Considering that AF9 mainly functions in hematopoietic stem or progenitor cells (30) and that its expression in most of the hematopoietic cell lines, including MLLr cell lines, are so low (39) that its loss may be of little consequence, we therefore chose to generate an AF9 KO cell line based on an AML cell line carrying one copy of (9;11) translocation for comparison of chromatin occupancy of MLL1 and MLL-AF9. This evidence concerns the gene MLLT3 and acute myeloid leukemia.