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 and 8 on mechanical ventilation), 18 of whom had increasing oxygen requirements at baseline. Over a 10- to 14-day treatment course, initiation of acalabrutinib treatment was associated with improved oxygenation in a majority of patients, often within 1 to 3 days, and had no discernable toxicity. Measures of inflammation - C-reactive protein and interleukin-6 (IL-6) - normalized quickly in most patients, as did lymphopenia, in correlation with improved oxygenation. At the end of acalabrutinib treatment, 8 of 11 (72.7%) patients in the supplemental oxygen cohort had been discharged on room air, and 4 of 8 (50%) patients in the mechanical ventilation cohort had been successfully extubated, with 2 of 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.