MEIS1 and leukemia: Indeed, the absence of Prep1 leads to increased Meis1 protein also in hematopoietic cells, and this level increases in the subsequent transplantations of the leukemic cells (Figure 2). Increased Meis1 is bound to affect the self-renewal of transduced cells, since Meis1 quantitatively regulates the leukemic stem cell frequency [32], and the aggressiveness of the leukemias, as Meis1 regulates the latency of MLL leukemias [22].