The gene involved in X-linked agammaglobulinaemia is a member of the src family of protein-tyrosine kinases

Orally effective FDA-approved protein kinase targeted covalent inhibitors (TCIs)

Because dysregulation of protein kinases owing to mutations or overexpression plays causal roles in human diseases, this family of enzymes has become one of the most important drug targets of the 21st century. Of the 62 protein kinases inhibitors that are approved by the FDA, seven of them form irreversible covalent adducts with their target enzymes. The clinical success of ibrutinib, an inhibitor of Bruton tyrosine kinase, in the treatment of mantle cell lymphomas following its approval in 2013 helped to overcome a general bias against the development of irreversible drug inhibitors. The other approved covalent drugs include acalabrutinib and zanubrutinib, which also inhibit Bruton tyrosine kinase. Furthermore afatinib, dacomitinib, and osimertinib, inhibitors of members of the epidermal growth factor receptor family (ErbB1/2/3/4), are used in the treatment of non-small cell lung cancers. Neratinib is an inhibitor of ErbB2 and is used in the treatment of ErbB2/HER2-positive breast cancer. The seven drugs considered in this review have a common mechanism of action; this process involves the addition of a protein cysteine thiolate anion (protein‒S:^-) to an acrylamide derivative (CH₂=CHC(=O)N(H)R) where R represents the pharmacophore. Such reactions are commonly referred to as Michael additions and each reaction results in the formation of a covalent bond between carbon and sulfur; the final product is a thioether. This process consists of two discrete steps; the first step involves the reversible association of the drug with its target enzyme so that a weakly electrophilic functionality, a warhead, is bound near an appropriately positioned nucleophilic cysteine. In the second step, a reaction occurs between the warhead and the target enzyme cysteine to form a covalently modified and inactive protein. For this process to work, the warhead must be appropriately juxtaposed in relationship to the cysteinyl thiolate so that the covalent addition can occur. Covalent inhibitors have emerged from the ranks of drugs to be avoided to become an emerging paradigm. Much of this recent success can be attributed to the clinical efficacy of ibrutinib as well as the other antagonists covered in this review. Moreover, the covalent inhibitor methodology is swiftly gaining acceptance as a valuable component of the medicinal chemist's toolbox and is primed to make a significant impact on the development of enzyme antagonists and receptor modulators.

PBMC-derived integration-free iPSCs line SDQLCHi039-A from a patient with X-linked agammaglobulinemia carrying a novel 9-bp in-frame deletion in BTK gene

X-linked agammaglobulinemia (XLA, OMIM #300755) is one of the most common pediatric primary immunodeficiencies characterized by failure to produce mature B lymphocytes and hypogammaglobulinemia, caused by mutation of the gene encoding Bruton's tyrosine kinase (BTK, OMIM *300300), a key regulator in B-cell development. Patientssuffering XLA are prone to recurrentbacterial infection. We established an induced pluripotent stem cells (iPSCs) line from a 3-year-5-month-old boy with XLA caused by a hemizygous in-frame 9-bp deletion in BTK (c.1530-1538delATACCTGGA, p.Y510_E513delEYLEinsE). The iPSCs was verified based on pluripotency markers, original gene mutation and demonstrated trilineage differentiation potential in vitro.

BTK gatekeeper residue variation combined with cysteine 481 substitution causes super-resistance to irreversible inhibitors acalabrutinib, ibrutinib and zanubrutinib

Irreversible inhibitors of Bruton tyrosine kinase (BTK), pioneered by ibrutinib, have become breakthrough drugs in the treatment of leukemias and lymphomas. Resistance variants (mutations) occur, but in contrast to those identified for many other tyrosine kinase inhibitors, they affect less frequently the "gatekeeper" residue in the catalytic domain. In this study we carried out variation scanning by creating 11 substitutions at the gatekeeper amino acid, threonine 474 (T474). These variants were subsequently combined with replacement of the cysteine 481 residue to which irreversible inhibitors, such as ibrutinib, acalabrutinib and zanubrutinib, bind. We found that certain double mutants, such as threonine 474 to isoleucine (T474I) or methionine (T474M) combined with catalytically active cysteine 481 to serine (C481S), are insensitive to ≥16-fold the pharmacological serum concentration, and therefore defined as super-resistant to irreversible inhibitors. Conversely, reversible inhibitors showed a variable pattern, from resistance to no resistance, collectively demonstrating the structural constraints for different classes of inhibitors, which may affect their clinical application.

Relevance of the Bruton Tyrosine Kinase as a Target for COVID-19 Therapy

The outbreak of the novel coronavirus disease 2019 (COVID-19) has emerged as one of the biggest global health threats worldwide. As of October 2020, more than 44 million confirmed cases and more than 1,160,000 deaths have been reported globally, and the toll is likely to be much higher before the pandemic is over. There are currently little therapeutic options available and new potential targets are intensively investigated. Recently, Bruton tyrosine kinase (BTK) has emerged as an interesting candidate. Elevated levels of BTK activity have been reported in blood monocytes from patients with severe COVID-19, compared with those from healthy volunteers. Importantly, various studies confirmed empirically that administration of BTK inhibitors (acalabrutinib and ibrutinib) decreased the duration of mechanical ventilation and mortality rate for hospitalized patients with severe COVID-19. Herein, we review the current information regarding the role of BTK in severe acute respiratory syndrome coronavirus 2 infections and the suitability of its inhibitors as drugs to treat COVID-19. The use of BTK inhibitors in the management of COVID-19 shows promise in reducing the severity of the immune response to the infection and thus mortality. However, BTK inhibition may be contributing in other ways to inhibit the effects of the virus and this will need to be carefully studied.

Increased antiviral response in circulating lymphocytes from hypogammaglobulinemia patients

BACKGROUND

B cells play a crucial role during rhinovirus (RV) infections by production of virus-neutralizing antibodies. A main feature of common variable immunodeficiency (CVID) is hypogammaglobulinemia (HG). HG patients have severely reduced levels of antibody-producing B cells and suffer from prolonged virus infections. Here, we addressed whether antiviral response of peripheral blood lymphocytes differs between HG patients and healthy individuals during natural RV infection.

METHODS

Using fluorescence-activated cell sorting, B-cell subsets were analyzed. Simultaneously, CD19 + B cells, CD14 + monocytes, and CD3 + T cells were sorted from frozen peripheral blood mononuclear cells from 11 RV-infected hypogammaglobulinemia patients, 7 RV-infected control subjects, and 14 noninfected control subjects. Real-time PCR was used to study expression of antiviral genes. A pan-RV PCR was used to detect RV genome in all samples.

RESULTS

In HG patients, total B-cell numbers, as well as IgA + and IgG + switched memory B cells, were reduced while naïve B cells and T cells were increased. STAT1 expression was increased in HG patients compared to controls in all lymphocyte subsets analyzed. The expression of antiviral genes IFITM1 and MX1 correlated with STAT1 expression in B cells and monocytes. RV RNA was found in 88.9% of monocytes from infected HG patients, 85.7% of monocytes from infected controls, and 7.1% of monocytes from uninfected controls.

CONCLUSIONS

We demonstrate an increased antiviral response in B cells and monocytes in HG patients and their correlation with STAT1 expression. Monocytes of infected HG patients and infected non-HG controls carry RV RNA.

Burton's Agammaglobulinemia and COVID-19

During the SARS-CoV-2 global pandemic, many patients who have co-morbid conditions are considered high risk for morbidity and mortality; however, those who are immunodeficient are at higher risk of becoming seriously ill. In this article, we present a 26-year old male with a history of X-linked agammaglobulinemia who presented to the hospital with fever and chills after exposure to a SARS-CoV-2 positive individual. The patient had a prolonged course in the hospital, but his symptoms improved quickly after receiving convalescent plasma. This case highlights the clinical course of a patient with severe immunoglobulin deficiency and a possible treatment approach for patients with concomitant agammaglobulinemia and COVID-19.

Influenza-specific IgG1+ memory B-cell numbers increase upon booster vaccination in healthy adults but not in patients with predominantly antibody deficiency

Background

Annual influenza vaccination is recommended to all individuals over 6 months of age, including predominantly antibody deficiency (PAD) patients. Vaccination responses are typically evaluated by serology, and because PAD patients are by definition impaired in generating IgG and receive immunoglobulin replacement therapy (IgRT), it remains unclear whether they can mount an antigen-specific response.

Objective

To quantify and characterise the antigen-specific memory B (Bmem) cell compartment in healthy controls and PAD patients following an influenza booster vaccination.

Methods

Recombinant hemagglutinin (HA) from the A/Michigan/2015 H1N1 (AM15) strain with an AviTag was generated in a mammalian cell line, and following targeted biotinylation, was tetramerised with BUV395 or BUV737 streptavidin conjugates. Multicolour flow cytometry was applied on blood samples before and 28 days after booster influenza vaccination in 16 healthy controls and five PAD patients with circulating Bmem cells.

Results

Recombinant HA tetramers were specifically recognised by 0.5-1% of B cells in previously vaccinated healthy adults. HA-specific Bmem cell numbers were significantly increased following booster vaccination and predominantly expressed IgG1. Similarly, PAD patients carried HA-specific Bmem cells, predominantly expressing IgG1. However, these numbers were lower than in controls and did not increase following booster vaccination.

Conclusion

We have successfully identified AM15-specific Bmem cells in healthy controls and PAD patients. The presence of antigen-specific Bmem cells could offer an additional diagnostic tool to aid in the clinical diagnosis of PAD. Furthermore, alterations in the number or immunophenotype of HA-specific Bmem cells post-booster vaccination could assist in the evaluation of immune responses in individuals receiving IgRT.

B cell signalling pathways-New targets for precision medicine in chronic lymphocytic leukaemia

The B cell receptor (BCR) is a master regulator of B cells, controlling cellular processes such as proliferation, migration and survival. Cell signalling downstream of the BCR is aberrantly activated in the B cell malignancy chronic lymphocytic leukaemia (CLL), supporting the pathophysiology of the disease. This insight has led to development and approval of small molecule inhibitors that target components of the BCR pathway. These advances have greatly improved the management of CLL, but the disease remains incurable. This may partly be explained by the inter-patient heterogeneity of the disease, also when it comes to treatment responses. Precision medicine is therefore required to optimize treatment and move towards a cure. Here, we discuss how the introduction of BCR signalling inhibitors has facilitated the development of functional in vitro assays to guide clinical treatment decisions on use of the same therapeutic agents in individual patients. The cellular responses to these agents can be analysed in high-throughput assays such as dynamic BH3 profiling, phospho flow experiments and drug sensitivity screens to identify predictive biomarkers. This progress exemplifies the positive synergy between basal and translational research needed to optimize patient care.

Discovery and Evaluation of Pyrazolo[3,4-d]pyridazinone as a Potent and Orally Active Irreversible BTK Inhibitor

The identification and lead optimization of a series of pyrazolo[3,4-d]pyridazinone derivatives are described as a novel class of potent irreversible BTK inhibitors, resulting in the discovery of compound 8. Compound 8 exhibited high potency against BTK kinase and acceptable PK profile. Furthermore, compound 8 demonstrated significant in vivo efficacy in a mouse-collagen-induced arthritis (CIA) model.

Inhibition of Bruton tyrosine kinase by acalabrutinib dampens lipopolysaccharide/galactosamine-induced hepatic damage

Bruton tyrosine kinase (BTK) sits at the crossroads of adaptive and innate immunities. Nevertheless, the detailed role of BTK activation in hepatic inflammatory disorders is still elusive to date. Accordingly, we investigated the impact of blocking BTK activation by acalabrutinib (ACB) on lipopolysaccharide/galactosamine (LPS/D-GaIN)-induced deleterious manifestations in the liver. This was achieved by pretreating mice with ACB (6, 12 or 24 mg/kg, oral) 2 h before challenge with LPS/D-GaIN (70 μg/kg and 700 mg/kg, respectively, i.p.) for 6 h. The results showed that ACB (6 and 12 mg/kg) (i) curbed LPS/D-GaIN-induced rise in biochemical (serum ALT, AST and LDH) and histological (necrosis, degeneration and congestion scores) indices of hepatocellular injury; (ii) attenuated LPS/D-GaIN-induced elevation in parameters of hepatocellular apoptosis (cleaved caspase 3) and proliferation (PCNA); and (iii) importantly, mitigated LPS/D-GaIN-induced recruitment and infiltration of the inflammatory cells to the liver evidenced by lowering elevated serum MCP-1 concentration and hepatic F4/80 immunostaining. These effects were linked to ACB dose-dependent inhibition of NF-κB nuclear translocation that subsequently reduced LPS/D-GaIN-mediated release of TNF-α, IL-1β and IL-22 in the blood circulation. However, a dose of 12 mg/kg of ACB elevated the hepatic TNF-α, IL-1β and IL-22 concentrations that arose from a compensatory activation of ERK and JNK. Inhibition of BTK also attenuated LPS/D-GaIN-induced overexpression of CD98, which is another contributor alongside cytokines for monocyte recruitment. Therapeutically, targeting BTK by ACB is an efficient approach for hitting multiple points with one agent that can dampen hepatocellular injury, death, immune cell recruitment and inflammation cascade.

Helicobacter cinaedi-Associated Refractory Cellulitis in Patients with X-Linked Agammaglobulinemia

X-linked agammaglobulinemia (XLA) is characterized by severe or recurrent infections, hypogammaglobulinemia, and circulating B cell deficiency. The frequent pathogens seen in patients with XLA include Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, and enterovirus as well as Campylobacter and Helicobacter species. Here, we describe two patients with XLA who developed cellulitis and bacteremia caused by Helicobacter cinaedi even when administered an appropriate immunoglobulin replacement therapy. H. cinaedi may be difficult to isolate using a conventional blood culture system and could be identified by sequence analysis and mass spectrometry. H. cinaedi infection causes recurrent symptoms frequently, and patients require a long course of antibiotic treatment. Recently, the case of non-H. pylori Helicobacter (NHPH) infection such as H. cinaedi and H. bilis infection is increasing in number in patients with XLA. Systemic NHPH infection should be suspected, and extensive microbiological analysis should be performed to appropriately treat patients with XLA who present with fever and skin lesions.

Novel deletion mutation in Bruton’s tyrosine kinase results in X-linked agammaglobulinemia: A case report

BACKGROUND

X-linked agammaglobulinemia is a primary immunodeficiency disease caused by gene mutations of Bruton’s tyrosine kinase (BTK). We found a new mutation point and summarized the correlation analysis and performed a literature review.

CASE SUMMARY

The proband was a 5-year-old boy. He was admitted to our hospital due to a recurrent cough and a fever that had persisted for a month. He had a history of multiple respiratory infections and sinusitis. There was no immunodeficiency or recurrent infection history among his family members. Agammaglobulinemia was characterized as follows: Immunoglobulin (Ig) A, 90.0 mg/dL (90-450 mg/dL); IgG, 20.0 mg/dL (800-1800 mg/dL); and IgM, 18.0 mg/dL (60-280 mg/dL). Notably, the assessment of IgG subtypes revealed the following very low levels: Subtype 1, 0.26 g/L (3.62-12.28 g/L); subtype 2, 0.10 g/L (0.57-2.9 g/L); subtype 3, 0.009 g/L (0.129-0.789 g/L); and subtype 4, 0.003 g/L (0.013-1.446 g/L). Cellular immunological test results were as follows: CD3, 74.6% (50%-84.0%); CD4, 47.3% (27.0%-51.0%); and CD8, 24.9% (15.0%-44.0%). A de novo hemizygous deletion in BTK was detected: c.902_c.904delAAG/p.E301del. Transcript levels of the mutant BTK were similar to those of the wild-type gene, though overexpression resulted in markedly reduced levels of mutant BTK (9.49% ± 1.58%), relative to the wild-type BTK (75.8% ± 2.98%, P < 0.01).

CONCLUSION

This case of X-linked agammaglobulinemia was attributed to a de novo hemizygous deletion mutation in BTK (c.902_c.904delAAG/p.E301del). The mutation resulted in markedly reduced BTK protein stability in vitro.

Discovery of BIIB068: A Selective, Potent, Reversible Bruton's Tyrosine Kinase Inhibitor as an Orally Efficacious Agent for Autoimmune Diseases

Autoreactive B cell-derived antibodies form immune complexes that likely play a pathogenic role in autoimmune diseases. In systemic lupus erythematosus (SLE), these antibodies bind Fc receptors on myeloid cells and induce proinflammatory cytokine production by monocytes and NETosis by neutrophils. Bruton's tyrosine kinase (BTK) is a non-receptor tyrosine kinase that signals downstream of Fc receptors and plays a transduction role in antibody expression following B cell activation. Given the roles of BTK in both the production and sensing of autoreactive antibodies, inhibitors of BTK kinase activity may provide therapeutic value to patients suffering from autoantibody-driven immune disorders. Starting from an in-house proprietary screening hit followed by structure-based rational design, we have identified a potent, reversible BTK inhibitor, BIIB068 (1), which demonstrated good kinome selectivity with good overall drug-like properties for oral dosing, was well tolerated across preclinical species at pharmacologically relevant doses with good ADME properties, and achieved >90% inhibition of BTK phosphorylation (pBTK) in humans.

An update on X-Linked agammaglobulinaemia: clinical manifestations and management

PURPOSE OF REVIEW

X-linked agammaglobulinaemia (XLA) is a congenital defect of development of B lymphocytes leading to agammaglobulinaemia. It was one of the first primary immunodeficiencies described, but treatment has remained relatively unchanged over the last 60 years. This summary aims to outline the current outcomes, treatments and future research areas for XLA.

RECENT FINDINGS

Immunoglobulin therapy lacks IgA and IgM, placing patients at theoretical risk of experiencing recurrent respiratory tract infections and developing bronchiectasis despite best current therapy. Recent cohort studies from Italy and the USA conform that bronchiectasis remains a major burden for this group despite best current efforts. However, gene therapy offers a potential cure for these patients with proven proof of concept murine models.

SUMMARY

The potential limitations of current immunoglobulin therapy appear to be confirmed by recent cohort studies, and therefore further work in the development of gene therapy is warranted. Until this is available, clinicians should strive to reduce the diagnostic delay, regularly monitor for lung disease and individualize target immunoglobulin doses to reduce infection rates for their patients.

Primary Antibody Deficiencies

Primary antibody deficiencies (PADs) are the most common types of inherited primary immunodeficiency diseases (PIDs) presenting at any age, with a broad spectrum of clinical manifestations including susceptibility to infections, autoimmunity and cancer. Antibodies are produced by B cells, and consequently, genetic defects affecting B cell development, activation, differentiation or antibody secretion can all lead to PADs. Whole exome and whole genome sequencing approaches have helped identify genetic defects that are involved in the pathogenesis of PADs. Here, we summarize the clinical manifestations, causal genes, disease mechanisms and clinical treatments of different types of PADs.

Low IgA Associated With Oropharyngeal Microbiota Changes and Lung Disease in Primary Antibody Deficiency

Common Variable Immunodeficiency (CVID) and X-linked agammaglobulinemia (XLA) are primary antibody deficiencies characterized by hypogammaglobulinemia and recurrent infections, which can lead to structural airway disease (AD) and interstitial lung disease (ILD). We investigated associations between serum IgA, oropharyngeal microbiota composition and severity of lung disease in these patients. In this cross-sectional multicentre study we analyzed oropharyngeal microbiota composition of 86 CVID patients, 12 XLA patients and 49 healthy controls (HC) using next-generation sequencing of the 16S rRNA gene. qPCR was used to estimate bacterial load. IgA was measured in serum. High resolution CT scans were scored for severity of AD and ILD. Oropharyngeal bacterial load was increased in CVID patients with low IgA (p = 0.013) and XLA (p = 0.029) compared to HC. IgA status was associated with distinct beta (between-sample) diversity (p = 0.039), enrichment of (Allo)prevotella, and more severe radiographic lung disease (p = 0.003), independently of recent antibiotic use. AD scores were positively associated with Prevotella, Alloprevotella, and Selenomonas, and ILD scores with Streptococcus and negatively with Rothia. In clinically stable patients with CVID and XLA, radiographic lung disease was associated with IgA deficiency and expansion of distinct oropharyngeal bacterial taxa. Our findings highlight IgA as a potential driver of upper respiratory tract microbiota homeostasis.

Bruton's Tyrosine Kinase Inhibitors: A New Therapeutic Target for the Treatment of SLE?

Systemic lupus erythematosus (SLE) is an autoimmune disease with a complex pathogenesis, which presents a great variability in its presentation and can affect almost all organs and systems. Multiple therapeutic targets have been discovered recently, but there also have been failed attempts to treat SLE using biologic agents. Bruton’s tyrosine kinase (BTK) is a cytoplasmic tyrosine kinase expressed in several types of cells of hematopoietic origin which participate in both innate and adaptive immunity. Ibrutinib, a BTK inhibitor, is approved for the treatment of several B cell malignancies, including some types of lymphoma and leukemia. As BTK is expressed on several immune cell types, the mechanism of action of BTK also suggests the use of BTK inhibitors in the treatment of autoimmune diseases. In this review, we will summarize what is known and what has been published so far about the treatment of mouse models of SLE and the human disease, using BTK inhibitors.

Susceptibility to infection in early life: a growing role for human genetics

The unique vulnerability to infection of newborns and young infants is generally explained by a constellation of differences between early-life immune responses and immune responses at later ages, often referred to as neonatal immune immaturity. This developmental view, corroborated by robust evidence, offers a plausible, population-level description of the pathogenesis of life-threatening infectious diseases during the early-life period, but provides little explanation on the wide inter-individual differences in susceptibility and resistance to specific infections during the first months of life. In this context, the role of individual human genetic variation is increasingly recognized. A life-threatening infection caused by an opportunistic pathogen in an otherwise healthy infant likely represents the first manifestation of an inborn error of immunity. Single-gene disorders may also underlie common infections in full-term infants with no comorbidities or in preterm infants. In addition, there is increasing evidence of a possible role for common genetic variation in the pathogenesis of infection in preterm infants. Over the past years, a unified theory of infectious diseases emerged, supporting a hypothetical, age-dependent general model of genetic architecture of human infectious diseases. We discuss here how the proposed genetic model can be reconciled with the widely accepted developmental view of early-life infections in humans.

Bruton's Tyrosine Kinase (BTK) Inhibitor (Ibrutinib)-Suppressed Migration and Invasion of Prostate Cancer

INTRODUCTION

Bruton's tyrosine kinase (BTK) inhibitors have long been known in the treatment of B-cell malignancies. Recently, BTK inhibitors have also become promising novel treatment reagents for prostate cancer. The current study was designed to investigate expression of BTK in prostate cancer tissues in comparison with benign hyperplasia and effect of BTK inhibitor on prostate cancer cell proliferation, migration and invasion.

METHODS

BTK expression was assessed by immunohistochemistry; migration and invasion prostate cancer cell lines (DU145 and PC3) were assessed by Transwell migration and wound-healing assay; cancer cell proliferation was assessed using MTT assay kit; expression of matrix metalloproteinases-2 and -9 (MMP-2 and MMP-9) was assessed by immunoblotting.

RESULTS

Strong expression of BTK was detected in the prostate cancer tissues, especially in the tumors from prostate cancer patients with bone metastasis. BTK inhibitor (Ibrutinib) significantly inhibited cell proliferation, migration and invasion of prostate cancer cells as well as protein synthesis of MMP-2 and MMP-9 by the tumor cells. Overexpressing BTK could partially but significantly block the inhibitory effect of Ibrutinib on cell proliferation, migration and invasion, and protein synthesis of MMP-2 and MMP-9 of the cancer cells.

CONCLUSION

These findings suggested that BTK could serve as not only a biomarker but also a therapeutic target for the prostate cancer and that Ibrutinib may be applied as a therapeutic drug for the prostate cancer.

Molecular and cellular mechanisms underlying defective antibody responses

Primary immune deficiency is caused by genetic mutations that result in immune dysfunction and subsequent susceptibility to infection. Over the last decade there has been a dramatic increase in the number of genetically defined causes of immune deficiency including those which affect B-cell function. This has not only identified critical nonredundant pathways that control the generation of protective antibody responses but also revealed that immunodeficiency and autoimmunity are often closely linked. Here we explore the molecular and cellular mechanisms of these rare monogenic conditions that disrupt antibody production, which also have implications for understanding the causes of more common polygenic immune dysfunction.

Genetics in community-acquired pneumonia

PURPOSE OF REVIEW

Host defense against community-acquired pneumonia depends on an intact innate and acquired immune system. This review analyses the correlation between specific defects and polymorphisms of immunity genes with susceptibility for pneumonia.

RECENT FINDINGS

Mutations in BTK, Bruton's tyrosine kinase, lead to X-linked agammaglobulinemia, a disease characterized by recurrent respiratory tract infections, including pneumonia. BTK inhibitors, which are used for treatment of leukemia, have pneumonia as side effect. Polymorphisms in B lymphocyte growth and differentiation factors, including IL-6 and IL-10, Fcg RIIa receptors, as well as genetic variants of ACE, angiotensin-converting enzyme, also are associated with increased susceptibility for pneumonia.

SUMMARY

Delineation of underlying genetic defects and polymorphisms may add in diagnosis, therapy, and prognosis of community-acquired pneumonia. In case of humoral immunodeficiency, antibody replacement therapy may be indicated.

Long-term follow-up of 168 patients with X-linked agammaglobulinemia reveals increased morbidity and mortality

BACKGROUND

X-linked agammaglobulinemia (XLA) is the prototype of primary humoral immunodeficiencies. Long-term follow-up studies regarding disease-related complications and outcome are scarce.

OBJECTIVE

Our aim was to describe the natural history of XLA.

METHODS

A nationwide multicenter study based on the Italian Primary Immunodeficiency Network registry was established in 2000 in Italy. Affected patients were enrolled by documenting centers, and the patients' laboratory, clinical, and imaging data were recorded on an annual base.

RESULTS

Data on the patients (N = 168) were derived from a cumulative follow-up of 1370 patient-years, with a mean follow-up of 8.35 years per patient. The mean age at diagnosis decreased after establishment of the Italian Primary Immunodeficiency Network registry (84 months before vs 23 months after). Respiratory, skin, and gastrointestinal manifestations were the most frequent clinical symptoms at diagnosis and during long-term follow-up. Regular immunoglobulin replacement treatment reduced the incidence of invasive infections. Affected patients developed chronic lung disease over time (47% after 40 years of follow-up) in the presence of chronic sinusitis (84%). Malignancies were documented in a minority of cases (3.7%). Overall survival for affected patients was significantly reduced when compared with that for the healthy male Italian population, and it further deteriorated in the presence of chronic lung disease.

CONCLUSIONS

This is the first detailed long-term follow-up study for patients with XLA, revealing that although immunoglobulin replacement treatment reduces the incidence of invasive infections, it does not appear to influence the development of chronic lung disease. The overall survival of affected patients is reduced. Further studies are warranted to improve patients' clinical management and increase awareness among physicians.

North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition Position Paper on the Evaluation and Management for Patients With Very Early-onset Inflammatory Bowel Disease

The rate of pediatric inflammatory bowel disease (IBD) has been increasing over the last decade and this increase has occurred most rapidly in the youngest children diagnosed <6 years, known as very early-onset inflammatory bowel disease (VEO-IBD). These children can present with more extensive and severe disease than older children and adults. The contribution of host genetics in this population is underscored by the young age of onset and the distinct, aggressive phenotype. In fact, monogenic defects, often involving primary immunodeficiency genes, have been identified in children with VEO-IBD and have led to targeted and life-saving therapy. This position paper will discuss the phenotype of VEO-IBD and outline the approach and evaluation for these children and what factors should trigger concern for an underlying immunodeficiency. We will then review the immunological assays and genetic studies that can facilitate the identification of the underlying diagnosis in patients with VEO-IBD and how this evaluation may lead to directed therapies. The position paper will also aid the pediatric gastroenterologist in recognizing when a patient should be referred to a center specializing in the care of these patients. These guidelines are intended for pediatricians, allied health professionals caring for children, pediatric gastroenterologists, pediatric pathologists, and immunologists.

Uncovering Low-Level Maternal Gonosomal Mosaicism in X-Linked Agammaglobulinemia: Implications for Genetic Counseling

X-linked agammaglobulinemia (XLA) is a clinically and genetically well-defined immunodeficiency and the most common form of agammaglobulinemia. It is characterized by susceptibility to recurrent bacterial infections, profound hypogammaglobulinemia, and few or no circulating B cells. XLA is caused by mutations in the BTK gene, which encodes Bruton's tyrosine kinase (BTK). Because of its X-linked recessive inheritance pattern, XLA virtually only affects males, and the mother is the carrier of the mutation in 80–85% of the males with this condition. In the remaining 15–20% of the cases, the affected male is considered to have a de novo mutation. Here, we present the case of a child with a diagnosis of XLA caused by a missense mutation in the BTK gene (c.494G>A/p.C165Y). Apparently, his mother was wild type for this gene, which implied that the mutation was de novo, but careful analysis of Sanger electropherograms and the use of high-coverage massive parallel sequencing revealed low-level maternal gonosomal mosaicism. The mutation was detected in various samples from the mother (blood, urine, buccal swab, and vaginal swab) at a low frequency of 2–5%, and the status of the patient's mutation changed from de novo to inherited. This study underscores the importance of accurately establishing the parents' status on detection of an apparently de novo mutation in a patient, as inadvertent low-level mosaicism may lead to misinterpretation of the risk of recurrence, vital for genetic counseling.

A non-covalent inhibitor XMU-MP-3 overrides ibrutinib-resistant BtkC481S mutation in B-cell malignancies

BACKGROUND AND PURPOSE

Bruton's tyrosine kinase (BTK) plays a key role in B-cell receptor signalling by regulating cell proliferation and survival in various B-cell malignancies. Covalent low-MW BTK kinase inhibitors have shown impressive clinical efficacy in B-cell malignancies. However, the mutant BtkC481S poses a major challenge in the management of B-cell malignancies by disrupting the formation of the covalent bond between BTK and irreversible inhibitors, such as ibrutinib. The present studies were designed to develop novel BTK inhibitors targeting ibrutinib-resistant BtkC481S mutation.

EXPERIMENTAL APPROACH

BTK-Ba/F3, BTK(C481S)-Ba/F3 cells, and human malignant B-cells JeKo-1, Ramos, and NALM-6 were used to evaluate cellular potency of BTK inhibitors. The in vitro pharmacological efficacy and compound selectivity were assayed via cell viability, colony formation, and BTK-mediated signalling. A tumour xenograft model with BTK-Ba/F3, Ramos and BTK(C481S)-Ba/F3 cells in Nu/nu BALB/c mice was used to assess in vivo efficacy of XMU-MP-3.

KEY RESULTS

XMU-MP-3 is one of a group of low MW compounds that are potent non-covalent BTK inhibitors. XMU-MP-3 inhibited both BTK and the acquired mutant BTKC481S, in vitro and in vivo. Further computational modelling, site-directed mutagenesis analysis, and structure-activity relationships studies indicated that XMU-MP-3 displayed a typical Type-II inhibitor binding mode.

CONCLUSION AND IMPLICATIONS

XMU-MP-3 directly targets the BTK signalling pathway in B-cell lymphoma. These findings establish XMU-MP-3 as a novel inhibitor of BTK, which could serve as both a tool compound and a lead for further drug development in BTK relevant B-cell malignancies, especially those with the acquired ibrutinib-resistant C481S mutation.

Predominantly Antibody-Deficient Patients With Non-infectious Complications Have Reduced Naive B, Treg, Th17, and Tfh17 Cells

Background: Patients with predominantly antibody deficiency (PAD) suffer from severe and recurrent infections that require lifelong immunoglobulin replacement and prophylactic antibiotic treatment. Disease incidence is estimated to be 1:25,000 worldwide, and up to 68% of patients develop non-infectious complications (NIC) including autoimmunity, which are difficult to treat, causing high morbidity, and early mortality. Currently, the etiology of NIC is unknown, and there are no diagnostic and prognostic markers to identify patients at risk.

Objectives: To identify immune cell markers that associate with NIC in PAD patients.

Methods: We developed a standardized 11-color flow cytometry panel that was utilized for in-depth analysis of B and T cells in 62 adult PAD patients and 59 age-matched controls.

Results: Nine males had mutations in Bruton's tyrosine kinase (BTK) and were defined as having X-linked agammaglobulinemia. The remaining 53 patients were not genetically defined and were clinically diagnosed with agammaglobulinemia (n = 1), common variable immunodeficiency (CVID) (n = 32), hypogammaglobulinemia (n = 13), IgG subclass deficiency (n = 1), and specific polysaccharide antibody deficiency (n = 6). Of the 53, 30 (57%) had one or more NICs, 24 patients had reduced B-cell numbers, and 17 had reduced T-cell numbers. Both PAD–NIC and PAD+NIC groups had significantly reduced Ig class-switched memory B cells and naive CD4 and CD8 T-cell numbers. Naive and IgM memory B cells, Treg, Th17, and Tfh17 cells were specifically reduced in the PAD+NIC group. CD21^lo B cells and Tfh cells were increased in frequencies, but not in absolute numbers in PAD+NIC.

Conclusion: The previously reported increased frequencies of CD21^lo B cells and Tfh cells are the indirect result of reduced naive B-cell and T-cell numbers. Hence, correct interpretation of immunophenotyping of immunodeficiencies is critically dependent on absolute cell counts. Finally, the defects in naive B- and T-cell numbers suggest a mild combined immunodeficiency in PAD patients with NIC. Together with the reductions in Th17, Treg, and Tfh17 numbers, these key differences could be utilized as biomarkers to support definitive diagnosis and to predict for disease progression.

Acute primary purulent pericarditis in an adult patient with unknown X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is a rare form of inherited immunodeficiency due to an impairment in B-lymphocyte differentiation and maturation. In the majority of cases XLA is diagnosed in childhood, particularly among males affected by recurrent infections and with a family history of immunodeficiency. Infections of respiratory tract, gastrointestinal apparatus, eyes, nose and ears are frequent in XLA patients; on the contrary, infections of myocardium, cardiac valves and pericardium are rarely described in XLA. A 34-year-old man with unknown XLA was hospitalized because of syncope, due to pericardial tamponade, caused by acute primary purulent pericarditis. Immediate pericardiocentesis was effective in improving hemodynamics, and empiric antibiotic therapy was successful in controlling the infection. Purulent pericarditis is a rare disease with high mortality rate: it is usually caused by hematogenous bacterial propagation, direct infection of pericardial space by chest wounds or thoracic surgery, or extension of infection from adjacent tissues. However, this patient had no recent local or systemic infections. Because of unusual clinical picture during hospitalization he underwent further clinical and laboratory evaluations, that showed low immunoglobulin levels. After exclusion of acquired immunodeficiency, genetic tests were performed: they detected deletion of exons 8-9-10 of Bruton Tyrosine Kinase gene on X chromosome, leading to the diagnosis of XLA. Acute purulent primary pericarditis may also occur in adult XLA patients as first clinical manifestation. According to this case report, a primary immunodeficiency syndrome should be considered in patients with atypical cardiac infections and no predisposing conditions, regardless of age.

Fluorescence anisotropy imaging in drug discovery

Non-invasive measurement of drug-target engagement can provide critical insights in the molecular pharmacology of small molecule drugs. Fluorescence polarization/fluorescence anisotropy measurements are commonly employed in protein/cell screening assays. However, the expansion of such measurements to the in vivo setting has proven difficult until recently. With the advent of high-resolution fluorescence anisotropy microscopy it is now possible to perform kinetic measurements of intracellular drug distribution and target engagement in commonly used mouse models. In this review we discuss the background, current advances and future perspectives in intravital fluorescence anisotropy measurements to derive pharmacokinetic and pharmacodynamic measurements in single cells and whole organs.

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.

Serious Infections in Patients Receiving Ibrutinib for Treatment of Lymphoid Cancer

Background

Ibrutinib is a Bruton tyrosine kinase inhibitor that is used for the treatment of lymphoid cancers, including chronic lymphocytic leukemia, Waldenström macroglobulinemia, and mantle cell lymphoma. Several case series have described opportunistic infections among ibrutinib recipients, but the full extent of these infections is unknown. We sought to determine the spectrum of serious infections associated with ibrutinib treatment.

Methods

We reviewed the electronic medical records of patients with lymphoid cancer at Memorial Sloan Kettering Cancer Center who received ibrutinib during a 5-year period from 1 January 2012 to 31 December 2016. Serious infections were identified by review of the relevant microbiology, clinical laboratory, and radiology data. Risk factors for infection were determined by means of univariate and multivariate analyses.

Results

We analyzed findings in 378 patients with lymphoid cancer who received ibrutinib. The most common underlying cancers were chronic lymphocytic leukemia and mantle cell lymphoma. 84% of patients received ibrutinib as monotherapy. Serious infection developed in 43 patients (11.4%), primarily during the first year of ibrutinib treatment. Invasive bacterial infections developed in 23 (53.5%) of these patients, and invasive fungal infections (IFIs) in 16 (37.2%) .The majority of patients with IFIs during ibrutinib therapy (62.5%) lacked classic clinical risk factors for fungal infection (ie, neutropenia, lymphopenia, and receipt of corticosteroids). Infection resulted in death in 6 of the 43 patients (14%).

Conclusions

Patients with lymphoid cancer receiving ibrutinib treatment are at risk for serious infections, including IFIs.

Lipid-targeting pleckstrin homology domain turns its autoinhibitory face toward the TEC kinases

Bruton’s tyrosine kinase (BTK) is targeted in treatment of immune cancers. As patients experience drug resistance, there is a need for alternative approaches to inhibit BTK. Other recently published findings clarify the role of the BTK pleckstrin homology (PH) domain in mediating activation via dimerization and sensing of ligand concentration at the membrane. Work presented here provides insight into the autoinhibitory BTK structure that has so far been elusive via crystallographic methods. In the resting state, the BTK PH domain binds to the activation loop face of the kinase domain and allosterically alters key sites within the kinase domain. The findings define a new regulatory site, the PH/kinase interface, that can be exploited in drug discovery efforts.

The pleckstrin homology (PH) domain is well known for its phospholipid targeting function. The PH-TEC homology (PHTH) domain within the TEC family of tyrosine kinases is also a crucial component of the autoinhibitory apparatus. The autoinhibitory surface on the PHTH domain has been previously defined, and biochemical investigations have shown that PHTH-mediated inhibition is mutually exclusive with phosphatidylinositol binding. Here we use hydrogen/deuterium exchange mass spectrometry, nuclear magnetic resonance (NMR), and evolutionary sequence comparisons to map where and how the PHTH domain affects the Bruton’s tyrosine kinase (BTK) domain. The data map a PHTH-binding site on the activation loop face of the kinase C lobe, suggesting that the PHTH domain masks the activation loop and the substrate-docking site. Moreover, localized NMR spectral changes are observed for non–surface-exposed residues in the active site and on the distal side of the kinase domain. These data suggest that the association of PHTH induces allosteric conformational shifts in regions of the kinase domain that are critical for catalysis. Through statistical comparisons of diverse tyrosine kinase sequences, we identify residues unique to BTK that coincide with the experimentally determined PHTH-binding surface on the kinase domain. Our data provide a more complete picture of the autoinhibitory conformation adopted by full-length TEC kinases, creating opportunities to target the regulatory domains to control the function of these kinases in a biological setting.

Effects of BTK signalling in pathogenic microorganism infections

As a cytoplasmic protein tyrosine kinase, Bruton's tyrosine kinase (Btk) is widely considered as a vital kinase in many aspects of different physiologic processes. It is engaged in many important signalling pathways related to the immune response, such as the B cell receptor pathway, pattern-recognition receptor pathway, and triggering receptor expressed on myeloid cell pathway. Recent studies have increasingly focused on the important role of Btk in various inflammatory diseases, which are related to Btk expression in myeloid innate immune cells, such as macrophages, dendritic cells and neutrophils. Although some investigations have explored the role of Btk in microbial infections, many aspects remain elusive, and some of the results are opposite and controversial. Considering the complicated and multiple roles of Btk in the immune system, we summarized the engagement of Btk signalling in various pathogenic microorganism infections, the possible mechanisms involved and its therapeutic potential in the control of infectious diseases.

Are We Ready to Treat Diffuse Large B-cell and High-Grade Lymphoma According to Major Genetic Subtypes?

Diffuse Large B-Cell Lymphoma (DLBCL) is a clinically and biologically heterogeneous disease. The revised Classification of Lymphoproliferative diseases published in 2016 (WHO, 2016) refined the previous DLBLC subtypes and identified four categories: DLBCL not otherwise specified (NOS), other lymphomas of large B cells, high grade B-cell lymphoma, and B-cell lymphoma unclassifiable. High grade B-cell lymphomas include the entities carrying MYC, BCL2 and/or BCL6 translocations or cases with blastoid morphology without DH translocations. This classification also acknowledges the cell of origin (COO) classification, that has only a limited impact on the choice of frontline treatment for DLBCL, as most patients still receive R-CHOP chemoimmunotherapy. Attempts to improve the outcomes of specific subgroups, especially COO groups, have so far had limited success. Newer analyses have further subdivided DLBCL into genomically distinct subsets, not yet incorporated in the WHO classification, which may facilitate targeted approaches to therapy. In this review, we discuss the subgroups that are recognized by the WHO 2016 classification, review the newer genomic data, and speculate on how this could alter the treatment landscape of DLBCL in the future. We also discuss novel approaches to salvage therapy in the broad context of the heterogeneity of DLBCL.

Metastatic colorectal cancer and severe hypocalcemia following irinotecan administration in a patient with X-linked agammaglobulinemia: a case report

Background

X-linked agammaglobulinemia (XLA) is a primary immunodeficiency disorder caused by germline mutations in the Bruton tyrosine kinase (BTK) gene on X chromosome. These mutations disturb B-cell development, decrease immunoglobulin levels, increase susceptibility to infection or neoplasms, and increase the risk of developing colorectal cancer (CRC). For occasional cases of CRC have been reported in XLA patients, low levels of B lymphocytes and immunoglobulins induced by congenital immune disorder make them more susceptible to drug-related toxicities (DRT). Therefore, gene sequencing, therapeutic drug monitoring and any possible measurement to predict DRT should be considered before determining the course of chemotherapy for XLA patients with CRC.

Case presentation

In this study, we reported a 21-year-old male who developed metastatic CRC in the context of XLA. Since the whole exome sequencing and therapeutic drug monitoring did not reveal any predictive markers of DRT, we applied standard first-line chemotherapy to the patient. However, progressive disease occurred after the fifth treatment cycle. Therefore, the administration of oxaliplatin was changed to irinotecan as second-line therapy. After that, the patient firstly suffered from severe hypocalcemia and eventually died due to metastatic CRC after the eighth treatment cycle. The overall survival time was 7.5 months.

Conclusions

This study reported the first written record of a Chinese XLA patient with metastatic CRC and severe hypocalcemia. Whole exome sequencing and bioinformatic analysis indicated the somatic mutations in ABCA6, C6 and PAX3 genes might contribute to the early-onset and metastasis CRC. Besides, a number of germline mutations in genes related to calcium metabolism (CACNA2D4, CD36, etc.) and the administration of irinotecan were speculated to be the causes of severe hypocalcemia. We therefore suggested that in order to avoid severe DRT, clinicians should take genetic background and therapeutic drug monitoring into consideration while planning chemotherapy treatment for XLA patients with CRC.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0880-1) contains supplementary material, which is available to authorized users.

Discovery of Zanubrutinib (BGB-3111), a Novel, Potent, and Selective Covalent Inhibitor of Bruton's Tyrosine Kinase

Aberrant activation of Bruton's tyrosine kinase (BTK) plays an important role in pathogenesis of B-cell lymphomas, suggesting that inhibition of BTK is useful in the treatment of hematological malignancies. The discovery of a more selective on-target covalent BTK inhibitor is of high value. Herein, we disclose the discovery and preclinical characterization of a potent, selective, and irreversible BTK inhibitor as our clinical candidate by using in vitro potency, selectivity, pharmacokinetics (PK), and in vivo pharmacodynamic for prioritizing compounds. Compound BGB-3111 (31a, Zanubrutinib) demonstrates (i) potent activity against BTK and excellent selectivity over other TEC, EGFR and Src family kinases, (ii) desirable ADME, excellent in vivo pharmacodynamic in mice and efficacy in OCI-LY10 xenograft models.

Mutations in topoisomerase IIβ result in a B cell immunodeficiency

B cell development is a highly regulated process involving multiple differentiation steps, yet many details regarding this pathway remain unknown. Sequencing of patients with B cell-restricted immunodeficiency reveals autosomal dominant mutations in TOP2B. TOP2B encodes a type II topoisomerase, an essential gene required to alleviate topological stress during DNA replication and gene transcription, with no previously known role in B cell development. We use Saccharomyces cerevisiae, and knockin and knockout murine models, to demonstrate that patient mutations in TOP2B have a dominant negative effect on enzyme function, resulting in defective proliferation, survival of B-2 cells, causing a block in B cell development, and impair humoral function in response to immunization.

Topoisomerases are required to release topological stress on DNA during replication and transcription. Here, Broderick et al. report genetic variants in TOP2B that cause a syndromic B cell immunodeficiency associated with reduced TOP2B function, defects in B cell development and B cell activation.

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.

Multidomain Control Over TEC Kinase Activation State Tunes the T Cell Response

Signaling through the T cell antigen receptor (TCR) activates a series of tyrosine kinases. Directly associated with the TCR, the SRC family kinase LCK and the SYK family kinase ZAP-70 are essential for all downstream responses to TCR stimulation. In contrast, the TEC family kinase ITK is not an obligate component of the TCR cascade. Instead, ITK functions as a tuning dial, to translate variations in TCR signal strength into differential programs of gene expression. Recent insights into TEC kinase structure have provided a view into the molecular mechanisms that generate different states of kinase activation. In resting lymphocytes, TEC kinases are autoinhibited, and multiple interactions between the regulatory and kinase domains maintain low activity. Following TCR stimulation, newly generated signaling modules compete with the autoinhibited core and shift the conformational ensemble to the fully active kinase. This multidomain control over kinase activation state provides a structural mechanism to account for ITK's ability to tune the TCR signal.

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.

Pharmacophore modeling and virtual screening in search of novel Bruton's tyrosine kinase inhibitors

Bruton's tyrosine kinase (BTK) is a known drug target for B cell malignancies and autoimmune diseases like rheumatoid arthritis. Consequently, efforts to develop BTK inhibitors have gained momentum in the last decade, resulting in a number of potential inhibitory molecules. However, to date, there are only two FDA approved drugs for B cell malignancies (Ibrutinib and Acalabrutinib), thus continued efforts are warranted. A large number of molecular scaffolds with potential BTK inhibitory activity are already available from these studies, and therefore we employed a ligand-based approach towards computer-aided drug design to develop a pharmacophore model for BTK inhibitors. Using over 400 molecules with known half maximal inhibitory concentrations (IC₅₀) for BTK, a four-point pharmacophore hypothesis was derived, with two aromatic rings (R), one hydrogen bond acceptor (A) and one hydrogen bond donor (D). Screening of two small-molecule databases against this pharmacophore returned 620 hits with matching chemical features. Docking these against the ATP-binding site of the BTK kinase domain through a virtual screening workflow yielded 30 hits from which ultimately two natural compounds (two best scoring poses for each) were prioritized. Molecular dynamics simulations of these four docked complexes confirmed the stability of protein-ligand binding over a 200 ns time period, and thus their suitability for lead molecule development with further optimization and experimental testing. Of note, the pharmacophore model developed in this study would also be further useful for de novo drug design and virtual screening efforts on a larger scale. Graphical abstract Pharmacophore modeling and virtual screening in search of novel Bruton's tyrosine kinase inhibitors.

Plasma therapy leads to an increase in functional IgA and IgM concentration in the blood and saliva of a patient with X-linked agammaglobulinemia

BACKGROUND

Patients with X-linked agammaglobulinemia (XLA) are protected against invasive bacterial infections due to IgG replacement therapy, but are still at higher risk for mucosal infections of the gut and respiratory tract. This might be explained by to the lack of IgA and IgM, as these antibodies are especially important for protection against invading bacterial pathogens on the mucosal surface.

METHODS

In an attempt to eliminate a chronic norovirus infection in a patient with X-linked agammaglobulinemia, fresh frozen plasma (FFP) was given two times a week for 3 weeks. At each visit, pre- and post-FFP infusion serum and saliva was collected to determine IgG-, IgA- and IgM-concentrations and serum half-life was calculated. Functionality of the immunoglobulins pre- and post-FFP infusion in both serum and saliva was tested by measuring complement activation, agglutination and killing of non-typeable Haemophilus influenzae (NTHi).

RESULTS

Administration of FFP failed to eradicate the chronic norovirus infection. Serum IgA and IgM half-life was 4.2 ± 0.3 and 3.8 ± 0.3 days, respectively. The presence of serum IgM was associated with increased complement binding and complement-mediated killing of NTHi. IgA in saliva was detectable post-FFP and was associated with increased agglutination of NTHi. IgM in saliva was not detectable.

CONCLUSIONS

We conclude that FFP treatment, although ineffective in clearing a chronic norovirus infection in this single patient, might be beneficial to prevent or eliminate bacterial infections in XLA patients by increasing IgM dependent complement-mediated killing in serum and IgA dependent bacterial agglutination on the mucosal surface.

A novel Bruton tyrosine kinase gene variation was found in an adult with X-linked agammaglobulinemia during blood cross-matching prior to surgical operation

AIMS/OBJECTIVES

To investigate the underlying molecular mechanism of the patient's ABO typing discrepancy.

BACKGROUND

ABO typing discrepancy was frequently seen in patients due to different causes. In this study, ABO typing discrepancy was found in a 24-year-old man with arthralgia, whose forward ABO grouping was O and reverse ABO grouping was AB. Primary immunodeficiency disease was speculated in this patient, especially X-linked agammaglobulinemia (XLA).

METHODS

Immunoglobulins of all isotypes were detected using a specific protein analyser. Lymphocyte subgroups were analysed by flow cytometry. All 19 exons and boundaries of BTK gene were amplified by polymerase chain reaction (PCR), and all PCR products were sequenced by a DNA analyser. BTK protein in the leukocytes and platelets was detected by Western blot.

RESULTS

No B lymphocytes could be detected in the peripheral blood of the patient. A novel BTK gene variation, c.817G>T, in the exon 9 of BTK gene was discovered. No BTK protein expression could be detected in the leukocytes and platelets of the patient.

CONCLUSIONS

XLA could be occasionally discovered by ABO typing discrepancy in some cases because of the deficiency of reciprocal IgM anti-A and/or anti-B antibodies in the serum of the patient. Humoral immunodeficiency is one of the causes of ABO typing discrepancy.

Optimization of novel reversible Bruton's tyrosine kinase inhibitors identified using Tethering-fragment-based screens

Since the approval of ibrutinib for the treatment of B-cell malignancies in 2012, numerous clinical trials have been reported using covalent inhibitors to target Bruton's tyrosine kinase (BTK) for oncology indications. However, a formidable challenge for the pharmaceutical industry has been the identification of reversible, selective, potent molecules for inhibition of BTK. Herein, we report application of Tethering-fragment-based screens to identify low molecular weight fragments which were further optimized to improve on-target potency and ADME properties leading to the discovery of reversible, selective, potent BTK inhibitors suitable for pre-clinical proof-of-concept studies.