Intra-tumoral hypoxia promotes CD8+ T cell dysfunction via chronic activation of integrated stress response transcription factor ATF4.

Metabolic stress in the tumor microenvironment (TME) promotes T cell dysfunction and immune checkpoint inhibitor (ICI) resistance. We examined the contribution of activating transcription factor 4 (ATF4), the central node of the integrated stress response (ISR), to T cell dysfunction in tumors. CD8+ tumor-infiltrating lymphocytes (TILs) in patient samples exhibited chronic ATF4 activity, which was reflected across various tumor models. Hypoxia in the TME imposed chronic ATF4 activity via the ISR kinases. ATF4 overexpression in CD8+ T cells induced metabolic polarity, mitochondrial oxidative stress, and cell death, impairing antitumor immunity. Chronic ATF4 transcriptional activity replicated the terminal exhaustion CD8+ T cell state independent of T cell receptor (TCR) stimulation. Genetic or pharmacologic attenuation of ATF4 reduced mitochondrial oxidative stress and promoted CD8+ TIL viability, enabling response to programmed cell death protein-1 (PD-1) inhibitor therapy and conferring protection from re-emergent disease. Thus, the ISR converges on chronic ATF4 activity in CD8+ TILs as a barrier to ICI response, positioning ISR therapeutics as candidates for immunotherapy.