DOT1L controls NK cell activation and lineage integrity [ChIP-seq]

Epigenetic modifiers are promising targets to improve therapies in patients with cancer. Targeting the methyltransferase DOT1L with small molecule inhibitors has shown promising effects on the control of cancerous cells. However, these small molecules are given systemically and may have a profound impact on non-cancerous cells, such as the cells of the immune system. In the innate immune system, natural killer (NK) cells are a critical subset of cells with important roles in controlling transformed cells and tumour inflammation. Previous studies have shown that NK cells can convert into ILC1-like cells in a TGFβ-rich tumour microenvironment (TME). Additionally, 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 proinflammatory cytokines and decreased granzyme B production. In this study, we identify DOT1L as a critical regulator of NK cell activation and lineage integrity. We generated NKp46-conditional DOT1L knockout mice (DOT1L.Ncr1) and observed increased frequencies of ILC1-like cells (CD49b+ CD49a+, CD62L-) and reduced frequencies of NK cells (CD49b+ CD49a-, CD62L+) in these mice. While the absence of DOT1L increases the sensitivity to TGFβ, the increased expression of CD49a is highly intrinsic and only partially dependent on TGFβ signalling. Functionally, the increased presence of ILC1-like cells in the tumour microenvironment of DOT1L.Ncr1 mice leads to decreased tumour control. Our assessment of the transcriptional program reveals alternative uses of transcription factors, such as the AP-1 family or SMAD2/3, to maintain NK cell activation and lineage integrity. Our findings provide evidence for a previously unknown role of DOT1L in NK cell biology, and demonstrate the importance of maintaining NK cell lineage integrity for effective tumour control. These findings have significant implications for the development of improved therapies for cancer or other NK cell-lineage dependent malignancies.