BTK and B-cell chronic lymphocytic leukemia: Increased basal activity has also been reported for other signaling molecules that are located further downstream along the BCR pathway, such as the kinases PI3K,22,23 BTK,24 PKC25 and ERK,26 and the transcription factors NF-kB and NF-AT.27–30 Importantly, inhibition or downregulation of many of these signaling molecules induces apoptosis in unstimulated CLL cells.