The treatment of immature acute leukemia of ambiguous lineage is a dilemma. It is a heterogeneous subgroup of patients with an unclear lineage of origin and therefore it is unclear whether they should be treated with a protocol for myeloid or for lymphoblastic leukemia. The prognosis for these patients is unfavorable, with survival rates of only 60% five years after diagnosis. Efforts must be made to better understand the origin and behavior of this subset of immature leukemias in order to identify novel therapeutic targets. Our unpublished results show that the transcription factor MEF2C plays an important role in the development of immature acute leukemia with multi-lineage expression markers. Based on these new insights, we are convinced that transient suppression of MEF2C expression or its oncogenic functions may be a valid targeted therapeutic strategy to better treat these patients. The aim of this project is to develop and optimize such a new therapeutic strategy.