BTK and infection: Initially, we studied a cohort of patients with chronic lymphocytic leukemia (CLL) undergoing treatment with ibrutinib, which suppresses B cell proliferation and survival by irreversibly inhibiting Bruton’s tyrosine kinase (BTK), all of whom (n = 7) had received two booster vaccinations (totaling four vaccine doses) after infection with SARS-CoV-2 (fig.