DOT1L controls NK cell maturation and lineage integrity [RNA-seq D5]

In the innate immune system, natural killer (NK) cells represent a highly important subset of cells with utmost importance in the control of transformed cell and tumour inflammation. Previous studies showed that NK cells can convert into ILC1-like cells in a TGF-β-rich tumour microenvironment (TME). In addition, cancer patients with acute myeloid leukemia (AML) or chronic lymphocytic leukemia (CLL) have increased frequencies of ILC1 cells in peripheral blood mononuclear cells (PBMCs), which show reduced production of the proinflammatory cytokines IFN-γ and TNF in addition to decreased granzyme B production. Here, we identify the histone methyltransferase DOT1L as a critical regulator of NK cell lineage integrity in vitro and in vivo. NK cells from NKp46-conditional DOT1L knockout mice (DOT1L.Ncr1) show increased frequencies of ILC1-like cells (CD49b+ CD49a+), and also express more of the ILC1 markers CD200R, TRAIL, while showing reduced expression of Ly49H. We further identify that the increased ILC1-like phenotype is largely independent of TGFβ. Assessment of transcription factor (TF) availability in the absence of DOT1L shows that the Myocyte-specific enhancer factor (MEF)2C is the highest downregulated TF in the absence of DOT1L. CRISPRCas9-mediated deletion of MEF2C ultimately provides evidence that this TF is limiting NK cell plasticity in vivo. Our findings provide evidence for a previously unknown role of DOT1L and MEF2C in NK cell biology for maintaining NK cell lineage integrity and may ultimately result in improved therapies for patients with leukemia or other NK cell-lineage dependent malignancies.