MEIS1 and acute myeloid leukemia: Moreover, Meis1 as well as Hoxa9 have been shown to be the most critical downstream targets of Mixed Lineage Leukemia (MLL) fusion proteins [17], and their co-expression is sufficient to induce acute myeloid leukemia [14], [16], recapitulating MLL-ENL-induced immortalization of myeloid progenitor cells [18].