Retroviral expression of MLL1-AF9 (ALL1-fused gene from chromosome 9, or MLLT3) in several hematopoietic compartments results in the generation of acute myeloid leukemia (AML) upon transplantation in mice, and has been used as a model to study AML and leukemia stem cells (LSCs, also known as leukemia-initiating cells) [33,34,35,36,37,38]. The gene discussed is KMT2A; the disease is leukemia.