BCL2L1 and neoplasm: However, the effects of the Bcl-x SSOs appear to vary depending on the expression profile of the target cells, which was suggested to be attributed to the endogenous levels of the Bcl-xL variant; tumor cells with higher endogenous levels of Bcl-xL were reported to be more susceptible to the effects of Bcl-x SSOs, which is likely to be due to the SSO being able to produce enough Bcl-xS to promote apoptosis due to the higher transcription levels of Bcl-x (Mercatante et al., 2001; Mercatante et al., 2002).