Tox reinforces the phenotype and longevity of exhausted T-cells in chronic viral infection [ATAC-seq]

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. C57BL/6 mice engrafted with wt or Tox∆Ex5 2x10^3 P14 T-cells were infected with 2x10^6 PFU of LCMV clone-13. On day 8 post infection, splenic wt and Tox∆Ex5 P14 T-cells were sorted into Tim-3+ and Tim-3- T-cells and whole-genome DNA methylation analysis was performed as previously described (Ghoneim, et al. Cell 2017, PMID: 28648661). On day 8 and day 13 post infection, ATAC-seq was performed on splenic wt and Tox∆Ex5 P14 T-cells.