It was previously shown that stromal cells induce CLL cells to express anti‐apoptotic MCL1 protein, which could account for HS5 chemoprotective effects.28 Thus, we assessed the effect of SEL24‐B489 on MCL1 expression in CLL cells co‐cultured with stromal cells. The gene discussed is MCL1; the disease is B-cell chronic lymphocytic leukemia.