MCL1 and B-cell chronic lymphocytic leukemia: Isolated pathological B cells from PAPTP-treated animals still responded to PAPTP, but Venetoclax did not trigger CLL B-cell death (Fig. 4d), in agreement with previous reports showing that spleen-derived cells are resistant to even 5 nM Venetoclax [52], probably due to dependence of these cells on anti-apoptotic proteins MCL1 (myeloid cell leukemia sequence 1) and BFL1 (BCL2-related protein A1).