O-GlcNAc Transferase Promotes Eomesodermin-mediated Exhaustion of CD8+ Cytotoxic T Lymphocytes

Prolonged exposure to antigens drives CD8+ cytotoxic T lymphocytes (CTLs) to a hypofunctional state known as exhaustion, which compromises their ability to control infections and cancer. Here, we identify O-GlcNAcylation (O-GlcNAc)—a nutrient-sensitive post-translational modification—as a critical regulator for CTL exhaustion. Exhausted CTLs elevated nucleus O-GlcNAc levels, coupled with increased levels of the cellular uridine diphosphate GlcNAc (UDP-GlcNAc) relative to their effector counterparts. Using quantitative chemoenzymatic O-GlcNAcomic analysis, we identified a T-box transcription factor downstream of TCF-1-centered exhaustion transition and sustenance, eomesodermin (Eomes), which undergoes intensive O-GlcNAcylation. Mechanistically, mutation of the primary O-GlcNAc sites on Eomes abolished its glycosylation, but their phosphorylation and interactions with O-GlcNAc transferase (OGT) were unaffected. OGT/Eomes was indispensable for interaction with TCF-1. OGT stabilized Eomes and increased its accumulation in the nucleus, where T-bet-to-Eomes transcriptional transition drives functional exhaustion. These results uncover a novel regulatory relationship between OGT and the TCF-1/Eomes axis in promoting CTL exhaustion and impairing their protective function.