Tox reinforces the phenotype and longevity of dysfunctional T cell populations during chronic viral infection [KO vs WT Day 8]

Chronic CD8 T-cell stimulation in persisting infections or tumors can induce a stable gene expression program, known as T-cell dysfunction or exhaustion, that limits the cell’s effector functions and anti-viral and anti-tumor immunity. Thus far, the underlaying molecular mechanisms that induce and stabilize this phenotype are vaguely understood. We report here that establishing this program requires the thymocyte selection-associated high mobility group-box protein (Tox). Genetic disruption of Tox augments effector function, decreases the expression of PD-1, and significantly enhances immunopathology. These changes are linked to a failure in fixing the dysfunctional phenotype in the critical Tcf1+ progenitor population and to impaired epigenetic programing. Surprisingly, the gains in effector function co-incide with declining numbers of Tcf1+ cells and result ultimately in reduced total numbers of pathogen-specific T-cells. Thus, we establish Tox as a critical factor for the development of T-cell dysfunction and establish a clear link between CD8 T-cell intrinsic suppression of effector function and protection against immune-pathology.