MCL1 and B-cell chronic lymphocytic leukemia: What regulates the dependency of these cell types on a specific BCL-2 family member is still unknown, as in addition to expressing the expected anti-apoptotic member required for their survival, namely BCL-2 for CLL, BCL-XL for MOLT-4 and MCL-1 for H929, other anti-apoptotic proteins were also expressed (Figure 1C) in agreement with earlier studies (Del Gaizo Moore et al, 2007, 2008).