Proteostatic Stress Response Drives T Cell Exhaustion and Immune Evasion

Chronic infections and cancer cause T cell dysfunction known as exhaustion due to persistent antigen exposure, suboptimal co-stimulation and a plethora of hostile factors, which dampens protective immunity and limits the efficacy of immunotherapies1-4. The mechanisms behind T cell exhaustion remain poorly understood. Herein, we dissected the proteome of CD8+ exhausted T cells (Tex) across multiple states of exhaustion in the context of both chronic viral infections and cancer. We found that there was a non-stochastic pathway-specific discordance between mRNA and protein dynamics in T effector (Teff) versus Tex cells. We identified a unique proteostatic stress response (PSR) in Tex cells which we termed TexPSR. Contrary to canonical stress responses with reduced protein synthesis5,6, the TexPSR involves increased global translation activity and an upregulation of specialized chaperones, characterized further by the accumulation of protein aggregates, stress granules and autophagy-dominant protein catabolism. We established that disruption of proteostasis alone can convert Teff to Tex cells, and linked TexPSR mechanistically to persistent Akt signaling. Finally, we found that disruption of TexPSR-associated chaperones in CD8+ T cells improved cancer immunotherapy preclinically and demonstrated that high TexPSR feature in T cells in cancer patients confers poor response to immunotherapy clinically. Our findings collectively highlight TexPSR as a hallmark and a mechanistic driver of T cell exhaustion, raising the possibility of targeting proteostasis as a potential novel approach for cancer immunotherapy.