MCL1 and B-cell chronic lymphocytic leukemia: However, we are encouraged to believe that the primary impact of TP-0903 is related to its targeting of Axl RTK as exposure of CLL B-cells to TP-0903 did consistently result in reduction of phosphorylated Axl and also reduced phosphorylated AKT and levels of anti-apoptotic proteins, Mcl-1 and XIAP.