Other mechanisms important in CLL-cell survival include overexpression of anti-apoptotic proteins such as BCL2, BCL-XL, BAG1, and MCL1 and underexpression of pro-apoptotic proteins such as BAX and BCL-XS; aberration of the ATM/p53 tumor suppressor pathway; deregulation of autocrine cytokines; and interaction with microenvironmental factors such as IL-4, CD40 ligand and accessory cells [20-24]. This evidence concerns the gene MCL1 and B-cell chronic lymphocytic leukemia.