To rule out the possibility of an incomplete BTK inhibition in the in vivo ibrutinib-treated CLL cells used in our experiments, both constitutive and anti-IgM–stimulated BTK phosphorylation and VLA-4 activation were analyzed after the addition of an excess of 1 μM ibrutinib to CLL cells collected at day 30 of ibrutinib therapy (n = 8). This evidence concerns the gene BTK and B-cell chronic lymphocytic leukemia.