KLF4 and acute myeloid leukemia: In the AML model induced by retroviral expression of the MLL-AF9 fusion in hematopoietic stem/progenitor cells followed by transplantation, the loss of KLF4 caused improved survival of leukemic mice, which was linked to a reduced frequency of LSCs identified in this model as granulocyte monocyte progenitor (GMP) cells that are positive for MLL-AF9 (Figure 4B) (39, 81).