BCR and B-cell chronic lymphocytic leukemia: Moreover, to definitely exclude the possibility that the observed BCR-induced VLA-4 activation characterizing CLL cells on ibrutinib treatment was caused by loss of BTK inhibition, CLL cells were tested by next-generation sequencing (NGS) for the presence of BTK and PLCγ2 mutations, which have been reported to confer ibrutinib resistance (Woyach et al., 2014a).