Targeting the histone methyltransferase DOT1L rewires CD8 T cells and enhances their intrinsic cytotoxic activity towards tumor cells [RNAseq_WT_KO_DMSO_EPZ]

Insights into the epigenetic mechanisms of CD8 T cell differentiation are delivering novel opportunities for modulating fate decisions and immune responses. The histone methyltransferase DOT1L is emerging as a central epigenetic regulator in immune cells. However, its cell-intrinsic role in CD8 T cell programming remains unclear as positive as well as negative roles have been ascribed to DOT1L. Here, we determined the cell-intrinsic role of DOT1L in mouse CD8 T cells using conditional ablation. In contrast to deletion of Dot1L early in the T cell lineage, conditional ablation of Dot1L in isolated mature CD8 T cells in vitro did not compromise the in vivo proliferative capacity and anti-tumor reactivity. In vitro, Dot1L knock-out CD8 T cells showed accelerated and enhanced antigen-specific cytotoxic activity towards tumor cells. Mechanistically, transcriptome and proteome profiling revealed that loss of DOT1L results in an altered cell-identity program with loss of T-cell and gain of NK-cell features. This role of DOT1L was linked to its catalytic activity since treatment with specific DOT1L inhibitors phenocopied genetic deletion of Dot1L. Our findings show that ablation of DOT1L activity is well-tolerated in mature CD8 T cells, rewires their cell identity in a tunable way towards the NK-cell lineage and enhances their cytolytic activity cell intrinsically.