paired t-test showed that the BTK gene was significantly underexpressed in NSCLC tissues. To further verify the above results, we detected the expression of the BTK gene in NSCLC cell lines A549, H1299, and H1650 at the RNA and protein levels by real-time fluorescent quantitative polymerase chain reaction and Western Blot analysis, respectively. The results showed that BTK was low expressed in NSCLC tissues and cells. More importantly, the expression of the BTK gene is also significantly related to the patient's age, gender, tumor range (T), lymph node invasion (N), tumor stage, and prognosis, and its expression level gradually decreases with the progress of the disease. It is speculated that BTK may be an independent prognostic factor of NSCLC. Our experimental results are consistent with the above clinical correlation analysis results. Overexpression of BTK can significantly inhibit the proliferation, migration, and invasion of NSCLC cells and can block the G0/G1 tumor cell cycle, indicating that overexpression of BTK can inhibit the growth, migration, and invasion of NSCLC cells.

First report of Wilson disease and Bruton agammaglobulinemia in the same patient caused by new mutations in ATP7B and BTK genes

INTRODUCTION

Wilson disease is characterized by an alteration in copper metabolism that causes its accumulation in different tissues. Its diagnosis is established by the combination of clinical manifestations and paraclinical and genetic studies. Bruton agammaglobulinemia is an X-linked recessive hereditary disease belonging to the group of primary immunodeficiencies and is produced by mutation in the Bruton tyrosine kinase (BTK) gene.

CASE REPORT

A 14-year-old Colombian patient with clinical characteristics of Bruton agammaglobulinemia presented with liver disease and clinically and molecularly diagnosed with Wilson disease.

DISCUSSION

Bruton agammaglobulinemia and Wilson disease are considered rare diseases because of their low prevalence. We report for the first time a pediatric patient from southwestern Colombia presenting with both entities, and diagnosed clinically and molecularly, an association so far not reported in the literature.

Bruton's Tyrosine Kinase Inhibitors: The Next Frontier of B-Cell-Targeted Therapies for Cancer, Autoimmune Disorders, and Multiple Sclerosis

Bruton's tyrosine kinase (BTK) is an important protein belonging to the tyrosine kinase family that plays a key role in the intracellular signaling and proliferation, migration, and survival of normal and malignant B-lymphocytes and myeloid cells. Understanding the role of BTK in the B-cell signaling pathway has led to the development of BTK inhibitors (BTKi) as effective therapies for malignancies of myeloid origin and exploration as a promising therapeutic option for other cancers. Given its central function in B-cell receptor signaling, inhibition of BTK is an attractive approach for the treatment of a wide variety of autoimmune diseases that involve aberrant B-cell function including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS). Here, we review the role of BTK in different cell signaling pathways, the development of BTKi in B-cell malignancies, and their emerging role in the treatment of MS and other autoimmune disorders.

Weighted gene co-expression network analysis identifies dysregulated B-cell receptor signaling pathway and novel genes in pulmonary arterial hypertension

Background

Pulmonary arterial hypertension (PAH) is a devastating cardio-pulmonary vascular disease in which chronic elevated pulmonary arterial pressure and pulmonary vascular remodeling lead to right ventricular failure and premature death. However, the exact molecular mechanism causing PAH remains unclear.

Methods

RNA sequencing was used to analyze the transcriptional profiling of controls and rats treated with monocrotaline (MCT) for 1, 2, 3, and 4 weeks. Weighted gene co-expression network analysis (WGCNA) was employed to identify the key modules associated with the severity of PAH. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed to explore the potential biological processes and pathways of key modules. Real-time PCR and western blot analysis were used to validate the gene expression. The hub genes were validated by an independent dataset obtained from the Gene Expression Omnibus database.

Results

A total of 26 gene modules were identified by WGCNA. Of these modules, two modules showed the highest correlation with the severity of PAH and were recognized as the key modules. GO analysis of key modules showed the dysregulated inflammation and immunity, particularly B-cell-mediated humoral immunity in MCT-induced PAH. KEGG pathway analysis showed the significant enrichment of the B-cell receptor signaling pathway in the key modules. Pathview analysis revealed the dysregulation of the B-cell receptor signaling pathway in detail. Moreover, a series of humoral immune response-associated genes, such as BTK, BAFFR, and TNFSF4, were found to be differentially expressed in PAH. Additionally, five genes, including BANK1, FOXF1, TLE1, CLEC4A1, and CLEC4A3, were identified and validated as the hub genes.

Conclusion

This study identified the dysregulated B-cell receptor signaling pathway, as well as novel genes associated with humoral immune response in MCT-induced PAH, thereby providing a novel insight into the molecular mechanisms underlying inflammation and immunity and therapeutic targets for PAH.

Bruton's Tyrosine Kinase Inhibitors in Multiple Sclerosis: Pioneering the Path Towards Treatment of Progression?

In multiple sclerosis (MS) persisting disability can derive from acute relapses or, alternatively, from slow and steady deterioration, termed chronic progression. Emerging data suggest that the latter process occurs largely independent from relapse activity or development of new central nervous system (CNS) inflammatory lesions. Pathophysiologically, acute relapses develop as a consequence of de novo CNS infiltration of immune cells, while MS progression appears to be driven by a CNS-trapped inflammatory circuit between CNS-established hematopoietic cells as well as CNS-resident cells, such as microglia, astrocytes, and oligodendrocytes. Within the last decades, powerful therapies have been developed to control relapse activity in MS. All of these agents were primarily designed to systemically target the peripheral immune system and/or to prevent CNS infiltration of immune cells. Based on the above described dichotomy of MS pathophysiology, it is understandable that these agents only exert minor effects on progression and that novel targets within the CNS have to be utilized to control MS progression independent of relapse activity. In this regard, one promising strategy may be the inhibition of the enzyme Bruton's tyrosine kinase (BTK), which is centrally involved in the activation of B cells as well as myeloid cells, such as macrophages and microglia. In this review, we discuss where and to what extent BTK is involved in the immunological and molecular cascades driving MS progression. We furthermore summarize all mechanistic, preclinical, and clinical data on the various BTK inhibitors (evobrutinib, tolebrutinib, fenebrutinib, remibrutinib, orelabrutinib, BIIB091) that are currently in development for treatment of MS, with a particular focus on the potential ability of either drug to control MS progression.

A nonneglectable stereochemical factor in drug development: Atropisomerism

Chirality is one of the key factors affecting the medicinal efficacy of compounds. In addition to central chirality, sterically hindered chiral axes commonly appear in drugs and the resulting chirality is known as atropisomerism. With developments in medicinal chemistry, atropisomerism has attracted increasing attention. This review discusses the classification, biological activity, pharmacokinetics, toxicity and side effects of atropisomers, and can serve as a reference in the research and development of potential chiral drugs.

Single-cell RNA Sequencing Analysis Reveals New Immune Disorder Complexities in Hypersplenism

Hypersplenism (HS) is a concomitant symptom of liver or blood disease. Not only does the treatment of HS face challenges, but the transcriptome of individual cells is also unknown. Here, the transcriptional profiles of 43,037 cells from four HS tissues and one control tissue were generated by the single-cell RNA sequencing and nine major cell types, including T-cells, B-cells, NK cells, hematopoietic stem cells, neutrophil cells, mast cells, endothelial cells, erythrocytes, and dendritic cells were identified. Strikingly, the main features were the lack of CCL5+ B-cells in HS and the presence of SESN1+ B cells in HS with hepatocellular carcinoma (HS-HCC). In cell-cell interaction analysis, CD74-COPA and CD94-HLA-E in HS were found to be up-regulated. We further explored HS-specifically enriched genes (such as FKBP5, ADAR, and RPS4Y1) and found that FKBP5 was highly expressed in HCC-HS, leading to immunosuppression. Taken together, this research provides new insights into the genetic characteristics of HS via comprehensive single-cell transcriptome analysis.

Current and Innovated Managements for Autoimmune Bullous Skin Disorders: An Overview

Autoimmune bullous skin disorders are a group of disorders characterized by the formation of numerous blisters and erosions on the skin and/or the mucosal membrane, arising from autoantibodies against the intercellular adhesion molecules and the structural proteins. They can be classified into intraepithelial or subepithelial autoimmune bullous dermatoses based on the location of the targeted antigens. These dermatoses are extremely debilitating and fatal in certain cases, depending on the degree of cutaneous and mucosal involvement. Effective treatments should be implemented promptly. Glucocorticoids serve as the first-line approach due to their rapid onset of therapeutic effects and remission of the acute phase. Nonetheless, long-term applications may lead to major adverse effects that outweigh the benefits. Hence, other adjuvant therapies are mandatory to minimize the potential harm and ameliorate the quality of life. Herein, we summarize the current therapeutic strategies and introduce promising therapies for intractable autoimmune bullous diseases.

Medicinal Chemistry Strategies for the Development of Bruton's Tyrosine Kinase Inhibitors against Resistance

Despite significant efficacy, one of the major limitations of small-molecule Bruton's tyrosine kinase (BTK) agents is the presence of clinically acquired resistance, which remains a major clinical challenge. This Perspective focuses on medicinal chemistry strategies for the development of BTK small-molecule inhibitors against resistance, including the structure-based design of BTK inhibitors targeting point mutations, e.g., (i) developing noncovalent inhibitors from covalent inhibitors, (ii) avoiding steric hindrance from mutated residues, (iii) making interactions with the mutated residue, (iv) modifying the solvent-accessible region, and (v) developing new scaffolds. Additionally, a comparative analysis of multi-inhibitions of BTK is presented based on cross-comparisons between 2916 unique BTK ligands and 283 other kinases that cover 7108 dual/multiple inhibitions. Finally, targeting the BTK allosteric site and uding proteolysis-targeting chimera (PROTAC) as two potential strategies are addressed briefly, while also illustrating the possibilities and challenges to find novel ligands of BTK.

Bruton's Kinase Inhibitors for the Treatment of Immunological Diseases: Current Status and Perspectives

The use of Bruton's tyrosine kinase (BTK) inhibitors has changed the management of patients with B-cell lymphoid malignancies. BTK is an important molecule that interconnects B-cell antigen receptor (BCR) signaling. BTK inhibitors (BTKis) are classified into three categories, namely covalent irreversible inhibitors, covalent reversible inhibitors, and non-covalent reversible inhibitors. Ibrutinib is the first covalent, irreversible BTK inhibitor approved in 2013 as a breakthrough therapy for chronic lymphocytic leukemia patients. Subsequently, two other covalent, irreversible, second-generation BTKis, acalabrutinib and zanubrutinib, have been developed for lymphoid malignancies to reduce the ibrutinib-mediated adverse effects. More recently, irreversible and reversible BTKis have been under development for immune-mediated diseases, including autoimmune hemolytic anemia, immune thrombocytopenia, multiple sclerosis, pemphigus vulgaris, atopic dermatitis, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, and chronic spontaneous urticaria, among others. This review article summarizes the preclinical and clinical evidence supporting the role of BTKis in various autoimmune, allergic, and inflammatory conditions.

Bruton's Tyrosine Kinase in Neutrophils Is Crucial for Host Defense against Klebsiella pneumoniae

Humans with dysfunctional Bruton's tyrosine kinase (Btk) are highly susceptible to bacterial infections. Compelling evidence indicates that Btk is essential for B cell-mediated immunity, whereas its role in myeloid cell-mediated immunity against infections is controversial. In this study, we determined the contribution of Btk in B cells and neutrophils to host defense against the extracellular bacterial pathogen Klebsiella pneumoniae, a common cause of pulmonary infections and sepsis. Btk-/- mice were highly susceptible to Klebsiella infection, which was not reversed by Btk re-expression in B cells and restoration of natural antibody levels. Neutrophil-specific Btk deficiency impaired host defense against Klebsiella to a similar extent as complete Btk deficiency. Neutrophil-specific Btk deficiency abolished extracellular reactive oxygen species production in response to Klebsiella. These data indicate that expression of Btk in neutrophils is crucial, while in B cells, it is dispensable for in vivo host defense against K. pneumoniae.

Chronic immune thrombocytopenia in a child with X-linked agammaglobulinemia-an uncommon phenotype

Autoimmune disorders are common in patients with primary immunodeficiency diseases (PIDs). However, the prevalence of autoimmunity is low in patients with X-linked agammaglobulinemia (XLA), mostly due to the absence of antibodies. Chronic or persistent immune thrombocytopenia (ITP), which is usually considered an antibody-mediated disease, is uncommon in patients with XLA. In this study, we detailly described a surprising autoimmune phenomenon, chronic ITP, in a small boy diagnosed with XLA. This is an interesting phenotype found in XLA, and it is helpful to understand the immune pathogenesis of autoimmunity in patients with XLA.

Regulation of the Tec family of non-receptor tyrosine kinases in cardiovascular disease

Tyrosine phosphorylation by protein tyrosine kinases (PTKs) is a type of post-translational modification. Tec kinases, which are a subfamily of non-receptor PTKs, were originally discovered in the hematopoietic system and include five members: Tec, Btk, Itk/Emt/Tsk, Etk/Bmx, and Txk/Rlk. With the progression of modern research, certain members of the Tec family of kinases have been found to be expressed outside the hematopoietic system and are involved in the development and progression of a variety of diseases. The role of Tec family kinases in cardiovascular disease is receiving increasing attention. Tec kinases are involved in the occurrence and progression of ischemic heart disease, atherosclerosis, cardiac dysfunction associated with sepsis, atrial fibrillation, myocardial hypertrophy, coronary atherosclerotic heart disease, and myocardial infarction and post-myocardial. However, no reviews have comprehensively clarified the role of Tec kinases in the cardiovascular system. Therefore, this review summarizes research on the role of Tec kinases in cardiovascular disease, providing new insights into the prevention and treatment of cardiovascular disease.

Regulation of B-Cell Receptor Signaling and Its Therapeutic Relevance in Aggressive B-Cell Lymphomas

The proliferation and survival signals emanating from the B-cell receptor (BCR) constitute a crucial aspect of mature lymphocyte's life. Dysregulated BCR signaling is considered a potent contributor to tumor survival in different subtypes of B-cell non-Hodgkin lymphomas (B-NHLs). In the last decade, the emergence of BCR-associated kinases as rational therapeutic targets has led to the development and approval of several small molecule inhibitors targeting either Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), or phosphatidylinositol 3 kinase (PI3K), offering alternative treatment options to standard chemoimmunotherapy, and making some of these drugs valuable assets in the anti-lymphoma armamentarium. Despite their initial effectiveness, these precision medicine strategies are limited by primary resistance in aggressive B-cell lymphoma such as diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL), especially in the case of first generation BTK inhibitors. In these patients, BCR-targeting drugs often fail to produce durable responses, and nearly all cases eventually progress with a dismal outcome, due to secondary resistance. This review will discuss our current understanding of the role of antigen-dependent and antigen-independent BCR signaling in DLBCL and MCL and will cover both approved inhibitors and investigational molecules being evaluated in early preclinical studies. We will discuss how the mechanisms of action of these molecules, and their off/on-target effects can influence their effectiveness and lead to toxicity, and how our actual knowledge supports the development of more specific inhibitors and new, rationally based, combination therapies, for the management of MCL and DLBCL patients.

B Lineage Cells in ANCA-Associated Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease that affects small sized blood vessels and can lead to serious complications in the lungs and kidneys. The prominent presence of ANCA autoantibodies in this disease implicates B cells in its pathogenesis, as these are the precursors of the ANCA-producing plasma cells (PCs). Further evidence supporting the potential role of B lineage cells in vasculitis are the increased B cell cytokine levels and the dysregulated B cell populations in patients. Confirmation of the contribution of B cells to pathology arose from the beneficial effect of anti-CD20 therapy (i.e., rituximab) in AAV patients. These anti-CD20 antibodies deplete circulating B cells, which results in amelioration of disease. However, not all patients respond completely, and this treatment does not target PCs, which can maintain ANCA production. Hence, it is important to develop more specific therapies for AAV patients. Intracellular signalling pathways may be potential therapeutic targets as they can show (disease-specific) alterations in certain B lineage cells, including pathogenic B cells, and contribute to differentiation and survival of PCs. Preliminary data on the inhibition of certain signalling molecules downstream of receptors specific for B lineage cells show promising therapeutic effects. In this narrative review, B cell specific receptors and their downstream signalling molecules that may contribute to pathology in AAV are discussed, including the potential to therapeutically target these pathways.

Inhibition of Bruton Tyrosine Kinase Reduces Neuroimmune Cascade and Promotes Recovery after Spinal Cord Injury

Microglia/astrocyte and B cell neuroimmune responses are major contributors to the neurological deficits after traumatic spinal cord injury (SCI). Bruton tyrosine kinase (BTK) activation mechanistically links these neuroimmune mechanisms. Our objective is to use Ibrutinib, an FDA-approved BTK inhibitor, to inhibit the neuroimmune cascade thereby improving locomotor recovery after SCI. Rat models of contusive SCI, Western blot, immunofluorescence staining imaging, flow cytometry analysis, histological staining, and behavioral assessment were used to evaluate BTK activity, neuroimmune cascades, and functional outcomes. Both BTK expression and phosphorylation were increased at the lesion site at 2, 7, 14, and 28 days after SCI. Ibrutinib treatment (6 mg/kg/day, IP, starting 3 h post-injury for 7 or 14 days) reduced BTK activation and total BTK levels, attenuated the injury-induced elevations in Iba1, GFAP, CD138, and IgG at 7 or 14 days post-injury without reduction in CD45RA B cells, improved locomotor function (BBB scores), and resulted in a significant reduction in lesion volume and significant improvement in tissue-sparing 11 weeks post-injury. These results indicate that Ibrutinib exhibits neuroprotective effects by blocking excessive neuroimmune responses through BTK-mediated microglia/astroglial activation and B cell/antibody response in rat models of SCI. These data identify BTK as a potential therapeutic target for SCI.

The role of Bruton's tyrosine kinase in the immune system and disease

Bruton's tyrosine kinase (BTK) is a TEC kinase with a multifaceted role in B-cell biology and function, highlighted by its position as a critical component of the B-cell receptor signalling pathway. Due to its role as a therapeutic target in several haematological malignancies including chronic lymphocytic leukaemia, BTK has been gaining tremendous momentum in recent years. Within the immune system, BTK plays a part in numerous pathways and cells beyond B cells (i.e. T cells, macrophages). Not surprisingly, BTK has been elucidated to be a driving factor not only in lymphoproliferative disorders but also in autoimmune diseases and response to infection. To extort this role, BTK inhibitors such as ibrutinib have been developed to target BTK in other diseases. However, due to rising levels of resistance, the urgency to develop new inhibitors with alternative modes of targeting BTK is high. To meet this demand, an expanding list of BTK inhibitors is currently being trialled. In this review, we synopsize recent discoveries regarding BTK and its role within different immune cells and pathways. Additionally, we discuss the broad significance and relevance of BTK for various diseases ranging from haematology and rheumatology to the COVID-19 pandemic. Overall, BTK signalling and its targetable nature have emerged as immensely important for a wide range of clinical applications. The development of novel, more specific and less toxic BTK inhibitors could be revolutionary for a significant number of diseases with yet unmet treatment needs.

Bruton's Tyrosine Kinase-Mediated Signaling in Myeloid Cells Is Required for Protective Innate Immunity During Pneumococcal Pneumonia

Bruton’s tyrosine kinase (Btk) is a cytoplasmic kinase expressed in B cells and myeloid cells. It is essential for B cell development and natural antibody-mediated host defense against bacteria in humans and mice, but little is known about the role of Btk in innate host defense in vivo. Previous studies have indicated that lack of (natural) antibodies is paramount for impaired host defense against Streptococcus (S.) pneumoniae in patients and mice with a deficiency in functional Btk. In the present study, we re-examined the role of Btk in B cells and myeloid cells during pneumococcal pneumonia and sepsis in mice. The antibacterial defense of Btk^-/- mice was severely impaired during pneumococcal pneumosepsis and restoration of natural antibody production in Btk^-/- mice by transgenic expression of Btk specifically in B cells did not suffice to protect against infection. Btk^-/- mice with reinforced Btk expression in MhcII⁺ cells, including B cells, dendritic cells and macrophages, showed improved antibacterial defense as compared to Btk^-/- mice. Bacterial outgrowth in Lysmcre-Btk^fl/Y mice was unaltered despite a reduced capacity of Btk-deficient alveolar macrophages to respond to pneumococci. Mrp8cre-Btk^fl/Y mice with a neutrophil specific paucity in Btk expression, however, demonstrated impaired antibacterial defense. Neutrophils of Mrp8cre-Btk^fl/Y mice displayed reduced release of granule content after pulmonary installation of lipoteichoic acid, a gram-positive bacterial cell wall component relevant for pneumococci. Moreover, Btk deficient neutrophils showed impaired degranulation and phagocytosis upon incubation with pneumococci ex vivo. Taken together, the results of our study indicate that besides regulating B cell-mediated immunity, Btk is critical for regulation of myeloid cell-mediated, and particularly neutrophil-mediated, innate host defense against S. pneumoniae in vivo.

Balancing Potential Benefits and Risks of Bruton Tyrosine Kinase Inhibitor Therapies in Multiple Sclerosis During the COVID-19 Pandemic

Bruton tyrosine kinase inhibitors (BTKis) encompass a new class of therapeutics currently being evaluated for the treatment of multiple sclerosis (MS). Whether BTKis affect COVID-19 risk or severity or reduce vaccine efficacy are important but unanswered questions. Here, we provide an overview on BTKi mechanisms relevant to COVID-19 infection and vaccination and review preliminary data on BTKi use in patients with COVID-19. BTKis block B-cell receptor– and myeloid fragment crystallizable receptor–mediated signaling, thereby dampening B-cell activation, antibody class-switching, expansion, and cytokine production. Beyond antibodies, COVID-19 severity and vaccine efficacy appear largely linked to T-cell responses and interferon induction, processes not directly affected by BTKis. Given that B cells have clear roles in antigen presentation to T cells, however, it is possible that BTKis may indirectly interfere with beneficial or detrimental T-cell responses during COVID-19 infection or vaccination. In addition to these possible effects on generating a protective immune response, BTKis may attenuate the hyperinflammatory dysregulation often seen in severe cases of COVID-19 that evolves as a key risk factor in this disease. Currently available outcomes from BTKi-treated patients with COVID-19 are discussed. Clinical trials are currently underway to evaluate the safety and efficacy of BTKis in individuals with MS. Although limited data suggest a potential benefit of BTKis on outcomes for some COVID-19 patients, data from adequately powered, prospective and randomized clinical trials are lacking. Likewise, the specific effect of BTKis on the safety and efficacy of COVID-19 vaccines remains to be determined. Any potential unknown risks that BTKi therapy may present to the patient relative to COVID-19 infection, severity, and vaccine efficacy must be balanced with the importance of timely intervention to prevent or minimize MS progression.

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.

Combined Treatment with Acalabrutinib and Rapamycin Inhibits Glioma Stem Cells and Promotes Vascular Normalization by Downregulating BTK/mTOR/VEGF Signaling

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults, with a median duration of survival of approximately 14 months after diagnosis. High resistance to chemotherapy remains a major problem. Previously, BTK has been shown to be involved in the intracellular signal transduction including Akt/mTOR signaling and be critical for tumorigenesis. Thus, we aim to evaluate the effect of BTK and mTOR inhibition in GBM. We evaluated the viability of GBM cell lines after treatment with acalabrutinib and/or rapamycin through a SRB staining assay. We then evaluated the effect of both drugs on GBM stem cell-like phenotypes through various in vitro assay. Furthermore, we incubated HUVEC cells with tumorsphere conditioned media and observed their angiogenesis potential, with or without treatment. Finally, we conducted an in vivo study to confirm our in vitro findings and analyzed the effect of this combination on xenograft mice models. Drug combination assay demonstrated a synergistic relationship between acalabrutinib and rapamycin. CSCs phenotypes, including tumorsphere and colony formation with the associated expression of markers of pluripotency are inhibited by either acalabrutinib or rapamycin singly and these effects are enhanced upon combining acalabrutinib and rapamycin. We showed that the angiogenesis capabilities of HUVEC cells are significantly reduced after treatment with acalabrutinib and/or rapamycin. Xenograft tumors treated with both drugs showed significant volume reduction with minimal toxicity. Samples taken from the combined treatment group demonstrated an increased Desmin/CD31 and col IV/vessel ratio, suggesting an increased rate of vascular normalization. Our results demonstrate that BTK-mTOR inhibition disrupts the population of GBM-CSCs and contributes to normalizing GBM vascularization and thus, may serve as a basis for developing therapeutic strategies for chemoresistant/radioresistant GBM.

Autoantibody-Specific Signalling in Pemphigus

Pemphigus is a severe autoimmune disease impairing barrier functions of epidermis and mucosa. Autoantibodies primarily target the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg 3 and induce loss of desmosomal adhesion. Strikingly, autoantibody profiles in pemphigus correlate with clinical phenotypes. Mucosal-dominant pemphigus vulgaris (PV) is characterised by autoantibodies (PV-IgG) against Dsg3 whereas epidermal blistering in PV and pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1. Therapy in pemphigus is evolving towards specific suppression of autoantibody formation and autoantibody depletion. Nevertheless, during the acute phase and relapses of the disease additional treatment options to stabilise desmosomes and thereby rescue keratinocyte adhesion would be beneficial. Therefore, the mechanisms by which autoantibodies interfere with adhesion of desmosomes need to be characterised in detail. Besides direct inhibition of Dsg adhesion, autoantibodies engage signalling pathways interfering with different steps of desmosome turn-over. With this respect, recent data indicate that autoantibodies induce separate signalling responses in keratinocytes via specific signalling complexes organised by Dsg1 and Dsg3 which transfer the signal of autoantibody binding into the cell. This hypothesis may also explain the different clinical pemphigus phenotypes.

Next-generation Bruton's tyrosine kinase inhibitor BIIB091 selectively and potently inhibits B cell and Fc receptor signaling and downstream functions in B cells and myeloid cells

Objectives

Bruton's tyrosine kinase (BTK) plays a non-redundant signaling role downstream of the B-cell receptor (BCR) in B cells and the receptors for the Fc region of immunoglobulins (FcR) in myeloid cells. Here, we characterise BIIB091, a novel, potent, selective and reversible small-molecule inhibitor of BTK.

Methods

BIIB091 was evaluated in vitro and in vivo in preclinical models and in phase 1 clinical trial.

Results

In vitro, BIIB091 potently inhibited BTK-dependent proximal signaling and distal functional responses in both B cells and myeloid cells with IC₅₀s ranging from 3 to 106 nm, including antigen presentation to T cells, a key mechanism of action thought to be underlying the efficacy of B cell-targeted therapeutics in multiple sclerosis. BIIB091 effectively sequestered tyrosine 551 in the kinase pocket by forming long-lived complexes with BTK with t _1/2 of more than 40 min, thereby preventing its phosphorylation by upstream kinases. As a key differentiating feature of BIIB091, this property explains the very potent whole blood IC₅₀s of 87 and 106 nm observed with stimulated B cells and myeloid cells, respectively. In vivo, BIIB091 blocked B-cell activation, antibody production and germinal center differentiation. In phase 1 healthy volunteer trial, BIIB091 inhibited naïve and unswitched memory B-cell activation, with an in vivo IC₅₀ of 55 nm and without significant impact on lymphoid or myeloid cell survival after 14 days of dosing.

Conclusion

Pharmacodynamic results obtained in preclinical and early clinical settings support the advancement of BIIB091 in phase 2 clinical trials.

B Cell Activation and Escape of Tolerance Checkpoints: Recent Insights from Studying Autoreactive B Cells

Autoreactive B cells are key drivers of pathogenic processes in autoimmune diseases by the production of autoantibodies, secretion of cytokines, and presentation of autoantigens to T cells. However, the mechanisms that underlie the development of autoreactive B cells are not well understood. Here, we review recent studies leveraging novel techniques to identify and characterize (auto)antigen-specific B cells. The insights gained from such studies pertaining to the mechanisms involved in the escape of tolerance checkpoints and the activation of autoreactive B cells are discussed. In addition, we briefly highlight potential therapeutic strategies to target and eliminate autoreactive B cells in autoimmune diseases.

Discovery of a Potent and Selective Covalent Inhibitor of Bruton's Tyrosine Kinase with Oral Anti-Inflammatory Activity

Bruton's tyrosine kinase (BTK) is a cytoplasmic tyrosine kinase that plays a critical role in the activation of B cells, macrophages, and osteoclasts. Given the key role of these cell types in the pathology of autoimmune disorders, BTK inhibitors have the potential to improve treatment outcomes in multiple diseases. Herein, we report the discovery and characterization of a novel potent and selective covalent 4-oxo-4,5-dihydro-3H-1-thia-3,5,8-triazaacenaphthylene-2-carboxamide BTK inhibitor chemotype. Compound 27 irreversibly inhibits BTK by targeting a noncatalytic cysteine residue (Cys481) for covalent bond formation. Compound 27 is characterized by selectivity for BTK, potent in vivo BTK occupancy that is sustained after it is cleared from systemic circulation, and dose-dependent efficacy at reducing joint inflammation in a rat collagen-induced arthritis model.

Loss of immune homeostasis in patients with idiopathic pulmonary arterial hypertension

INTRODUCTION

Autoreactivity against pulmonary vascular structures is thought to be involved in idiopathic pulmonary arterial hypertension (IPAH), but the underlying mechanisms remain poorly understood. We hypothesised that aberrant B-cell activation contributes to IPAH aetiology.

METHODS

Mice with enhanced B-cell activation due to B-cell-specific overexpression of the B-cell receptor (BCR) signalling molecule Bruton's tyrosine kinase (BTK) were subjected to lung injury and examined for several pulmonary hypertension (PH) indices. Peripheral blood lymphocytes from patients with IPAH (n=13), connective tissue disease-associated PAH (CTD-PAH, n=9), congenital heart disease PAH (n=7), interstitial lung disease associated PH (n=17) and healthy controls (n=19) were characterised by 14-colour flow cytometry.

RESULTS

Following pulmonary injury, BTK-overexpressing mice showed prolonged activation of B cells and CXCR5⁺ follicular T-helper (Tfh) cells, as well as features of PH development. Patients with CTD-PAH and CHD-PAH displayed reduced proportions of circulating non-switched-memory B cells (p=0.03, p=0.02, respectively). Interestingly, we observed increased BTK protein expression in naive (p=0.007) and memory B-cell subsets of patients with IPAH and CTD-PAH. BTK was particularly high in patients with IPAH with circulating autoantibodies (p=0.045). IPAH patients had low frequencies of circulating CXCR5⁺ Tfh cells (p=0.005). Hereby, the increased BTK protein expression in B cells was associated with high proportions of Tfh17 (p=0.018) and Tfh17.1 (p=0.007) cells within the circulating Tfh population.

CONCLUSIONS

Our study shows that pulmonary injury in combination with enhanced B-cell activation is sufficient to induce PH symptoms in mice. In parallel, immune homeostasis in patients with IPAH is compromised, as evidenced by increased BCR signalling and cTfh17 polarisation, indicating that adaptive immune activation contributes to IPAH disease induction or progression.

The Results of Well-conducted Negative Clinical Trials Should Be Reported in a Peer-reviewed Journal

We expect that the pathogenesis, manifestations, and successful management of disease will be fully reported in peer-reviewed journals. However, there are multiple publications addressing the likelihood that clinical trials that do not report a positive result are underreported in the medical literature, with a maximum of 50% of negative studies published, even after 5 years of availability of their results1,2.

ANCA-Associated Vasculitis: An Update

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) represents a group of small vessel vasculitides characterized by granulomatous and neutrophilic tissue inflammation, often associated with the production of antibodies that target neutrophil antigens. The two major antigens targeted by ANCAs are leukocyte proteinase 3 (PR3) and myeloperoxidase (MPO). AAV can be classified into 3 categories based on patterns of clinical involvement: namely, granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic GPA (EGPA). Clinically, AAV involves many organ systems including the lungs, kidneys, skin, and nervous system. The prognosis of AAV has improved dramatically due to advances in the understanding of its pathogenesis and treatment modalities. This review will highlight some of the recent updates in our understanding of the pathogenesis, clinical manifestations, and treatment options in patients with AAV focusing on kidney involvement.

Recent Advances in Lupus B Cell Biology: PI3K, IFNγ, and Chromatin

In the autoimmune disease Systemic Lupus Erythematosus (SLE), autoantibodies are formed that promote inflammation and tissue damage. There has been significant interest in understanding the B cell derangements involved in SLE pathogenesis. The past few years have been particularly fruitful in three domains: the role of PI3K signaling in loss of B cell tolerance, the role of IFNγ signaling in the development of autoimmunity, and the characterization of changes in chromatin accessibility in SLE B cells. The PI3K pathway coordinates various downstream signaling molecules involved in B cell development and activation. It is governed by the phosphatases PTEN and SHIP-1. Murine models lacking either of these phosphatases in B cells develop autoimmune disease and exhibit defects in B cell tolerance. Limited studies of human SLE B cells demonstrate reduced expression of PTEN or increased signaling events downstream of PI3K in some patients. IFNγ has long been known to be elevated in both SLE patients and mouse models of lupus. New data suggests that IFNγR expression on B cells is required to develop autoreactive germinal centers (GC) and autoantibodies in murine lupus. Furthermore, IFNγ promotes increased transcription of BCL6, IL-6 and T-bet in B cells, which also promote GC and autoantibody formation. IFNγ also induces epigenetic changes in human B cells. SLE B cells demonstrate significant epigenetic reprogramming, including enhanced chromatin accessibility at transcription factor motifs involved in B cell activation and plasma cell (PC) differentiation as well as alterations in DNA methylation and histone modifications. Histone deacetylase inhibitors limit disease development in murine lupus models, at least in part via their ability to prevent B cell class switching and differentiation into plasma cells. This review will discuss relevant discoveries of the past several years pertaining to these areas of SLE B cell biology.

B Cells and Antibodies as Targets of Therapeutic Intervention in Neuromyelitis Optica Spectrum Disorders

The first description of neuromyelitis optica by Eugène Devic and Fernand Gault dates back to the 19th century, but only the discovery of aquaporin-4 autoantibodies in a major subset of affected patients in 2004 led to a fundamentally revised disease concept: Neuromyelits optica spectrum disorders (NMOSD) are now considered autoantibody-mediated autoimmune diseases, bringing the pivotal pathogenetic role of B cells and plasma cells into focus. Not long ago, there was no approved medication for this deleterious disease and off-label therapies were the only treatment options for affected patients. Within the last years, there has been a tremendous development of novel therapies with diverse treatment strategies: immunosuppression, B cell depletion, complement factor antagonism and interleukin-6 receptor blockage were shown to be effective and promising therapeutic interventions. This has led to the long-expected official approval of eculizumab in 2019 and inebilizumab in 2020. In this article, we review current pathogenetic concepts in NMOSD with a focus on the role of B cells and autoantibodies as major contributors to the propagation of these diseases. Lastly, by highlighting promising experimental and future treatment options, we aim to round up the current state of knowledge on the therapeutic arsenal in NMOSD.

Complementary Chinese Herbal Medicine Therapy Improves Survival in Patients With Pemphigus: A Retrospective Study From a Taiwan-Based Registry

Pemphigus is a life-threatening and skin-specific inflammatory autoimmune disease, characterized by intraepidermal blistering between the mucous membranes and skin. Chinese herbal medicine (CHM) has been used as an adjunct therapy for treating many diseases, including pemphigus. However, there are still limited studies in effects of CHM treatment in pemphigus, especially in Taiwan. To more comprehensively explore the effect of long-term CHM treatment on the overall mortality of pemphigus patients, we performed a retrospective analysis of 1,037 pemphigus patients identified from the Registry for Catastrophic Illness Patients database in Taiwan. Among them, 229 and 177 patients were defined as CHM users and non-users, respectively. CHM users were young, predominantly female, and had a lesser Charlson comorbidity index (CCI) than non-CHM users. After adjusting for age, sex, prednisolone use, and CCI, CHM users had a lower overall mortality risk than non-CHM users (multivariate model: hazard ratio (HR): 0.422, 95% confidence interval (CI): 0.242–0.735, p = 0.0023). The cumulative incidence of overall survival was significantly higher in CHM users than in non-users (p = 0.0025, log rank test). Association rule mining and network analysis showed that there was one main CHM cluster with Qi–Ju–Di–Huang–Wan (QJDHW), Dan–Shen (DanS; Radix Salviae miltiorrhizae; Salvia miltiorrhiza Bunge), Jia–Wei–Xiao–Yao-–San (JWXYS), Huang–Lian (HL; Rhizoma coptidis; Coptis chinensis Franch.), and Di–Gu–Pi (DGP; Cortex lycii; Lycium barbarum L.), while the second CHM cluster included Jin–Yin–Hua (JYH; Flos lonicerae; Lonicera hypoglauca Miq.) and Lian–Qiao (LQ; Fructus forsythiae; Forsythia suspensa (Thunb.) Vahl). In Taiwan, CHMs used as an adjunctive therapy reduced the overall mortality to approximately 20% among pemphigus patients after a follow-up of more than 6 years. A comprehensive CHM list may be useful in future clinical trials and further scientific investigations to improve the overall survival in these patients.

Inhibition of Bruton's tyrosine kinase interferes with pathogenic B-cell development in inflammatory CNS demyelinating disease

Anti-CD20-mediated B-cell depletion effectively reduces acute multiple sclerosis (MS) flares. Recent data shows that antibody-mediated extinction of B cells as a lasting immune suppression, harbors the risk of developing humoral deficiencies over time. Accordingly, more selective, durable and reversible B-cell-directed MS therapies are needed. We here tested inhibition of Bruton's tyrosine kinase (BTK), an enzyme centrally involved in B-cell receptor signaling, as the most promising approach in this direction. Using mouse models of MS, we determined that evobrutinib, the first BTK inhibiting molecule being developed, dose-dependently inhibited antigen-triggered activation and maturation of B cells as well as their release of pro-inflammatory cytokines. Most importantly, evobrutinib treatment functionally impaired the capacity of B cells to act as antigen-presenting cells for the development of encephalitogenic T cells, resulting in a significantly reduced disease severity in mice. In contrast to anti-CD20, BTK inhibition silenced this key property of B cells in MS without impairing their frequency or functional integrity. In conjunction with a recent phase II trial reporting that evobrutinib is safe and effective in MS, our mechanistic data highlight therapeutic BTK inhibition as a landmark towards selectively interfering with MS-driving B-cell properties.

Bruton's Tyrosine Kinase Inhibition Promotes Myelin Repair

Background:

Microglia are the resident macrophages of the central nervous system (CNS). In multiple sclerosis (MS) and related experimental models, microglia have either a pro-inflammatory or a pro-regenerative/pro-remyelinating function. Inhibition of Bruton’s tyrosine kinase (BTK), a member of the Tec family of kinases, has been shown to block differentiation of pro-inflammatory macrophages in response to granulocyte–macrophage colony-stimulating factor in vitro. However, the role of BTK in the CNS is unknown.

Methods:

Our aim was to investigate the effect of BTK inhibition on myelin repair in ex vivo and in vivo experimental models of demyelination and remyelination. The remyelination effect of a BTK inhibitor (BTKi; BTKi-1) was then investigated in LPC-induced demyelinated cerebellar organotypic slice cultures and metronidazole-induced demyelinated Xenopus MBP-GFP-NTR transgenic tadpoles.

Results:

Cellular detection of BTK and its activated form BTK-phospho-Y223 (p-BTK) was determined by immunohistochemistry in organotypic cerebellar slice cultures, before and after lysophosphatidylcholine (LPC)-induced demyelination. A low BTK signal detected by immunolabeling under normal conditions in cerebellar slices was in sharp contrast to an 8.5-fold increase in the number of BTK-positive cells observed in LPC-demyelinated slice cultures. Under both conditions, approximately 75% of cells expressing BTK and p-BTK were microglia and 25% were astrocytes. Compared with spontaneous recovery, treatment of demyelinated slice cultures and MTZ-demyelinated transgenic tadpoles with BTKi resulted in at least a 1.7-fold improvement of remyelination.

Conclusion:

Our data demonstrate that BTK inhibition is a promising therapeutic strategy for myelin repair.

Identification of novel therapeutic targets for blocking acantholysis in pemphigus

Background and Purpose

Pemphigus is caused by autoantibodies against desmoglein (Dsg) 1, Dsg3, and/or non‐Dsg antigens. Pemphigus vulgaris (PV) is the most common manifestation of pemphigus, with painful erosions on mucous membranes. In most cases, blistering also occurs on the skin, leading to areas of extensive denudation. Despite improvements in pemphigus treatment, time to achieve remission is long, severe adverse events are frequent and 20% of patients do not respond adequately. Current clinical developments focus exclusively on modulating B cell function or autoantibody half‐life. However, topical modulation of PV autoantibody‐induced blistering is an attractive target because it could promptly relieve symptoms.

Experimental Approach

To address this issue, we performed an unbiased screening in a complex biological system using 141 low MW inhibitors from a chemical library. Specifically, we evaluated PV IgG‐induced Dsg3 internalization in HaCaT keratinocytes. Validation of the 20 identified compounds was performed using keratinocyte fragmentation assays, as well as a human skin organ culture (HSOC) model.

key Results

Overall, this approach led to the identification of four molecules involved in PV IgG‐induced skin pathology: MEK1, TrkA, PI3Kα, and VEGFR2.

Conclusion and Implications

This unbiased screening revealed novel mechanisms by which PV autoantibodies induce blistering in keratinocytes and identified new treatment targets for this severe and potentially life‐threatening skin disease.

Overexpression of FcγRIIB regulates downstream protein phosphorylation and suppresses B cell activation to ameliorate systemic lupus erythematosus

The present study aimed to examine the effects of FcγRIIB on systemic lupus erythematosus (SLE) and to investigate the underlying mechanisms. For this purpose, lentiviral vector carrying the membrane-bound type FcγRIIB gene (mFcγRIIB lentivirus) and soluble FcγRIIB (sFcγRIIB) protein were used to treat B cells from patients with SLE. The B cells were treated with calf thymus DNA (ctDNA) and anti-calf thymus DNA-immune complexes (anti-ctDNA-IC). mFcγRIIB lentivirus and sFcγRIIB protein were also injected into MRL/lpr SLE mice. The results revealed that anti-ctDNA-IC treatment significantly downregulated the IgG antibody secretion of B cells treated with mFcγRIIB lentivirus. mFcγRIIB and sFcγRIIB decreased the phosphorylation level of Bruton's tyrosine kinase (BTK) in B cells, and increased the phosphorylation level of Lyn proto-oncogene (Lyn), docking protein 1 (DOK1) and inositol polyphosphate-5-phospha-tase D (SHIP). mFcγRIIB promoted the apoptosis of B cells. Following the treatment of MRL/lpr SLE mice with mFcγRIIB lentivirus, the levels of urinary protein, serum anti-nuclear and anti-dsDNA antibodies were decreased, while the levels of mFcγRIIB in B cells were increased. mFcγRIIB ameliorated the pathologies of the kidneys, liver and lymph node tissues of the MRL/lpr SLE mice. Following treatment of the MRL/lpr SLE mice with sFcγRIIB, the levels of urinary protein, serum anti-dsDNA antibody and BTK and SHIP phosphorylation levels in B cells were decreased, while the serum sFcγRIIB and sFcγRIIB-IgG levels were increased. On the whole, the findings of the present study demonstrate that recombinant FcγRIIB inhibits the secretion of IgG antibody by B cells from patients with SLE, ameliorates the symptoms of SLE in mice, and alters the phosphorylation levels of downstream proteins of the FcγRIIB signaling pathway in B cells. These results suggest that FcγRIIB may play preventive and therapeutic roles in SLE by inhibiting B cell activation via the FcγRIIB signaling pathway, which provides a novel theory and strategy for the prevention and treatment of SLE.

Efficacy and Safety of PF-06651600 (Ritlecitinib), a Novel JAK3/TEC Inhibitor, in Patients With Moderate-to-Severe Rheumatoid Arthritis and an Inadequate Response to Methotrexate

Objective

To evaluate the efficacy and safety of PF‐06651600 (ritlecitinib), an irreversible inhibitor of JAK3 and the tyrosine kinase expressed in hepatocellular carcinoma (TEC) kinase family, in comparison with placebo in patients with rheumatoid arthritis (RA).

Methods

An 8‐week, phase II, double‐blind, parallel‐group study was conducted. Seventy patients who were seropositive for anti–citrullinated protein antibodies and/or rheumatoid factor were randomized 3:2 to receive oral PF‐06651600 (200 mg once daily) or placebo for 8 weeks. Eligible patients had an inadequate response to methotrexate, and the study design allowed up to 50% of patients to have previously received 1 tumor necrosis factor inhibitor that was inadequately effective and/or not tolerated. The primary end point was change from baseline in the Simplified Disease Activity Index (SDAI) score at week 8, assessed by Bayesian analysis using an informative prior distribution for placebo response.

Results

Mean change from baseline in the SDAI score at week 8 was greater in the PF‐06651600 group (−26.1 [95% credible interval −29.7, −22.4]) than in the placebo group (−16.8 [95% credible interval −20.9, −12.7]; P < 0.001). Most adverse events (AEs) were mild in severity, and no treatment‐related serious AEs, severe AEs, or deaths were reported. The most common classes of AE were infections and infestations as well as skin and subcutaneous tissue disorders; there was 1 mild case of herpes simplex in the PF‐06651600 group that was considered to be treatment related, which resolved within 3 days without study treatment discontinuation or antiviral therapy.

Conclusion

Treatment with the oral JAK3/TEC inhibitor PF‐06651600 (200 mg once daily) was associated with significant improvements in RA disease activity and was generally well‐tolerated in this small 8‐week study.

Fenebrutinib versus Placebo or Adalimumab in Rheumatoid Arthritis: A Randomized, Double-Blind, Phase II Trial (ANDES Study)

OBJECTIVE

To evaluate fenebrutinib, an oral and highly selective non-covalent inhibitor of Bruton's tyrosine kinase (BTK), in patients with active rheumatoid arthritis (RA).

METHODS

Patients with RA and inadequate response to methotrexate (cohort 1, n=480) were randomized to fenebrutinib (50 mg once daily, 150 mg once daily, 200 mg twice daily), 40 mg adalimumab every other week, or placebo. Patients with RA and inadequate response to tumor necrosis factor inhibitors (cohort 2, n=98) received fenebrutinib (200 mg twice daily) or placebo. Both cohorts continued methotrexate therapy.

RESULTS

In cohort 1, American College of Rheumatology scores (ACR50) at week 12 were similar for fenebrutinib 50 mg once daily and placebo, and higher for fenebrutinib 150 mg once daily (28%) and 200 mg twice daily (35%) than placebo (15%) (p=0.017; p=0.0003). Fenebrutinib 200 mg twice daily and adalimumab (36%) were comparable (p=0.81). In cohort 2, more patients achieved ACR50 with fenebrutinib 200 mg twice daily (25%) than placebo (12%) (p=0.072). The most common adverse events for fenebrutinib included nausea, headache, anemia, and upper respiratory tract infections. Fenebrutinib had significant effects on myeloid and B cell biomarkers (CCL4 and rheumatoid factor). Fenebrutinib and adalimumab caused overlapping as well as distinct changes in B cell and myeloid biomarkers.

CONCLUSION

Fenebrutinib demonstrated efficacy comparable to adalimumab in patients with an inadequate response to methotrexate, and safety consistent with existing immunomodulatory therapies for RA. These data support targeting both B and myeloid cells via this novel mechanism for potential efficacy in the treatment of RA.

Evidence for enhanced Bruton's tyrosine kinase activity in transitional and naïve B cells of patients with granulomatosis with polyangiitis

OBJECTIVES

To determine Bruton's tyrosine kinase (BTK) protein and phosphorylation levels in B cell subsets of granulomatosis with polyangiitis (GPA) patients and to investigate the effect of BTK blockade on in vitro B cell cytokine production, subset distribution and (auto)antibody production.

METHODS

BTK protein and phosphorylation levels were determined by flow cytometry in peripheral blood B cells of 29 untreated GPA patients [9 active and 20 remission GPA patients (10 ANCA- and 10 ANCA+)], 9 age- and sex-matched healthy controls (HCs) and 9 untreated active RA patients. The effect of BTK blockade on in vitro B cell cytokine production, subset distribution and (auto)antibody production was determined in the same donors in peripheral blood mononuclear cell cultures.

RESULTS

BTK protein levels were significantly increased in transitional and naïve B cells of active GPA and RA patients compared with remission GPA patients and HCs. Both B cell subsets of active patients were more sensitive to B cell receptor stimulation, as BTK and phospholipase Cγ2 phosphorylation were increased in these patients. In vitro BTK blockade had profound effects on B cell cytokine production, plasma cell formation and (auto)antibody production in both GPA patients and HCs. Interestingly, the effect of BTK blockade was less pronounced in active GPA patients, possibly due to increased activation of B cells.

CONCLUSION

We show that BTK protein and phosphorylation levels are most profoundly increased in newly emerging B cells of active GPA patients compared with remission patients. BTK blockade greatly inhibits in vitro B cell effector functions in GPA patients and HCs. These promising data identify BTK as an interesting novel therapeutic target in the treatment of GPA.

Safety, Tolerability, Pharmacokinetics, Target Occupancy, and Concentration-QT Analysis of the Novel BTK Inhibitor Evobrutinib in Healthy Volunteers

Bruton's tyrosine kinase (BTK) is a key regulator of B cell receptor and Fc receptor signaling, and a rational therapeutic target for autoimmune diseases. This first‐in‐human phase I, double‐blind, placebo‐controlled trial investigated the safety, tolerability, pharmacokinetics (PK), target occupancy, and effects on QT interval of evobrutinib, a highly selective, oral inhibitor of BTK, in healthy subjects. This dose escalation trial consisted of two parts. Part 1 included 48 subjects in 6 ascending dose cohorts (25, 50, 100, 200, 350, and 500 mg) randomized to a single dose of evobrutinib or placebo. Part 2 included 36 subjects in 3 ascending dose cohorts (25, 75, and 200 mg/day) randomized to evobrutinib or placebo once daily for 14 days. Safety and tolerability, as well as PK and target occupancy (total and free BTK in peripheral blood mononuclear cells), were assessed following single and multiple dosing. PK parameters were determined by noncompartmental methods. QT interval was obtained from 12‐lead electrocardiogram recordings and corrected for heart rate by Fridericia's method (QTcF). Treatment‐emergent adverse events (TEAEs) were mostly mild, occurring in 25% of subjects after single dosing, and 48.1% after multiple dosing. There was no apparent dose relationship regarding frequency or type of TEAE among evobrutinib‐treated subjects. Absorption was rapid (time to reach maximum plasma concentration (T_max) ~ 0.5 hour), half‐life short (~ 2 hours), and PK dose‐proportional, with no accumulation or time dependency on repeat dosing. BTK occupancy was dose‐dependent, reaching maximum occupancy of > 90% within ~ 4 hours after single doses ≥ 200 mg; the effect was long‐lasting (> 50% occupancy at 96 hours with ≥ 100 mg). After multiple dosing, full BTK occupancy was achieved with 25 mg, indicating slow turnover of BTK protein in vivo. Concentration‐QTcF analyses did not show any impact of evobrutinib concentration on corrected QT (QTc). In summary, evobrutinib was well‐tolerated, showed linear and time‐independent PK, induced long‐lasting BTK inhibition, and was associated with no prolongation of QT/QTc interval in healthy subjects. Evobrutinib is, therefore, suitable for investigation in autoimmune diseases.

Enhanced Bruton's tyrosine kinase in B-cells and autoreactive IgA in patients with idiopathic pulmonary fibrosis

Rationale

Idiopathic Pulmonary Fibrosis (IPF) is thought to be triggered by repeated alveolar epithelial cell injury. Current evidence suggests that aberrant immune activation may contribute. However, the role of B-cell activation remains unclear. We determined the phenotype and activation status of B-cell subsets and evaluated the contribution of activated B-cells to the development of lung fibrosis both in humans and in mice.

Methods

B-cells in blood, mediastinal lymph node, and lung single-cell suspensions of IPF patients and healthy controls (HC) were characterized using 14-color flow cytometry. Mice were exposed to bleomycin to provoke pulmonary fibrosis.

Results

More IgA⁺ memory B-cells and plasmablasts were found in blood (n = 27) and lungs (n = 11) of IPF patients compared to HC (n = 21) and control lungs (n = 9). IPF patients had higher levels of autoreactive IgA in plasma, which correlated with an enhanced decline of forced vital capacity (p = 0.002, r = − 0.50). Bruton’s tyrosine kinase expression was higher in circulating IPF B-cells compared to HC, indicating enhanced B-cell activation. Bleomycin-exposed mice had increased pulmonary IgA⁺ germinal center and plasma cell proportions compared to control mice. The degree of lung fibrosis correlated with pulmonary germinal center B-cell proportions (p = 0.010, r = 0.88).

Conclusion

Our study demonstrates that IPF patients have more circulating activated B-cells and autoreactive IgA, which correlate with disease progression. These B-cell alterations were also observed in the widely used mouse model of experimental pulmonary fibrosis. Autoreactive IgA could be useful as a biomarker for disease progression in IPF.

Drosophila Bruton's Tyrosine Kinase Regulates Habituation Latency and Facilitation in Distinct Mushroom Body Neurons

Habituation is the adaptive behavioral outcome of processes engaged in timely devaluation of non-reinforced repetitive stimuli, but the neuronal circuits and molecular mechanisms that underlie them are not well understood. To gain insights into these processes we developed and characterized a habituation assay to repetitive footshocks in mixed sex Drosophila groups and demonstrated that acute neurotransmission from adult α/β mushroom body (MB) neurons prevents premature stimulus devaluation. Herein we demonstrate that activity of the non-receptor tyrosine kinase dBtk protein is required within these neurons to prevent premature habituation. Significantly, we also demonstrate that the complementary process of timely habituation to the repetitive stimulation is facilitated by α'/β' MB neurons and also requires dBtk activity. Hence our results provide initial insights into molecular mechanisms engaged in footshock habituation within distinct MB neurons. Importantly, dBtk attenuation specifically within α'/β' neurons leads to defective habituation, which is readily reversible by administration of the antipsychotics clozapine and risperidone suggesting that the loss of the kinase may dysregulate monoamine receptors within these neurons, whose activity underlies the failure to habituate.SIGNIFICANCE STATEMENT Habituation refers to processes underlying decisions to attend or ignore stimuli, which are pivotal to brain function as they underlie selective attention and learning, but the circuits involved and the molecular mechanisms engaged by the process therein are poorly understood. We demonstrate that habituation to repetitive footshock involves two phases mediated by distinct neurons of the Drosophila mushroom bodies and require the function of the dBtk non-receptor tyrosine kinase. Moreover, habituation failure upon dBtk abrogation in neurons where it is required to facilitate the process is readily reversible by antipsychotics, providing conceptual links to particular symptoms of schizophrenia in humans, also characterized by habituation defects and ameliorated by these pharmaceuticals.

Tyrosine Kinases in Autoimmune and Inflammatory Skin Diseases

Tyrosine kinases relay signals from diverse leukocyte antigen receptors, innate immune receptors, and cytokine receptors, and therefore mediate the recruitment and activation of various leukocyte populations. Non-receptor tyrosine kinases of the Jak, Src, Syk, and Btk families play major roles in various immune-mediated disorders, and small-molecule tyrosine kinase inhibitors are emerging novel therapeutics in a number of those diseases. Autoimmune and inflammatory skin diseases represent a broad spectrum of immune-mediated diseases. Genetic and pharmacological studies in humans and mice support the role of tyrosine kinases in several inflammatory skin diseases. Atopic dermatitis and psoriasis are characterized by an inflammatory microenvironment which activates cytokine receptors coupled to the Jak-Stat signaling pathway. Jak kinases are also implicated in alopecia areata and vitiligo, skin disorders mediated by cytotoxic T lymphocytes. Genetic studies indicate a critical role for Src-family kinases and Syk in animal models of autoantibody-mediated blistering skin diseases. Here, we review the various tyrosine kinase signaling pathways and their role in various autoimmune and inflammatory skin diseases. Special emphasis will be placed on identification of potential therapeutic targets, as well as on ongoing preclinical and clinical studies for the treatment of inflammatory skin diseases by small-molecule tyrosine kinase inhibitors.

Pemphigus: Current and Future Therapeutic Strategies

Pemphigus encompasses a heterogeneous group of autoimmune blistering diseases, which affect both mucous membranes and the skin. The disease usually runs a chronic-relapsing course, with a potentially devastating impact on the patients' quality of life. Pemphigus pathogenesis is related to IgG autoantibodies targeting various adhesion molecules in the epidermis, including desmoglein (Dsg) 1 and 3, major components of desmosomes. The pathogenic relevance of such autoantibodies has been largely demonstrated experimentally. IgG autoantibody binding to Dsg results in loss of epidermal keratinocyte adhesion, a phenomenon referred to as acantholysis. This in turn causes intra-epidermal blistering and the clinical appearance of flaccid blisters and erosions at involved sites. Since the advent of glucocorticoids, the overall prognosis of pemphigus has largely improved. However, mortality persists elevated, since long-term use of high dose corticosteroids and adjuvant steroid-sparing immunosuppressants portend a high risk of serious adverse events, especially infections. Recently, rituximab, a chimeric anti CD20 monoclonal antibody which induces B-cell depletion, has been shown to improve patients' survival, as early rituximab use results in higher disease remission rates, long term clinical response and faster prednisone tapering compared to conventional immunosuppressive therapies, leading to its approval as a first line therapy in pemphigus. Other anti B-cell therapies targeting B-cell receptor or downstream molecules are currently tried in clinical studies. More intriguingly, a preliminary study in a preclinical mouse model of pemphigus has shown promise regarding future therapeutic application of Chimeric Autoantibody Receptor T-cells engineered using Dsg domains to selectively target autoreactive B-cells. Conversely, previous studies from our group have demonstrated that B-cell depletion in pemphigus resulted in secondary impairment of T-cell function; this may account for the observed long-term remission following B-cell recovery in rituximab treated patients. Likewise, our data support the critical role of Dsg-specific T-cell clones in orchestrating the inflammatory response and B-cell activation in pemphigus. Monitoring autoreactive T-cells in patients may indeed provide further information on the role of these cells, and would be the starting point for designating therapies aimed at restoring the lost immune tolerance against Dsg. The present review focuses on current advances, unmet challenges and future perspectives of pemphigus management.

Noncovalent inhibitors reveal BTK gatekeeper and auto-inhibitory residues that control its transforming activity

Inhibition of Bruton tyrosine kinase (BTK) is a breakthrough therapy for certain B cell lymphomas and B cell chronic lymphatic leukemia. Covalent BTK inhibitors (e.g., ibrutinib) bind to cysteine C481, and mutations of this residue confer clinical resistance. This has led to the development of noncovalent BTK inhibitors that do not require binding to cysteine C481. These new compounds are now entering clinical trials. In a systematic BTK mutagenesis screen, we identify residues that are critical for the activity of noncovalent inhibitors. These include a gatekeeper residue (T474) and mutations in the kinase domain. Strikingly, co-occurrence of gatekeeper and kinase domain lesions (L512M, E513G, F517L, L547P) in cis results in a 10- to 15-fold gain of BTK kinase activity and de novo transforming potential in vitro and in vivo. Computational BTK structure analyses reveal how these lesions disrupt an intramolecular mechanism that attenuates BTK activation. Our findings anticipate clinical resistance mechanisms to a new class of noncovalent BTK inhibitors and reveal intramolecular mechanisms that constrain BTK's transforming potential.

Aminopyrazole Carboxamide Bruton's Tyrosine Kinase Inhibitors. Irreversible to Reversible Covalent Reactive Group Tuning

Potent covalent inhibitors of Bruton's tyrosine kinase (BTK) based on an aminopyrazole carboxamide scaffold have been identified. Compared to acrylamide-based covalent reactive groups leading to irreversible protein adducts, cyanamide-based reversible-covalent inhibitors provided the highest combined BTK potency and EGFR selectivity. The cyanamide covalent mechanism with BTK was confirmed through enzyme kinetic, NMR, MS, and X-ray crystallographic studies. The lead cyanamide-based inhibitors demonstrated excellent kinome selectivity and rat pharmacokinetic properties.