Control of naive T cell reactivity and peripheral tolerance by ascorbate and TET activity.

Abstract

Peripheral tolerance depends on limiting conventional T cell responses to self-antigens. To define the contribution of nutritional factors and related epigenetic regulation, we perform in vivo CRISPR screening and identify the ascorbate transporter Slc23a2 as a key regulator of naive T cell (Tn) reactivity. T cell-specific loss of <i>Slc23a2</i> reduces intracellular ascorbate, induces regional DNA hypermethylation, enhances differentiation of Tn cells into effector and memory populations, and promotes low-grade autoimmune inflammation. These phenotypes mirror those caused by ascorbate deprivation, <i>TET</i> dioxygenase deficiency, and aging. Mechanistically, Slc23a2 maintains TET enzymatic activity through ascorbate, dampens proximal TCR signaling, represses helper T cell lineage programs, and sustains Tcf1 expression and chromatin binding in Tn cells. Deletion of <i>Tcf7</i> partially phenocopies <i>Slc23a2</i> deficiency, whereas Tcf1 overexpression mitigates the effects. Together, these findings identify ascorbate and TET-dependent DNA demethylation as a checkpoint that restrains Tn cell reactivity to self-antigens, thereby maintaining peripheral tolerance, a process compromised with aging.