Continuous expression of TOX safeguards exhausted CD8 T cell epigenetic fate

Although checkpoint blockade temporarily improves exhausted CD8 T (Tex) cell function, the underlying Tex epigenetic landscape remains largely unchanged, preventing durable Tex "reinvigoration" in cancer and chronic infections. The transcription factor TOX initiates Tex epigenetic programming, yet it remains unclear whether TOX continually preserves Tex biology after Tex establishment. Here, we demonstrated that induced TOX ablation in committed Tex cells resulted in apoptotic-driven loss of Tex cells, reduced expression of inhibitory receptors, and decreased terminal differentiation. Gene expression and epigenetic profiling revealed a critical role for TOX in maintaining chromatin accessibility and transcriptional patterns in committed Tex cells. Moreover, TOX removal endows established Tex cells with greater fate flexibility to differentiate into more functional effector-like T cells. Thus, continuous TOX expression in established Tex cells acts as a durable epigenetic barrier reinforcing the Tex developmental fate. TOX manipulation even after Tex establishment could therefore provide therapeutic opportunities to rewire Tex cells in chronic infections or cancer.