Reinvigoration of translational activity in dysfunctional T cells initiates theearly intratumoral response to PD-1 blockade

T cells are key effectors of antitumor responses elicited by PD-1 blockade. However, it remains elusive by which mechanism(s) PD-1 blockade initiates T cell-driven antitumor immunity in cancer tissues. Here, we dissect early T cell reactivation upon anti-PD-1 in patient-derived tumor fragments. Using bispecific antibodies to target anti-PD-1 to individual T cell subsets, we demonstrate that intratumoral CD8+ and CD4+ T cells can independently drive immune remodeling of the tumor microenvironment. The CD8+ and CD4+ T cells that respond to anti- PD-1 exhibit a shared dysfunctional gene program, characterized by tumor-reactivity, terminal exhaustion, effector capacity, and reduced translational activity. Notably, rather than acting through transcriptional rewiring, anti-PD-1 reinvigorates dysfunctional T cells by overcoming this translational barrier, resulting in restored effector function. Altogether, these results reveal dysfunctional T cells as initiators of early tissue responses to PD-1 blockade and identify a novel mode of their therapeutic reinvigoration through restoration of translational control. One Sentence SummaryTranslational reactivation of tumor-residing dysfunctional T cells drives early intratumoral immune activity upon PD-1 blockade.