Proteostasis sustains T cell differentiation potential and tumor-infiltrating lymphocyte function [CITE-seq]

CD8+ tumor-infiltrating lymphocytes (TIL) often fail to restrain tumor growth due to differentiation to T cell exhaustion. In healthy tissues, tissue-resident memory T cells (TRM) survey tissues and sustain protective capacity for years, and tumors that contain TIL with TRM-features are associated with better patient prognosis. We identified protein homeostasis (proteostasis) significant in distinguishing TRM and progenitor-exhausted TIL (TPEX) from terminally-exhausted TIL (TEX) by identifying multiple E3 ubiquitin ligases that maintain T cell differentiation potential. Sustained ligase-expression in TIL enhanced T cell accumulation, preserved stem-like TCF1+ populations, and improved anti-tumor function, whereas ligase loss-of-function impaired TIL and altered T cell differentiation in acute infection. TEX experience a loss of proteostasis, marked by unfolded protein accumulation despite functional proteasomes. Enforced ligase expression rescued this unfolded protein accumulation in TIL and improved immunotherapy responses, demonstrating the role of proteostasis in maintaining differentiation potential and identifying new avenues for advancing cancer immunotherapies.