ECSIT facilitates memory CD8 T cell development by mediating fumarate synthesis during viral infection and tumorigenesis.

Memory CD8 T cells play a crucial role in infection and cancer and mount rapid responses to repeat antigen exposure. Although memory cell transcriptional programmes have been previously identified, the regulatory mechanisms that control the formation of CD8 T cells have not been resolved. Here we report ECSIT as an essential mediator of memory CD8 T cell differentiation. Ablation of ECSIT in T cells resulted in loss of fumarate synthesis and abrogated TCF-1 expression via demethylation of the TCF-1 promoter by the histone demethylase KDM5, thereby impairing memory CD8 T cell development in a cell-intrinsic manner. In addition, ECSIT expression correlated positively with stem-like memory progenitor exhausted CD8 T cells and the survival of patients with cancer. Our study demonstrates that ECSIT-mediated fumarate synthesis stimulates TCF-1 activity and memory CD8 T cell development during viral infection and tumorigenesis and highlights the utility of therapeutic fumarate analogues and PD-L1 inhibition for tumour immunotherapy.