Significance
We identified a highly proliferative, overactivated, and apoptotic dysfunctional CD8+ tumor-infiltrating subpopulation that is functionally distinct from previously described exhausted T cells. This population is expanded in lung cancer tissues in a PD-1/B7-H1-dependent manner, and its abundance is associated with resistance to cancer immunotherapy, thus becoming a potential tissue biomarker.This article is highlighted in the In This Issue feature, p. 1601.