Mature B-cells, both normal and leukemic (CLL), are highly sensitive to BCL2 inhibition by ABT-199, which induces BAX/BAK-mediated apoptosis triggered mainly by BIM (46), but ABT-199 is much less effective against CLL cells that have received survival signals from the microenvironment (47). Here, BCL2 is linked to B-cell chronic lymphocytic leukemia.