Acute Myeloid Leukaemia (AML) is characterized by aberrant proliferation of clonal myeloid stem and progenitor cells. Mutations in the DNA Methyltransferase 3a (DNMT3A) and other epigenetic regulators have been identified as initiating events in AML. DNMT3A is mutated in ~20% of AMLs making it one of the most frequently mutated genes. Therefore, we have used CRISPR/Cas9 technology to introduce the most prevalent mutation found in human DNMT3a in mice by mutating R878 (murine homologue of R882) to histidine. The DNMT3Amut mice do not spontaneously develop AML, which is consistent with previous studies that suggest that other oncogenic drivers, such as NRASmut or IDH2mut, are required for malignant transformation. Therefore, we have transduced haematopoietic stem and progenitor cells (HSPCs) derived from DNMT3Amut and wildtype foetal liver cells with retroviral constructs encoding for NRASG12D and IDH2R140Q and transplanted them into lethally irradiated recipient mice. While co-expression of IDH2mut in DNMT3amut foetal liver cells led with very low penetrance and long latency (~300 days) to increased HSC frequencies and first signs of malignancy, NRASmut co-expression induced T-ALL in a high proportion of mice transplanted with DNMT3amut/ NRASmut foetal liver cells. We are currently establishing cell lines from the different DNMT3amut cancer cells allowing us to compare the epigenetic landscape between wildtype and DNMT3amut cells. In order to test, whether DNMT3amut is required for the sustained growth of the malignant cells, we have introduced an additional sgRNA binding site into the mutant DNMT3A allele. By targeting this allele, we can effectively delete the mutant DNMT3A in the cancer cells and track the survival of leukaemic cells in vitro and in vivo. These experiments will be combined with standard chemotherapy and targeted therapies to find potential treatment regimens useful in the clinic for patients presenting with DNMT3amut cancers.