As most cells express multiple pro-survival proteins, we postulate that in these assays on permeabilized cells treated with the selective agents (e.g. venetoclax or BIMBAD on CLL cells; Fig. 1A, S2F), MOMP could not efficiently proceed because of the actions of other, ancillary pro-survival proteins (e.g., MCL1 in permeabilized CLL cells) even when the principal pro-survival protein they harbor (e.g., BCL2 in CLL leukemic cells) was inhibited. Here, MCL1 is linked to B-cell chronic lymphocytic leukemia.