Chronic XBP1s-mediated activation of the unfolded protein response impairs CD8+ T cell anti-tumor immunity.

CD8+ T cells play a crucial role in anti-tumor immunity; however, their functionality is compromised by exhaustion driven by chronic antigen exposure, poor tumor microenvironment, and metabolic dysfunction. Activated CD8+ T cells undergo extensive proteomic remodeling, which includes the induction of the IRE1-XBP1 signaling axis of the unfolded protein response. However, the functional consequences of sustained IRE1-XBP1 activation in exhausted CD8+ T cells remain elusive. Using a model of constitutive XBP1 activation in CD8+ T cells, we demonstrate that sustained XBP1s signaling leads to reduced homeostatic CD8+ T cell populations, impaired migratory capacity, and dampened anti-tumor immunity. Notably, pharmacological inhibition of the IRE1-XBP1 axis significantly reduces tumor burden through a dual mechanism that targets both tumor cells and the immune compartment. Our findings reveal a previously unappreciated role for XBP1s in regulating CD8+ T cell biology and highlight the IRE1-XBP1 axis as a therapeutic target in solid tumors.