AFF1 and leukemia: In line with the increased sensitivity of KOPN-8 cells to DOT1L inhibitors, after 72 h of EPZ-5676 treatment, we found a significant depletion of the active histone mark H3K27ac at oncofusion protein-binding sites in KOPN-8 cells but not at KMT2A–AF4-bound sites in the SEM or RS4;11 leukemia cell lines (Fig. 4e).