Ibrutinib, an irreversible Bruton’s tyrosine kinase (BTK) inhibitor commonly used for the treatment of CLL, was shown to inhibit interleukin-2-inducible T-cell kinase (ITK), which is important for the activity of T-cells [99], as reviewed recently by Mhibik et al. [100]. The gene discussed is ITK; the disease is B-cell chronic lymphocytic leukemia.