MLLT3 and acute myeloid leukemia: However, when C/EBPα or PU.1 is knocked out in MLL-AF9 AML cells, the increased chromatin accessibility is diminished which indicates that both of these factors are necessary for changes to chromatin conformation after LSD1 inhibition, and when either factor is deleted, this confers resistance to LSD1 inhibition in this context (29).