key: cord-0735458-6uwo81wn authors: McGee, Michael C.; August, Avery; Huang, Weishan title: BTK/ITK dual inhibitors: Modulating immunopathology and lymphopenia for COVID‐19 therapy date: 2020-07-08 journal: J Leukoc Biol DOI: 10.1002/jlb.5covr0620-306r sha: d310f1ddc93bd3e06a70aaa90e762f99bf6407cf doc_id: 735458 cord_uid: 6uwo81wn 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. An overrepresentation of proinflammatory macrophages has been observed in the bronchoalveolar lavage (BAL) of severe cases compared with mild cases, 2 and elevated IL-6 in the sera is correlated with higher mortality. 3 Lymphopenia and increased number of blood neutrophils are associated with severe and fatal COVID-19. 4 These observations suggest that targeting the host's immune response including those leading to cytokine release syndrome (CRS) may be beneficial in treating immunopathology and the associated severe symptoms of the infection (Fig. 1) . We write here to draw attention to lymphopenia and the potential of modulating T cells through targeting IL-2inducible T-cell kinase (ITK) using Bruton's tyrosine kinase (BTK)/ITK dual inhibitors being evaluated for COVID-19 therapy. patients treated with acalabrutinib for 10-14 days found the levels of IL-6 in serum decreased during this time. 7 By the end of treatment, 8 out of 11 and 2 out of 8 patients that began on supplemental oxygen or mechanical ventilation, respectively, had been discharged on room air. 7 In clinical practice, acalabrutinib is US FDA approved for treating chronic lymphocytic leukemia (CLL), and zanubrutinib received accelerated approval for treating mantle cell lymphoma (MCL). A robust and balanced adaptive immune response is important for This speculation is further supported by recent findings that SARS-CoV-2 is able to enter human T cells, although replication inside T cells was not observed (as determined via RT-qPCR with probes targeting the viral Nucleocapsid, 5 ′ UTR, or Envelope genes). 12, 13 Despite the apparent lack of viral genome replication, the SARS-CoV-2 nucleocapsid protein can persist within T cells up to 24 h postinfection 13 ; and viral particles could be observed via electron microscopy in SARS-CoV-2-infected primary PBMCs (from healthy donors) in CD4 + T cells but not CD8 + T cells, at 48 h post in vitro infection. 12 Given that this was observed with PBMCs infected in vitro, further studies are required to determine whether this represents a true preference in COVID-19. Although the consequences of T cell infection by SARS-CoV-2 have not been investigated at this time, MERS-CoV has been reported to be able to infect and induce apoptosis of human T cells, with a preference for CD4 + over CD8 + T cells. 14 Lymphopenia is positively associated with severity and fatality of COVID-19 cases, 4 and there is a possibility that virus-induced apoptosis may be a potential explanation. It should be stressed that at the time of writing this article, the consequences of viral entry into human T cells is unknown. However, although potential SARS-CoV-2 infection of T cells is a fascinating finding, much more investigation is required to get a better understanding of the mechanism of its entry, consequences on T cell function, and its physiologic impact in COVID-19 patients. Given this backdrop, targeting molecules that play critical signaling functions in T lymphocytes, ideally those that preferentially regulate T cell apoptosis and exhaustion over activation, may be a potential strategy for treating patients with severe COVID-19. ITK is highly expressed in T cells, and regulates the activation and function of both CD4 + and CD8 + T cells, including cytokine production and cytotoxic function. 15 In addition to acalabrutinib and zanubrutinib, ibrutinib is also a US FDA-approved BTK inhibitor, but is less specific as it also inhibits ITK and TEC kinases, both of which are highly expressed in T cells. Ibrutinib has been approved for treating CLL, MCL, chronic graftversus-host disease, and others. High expression of Fas coinciding with increased lymphocyte apoptosis has been observed in the lymph nodes and spleens of patients that died of COVID-19 compared with the healthy controls. 8 Along with alterations in B cells, CLL patients treated with ibrutinib displayed an increase in total number of T cells, which is not seen in patients treated with the more specific acalabrutinib. 16 The observed accumulation of T cells may be due to a decrease in activation-induced cell death, which has been shown to be a result of the ITK signaling- to be hospitalized because of severe symptoms and had to restart ibrutinib treatment; eventually, all recovered from the infection. 26 Similarly, in patients who were on BTK inhibitor treatment for CLL, 2 (out of 8) who continued with regular dosage of ibrutinib after contracting COVID-19 developed milder symptoms and required significantly shorter time of hospitalization than 6 (out of 8) who held BTK inhibitor treatment. 27 It is unclear whether ibrutinib treatment changed viral growth in the hosts, altered T cell activation, survival and function, and so provided benefits in disease controls against viral pneumonia. All current studies focused the discussion of the effects of ibrutinib on macrophage and cytokine-mediated lung inflammation, without mentioning the potential roles of T cell immunity. The potential of modulating T cells through BTK/ITK dual inhibitors such as ibrutinib for COVID-19 therapy has not been considered to date. A clinical trial using ibrutinib to treat COVID-19 (NCT04375397) began in early May 2020. When interpreting results of clinical trials of BTK inhibitors in COVID-19, along with anti-inflammatory therapeutic effects and the potential adverse effects/toxicity of these drug candidates, 28 the effects of such inhibitors on T cell activation, survival, and function will need to be fully considered and carefully evaluated ( Fig. 1) . We have provided a brief summary here of the rapidly evolv- Clinical features of patients infected with 2019 novel coronavirus in Wuhan Single-cell landscape of bronchoalveolar immune cells in patients with COVID-19 Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus-infected pneumonia in Wuhan, China Effective treatment of severe COVID-19 patients with tocilizumab Bruton's tyrosine kinase: an emerging key player in innate immunity Inhibition of Bruton tyrosine kinase in patients with severe COVID-19 The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) directly decimates human spleens and lymph nodes Elevated exhaustion levels and reduced functional diversity of T cells in peripheral blood may predict severe progression in COVID-19 patients Functional exhaustion of antiviral lymphocytes in COVID-19 patients Interferon-mediated immunopathological events are associated with atypical innate and adaptive immune responses in patients with severe acute respiratory syndrome Isolation, sequence, infectivity and replication kinetics of SARS-CoV-2. bioRxiv SARS-CoV-2 infects T lymphocytes through its spike protein-mediated membrane fusion Middle east respiratory syndrome coronavirus efficiently infects human primary T lymphocytes and activates the extrinsic and intrinsic apoptosis pathways Non-receptor tyrosine kinase signaling in autoimmunity and therapeutic implications Ibrutinib treatment improves T cell number and function in CLL patients Inhibition of the kinase ITK in a mouse model of asthma reduces cell death and fails to inhibit the inflammatory response Broad and strong memory CD4+ and CD8+ T cells induced by SARS-CoV-2 in UK convalescent COVID-19 patients Targets of T cell responses to SARS-CoV-2 coronavirus in humans with COVID-19 disease and unexposed individuals Phenotype of SARS-CoV-2-specific T-cells in COVID-19 patients with acute respiratory distress syndrome SARS-CoV-2-specific T cells exhibit unique features characterized by robust helper function, lack of terminal differentiation, and high proliferative potential Airway memory CD4(+) T cells mediate protective immunity against emerging respiratory coronaviruses Cellular immune responses to severe acute respiratory syndrome coronavirus (SARS-CoV) infection in senescent BALB/c mice: cD4+ T cells are important in control of SARS-CoV infection Ibrutinib is an irreversible molecular inhibitor of ITK driving a Th1-selective pressure in T lymphocytes Inhibiting Bruton's tyrosine kinase rescues mice from lethal influenza-induced acute lung injury The BTK inhibitor ibrutinib may protect against pulmonary injury in COVID-19-infected patients Protective role of Bruton tyrosine kinase inhibitors in patients with chronic lymphocytic leukaemia and COVID-19 Management of adverse effects/toxicity of ibrutinib BTK/ITK dual inhibitors: Modulating immunopathology and lymphopenia for COVID-19 therapy