Consistent with this paradigm, genetic deletion of DOT1L stops the leukemic transformation of hematopoietic stem cells (HSC) transfected to express MLL fusions, and new small molecule inhibitors of DOT1L are selectively toxic to MLL fusion driven leukemia cells in vitro and in xenograft models [7,8,9,10,11]. The gene discussed is KMT2A; the disease is leukemia.