Deficient expression of a B cell cytoplasmic tyrosine kinase in human X-linked agammaglobulinemia

E41K Mutation Activates Bruton's Tyrosine Kinase by Stabilizing an Inositol Hexakisphosphate dependent Invisible Dimer

Bruton's tyrosine kinase (BTK) regulates diverse cellular signaling of the innate and adaptive immune system in response to microbial pathogens. Downregulation or constitutive activation of BTK is reported in patients with autoimmune diseases or various B-cell leukemias. BTK is a multidomain protein tyrosine kinase that adopts an Src-like autoinhibited conformation maintained by the interaction between the kinase and PH-TH domains. The PH-TH domain plays a central role in regulating BTK function. BTK is activated by binding to PIP3 at the plasma membrane upon stimulation by the B-cell receptor (BCR). The PIP3 binding allows dimerization of the PH-TH domain and subsequent transphosphorylation of the activation loop. Alternatively, a recent study shows that the multivalent T-cell-independent (TI) antigen induces BCR response by activating BTK independently of PIP3 binding. It was proposed that a transiently stable IP6-dependent PH-TH dimer may activate BTK during BCR activation by the TI antigens. However, no IP6-dependent PH-TH dimer has been identified yet. Here, we investigated a constitutively active PH-TH mutant (E41K) to determine if the elusive IP6-dependent PH-TH dimer exists. We showed that the constitutively active E41K mutation activates BTK by stabilizing the IP6-dependent PH-TH dimer. We observed that a downregulating mutation in the PH-TH domain (R28H) linked to X-linked agammaglobulinemia impairs BTK activation at the membrane and in the cytosol by preventing PH-TH dimerization. We conclude that the IP6 dynamically remodels the BTK active fraction between the membrane and cytoplasm. Stimulating with IP6 increases the cytosolic fraction of the activated BTK.

In BTK, phosphorylated Y223 in the SH3 domain mirrors catalytic activity, but does not influence biological function

ABSTRACT

Bruton's tyrosine kinase (BTK) is an enzyme needed for B-cell survival, and its inhibitors have become potent targeted medicines for the treatment of B-cell malignancies. The initial activation event of cytoplasmic protein-tyrosine kinases is the phosphorylation of a conserved regulatory tyrosine in the catalytic domain, which in BTK is represented by tyrosine 551. In addition, the tyrosine 223 (Y223) residue in the SRC homology 3 (SH3) domain has, for more than 2 decades, generally been considered necessary for full enzymatic activity. The initial recognition of its potential importance stems from transformation assays using nonlymphoid cells. To determine the biological significance of this residue, we generated CRISPR-Cas-mediated knockin mice carrying a tyrosine to phenylalanine substitution (Y223F), maintaining aromaticity and bulkiness while prohibiting phosphorylation. Using a battery of assays to study leukocyte subsets and the morphology of lymphoid organs, as well as the humoral immune responses, we were unable to detect any difference between wild-type mice and the Y223F mutant. Mice resistant to irreversible BTK inhibitors, through a cysteine 481 to serine substitution (C481S), served as an additional immunization control and mounted similar humoral immune responses as Y223F and wild-type animals. Collectively, our findings suggest that phosphorylation of Y223 serves as a useful proxy for phosphorylation of phospholipase Cγ2 (PLCG2), the endogenous substrate of BTK. However, in contrast to a frequently held conception, this posttranslational modification is dispensable for the function of BTK.

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

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

The trajectory of human B-cell function, immune deficiency, and allergy revealed by inborn errors of immunity

The essential role of B cells is to produce protective immunoglobulins (Ig) that recognize, neutralize, and clear invading pathogens. This results from the integration of signals provided by pathogens or vaccines and the stimulatory microenvironment within sites of immune activation, such as secondary lymphoid tissues, that drive mature B cells to differentiate into memory B cells and antibody (Ab)-secreting plasma cells. In this context, B cells undergo several molecular events including Ig class switching and somatic hypermutation that results in the production of high-affinity Ag-specific Abs of different classes, enabling effective pathogen neutralization and long-lived humoral immunity. However, perturbations to these key signaling pathways underpin immune dyscrasias including immune deficiency and autoimmunity or allergy. Inborn errors of immunity that disrupt critical immune pathways have identified non-redundant requirements for eliciting and maintaining humoral immune memory but concomitantly prevent immune dysregulation. Here, we will discuss our studies on human B cells, and how our investigation of cytokine signaling in B cells have identified fundamental requirements for memory B-cell formation, Ab production as well as regulating Ig class switching in the context of protective versus allergic immune responses.

Gene regulation in inborn errors of immunity: Implications for gene therapy design and efficacy

Inborn errors of immunity (IEI) present a unique paradigm in the realm of gene therapy, emphasizing the need for precision in therapeutic design. As gene therapy transitions from broad-spectrum gene addition to careful modification of specific genes, the enduring safety and effectiveness of these therapies in clinical settings have become crucial. This review discusses the significance of IEIs as foundational models for pioneering and refining precision medicine. We explore the capabilities of gene addition and gene correction platforms in modifying the DNA sequence of primary cells tailored for IEIs. The review uses four specific IEIs to highlight key issues in gene therapy strategies: X-linked agammaglobulinemia (XLA), X-linked chronic granulomatous disease (X-CGD), X-linked hyper IgM syndrome (XHIGM), and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX). We detail the regulatory intricacies and therapeutic innovations for each disorder, incorporating insights from relevant clinical trials. For most IEIs, regulated expression is a vital aspect of the underlying biology, and we discuss the importance of endogenous regulation in developing gene therapy strategies.

Inborn errors of immunity: A field without frontiers

The study of primary immunodeficiencies or inborn errors of immunity continues to drive our knowledge of the function of the human immune system. From the outset, the study of inborn errors has focused on unraveling genetic etiologies and molecular mechanisms. Aided by the continuous growth in genetic diagnostics, the field has moved from the study of an infection dominated phenotype to embrace and unravel diverse manifestations of autoinflammation, autoimmunity, malignancy, and severe allergy in all medical disciplines. It has now moved from the study of ultrarare presentations to producing meaningful impact in conditions as diverse as inflammatory bowel disease, neurological conditions, and hematology. Beyond offering immunogenetic diagnosis, the study of underlying inborn errors of immunity in these conditions points to targeted treatment which can be lifesaving.

Properties of FDA-approved small molecule protein kinase inhibitors: A 2024 update

Owing to the dysregulation of protein kinase activity in many diseases including cancer, this enzyme family has become one of the most important drug targets in the 21st century. There are 80 FDA-approved therapeutic agents that target about two dozen different protein kinases and seven of these drugs were approved in 2023. Of the approved drugs, thirteen target protein-serine/threonine protein kinases, four are directed against dual specificity protein kinases (MEK1/2), twenty block nonreceptor protein-tyrosine kinases, and 43 inhibit receptor protein-tyrosine kinases. The data indicate that 69 of these drugs are prescribed for the treatment of neoplasms. Six drugs (abrocitinib, baricitinib, deucravacitinib, ritlecitinib, tofacitinib, upadacitinib) are used for the treatment of inflammatory diseases (atopic dermatitis, rheumatoid arthritis, psoriasis, alopecia areata, and ulcerative colitis). Of the 80 approved drugs, nearly two dozen are used in the treatment of multiple diseases. The following seven drugs received FDA approval in 2023: capivasertib (HER2-positive breast cancer), fruquintinib (metastatic colorectal cancer), momelotinib (myelofibrosis), pirtobrutinib (mantle cell lymphoma, chronic lymphocytic leukemia, small lymphocytic lymphoma), quizartinib (Flt3-mutant acute myelogenous leukemia), repotrectinib (ROS1-positive lung cancer), and ritlecitinib (alopecia areata). All of the FDA-approved drugs are orally effective with the exception of netarsudil, temsirolimus, and trilaciclib. This review summarizes the physicochemical properties of all 80 FDA-approved small molecule protein kinase inhibitors including the molecular weight, number of hydrogen bond donors/acceptors, polar surface area, potency, solubility, lipophilic efficiency, and ligand efficiency.

Bruton's Tyrosine Kinase Inhibitors for Multiple Sclerosis Treatment: A New Frontier

Multiple sclerosis (MS) can cause significant disability to patients via relapse-associated worsening and progression independent of relapses. The causes of neuronal and myelin damage can include lymphocyte-mediated inflammation and microglial activation. Bruton's tyrosine kinase (BTK) is an enzyme that mediates B cell activation and the proinflammatory phenotype of microglia. Inhibiting BTK provides a novel therapeutic target for MS but also has a complicated pharmacology based on binding specificity, CNS penetration, half-life, and enzyme inhibition characteristics. Multiple agents are being studied in phase 3 trials, and each agent will have unique efficacy and safety profiles that must be considered individually.

Bruton's Tyrosine Kinase Inhibitors with Distinct Binding Modes Reveal Differential Functional Impact on B-Cell Receptor Signaling

Small molecule inhibitors of Bruton's tyrosine kinase (BTK) have been approved for the treatment of multiple B-cell malignancies and are being evaluated for autoimmune and inflammatory diseases. Various BTK inhibitors (BTKi) have distinct potencies, selectivity profiles, and binding modes within the ATP-binding site. On the basis of the latter feature, BTKis can be classified into those that occupy the back-pocket, H3 pocket, and the hinge region only. Hypothesizing that differing binding modes may have differential impact on the B-cell receptor (BCR) signaling pathway, we evaluated the activities of multiple BTKis in B-cell lymphoma models in vitro and in vivo. We demonstrated that, although all three types of BTKis potently inhibited BTK-Y223 autophosphorylation and phospholipase C gamma 2 (PLCγ2)-Y1217 transphosphorylation, hinge-only binders were defective in inhibiting BTK-mediated calcium mobilization upon BCR activation. In addition, PLCγ2 activation was effectively blocked by back-pocket and H3 pocket binders but not by hinge-only binders. Further investigation using TMD8 cells deficient in Rac family small GTPase 2 (RAC2) revealed that RAC2 functioned as a bypass mechanism, allowing for residual BCR signaling and PLCγ2 activation when BTK kinase activity was fully inhibited by the hinge-only binders. These data reveal a kinase activity-independent function of BTK, involving RAC2 in transducing BCR signaling events, and provide mechanistic rationale for the selection of clinical candidates for B-cell lymphoma indications.

Screening and Characterization of Allosteric Small Molecules Targeting Bruton's Tyrosine Kinase

Bruton's Tyrosine Kinase (BTK) is a nonreceptor tyrosine kinase that belongs to the TEC family. Mutations in the BTK gene cause X-linked agammaglobulinemia (XLA) leading to an arrest in B-cell development. BTK is also a drug target for B-cell lymphomas that rely on an intact B-cell receptor signaling cascade for survival. All FDA approved drugs for BTK target the ATP binding site of the catalytic kinase domain, leading to potential adverse events due to off-target inhibition. In addition, acquired resistance mutations occur in a subset of patients, rendering available BTK inhibitors ineffective. Therefore, allosteric sites on BTK should be explored for drug development to target BTK more specifically and in combination with active site inhibitors. Virtual screening against nonactive site pockets and in vitro experiments resulted in a series of small molecules that bind to BTK outside of the active site. We characterized these compounds using biochemical and biophysical techniques and narrowed our focus to compound "C2". C2 activates full-length BTK and smaller multidomain BTK fragments but not the isolated kinase domain, consistent with an allosteric mode of action. Kinetic experiments reveal a C2-mediated decrease in Km and an increase in kcat leading to an overall increase in the catalytic efficiency of BTK. C2 is also capable of activating the BTK XLA mutants. These proof-of-principle data reveal that BTK can be targeted allosterically with small molecules, providing an alternative to active site BTK inhibitors.

Synthesis and Biological Evaluation of Oxindole Sulfonamide Derivatives as Bruton's Tyrosine Kinase Inhibitors

Bruton's tyrosine kinase (BTK) is a promising molecular target for several human B-cell-related autoimmune disorders, inflammation, and haematological malignancies. The pathogenic alterations in various cancer tissues depend on mutant BTK for cell proliferation and survival, and BTK is also overexpressed in a range of hematopoietic cells. Due to this, BTK is emerging as a potential drug target to treat various human diseases, and several reversible and irreversible inhibitors have been developed and are being developed. As a result, BTK inhibition, clinically validated as an anticancer treatment, is finding great interest in B-cell malignancies and solid tumours. This study focuses on the design and synthesis of new oxindole sulfonamide derivatives as promising inhibitors of BTK with negligible off-target effects. The most cytotoxic compounds with greater basicity were PID-4 (2.29±0.52 μM), PID-6 (9.37±2.47 μM), and PID-19 (2.64±0.88 μM). These compounds caused a selective inhibition of Burkitt's lymphoma RAMOS cells without significant cytotoxicity in non-BTK cancerous and non-cancerous cell lines. Further, PID-4 showed promising activity in inhibiting BTK and downstream signalling cascades. As a potent inhibitor of Burkitt's lymphoma cells, PID-4 is a promising lead for developing novel chemotherapeutics.

Dissecting the Immune System through Gene Regulation

The immune system plays a dual role in human health, functioning both as a protector against pathogens and, at times, as a contributor to disease. This feature emphasizes the importance to uncover the underlying causes of its malfunctions, necessitating an in-depth analysis in both pathological and physiological conditions to better understand the immune system and immune disorders. Recent advances in scientific technology have enabled extensive investigations into gene regulation, a crucial mechanism governing cellular functionality. Studying gene regulatory mechanisms within the immune system is a promising avenue for enhancing our understanding of immune cells and the immune system as a whole. The gene regulatory mechanisms, revealed through various methodologies, and their implications in the field of immunology are discussed in this chapter.

AI & experimental-based discovery and preclinical IND-enabling studies of selective BMX inhibitors for development of cancer therapeutics

The current work aims to design and provide a preliminary IND-enabling study of selective BMX inhibitors for cancer therapeutics development. BMX is an emerging target, more notably in oncological and immunological diseases. In this work, we have employed a predictive AI-based platform to design the selective inhibitors considering the novelty, IP prior protection, and drug-likeness properties. Furthermore, selected top candidates from the initial iteration of the design were synthesized and chemically characterized utilizing 1H NMR and LC-MS. Employing a panel of biochemical (enzymatic) and cancer cell lines, the selected molecules were tested against these assays. In addition, we used artificial intelligence to predict and evaluate several critical IND-focused physicochemical and pharmacokinetics values of the selected molecules. A secondary objective of the current work was also to validate the sole role of BMX in animal models known to be mediated by BMX. More than 50 molecules were designed in the present study employing five novel discovered scaffolds. Two molecules were nominated for further IND-focused studies. Compound II showed promising in-vitro activity against BMX in both enzymatic assays compared to other kinases and in cancer cell lines with known BMX overexpression. Interestingly, compound II showed very favorable physicochemical and pharmacokinetics properties as predicted by the used platforms. The animal study further confirmed the sole role of BMX in the disease model. The current work provides promising data on a selective BMX inhibitor as a potential lead for therapeutics development, and the asset is currently in the optimization stage. Notably, the current study shows a framework for a combined approach employing both AI and experimentation that can be used by academic labs in their research programs to more streamline programs into IND-focused to be bridged easily for further clinical development with industrial partners.

Cutaneous adverse reactions resulting from targeted cancer therapies: histopathologic and clinical findings

Targeted cancer treatments-designed to interfere with specific molecular signals responsible for tumor survival and progression-have shown benefit over conventional chemotherapies but may lead to diverse cutaneous adverse effects. This review highlights clinically significant dermatologic toxicities and their associated histopathologic findings, resulting from various targeted cancer drugs. Case reports and series, clinical trials, reviews, and meta-analyses are included for analysis and summarized herein. Cutaneous side effects resulting from targeted cancer therapies were reported with incidences as high as 90% for certain medications, and reactions are often predictable based on mechanism(s) of action of a given drug. Common and important reaction patterns included: acneiform eruptions, neutrophilic dermatoses, hand-foot skin reaction, secondary cutaneous malignancies, and alopecia. Clinical and histopathologic recognition of these toxicities remains impactful for patient care.

Clinical features and mutational analysis of X-linked agammaglobulinemia patients in Malaysia

Background

Bruton's tyrosine kinase (BTK) is a cytoplasmic protein involved in the B cell development. X-linked agammaglobulinemia (XLA) is caused by mutation in the BTK gene, which results in very low or absent B cells. Affected males have markedly reduced immunoglobulin levels, which render them susceptible to recurrent and severe bacterial infections. Methods: Patients suspected with X-linked agammaglobulinemia were enrolled during the period of 2010-2018. Clinical summary, and immunological profiles of these patients were recorded. Peripheral blood samples were collected for monocyte BTK protein expression detection and BTK genetic analysis. The medical records between January 2020 and June 2023 were reviewed to investigate COVID-19 in XLA.

Results

Twenty-two patients (from 16 unrelated families) were molecularly diagnosed as XLA. Genetic testing revealed fifteen distinct mutations, including four splicing mutations, four missense mutations, three nonsense mutations, three short deletions, and one large indel mutation. These mutations scattered throughout the BTK gene and mostly affected the kinase domain. All mutations including five novel mutations were predicted to be pathogenic or deleterious by in silico prediction tools. Genetic testing confirmed that eleven mothers and seven sisters were carriers for the disease, while three mutations were de novo. Flow cytometric analysis showed that thirteen patients had minimal BTK expression (0-15%) while eight patients had reduced BTK expression (16-64%). One patient was not tested for monocyte BTK expression due to insufficient sample. Pneumonia (n=13) was the most common manifestation, while Pseudomonas aeruginosa was the most frequently isolated pathogen from the patients (n=4). Mild or asymptomatic COVID-19 was reported in four patients.

Conclusion

This report provides the first overview of demographic, clinical, immunological and genetic data of XLA in Malaysia. The combination of flow cytometric assessment and BTK genetic analysis provides a definitive diagnosis for XLA patients, especially with atypical clinical presentation. In addition, it may also allow carrier detection and assist in genetic counselling and prenatal diagnosis.

Overcoming immune checkpoint blockade resistance in solid tumors with intermittent ITK inhibition

Cytotoxic CD8 + T cell (CTL) exhaustion is driven by chronic antigen stimulation. Reversing CTL exhaustion with immune checkpoint blockade (ICB) has provided clinical benefits in different types of cancer. We, therefore, investigated whether modulating chronic antigen stimulation and T-cell receptor (TCR) signaling with an IL2-inducible T-cell kinase (ITK) inhibitor, could confer ICB responsiveness to ICB resistant solid tumors. In vivo intermittent treatment of 3 ICB-resistant solid tumor (melanoma, mesothelioma or pancreatic cancer) with ITK inhibitor significantly improved ICB therapy. ITK inhibition directly reinvigorate exhausted CTL in vitro as it enhanced cytokine production, decreased inhibitory receptor expression, and downregulated the transcription factor TOX. Our study demonstrates that intermittent ITK inhibition can be used to directly ameliorate CTL exhaustion and enhance immunotherapies even in solid tumors that are ICB resistant.

Zanubrutinib: past, present, and future

In recent years, Bruton tyrosine kinase (BTK) inhibitors have provided significant advances in the treatment of patients with B-cell malignancies. Ibrutinib was the first BTK inhibitor to be approved, and it changed the standard-of-care treatment for diseases such as chronic lymphocytic leukemia, mantle cell lymphoma, marginal zone lymphoma, and Waldenström macroglobulinemia, improving efficacy outcomes and safety compared to chemotherapy. In this article, we review the development of zanubrutinib, a next-generation BTK inhibitor, from molecular design to patient-related outcomes. We start this journey by providing insights into the discovery of BTK and the physiologic, genetic, and molecular characterization of patients lacking this kinase, together with the brief treatment landscape in the era of chemo-immunotherapies. Zanubrutinib was originally developed by applying a structure-activity strategy to enhance the specificity as well as enzymatic and pharmacokinetic properties. Preclinical studies confirmed greater specificity and better bioavailability of zanubrutinib compared with that of ibrutinib, which supported the initiation of clinical trials in humans. Preliminary clinical results indicated activity in B-cell malignancies together with an improved safety profile, in line with less off-target effects described in the preclinical studies. The clinical program of zanubrutinib has since expanded significantly, with ongoing studies in a wide range of hemato-oncological diseases and in combination with many other therapies. Zanubrutinib currently is approved for various B-cell malignancies in multiple countries. This story highlights the importance of multidisciplinary collaborative research, from bench to bedside, and provides an example of how the commitment to finding improved treatment options should always run parallel to patient care.

Pleckstrin Homology [PH] domain, structure, mechanism, and contribution to human disease

The pleckstrin homology [PH] domain is a structural fold found in more than 250 proteins making it the 11th most common domain in the human proteome. 25% of family members have more than one PH domain and some PH domains are split by one, or several other, protein domains although still folding to give functioning PH domains. We review mechanisms of PH domain activity, the role PH domain mutation plays in human disease including cancer, hyperproliferation, neurodegeneration, inflammation, and infection, and discuss pharmacotherapeutic approaches to regulate PH domain activity for the treatment of human disease. Almost half PH domain family members bind phosphatidylinositols [PIs] that attach the host protein to cell membranes where they interact with other membrane proteins to give signaling complexes or cytoskeleton scaffold platforms. A PH domain in its native state may fold over other protein domains thereby preventing substrate access to a catalytic site or binding with other proteins. The resulting autoinhibition can be released by PI binding to the PH domain, or by protein phosphorylation thus providing fine tuning of the cellular control of PH domain protein activity. For many years the PH domain was thought to be undruggable until high-resolution structures of human PH domains allowed structure-based design of novel inhibitors that selectively bind the PH domain. Allosteric inhibitors of the Akt1 PH domain have already been tested in cancer patients and for proteus syndrome, with several other PH domain inhibitors in preclinical development for treatment of other human diseases.

The membrane surface as a platform that organizes cellular and biochemical processes

Membranes are essential for life. They act as semi-permeable boundaries that define cells and organelles. In addition, their surfaces actively participate in biochemical reaction networks, where they confine proteins, align reaction partners, and directly control enzymatic activities. Membrane-localized reactions shape cellular membranes, define the identity of organelles, compartmentalize biochemical processes, and can even be the source of signaling gradients that originate at the plasma membrane and reach into the cytoplasm and nucleus. The membrane surface is, therefore, an essential platform upon which myriad cellular processes are scaffolded. In this review, we summarize our current understanding of the biophysics and biochemistry of membrane-localized reactions with particular focus on insights derived from reconstituted and cellular systems. We discuss how the interplay of cellular factors results in their self-organization, condensation, assembly, and activity, and the emergent properties derived from them.

Bruton tyrosine kinase inhibitors: can they be optimized for the treatment of neuroinflammatory disorders?

INTRODUCTION

Bruton's tyrosine kinase (BTK) is a multifaceted player of the immune system which has been involved in the survival of hematological malignancies but also in the pathogenesis of immune-mediated diseases. Oral BTK inhibitors (BTKi) have become a cornerstone for the treatment of patients with B-cell malignancies, and are under investigation for several immune-mediated diseases.

AREAS COVERED

We reviewed the biology of BTK and emerging data on BTKi in patients with neuroinflammatory disorders of both the peripheral and central nervous system.

EXPERT OPINION

We support the use of BTKi in relapsed/refractory patients with multiple sclerosis and anti-MAG antibody neuropathies. However, other immune-mediated neuroinflammatory disorders are likely to benefit from BTKi. Whether BTKi will improve the response rates than conventional therapies in previously untreated patients is unknown and will be assessed within future clinical trials. Furthermore, the availability of more selective BTKi, with less adverse events, will improve patients' tolerability and expand our treatment landscape.

A Registry Study of 240 Patients with X-Linked Agammaglobulinemia Living in the USA

PURPOSE

To understand the natural history and clinical outcomes for patients with X-linked agammaglobulinemia (XLA) in the United States utilizing the United States Immunodeficiency Network (USIDNET) patient registry.

METHODS

The USIDNET registry was queried for data from XLA patients collected from 1981 to 2019. Data fields included demographics, clinical features before and after diagnosis of XLA, family history, genetic mutation in Bruton's tyrosine kinase (BTK), laboratory findings, treatment modalities, and mortality.

RESULTS

Data compiled through the USIDNET registry on 240 patients were analyzed. Patient year of birth ranged from 1945 to 2017. Living status was available for 178 patients; 158/178 (88.8%) were alive. Race was reported for 204 patients as follows: White, 148 (72.5%); Black/African American, 23 (11.2%); Hispanic, 20 (9.8%); Asian or Pacific Islander, 6 (2.9%), and other or more than one race, 7 (3.4%). The median age at last entry, age at disease onset, age at diagnosis, and length of time with XLA diagnosis was 15 [range (r) = 1-52 years], 0.8 [r = birth-22.3 years], 2 [r = birth-29 years], and 10 [r = 1-56 years] years respectively. One hundred and forty-one patients (58.7%) were < 18 years of age. Two hundred and twenty-one (92%) patients were receiving IgG replacement (IgGR), 58 (24%) were on prophylactic antibiotics, and 19 (7.9%) were on immunomodulatory drugs. Eighty-six (35.9%) patients had undergone surgical procedures, two had undergone hematopoietic cell transplantation, and two required liver transplantation. The respiratory tract was the most affected organ system (51.2% of patients) followed by gastrointestinal (40%), neurological (35.4%), and musculoskeletal (28.3%). Infections were common both before and after diagnosis, despite IgGR therapy. Bacteremia/sepsis and meningitis were reported more frequently before XLA diagnosis while encephalitis was more commonly reported after diagnosis. Twenty patients had died (11.2%). The median age of death was 21 years (range = 3-56.7 years). Neurologic condition was the most common underlying co-morbidity for those XLA patients who died.

CONCLUSIONS

Current therapies for XLA patients reduce early mortality, but patients continue to experience complications that impact organ function. With improved life expectancy, more efforts will be required to improve post-diagnosis organ dysfunction and quality of life. Neurologic manifestations are an important co-morbidity associated with mortality and not yet clearly fully understood.

Bruton tyrosine kinase inhibitors for multiple sclerosis

Current therapies for multiple sclerosis (MS) reduce both relapses and relapse-associated worsening of disability, which is assumed to be mainly associated with transient infiltration of peripheral immune cells into the central nervous system (CNS). However, approved therapies are less effective at slowing disability accumulation in patients with MS, in part owing to their lack of relevant effects on CNS-compartmentalized inflammation, which has been proposed to drive disability. Bruton tyrosine kinase (BTK) is an intracellular signalling molecule involved in the regulation of maturation, survival, migration and activation of B cells and microglia. As CNS-compartmentalized B cells and microglia are considered central to the immunopathogenesis of progressive MS, treatment with CNS-penetrant BTK inhibitors might curtail disease progression by targeting immune cells on both sides of the blood-brain barrier. Five BTK inhibitors that differ in selectivity, strength of inhibition, binding mechanisms and ability to modulate immune cells within the CNS are currently under investigation in clinical trials as a treatment for MS. This Review describes the role of BTK in various immune cells implicated in MS, provides an overview of preclinical data on BTK inhibitors and discusses the (largely preliminary) data from clinical trials.

Stimulation of the catalytic activity of the tyrosine kinase Btk by the adaptor protein Grb2

The Tec-family kinase Btk contains a lipid-binding Pleckstrin homology and Tec homology (PH-TH) module connected by a proline-rich linker to a 'Src module', an SH3-SH2-kinase unit also found in Src-family kinases and Abl. We showed previously that Btk is activated by PH-TH dimerization, which is triggered on membranes by the phosphatidyl inositol phosphate PIP3, or in solution by inositol hexakisphosphate (IP6) (Wang et al., 2015, https://doi.org/10.7554/eLife.06074). We now report that the ubiquitous adaptor protein growth-factor-receptor-bound protein 2 (Grb2) binds to and substantially increases the activity of PIP3-bound Btk on membranes. Using reconstitution on supported-lipid bilayers, we find that Grb2 can be recruited to membrane-bound Btk through interaction with the proline-rich linker in Btk. This interaction requires intact Grb2, containing both SH3 domains and the SH2 domain, but does not require that the SH2 domain be able to bind phosphorylated tyrosine residues - thus Grb2 bound to Btk is free to interact with scaffold proteins via the SH2 domain. We show that the Grb2-Btk interaction recruits Btk to scaffold-mediated signaling clusters in reconstituted membranes. Our findings indicate that PIP3-mediated dimerization of Btk does not fully activate Btk, and that Btk adopts an autoinhibited state at the membrane that is released by Grb2.

Differential Regulation of GPVI-Induced Btk and Syk Activation by PKC, PKA and PP2A in Human Platelets

Bruton's tyrosine kinase (Btk) and spleen tyrosine kinase (Syk) are major signaling proteins in human platelets that are implicated in atherothrombosis and thrombo-inflammation, but the mechanisms controlling their activities are not well understood. Previously, we showed that Syk becomes phosphorylated at S297 in glycoprotein VI (GPVI)-stimulated human platelets, which limits Syk activation. Here, we tested the hypothesis that protein kinases C (PKC) and A (PKA) and protein phosphatase 2A (PP2A) jointly regulate GPVI-induced Btk activation in platelets. The GPVI agonist convulxin caused rapid, transient Btk phosphorylation at S180 (pS180↑), Y223 and Y551, while direct PKC activation strongly increased Btk pS180 and pY551. This increase in Btk pY551 was also Src family kinase (SFK)-dependent, but surprisingly Syk-independent, pointing to an alternative mechanism of Btk phosphorylation and activation. PKC inhibition abolished convulxin-stimulated Btk pS180 and Syk pS297, but markedly increased the tyrosine phosphorylation of Syk, Btk and effector phospholipase Cγ2 (PLCγ2). PKA activation increased convulxin-induced Btk activation at Y551 but strongly suppressed Btk pS180 and Syk pS297. PP2A inhibition by okadaic acid only increased Syk pS297. Both platelet aggregation and PLCγ2 phosphorylation with convulxin stimulation were Btk-dependent, as shown by the selective Btk inhibitor acalabrutinib. Together, these results revealed in GPVI-stimulated platelets a transient Syk, Btk and PLCγ2 phosphorylation at multiple sites, which are differentially regulated by PKC, PKA or PP2A. Our work thereby demonstrated the GPVI-Syk-Btk signalosome as a tightly controlled protein kinase network, in agreement with its role in atherothrombosis.

The Role of m6A Modifications in B-Cell Development and B-Cell-Related Diseases

B cells are a class of professional antigen-presenting cells that produce antibodies to mediate humoral immune response and participate in immune regulation. m⁶A modification is the most common RNA modification in mRNA; it involves almost all aspects of RNA metabolism and can affect RNA splicing, translation, stability, etc. This review focuses on the B-cell maturation process as well as the role of three m⁶A modification-related regulators-writer, eraser, and reader-in B-cell development and B-cell-related diseases. The identification of genes and modifiers that contribute to immune deficiency may shed light on regulatory requirements for normal B-cell development and the underlying mechanism of some common diseases.

BTK Isoforms p80 and p65 Are Expressed in Head and Neck Squamous Cell Carcinoma (HNSCC) and Involved in Tumor Progression

Here, we describe the expression of Bruton's Tyrosine Kinase (BTK) in head and neck squamous cell carcinoma (HNSCC) cell lines as well as in primary HNSCC samples. BTK is a kinase initially thought to be expressed exclusively in cells of hematopoietic origin. Apart from the 77 kDa BTK isoform expressed in immune cells, particularly in B cells, we identified the 80 kDa and 65 kDa BTK isoforms in HNSCC, recently described as oncogenic. Importantly, we revealed that both isoforms are products of the same mRNA. By investigating the mechanism regulating oncogenic BTK-p80/p65 expression in HNSSC versus healthy or benign tissues, our data suggests that the epigenetic process of methylation might be responsible for the initiation of BTK-p80/p65 expression in HNSCC. Our findings demonstrate that chemical or genetic abrogation of BTK activity leads to inhibition of tumor progression in terms of proliferation and vascularization in vitro and in vivo. These observations were associated with cell cycle arrest and increased apoptosis and autophagy. Together, these data indicate BTK-p80 and BTK-p65 as novel HNSCC-associated oncogenes. Owing to the fact that abundant BTK expression is a characteristic feature of primary and metastatic HNSCC, targeting BTK activity appears as a promising therapeutic option for HNSCC patients.

Advances and Challenges of the Decade: The Ever-Changing Clinical and Genetic Landscape of Immunodeficiency

In the past 10 years, we have witnessed major advances in clinical immunology. Newborn screening for severe combined immunodeficiency has become universal in the United States and screening programs are being extended to severe combined immunodeficiency and other inborn errors of immunity globally. Early genetic testing is becoming the norm for many of our patients and allows for informed selection of targeted therapies including biologics repurposed from other specialties. During the COVID-19 pandemic, our understanding of essential immune responses expanded and the discovery of immune gene defects continued. Immunoglobulin products, the backbone of protection for antibody deficiency syndromes, came into use to minimize side effects. New polyclonal and monoclonal antibody products emerged with increasing options to manage respiratory viral agents such as SARS-CoV-2 and respiratory syncytial virus. Against these advances, we still face major challenges. Atypical is becoming typical as phenotypes of distinct genetic disease overlap whereas the clinical spectrum of the same genetic defect widens. Therefore, clinical judgment needs to be paired with repeated deep immune phenotyping and upfront genetic testing, as technologies rapidly evolve, and clinical disease often progresses with age. Managing patients with organ damage resulting from immune dysregulation poses a special major clinical challenge and management often lacks standardization, from autoimmune cytopenias, granulomatous interstitial lung disease, enteropathy, and liver disease to endocrine, rheumatologic, and neurologic complications. Clinical, translational, and basic science networks will continue to advance the field; however, cross-talk and education with practicing allergists/immunologists are essential to keep up with the ever-changing clinical and genetic landscape of inborn errors of immunity.

Managing Waldenström's macroglobulinemia with BTK inhibitors

Bruton's tyrosine kinase (BTK) inhibition is one of the treatment standards for patients with relapsed/refractory Waldenström's macroglobulinemia (WM) and for patients with WM who are unsuitable for immunochemotherapy (ICT). It offers deep and durable responses with a manageable safety profile that is generally favorable compared with ICT regimens. However, the limitations of the first approved BTK inhibitor (BTKi), ibrutinib, include reduced efficacy in patients lacking the characteristic WM mutation (MYD88L265P) and toxicities related to off-target activity. The risk of atrial fibrillation (AF) and other cardiovascular side effects are a notable feature of ibrutinib therapy. Several next-generation covalent BTKis with greater selectivity for BTK are at various stages of development. In November 2021, zanubrutinib became the first of these agents to be approved by the European Medicines Agency for the treatment of WM. Head-to-head trial data indicate that it has comparable efficacy to ibrutinib for patients with WM overall, although it may be more effective in patients with CXCR4 mutations or wild-type MYD88. In the clinical trial setting, its greater selectivity translates into a reduced risk of cardiovascular side effects, including AF. Acalabrutinib, which is pre-approval in WM, appears to offer similar advantages over ibrutinib in terms of its safety profile. Beyond the next-generation covalent BTKis, non-covalent BTKis are an emerging class with the potential to provide a therapeutic option for patients who relapse on covalent BTKis. In the future, BTKis may be increasingly utilized within combination regimens. Several ongoing trials in WM are investigating the potential for BTKi use in combination with established and novel targeted agents.

Therapeutic effect of ibrutinib, a selective Bruton's tyrosine kinase inhibitor, in orbital fibroblasts from patients with Graves' orbitopathy

PURPOSE

Bruton's tyrosine kinase (BTK) is an essential protein in B-cell antigen receptor (BCR) signaling pathway and is known to be related to pathogenetic effect on B-cell related malignancies and various autoimmune diseases. In this study, we investigated the therapeutic effect of ibrutinib, an orally bioavailable BTK inhibitor in the pathogenesis of Graves' orbitopathy (GO) in in vitro model.

METHODS

Expression of BTK in orbital tissues from GO and normal control subjects were evaluated by real-time polymerase chain reaction (PCR). Primary cultured orbital fibroblasts from each subject were exposed to ibrutinib and stimulated with interleukin (IL)-1β or insulin like growth factor (IGF)-1. Production of inflammatory cytokines was evaluated by real time PCR and enzyme-linked immunosorbent assays (ELISA). The downstream transcription factors were also determined by western blot assays.

RESULTS

The expression of BTK in GO tissues were significantly higher than in healthy controls. After stimulation of GO orbital fibroblasts with IL-1β or IGF-1, BTK mRNA and phosphorylated (p)- BTK protein expression was also enhanced. Ibrutinib reduced the expression of BTK mRNA and proteins of p-BTK, and inhibited the IL-1β- and IGF-1-induced production of proinflammatory cytokines including IL-6, IL-8 and COX-2 in both GO and normal cells. Ibrutinib also significantly attenuated phosphorylation of Akt, p38, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) in IL-1β stimulated GO cells and Akt, JNK, and NF-κB in IL-1ß stimulated normal cells.

CONCLUSIONS

BTK expression is enhanced in GO tissue and orbital fibroblasts. Ibrutinib, a BTK inhibitor suppresses proinflammatory cytokine production as well as phosphorylation of Akt and NF-κB protein. Our results suggest the potential role of BTK in GO inflammatory pathogenesis and possibility of a novel therapeutic target of GO.

Dysregulated inflammasome activity in intestinal inflammation - Insights from patients with very early onset IBD

Inflammatory bowel disease (IBD) is a multifactorial disorder triggered by imbalances of the microbiome and immune dysregulations in genetically susceptible individuals. Several mouse and human studies have demonstrated that multimeric inflammasomes are critical regulators of host defense and gut homeostasis by modulating immune responses to pathogen- or damage-associated molecular patterns. In the context of IBD, excessive production of pro-inflammatory Interleukin-1β has been detected in patient-derived intestinal tissues and correlated with the disease severity or failure to respond to anti-tumor necrosis factor therapy. Correspondingly, genome-wide association studies have suggested that single nucleotide polymorphisms in inflammasome components might be associated with risk of IBD development. The relevance of inflammasomes in controlling human intestinal homeostasis has been further exemplified by the discovery of very early onset IBD (VEO-IBD) patients with monogenic defects affecting different molecules in the complex regulatory network of inflammasome activity. This review provides an overview of known causative monogenic entities of VEO-IBD associated with altered inflammasome activity. A better understanding of the molecular mechanisms controlling inflammasomes in monogenic VEO-IBD may open novel therapeutic avenues for rare and common inflammatory diseases.

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

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

BTK inhibitors in the treatment of hematological malignancies and inflammatory diseases: mechanisms and clinical studies

Bruton's tyrosine kinase (BTK) is an essential component of multiple signaling pathways that regulate B cell and myeloid cell proliferation, survival, and functions, making it a promising therapeutic target for various B cell malignancies and inflammatory diseases. Five small molecule inhibitors have shown remarkable efficacy and have been approved to treat different types of hematological cancers, including ibrutinib, acalabrutinib, zanubrutinib, tirabrutinib, and orelabrutinib. The first-in-class agent, ibrutinib, has created a new era of chemotherapy-free treatment of B cell malignancies. Ibrutinib is so popular and became the fourth top-selling cancer drug worldwide in 2021. To reduce the off-target effects and overcome the acquired resistance of ibrutinib, significant efforts have been made in developing highly selective second- and third-generation BTK inhibitors and various combination approaches. Over the past few years, BTK inhibitors have also been repurposed for the treatment of inflammatory diseases. Promising data have been obtained from preclinical and early-phase clinical studies. In this review, we summarized current progress in applying BTK inhibitors in the treatment of hematological malignancies and inflammatory disorders, highlighting available results from clinical studies.

Atopic Dermatitis-like Genodermatosis: Disease Diagnosis and Management

Eczema is a classical characteristic not only in atopic dermatitis but also in various genodermatosis. Patients suffering from primary immunodeficiency diseases such as hyper-immunoglobulin E syndromes, Wiskott-Aldrich syndrome, immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, STAT5B deficiency, Omenn syndrome, atypical complete DiGeorge syndrome; metabolic disorders such as acrodermatitis enteropathy, multiple carboxylase deficiency, prolidase deficiency; and other rare syndromes like severe dermatitis, multiple allergies and metabolic wasting syndrome, Netherton syndrome, and peeling skin syndrome frequently perform with eczema-like lesions. These genodermatosis may be misguided in the context of eczematous phenotype. Misdiagnosis of severe disorders unavoidably affects appropriate treatment and leads to irreversible outcomes for patients, which underlines the importance of molecular diagnosis and genetic analysis. Here we conclude clinical manifestations, molecular mechanism, diagnosis and management of several eczema-related genodermatosis and provide accessible advice to physicians.

Development of a UPLC-MS/MS method for the determination of orelabrutinib in rat plasma and its application in pharmacokinetics

The aim of the present study was to establish an ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for the determination of orelabrutinib in rat plasma using futibatinib as internal standard (IS), and to apply it for a pharmacokinetic study in rats. Orelabrutinib was extracted from plasma by protein precipitation and quantitatively analyzed by UPLC-MS/MS. An Acquity UPLC BEH C18 column was used for rapid separation by gradient elution using 0.1% formic acid and acetonitrile as mobile phases. The validation results of bioanalytical methodology showed that the linearity of orelabrutinib in plasma samples was good within the concentration range of 1–2000 ng/ml. The lower limit of quantification (LLOQ) was 1 ng/ml. The precision of orelabrutinib ranged from 1.4% to 11.5%, with intra-day and inter-day accuracy ranging from −5.7% to 7.7% and −0.2% to 12.5%, respectively. The selectivity, stability, matrix effect and recovery of the method all met the requirements of quantitative analysis of biological samples. The method was simple, sensitive, accurate and specific, and had high recovery rate. It also could be successfully applied to the pharmacokinetic study of rats.

BTK, the new kid on the (oncology) block?

In the last decade data piled up indicating that BTK – for twenty years considered as a “private matter” of bone marrow-derived cells – it is expressed and plays important and different roles also outside of the hematopoietic compartment and, most notably, in tumor cells. Initial evidence that BTK plays a critical role in B cell-derived malignancies prompted the chase for specific inhibitors, the forefather of which entered the clinic in a record time and paved the way for an ever increasing number of new molecules to be trialed. The growing interests in BTK also led to the discovery that, in solid tumors, two novel isoforms are mainly expressed and actionable liabilities for target therapy. Remarkably, the different isoforms appear to be involved in different signaling pathways which will have to be attentively specified in order to define the area of therapeutic intervention. In this perspective we briefly summarize the progress made in the last decade in studying BTK and its isoforms in cancer cells and define the open questions to be addressed in order to get the most benefits from its targeting for therapeutic purposes.

Liver cirrhosis and immune dysfunction

Cirrhosis is end-stage liver disease resulting from various etiologies and is a common cause of death worldwide. The progression from compensated to decompensated cirrhosis to acute-on-chronic liver failure (ACLF) is due to multiple factors, including continuation of alcohol use or continued exposure to other toxins, an imbalance of the gut microbiota (dysbiosis), increased gut permeability and a disrupted immune response. This disrupted immune response is also named cirrhosis-associated immune dysfunction, which is characterized by worsening systemic inflammation with concomitant immune paralysis, as liver disease deteriorates. This review highlights central immunologic events during the exacerbation of cirrhosis and characterizes the different immune cell populations involved therein.

Autoimmunity in Primary Immunodeficiencies (PID)

Primary immunodeficiency (PID) may impact any component of the immune system. The number of PID and immune dysregulation disorders is growing steadily with advancing genetic detection methods. These expansive recognition methods have changed the way we characterize PID. While PID were once characterized by their susceptibility to infection, the increase in genetic analysis has elucidated the intertwined relationship between PID and non-infectious manifestations including autoimmunity. The defects permitting opportunistic infections to take hold may also lead the way to the development of autoimmune disease. In some cases, it is the non-infectious complications that may be the presenting sign of PID autoimmune diseases, such as autoimmune cytopenia, enteropathy, endocrinopathies, and arthritis among others, have been reported in PID. While autoimmunity may occur with any PID, this review will look at certain immunodeficiencies most often associated with autoimmunity, as well as their diagnosis and management strategies.

Novel treatments in B cell non-Hodgkin's lymphomas

The improved understanding of lymphoma biology and recent advances in the field of cancer immunology have paved the way for the development of many effective small molecule inhibitors and immunotherapies in B cell non-Hodgkin's lymphomas. This article reviews novel treatments that have been approved recently by the US Food and Drug Administration and are now routinely used in clinical practice. It discusses their mechanisms of action, efficacy and safety, current therapeutic roles, and future directions in the treatment paradigm of different types of B cell non-Hodgkin's lymphoma. It also reviews other exciting novel treatments that are not yet approved but have unique mechanisms of action and have shown encouraging early results.

Molecular alterations in the integrated diagnosis of pediatric glial and glioneuronal tumors: A single center experience

Objectives: Tumors of the central nervous system (CNS) are the most common pediatric solid tumors, where low grade (LGG) and high grade gliomas (HGG) represent up to 55% of CNS tumors. Current molecular classification of these tumors results in a more accurate diagnosis and risk stratification, which ultimately enables individualized treatment strategies. Identifying known alterations is a suitable approach, particularly in developing countries, where NGS approaches are not easily accessible. We sought to assess molecular alterations in BRAF and histone 3 genes. Study design: FISH, IHC and Sanger sequencing were performed in a series of 102 pediatric glial and glioneuronal tumors. We also correlated these results with clinical and histological findings to evaluate their usefulness as diagnostic and/or prognostic tools. Results: We found that the KIAA1549-BRAF gene fusion was a relevant diagnostic tool for pilocytic astrocytoma, but not related to progression free survival (PFS) and overall survival (OS). BRAFV600E mutation was associated with a decreased OS in LGG, and with decreased PFS and OS among pilocytic astrocytomas. All HGG of the midline were H3K27M mutants, while H3G34R mutant cases were located in brain hemispheres. HGG harboring the H3K27M variant were associated with a decreased PFS and OS. Conclusions: Assessing druggable molecular markers with prognostic value is particularly important in those cases where complete resection or further radiation therapy is not possible. These potential diagnostic/prognostic markers may be suitable as further screening tests to reduce the requirement on NGS, which is not available in all laboratories. Furthermore, these results broaden data on BRAF and Histone 3 alterations in children from geographic regions, other than USA and Europe.

Bruton's tyrosine kinase inhibition-An emerging therapeutic strategy in immune-mediated dermatological conditions

Bruton's tyrosine kinase (BTK), a member of the Tec kinase family, is critically involved in a range of immunological pathways. The clinical application of BTK inhibitors for B‐cell malignancies has proven successful, and there is strong rationale for the potential benefits of BTK inhibitors in some autoimmune and allergic conditions, including immune‐mediated dermatological diseases. However, the established risk‐to‐benefit profile of “first‐generation” BTK inhibitors cannot be extrapolated to these emerging, non‐oncological, indications. “Next‐generation” BTK inhibitors such as remibrutinib and fenebrutinib entered clinical development for chronic spontaneous urticaria (CSU); rilzabrutinib and tirabrutinib are being studied as potential treatments for pemphigus. Promising data from early‐phase clinical trials in CSU suggest potential for these agents to achieve strong pathway inhibition, which may translate into measurable clinical benefits, as well as other effects such as the disruption of autoantibody production. BTK inhibitors may help to overcome some of the shortcomings of monoclonal antibody treatments for immune‐mediated dermatological conditions such as CSU, pemphigus, and systemic lupus erythematosus. In addition, the use of BTK inhibitors may improve understanding of the pathophysiological roles of mast cells, basophils, and B cells in such conditions.

Retrospective study of 98 patients with X-linked agammaglobulinemia complicated with arthritis

OBJECTIVE

We preformed this retrospective study of clinical manifestation, imaging feature, and mutations to describe joint involvement in X-linked agammaglobulinemia (XLA) patients, aimed to provide recommendation for physicians.

METHODS

A total number of 98 XLA patients who have been diagnosed between January 2000 and February 2020 were enrolled and grouped based on whether they developed arthritis and analyzed for the clinical, imaging, and gene mutation data using the t test or the Mann-Whitney test.

RESULTS

Forty-five out of 98 patients (45.9%) had joint involvement, 40.8% had symptom prior to the diagnosis of XLA, and 54.1% had no articular symptom. Patients with joint involvement had a higher median diagnostic age of XLA and initial IgG level than patients without it, while their intravenous immunoglobulin was lower (p < 0.05). Knee, hip, and ankle were the most frequent joint, and oligoarthritis (≦ 4 joints) was more common than polyarthritis (88.9% vs 11.1%). Red and tenderness were the most frequent clinical symptoms (80%) with 24.4% reporting limited activity and 8.9% reporting deformity. Imaging data collected from 32 patients indicated that joint effusion (53.3%), synovitis (15.5%), and swollen soft tissue (15.5%) were the most common feature. Seventeen patients were treated by antibiotics plus intravenous immunoglobulin (IVIG) with an effective rate of 70.6%, and 28 patients only received IVIG with an effective rate of 67.9%. In comparison to patients without arthritis who have higher frequency nonsense and frameshift mutation, patients with arthritis had a higher incidence of missense mutation (p < 0.05).

CONCLUSION

High prevalence of arthritis among X-linked agammaglobulinemia patients and subsequent progression through IVIG replacement therapy highlight the importance of timely diagnosis and better management of these patients. Our finding indicated a potential correlation between genotype and phenotype, and further research on the mechanism of arthritis in XLA patients could increase physicians' awareness and improve patients' prognosis. Key Points • This study described the feature of arthritis in XLA patients and indicated a potential correlation between this complication and genotype.

Acalabrutinib and its use in the treatment of chronic lymphocytic leukemia

Bruton's tyrosine kinase inhibitors have changed the treatment landscape for chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL) and lymphoplasmacytic lymphoma dramatically. In 2019, acalabrutinib was approved by the US FDA for the treatment of treatment-naive and relapsed/refractory CLL and MCL. Acalabrutinib monotherapy was found to be effective and safe in CLL patients. In ASCEND and ELEVATE treatment-naive studies, acalabrutinib monotherapy and the combination with obinutuzumab demonstrated improved efficacy and an acceptable safety profile. The triple combination with venetoclax showed a high rate of molecular remission without an impaired safety profile. Adverse events, with an occurrence rate of >20%, were as follows: grade 1-2 myelosuppression, gastrointestinal toxicity, rash, constitutional symptoms; grade 3 or 4 toxicities were syncope, pneumonia, hypertension, atrial fibrillation, neutropenia and thrombocytopenia.

Challenges of CAR T-cell Therapy in CLL: Lessons Learned

Development of chimeric antigen receptor T (CART) cell therapy has led to unprecedented success against B cell leukemia and lymphoma and resulted in FDA-approved treatment protocols. Despite the initial clinical response in B cell-related malignancies, high relapse rates suggest that much work is needed to uncover mechanisms of resistance. In chronic lymphocytic leukemia (CLL), the durable activity of CAR T-cells is limited, and CART cell success is lower than in other malignancies. T cells from these patients are vulnerable to a state of dysfunction due to stresses including chronic infection, rapid cell cycle upon antigen recognition, immunosuppressive tumor microenvironment, and cancer-related treatments. T cells are also introduced to additional stresses when cultured ex vivo during the CART manufacturing process. All these factors contribute to the limited regenerative capacity of T cells, which can lead to CART treatment failure. In this short report, we will review the challenges of CAR T-cell therapy in patients with CLL and discuss potential strategies to overcome these challenges.

Optimization of a novel piperazinone series as potent selective peripheral covalent BTK inhibitors

BTK is a tyrosine kinase playing an important role in B cell and myeloid cell functions through B cell receptor (BCR) signaling and Fc receptor (FcR) signaling. Selective inhibition of BTK has the potential to provide therapeutical benefits to patients suffering from autoimmune diseases. Here we report the design, optimization, and characterization of novel potent and highly selective covalent BTK inhibitors. Starting from a piperazinone hit derived from a selective reversible inhibitor, we solved the whole blood cellular potency issue by introducing an electrophilic warhead to reach Cys481. This design led to a covalent irreversible BTK inhibitor series with excellent kinase selectivity as well as excellent CD69 cellular potency. Optimization of metabolic stability led to representative compound like 42, which demonstrated strong cellular potency based on BTK target occupancy and the inhibition of B-cell proliferation as readouts of proximal and distal functional activity.

B cell repertoire in patients with a novel BTK mutation: expanding the spectrum of atypical X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is caused by mutations in the Bruton tyrosine kinase) BTK) gene. Affected patients have severely reduced amounts of circulating B cells. Patients with atypical XLA may have residual circulating B cells, and there are few studies exploring these cells' repertoire. We aimed to study the B cell repertoire of a novel hypomorphic mutation in the BTK gene, using the next generation sequencing (NGS) technology. Clinical data was collected from our clinical records. Real-time PCR was used to determine KREC copies, and NGS was used to determine the immunoglobulin (Ig) heavy chain (IgH) repertoire diversity. Both patients had a relatively mild clinical and laboratory phenotype, residual BTK protein expression, and the same novel mutation in the BTK gene, c.1841 T > C, p. L614P. Signal-joint kappa-deleting recombination excision circles (sj-KREC) for both patients were completely absent reflecting lack of naïve B cells. The intron RSS-Kde coding joints (cj) were significantly reduced, reflecting residual replicating B cells. NGS displayed restricted IgH repertoire with highly uneven distribution of clones, especially for Pt2. We report a novel BTK mutation, c.1841 T > C (p. L614P) that is associated with a relatively mild phenotype. We conclude that the IgH repertoire in atypical XLA is restricted with highly uneven distribution of clones. This phenomenon may be explained by extremely reduced to non-existent levels of BTK in B cells. This report sheds further light on atypical cases of XLA.

Nodular regenerative hyperplasia in X-linked agammaglobulinemia: An underestimated and severe complication

BACKGROUND

Late-onset complications in X-linked agammaglobulinemia (XLA) are increasingly recognized. Nodular regenerative hyperplasia (NRH) has been reported in primary immunodeficiency but data in XLA are limited.

OBJECTIVES

This study sought to describe NRH prevalence, associated features, and impact in patients with XLA.

METHODS

Medical records of all patients with XLA referred to the National Institutes of Health between October 1994 and June 2019 were reviewed. Liver biopsies were performed when clinically indicated. Patients were stratified into NRH+ or NRH- groups, according to their NRH biopsy status. Fisher exact test and Mann-Whitney test were used for statistical comparisons.

RESULTS

Records of 21 patients with XLA were reviewed, with a cumulative follow-up of 129 patient-years. Eight patients underwent ≥1 liver biopsy of whom 6 (29% of the National Institutes of Health XLA cohort) were NRH+. The median age at NRH diagnosis was 20 years (range, 17-31). Among patients who had liver biopsies, alkaline phosphatase levels were only increased in patients who were NRH+ (P = .04). Persistently low platelet count (<100,000 per μL for >6 months), mildly to highly elevated hepatic venous pressure gradient and either hepatomegaly and/or splenomegaly were present in all patients who were NRH+. In opposition, persistently low platelet counts were not seen in patients who were NRH-, and hepatosplenomegaly was observed in only 1 patient who was NRH-. Hepatic venous pressure gradient was normal in the only patient tested who was NRH-. All-cause mortality was higher among patients who were NRH+ (5 of 6, 83%) than in the rest of the cohort (1 of 15, 7% among patients who were NRH- and who were classified as unknown; P = .002).

CONCLUSIONS

NRH is an underreported, frequent, and severe complication in XLA, which is associated with increased morbidity and mortality.

An X-linked agammaglobulinemia (XLA) patient with fever and disturbance of consciousness: infection with Torque teno virus?

This is the first report of meningoencephalitis in an adult male with X-linked agammaglobulinemia caused by a probable Torque teno virus (TTV) infection. TTV was detected in the cerebrospinal fluid samples of the patient by high-throughput sequencing technology. The patient was treated successfully. Abstract X-linked agammaglobulinemia (XLA) is a rare primary immunodeficiency disease caused by mutations in the Bruton's tyrosine kinase (Btk) gene, characterized by recurrent infections and low or undetectable immunoglobulin levels. The most recommended treatment for XLA is lifelong intravenous immunoglobulin (IVIG) replacement therapy. Without treatment, XLA patients are vulnerable to bacterial and viral infections. Meningoencephalitis is a common complication in patients with XLA. Torque teno viruses (TTVs) are ubiquitous in various tissues of healthy people, while TTV infections have been reported only recently. This case study presents the first reported case on the Chinese mainland of meningoencephalitis in an adult male with XLA, most likely caused by TTV. A 27-year-old male presented with fever and severe disturbance of consciousness. Conventional tests, including blood culture and cerebrospinal fluid (CSF) culture, did not reveal any bacterial infections. The clinical presentation, neuroimaging findings, and results of CSF were suggestive of viral meningoencephalitis. Next, TTV was detected in CSF by high-throughput sequencing (HTS) technology. This case suggests that TTV can have a pathogenic effect on patients with severe immunodeficiency disease, and can produce severe clinical symptoms.