An epigenetic switch in vascular phenotype augments anti-tumor immunity

The abnormal tumor vasculature can present a barrier to the infiltration of anti-tumor immune cells, which impairs immune surveillance and response to immunotherapy. Here, we show that targeting the epigenetic factor DNA methyltransferase 1 in endothelial cells (ECs) reduces angiogenesis while imparting profound changes to the tumor immune microenvironment (TIME), including increased proportions of CD4+ memory T-cells and NK cells. Depleting CD4+ T-cells, or blocking lymphocyte egress from the lymph nodes with FTY720, rescues tumor growth in mice with conditional deletion of Dnmt1 in ECs (Dnmt1iECKO) and dramatically shortens overall survival, whereas NK cells are dispensable. Tumors implanted in Dnmt1iECKO mice show reduced vascular branching, elevated expression of Vcam1, increased vessel-associated T-cells, and a shift in vascular specification including increased proportions of immune-permissive post-capillary venules (PCVs) and interferon-stimulated ECs (IFN-ECs). Deleting Dnmt1 in EC cultures strikingly potentiates responses to combinations of IFN{gamma} and TNF and, notably, up-regulates important T-cell co-stimulatory molecules for memory CD4+ T-cells, including Icosl, Cd40, and Tnfsf4. Finally, immune checkpoint blockade (ICB) administered to Dnmt1iECKO mice with experimental melanoma lung metastasis reduces tumor burden, with some mice showing tumor eradication. Our findings identify endothelial Dnmt1 as a key regulator of vascular-mediated anti-tumor immunity, providing a rationale for integrating epigenetic modulation of the vasculature with cancer immunotherapy regimens.