MCL1 and Thrombocytopenia: Interestingly, the combination treatment did not lower BCL-xL expression in ABT199-R cells, which would be beneficial in the clinic, as it would probably not lead to thrombocytopenia in patients as reported with navitoclax.16 It should be noted that although both BCL-xL and MCL-1 were required for developing acquired ABT-199-R, targeting only one sensitized resistant cells to ABT-199.