A critical role of MCL-1 in cell survival was demonstrated in an elegant study using bone marrow HSCs/HSPCs transformed with the oncogenes mixed-lineage leukemia (MLL)-eleven nineteen leukemia (MLL-ENL) and MLL-ALL1-fused gene from chromosome 9 (MLL-AF9), and corresponding AML mouse models. The gene discussed is KMT2A; the disease is acute myeloid leukemia.