Continuous expression of TOX safeguards exhausted CD8 T cell epigenetic fate

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