Enhancing Proteasome Activity in T Cells Alleviates Exhaustion and Improves Antitumor Immunity

Chronic T cell receptor (TCR) stimulation combined with adverse conditions in the tumor microenvironment (TME), such as hypoxia and nutrient deprivation, frequently results in T cell exhaustion. Exhausted T cells (TEX) experience oxidative stress, which causes an accumulation of oxidized proteins within the cells. We hypothesized that oxidized protein formation might exceed proteasomal degradation capacity, leading to their accumulation and impairing T cell fitness. Single-cell transcriptomics analysis across 16 tumor types revealed increased expression of proteasome genes in TEX compared to non-exhausted T cells. In a robust in vitro model for the generation of human TEX, the cells exhibited hallmarks of exhaustion, with higher levels of reactive oxygen species (ROS)-induced protein oxidation and increased expression of proteasome genes. Pharmacological and genetic enhancement of proteasome activity delayed the onset of T cell exhaustion, improved T cell fitness, and translated into superior antitumor immunity and tumor control. These findings identify proteasome modulation as a promising strategy to counteract TME-driven T cell dysfunction, potentially overcoming a major obstacle to the efficacy of cell-based immunotherapies in solid tumors. Overall design: Exhausted human CD8+ T cells were generated by two stimulations with anti-CD3 and anti-CD28 antibodies in the presence of IL-2, followed by two additional stimulations under reduced glucose and normoxia (21% O2) or hypoxia (1% O2). Non-exhausted T cells were generated by a single stimulation cultured with standard glucose levels in normoxia.