Diagnosis and Treatment of Chronic Lymphocytic Leukemia: A Review.

Importance: Chronic lymphocytic leukemia (CLL), defined by a minimum of 5 × 109/L monoclonal B cells in the blood, affects more than 200 000 people and is associated with approximately 4410 deaths in the US annually. CLL is associated with an immunocompromised state and an increased rate of complications from infections. Observations: At the time of diagnosis, the median age of patients with CLL is 70 years, and an estimated 95% of patients have at least 1 medical comorbidity. Approximately 70% to 80% of patients with CLL are asymptomatic at the time of diagnosis, and one-third will never require treatment for CLL. Prognostic models have been developed to estimate the time to first treatment and the overall survival, but for patients who are asymptomatic, irrespective of disease risk category, clinical observation is the standard of care. Patients with symptomatic disease who have bulky or progressive lymphadenopathy or hepatosplenomegaly and those with a low neutrophil count, anemia, or thrombocytopenia and/or symptoms of fever, drenching night sweats, and weight loss (B symptoms) should be offered treatment. For these patients, first-line treatment consists of a regimen containing either a covalent Bruton tyrosine kinase (BTK) inhibitor (acalabrutinib, zanubrutinib, or ibrutinib) or a B-cell leukemia/lymphoma 2 (BCL2) inhibitor (venetoclax). There is no evidence that starting either class before the other improves outcomes. The covalent BTK inhibitors are typically used indefinitely. Survival rates are approximately 88% at 4 years for acalabrutinib, 94% at 2 years for zanubrutinib, and 78% at 7 years for ibrutinib. Venetoclax is prescribed in combination with obinutuzumab, a monoclonal anti-CD20 antibody, in first-line treatment for 1 year (overall survival, 82% at 5-year follow-up). A noncovalent BTK inhibitor, pitobrutinib, has shown an overall response rate of more than 70% after failure of covalent BTK inhibitors and venetoclax. Phosphoinositide 3'-kinase (PI3K) inhibitors (idelalisib and duvelisib) can be prescribed for disease that progresses with BTK inhibitors and venetoclax, but patients require close monitoring for adverse events such as autoimmune conditions and infections. In patients with multiple relapses, chimeric antigen receptor T-cell (CAR-T) therapy with lisocabtagene maraleucel was associated with a 45% complete response rate. The only potential cure for CLL is allogeneic hematopoietic cell transplant, which remains an option after use of targeted agents. Conclusions and Relevance: More than 200 000 people in the US are living with a CLL diagnosis, and CLL causes approximately 4410 deaths each year in the US. Approximately two-thirds of patients eventually need treatment. Highly effective novel targeted agents include BTK inhibitors such as acalabrutinib, zanubrutinib, ibrutinib, and pirtobrutinib or BCL2 inhibitors such as venetoclax.

The Development of BTK Inhibitors: A Five-Year Update.

Bruton's tyrosine kinase (BTK) represented, in the past ten years, an important target for the development of new therapeutic agents that could be useful for cancer and autoimmune disorders. To date, five compounds, able to block BTK in an irreversible manner, have been launched in the market, whereas many reversible BTK inhibitors (BTKIs), with reduced side effects that are more useful for long-term administration in autoimmune disorders, are under clinical investigation. Despite the presence in the literature of many articles and reviews, studies on BTK function and BTKIs are of great interest for pharmaceutical companies as well as academia. This review is focused on compounds that have appeared in the literature from 2017 that are able to block BTK in an irreversible or reversible manner; also, new promising tunable irreversible inhibitors, as well as PROTAC molecules, have been reported. This summary could improve the knowledge of the chemical diversity of BTKIs and provide information for future studies, particularly from the medicinal chemistry point of view. Data reported here are collected from different databases (Scifinder, Web of Science, Scopus, Google Scholar, and Pubmed) using "BTK" and "BTK inhibitors" as keywords.

Efficacy of booster doses in augmenting waning immune responses to COVID-19 vaccine in patients with cancer.

Anti-COVID-19 immunity dynamics were assessed in patients with cancer in a prospective clinical trial. Waning of immunity was detected 4-6 months post-vaccination with significant increases in anti-spike IgG titers after booster dosing, and 56% of seronegative patients seroconverted post-booster vaccination. Prior anti-CD20/BTK inhibitor therapy was associated with reduced vaccine efficacy.

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

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

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

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

Btk Inhibitors: A Medicinal Chemistry and Drug Delivery Perspective.

In the past few years, Bruton's tyrosine Kinase (Btk) has emerged as new target in medicinal chemistry. Since approval of ibrutinib in 2013 for treatment of different hematological cancers (as leukemias and lymphomas), two other irreversible Btk inhibitors have been launched on the market. In the attempt to overcome irreversible Btk inhibitor limitations, reversible compounds have been developed and are currently under evaluation. In recent years, many Btk inhibitors have been patented and reported in the literature. In this review, we summarized the (ir)reversible Btk inhibitors recently developed and studied clinical trials and preclinical investigations for malignancies, chronic inflammation conditions and SARS-CoV-2 infection, covering advances in the field of medicinal chemistry. Furthermore, the nanoformulations studied to increase ibrutinib bioavailability are reported.

Structure-Based Virtual Screening Reveals Ibrutinib and Zanubrutinib as Potential Repurposed Drugs against COVID-19.

Coronavirus disease (COVID)-19 is the leading global health threat to date caused by a severe acute respiratory syndrome coronavirus (SARS-CoV-2). Recent clinical trials reported that the use of Bruton's tyrosine kinase (BTK) inhibitors to treat COVID-19 patients could reduce dyspnea and hypoxia, thromboinflammation, hypercoagulability and improve oxygenation. However, the mechanism of action remains unclear. Thus, this study employs structure-based virtual screening (SBVS) to repurpose BTK inhibitors acalabrutinib, dasatinib, evobrutinib, fostamatinib, ibrutinib, inositol 1,3,4,5-tetrakisphosphate, spebrutinib, XL418 and zanubrutinib against SARS-CoV-2. Molecular docking is conducted with BTK inhibitors against structural and nonstructural proteins of SARS-CoV-2 and host targets (ACE2, TMPRSS2 and BTK). Molecular mechanics-generalized Born surface area (MM/GBSA) calculations and molecular dynamics (MD) simulations are then carried out on the selected complexes with high binding energy. Ibrutinib and zanubrutinib are found to be the most potent of the drugs screened based on the results of computational studies. Results further show that ibrutinib and zanubrutinib could exploit different mechanisms at the viral entry and replication stage and could be repurposed as potential inhibitors of SARS-CoV-2 pathogenesis.

BTK/ITK dual inhibitors: Modulating immunopathology and lymphopenia for COVID-19 therapy.

Bruton's tyrosine kinase (BTK) signaling is involved in innate immune responses and regulates the production of proinflammatory cytokines that can contribute to COVID-19 immunopathology. Clinical trials with BTK inhibitors in COVID-19 treatment have been proposed, and previous studies have attempted to investigate the therapeutic effects of ibrutinib and underlying mechanisms in treating viral pneumonia. These attempts, however, did not consider potential off target effect of BTK inhibitors on T cell differentiation, function, and survival, which may be beneficial in treatment for COVID-19. Here, we summarize the current knowledge of BTK/IL-2-inducible T-cell kinase (ITK) signaling in immunopathology and lymphopenia and discuss the potential of BTK/ITK dual inhibitors such as ibrutinib in modulating immunopathology and lymphopenia, for COVID-19 therapy.

Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT): Targeting Pathomechanisms with Bruton Tyrosine Kinase Inhibitors.

A series of cases with rare thromboembolic incidents including cerebral sinus vein thrombosis (some of them fatal) and concomitant thrombocytopenia occurring shortly after vaccination with the coronavirus disease 2019 (COVID-19) vaccine AZD1222 (Vaxzevria) have caused significant concern and led to its temporary suspension in many countries. Immediate laboratory efforts in four of these patients have identified a tentative pathomechanism underlying this syndrome termed initially vaccine-induced prothrombotic immune thrombocytopenia (VIPIT) and renamed recently vaccine-induced immune thrombotic thrombocytopenia (VITT). It encompasses the presence of platelet-activating antibodies to platelet factor-4/heparin complexes, possibly emulated by polyanionic constituents of AZD1222, and thus resembles heparin-induced thrombocytopenia (HIT). Because these immune complexes bind and activate platelets via Fcγ receptor IIA (FcγRIIA), high-dose intravenous immunoglobulin G has been suggested for treatment of VITT in addition to non-heparin anticoagulants. Here we propose inhibitors of Bruton tyrosine kinase (Btk) approved for B cell malignancies (e.g., ibrutinib) as another therapeutic option in VITT, as they are expected to pleiotropically target multiple pathways downstream of FcγRIIA-mediated Btk activation, for example, as demonstrated for the effective inhibition of platelet aggregation, dense granule secretion, P-selectin expression and platelet-neutrophil aggregate formation stimulated by FcγRIIA cross-linking. Moreover, C-type lectin-like receptor CLEC-2- and GPIb-mediated platelet activation, the interactions and activation of monocytes and the release of neutrophil extracellular traps, as encountered in HIT, could be attenuated by Btk inhibitors. As a paradigm for emergency repurposing of approved drugs in COVID-19, off-label use of Btk inhibitors in a low-dose range not affecting haemostatic functions could thus be considered a sufficiently safe option to treat VITT.

The role of ibrutinib in COVID-19 hyperinflammation: A case report.

Immune modulation in COVID-19 is emerging as an important therapeutic strategy as increasing evidence suggests that inflammatory pathways are implicated in lung damage. Bruton tyrosine kinase inhibitors (BTKi), such as ibrutinib, are commonly used to treat indolent B-cell neoplasms and chronic graft-versus-host disease (GvHD). Given their potential to suppress pulmonary inflammatory cytokines and lessen acute lung injury, this could be applicable in the context of hospitalised COVID-19 patients. We describe an 81 year-old male receiving ibrutinib for Waldenstrom macroglobulinaemia (WM) who was hospitalised with COVID-19. On stopping the BTKi due to concerns of additional immunosuppression, he required non-invasive ventilation (NIV) in the intensive care unit (ICU) and demonstrated prompt clinical recovery when ibrutinib was reinstated. Continuing ibrutinib in patients with COVID-19 may be advantageous given its immunomodulatory properties and withdrawal of ibrutinib therapy may be detrimental. Further evidence is required to explore the potential therapeutic impact of BTKis and other immunomodulatory agents on the clinical course of COVID-19 as is currently being carried out in a number of clinical trials.

Kinase inhibitors developed for treatment of hematologic malignancies: implications for immune modulation in COVID-19.

Tyrosine kinase inhibitors (TKIs) are used to target dysregulated signaling pathways in virtually all hematologic malignancies. Many of the targeted signaling pathways are also essential in nonmalignant immune cells. The current coronavirus severe acute respiratory syndrome coronavirus 2 pandemic catalyzed clinical exploration of TKIs in the treatment of the various stages of COVID-19, which are characterized by distinct immune-related complications. Most of the reported effects of TKIs on immune regulation have been explored in vitro, with different class-specific drugs having nonoverlapping target affinities. Moreover, many of the reported in vivo effects are based on artificial animal models or on observations made in symptomatic patients with a hematologic malignancy who often already suffer from disturbed immune regulation. Based on in vitro and clinical observations, we attempt to decipher the impact of the main TKIs approved or in late-stage development for the treatment of hematological malignancies, including inhibitors of Bruton's tyrosine kinase, spleen tyrosine kinase, BCR-Abl, phosphatidylinositol 3-kinase/ mammalian target of rapamycin, JAK/STAT, and FMS-like tyrosine kinase 3, to provide a rationale for how such inhibitors could modify clinical courses of diseases, such as COVID-19.

Observations on the use of Bruton's tyrosine kinase inhibitors in SAR-CoV-2 and cancer.

Bruton's tyrosine kinase (BTK) inhibitors, drugs utilized in cancer, are being repurposed for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) (COVID-19). Recently, BTK inhibitors acalabrutinib and ibrutinib have been found to protect against pulmonary injury in a small group of patients infected with SARS-CoV-2. The high levels of pro-inflammatory cytokines found in the circulation of COVID-19 patients with severe lung disease suggest the involvement of the innate immune system in this process. Understanding the potential mechanism of action of BTK inhibition in SARS-CoV-2 is clearly of importance to determine how acalabrutinib, ibrutinib and possibly other BTK inhibitors may provide protection against lung injury.

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.

Effect of Bruton tyrosine kinase inhibitor on efficacy of adjuvanted recombinant hepatitis B and zoster vaccines.

Vaccinations are effective in preventing infections; however, it is unknown if patients with chronic lymphocytic leukemia (CLL) who are treatment naïve (TN) or receiving Bruton tyrosine kinase inhibitors (BTKi's) respond to novel adjuvanted vaccines. Understanding the effect of BTKi's on humoral immunity is timely because BTKi's are widely used and vaccination against coronavirus disease 2019 is urgently needed. In 2 open-label, single-arm clinical trials, we measured the effect of BTKi's on de novo immune response against recombinant hepatitis B vaccine (HepB-CpG) and recall response against recombinant zoster vaccine (RZV) in CLL patients who were TN or on BTKi. The primary end point was serologic response to HepB-CpG (anti-hepatitis B surface antibodies ≥10 mIU/mL) and RZV (≥fourfold increase in anti-glycoprotein E). The response rate to HepB-CpG was lower in patients on BTKi (3.8%; 95% confidence interval [CI], 0.7-18.9) than patients who were TN (28.1%; 95% CI, 15.6-45.4; P = .017). In contrast, the response rate to RZV did not differ significantly between the BTKi (41.5%; 95% CI, 27.8-56.6) and TN cohorts (59.1%; 95% CI, 38.7-76.7; P = .2). BTKi's were associated with a decreased de novo immune response following HepB-CpG, whereas recall immune response following RZV was not significantly affected by BTKi therapy. These trials were registered at www.clinicaltrials.gov as #NCT03685708 (Hep-CpG) and #NCT03702231 (RZV).

Differential impact of BTK active site inhibitors on the conformational state of full-length BTK.

Bruton's tyrosine kinase (BTK) is targeted in the treatment of B-cell disorders including leukemias and lymphomas. Currently approved BTK inhibitors, including Ibrutinib, a first-in-class covalent inhibitor of BTK, bind directly to the kinase active site. While effective at blocking the catalytic activity of BTK, consequences of drug binding on the global conformation of full-length BTK are unknown. Here, we uncover a range of conformational effects in full-length BTK induced by a panel of active site inhibitors, including large-scale shifts in the conformational equilibria of the regulatory domains. Additionally, we find that a remote Ibrutinib resistance mutation, T316A in the BTK SH2 domain, drives spurious BTK activity by destabilizing the compact autoinhibitory conformation of full-length BTK, shifting the conformational ensemble away from the autoinhibited form. Future development of BTK inhibitors will need to consider long-range allosteric consequences of inhibitor binding, including the emerging application of these BTK inhibitors in treating COVID-19.

Treatments for blood cancers, such as leukemia and lymphoma, rely heavily on chemotherapy, using drugs that target a vulnerable aspect of the cancer cells. B-cells, a type of white blood cell that produces antibodies, require a protein called Bruton's tyrosine kinase, or BTK for short, to survive. The drug ibrutinib (Imbruvica) is used to treat B-cell cancers by blocking BTK. The BTK protein consists of several regions. One of them, known as the kinase domain, is responsible for its activity as an enzyme (which allows it to modify other proteins by adding a 'tag' known as a phosphate group). The other regions of BTK, known as regulatory modules, control this activity. In BTK's inactive form, the regulatory modules attach to the kinase domain, blocking the regulatory modules from interacting with other proteins. When BTK is activated, it changes its conformation so the regulatory regions detach and become available for interactions with other proteins, at the same time exposing the active kinase domain. Ibrutinib and other BTK drugs in development bind to the kinase domain to block its activity. However, it is not known how this binding affects the regulatory modules. Previous efforts to study how drugs bind to BTK have used a version of the protein that only had the kinase domain, instead of the full-length protein. Now, Joseph et al. have studied full-length BTK and how it binds to five different drugs. The results reveal that ibrutinib and another drug called dasatinib both indirectly disrupt the normal position of the regulatory domains pushing BTK toward a conformation that resembles the activated state. By contrast, the three other compounds studied do not affect the inactive structure. Joseph et al. also examined a mutation in BTK that confers resistance against ibrutinib. This mutation increases the activity of BTK by disrupting the inactive structure, leading to B cells surviving better. Understanding how drug resistance mechanisms can work will lead to better drug treatment strategies for cancer. BTK is also a target in other diseases such as allergies or asthma and even COVID-19. If interactions between partner proteins and the regulatory domain are important in these diseases, then they may be better treated with drugs that maintain the regulatory modules in their inactive state. This research will help to design drugs that are better able to control BTK activity.

BTK Inhibitors in Cancer Patients with COVID-19: "The Winner Will be the One Who Controls That Chaos" (Napoleon Bonaparte).

As the SARS-CoV-2 (COVID-19) pandemic spreads and the number of Bruton's tyrosine kinase inhibitor (BTKi)-treated COVID-19-affected patients grows, we must consider the pros and cons of BTKi discontinuation for our patients. In favor of BTKi continuation, BTK plays an active role in macrophage polarization. By modulating key transcription factors, BTK may regulate macrophage polarization downstream of classic M1 and M2 polarizing stimuli and mitigate the hyperinflammatory state associated with COVID-19. In favor of BTKi discontinuation, we note a potentially increased risk of secondary infections and impaired humoral immunity. We hypothesize that the potential benefit of blunting a hyperinflammatory response to SARS-CoV-2 through attenuation of M1 polarization outweighs the potential risk of impaired humoral immunity, not to mention the risk of rapid progression of B-cell malignancy following BTKi interruption. On the basis of this, we suggest continuing BTKi in patients with COVID-19.

Outcomes of COVID-19 in patients with CLL: a multicenter international experience.

Given advanced age, comorbidities, and immune dysfunction, chronic lymphocytic leukemia (CLL) patients may be at particularly high risk of infection and poor outcomes related to coronavirus disease 2019 (COVID-19). Robust analysis of outcomes for CLL patients, particularly examining effects of baseline characteristics and CLL-directed therapy, is critical to optimally manage CLL patients through this evolving pandemic. CLL patients diagnosed with symptomatic COVID-19 across 43 international centers (n = 198) were included. Hospital admission occurred in 90%. Median age at COVID-19 diagnosis was 70.5 years. Median Cumulative Illness Rating Scale score was 8 (range, 4-32). Thirty-nine percent were treatment naive ("watch and wait"), while 61% had received ≥1 CLL-directed therapy (median, 2; range, 1-8). Ninety patients (45%) were receiving active CLL therapy at COVID-19 diagnosis, most commonly Bruton tyrosine kinase inhibitors (BTKi's; n = 68/90 [76%]). At a median follow-up of 16 days, the overall case fatality rate was 33%, though 25% remain admitted. Watch-and-wait and treated cohorts had similar rates of admission (89% vs 90%), intensive care unit admission (35% vs 36%), intubation (33% vs 25%), and mortality (37% vs 32%). CLL-directed treatment with BTKi's at COVID-19 diagnosis did not impact survival (case fatality rate, 34% vs 35%), though the BTKi was held during the COVID-19 course for most patients. These data suggest that the subgroup of CLL patients admitted with COVID-19, regardless of disease phase or treatment status, are at high risk of death. Future epidemiologic studies are needed to assess severe acute respiratory syndrome coronavirus 2 infection risk, these data should be validated independently, and randomized studies of BTKi's in COVID-19 are needed to provide definitive evidence of benefit.

Inhibition of Bruton tyrosine kinase in patients with severe COVID-19.

Patients with severe COVID-19 have a hyperinflammatory immune response suggestive of macrophage activation. Bruton tyrosine kinase (BTK) regulates macrophage signaling and activation. Acalabrutinib, a selective BTK inhibitor, was administered off-label to 19 patients hospitalized with severe COVID-19 (11 on supplemental oxygen; 8 on mechanical ventilation), 18 of whom had increasing oxygen requirements at baseline. Over a 10-14 day treatment course, acalabrutinib improved oxygenation in a majority of patients, often within 1-3 days, and had no discernable toxicity. Measures of inflammation - C-reactive protein and IL-6 - normalized quickly in most patients, as did lymphopenia, in correlation with improved oxygenation. At the end of acalabrutinib treatment, 8/11 (72.7%) patients in the supplemental oxygen cohort had been discharged on room air, and 4/8 (50%) patients in the mechanical ventilation cohort had been successfully extubated, with 2/8 (25%) discharged on room air. Ex vivo analysis revealed significantly elevated BTK activity, as evidenced by autophosphorylation, and increased IL-6 production in blood monocytes from patients with severe COVID-19 compared with blood monocytes from healthy volunteers. These results suggest that targeting excessive host inflammation with a BTK inhibitor is a therapeutic strategy in severe COVID-19 and has led to a confirmatory international prospective randomized controlled clinical trial.