Abstract 906: High K+ in tumors impairs T cell effector activity via lysosomal acidification-induced autophagy

Abstract Effective antitumor T cell response necessitates nutrient uptake and utilization. Here, we demonstrate that potassium (K+) accumulation within the tumor microenvironment (TME) drives adaptive changes in T cell metabolism via K+-dependent lysosomal acidification. We found that lysosomal acidification promotes a catabolic state in CD8+ T cells that persists independently of extracellular glucose levels (i.e. functional caloric restriction) and limits T cell effector functions while enhancing persistence.We previously identified a specific elevation in extracellular K+ (↑[K+]ex) within tumors, which dampens mTOR activation and effector functions in both CD8+ and CD4+ T cells (Eil et al, Nature 2016). ↑[K+]ex increased intracellular K+ ([K+]in) and drove selective mitochondrial acetyl-CoA accumulation at the expense of nuclear histone acetylation, enhancing mitochondrial function and limited epigenetic programming of T cells (Eil & Vodnala et al, Science 2019). Here, we report that ↑[K+]ex in the TME also produced reduced glycolytic flux, even in the presence of abundant glucose, highlighting a rerouting of nutrient processing under K+-rich conditions. The prior theoretical model of K+ as a solely a regulator Vm, and thereby TCR induced Ca2+ influx, fails to account for the metabolic reprogramming observed under K+-rich conditions in the TME.To support the development of a new model defining effective ionic T cell responses to the high K+ TME, we pursued an in vivo CRISPR-Cas9 screen targeting ion transporters in a syngeneic melanoma model. Our results pointed to the critical role of lysosomal H+ importers in CD8+ T cell persistence. Genetic or pharmacologic enhancement of lysosomal H+ importers augmented autophagy, lysosomal acidification and function, and T cell persistence. Moreover, while ↑[K+]ex enhanced lysosomal acidification and persistence, genetic depletion of [K+]in produced lysosomal de-acidification, unleashed Akt-mTOR activation, and compromised persistence. These findings reveal lysosomal pH as a key determinant of T cell persistence in the TME, highlighting a mechanism of dynamic metabolic adaptation of T cells required to perform in differential ionic environments.Our findings suggest a model whereby lysosomal ion transport governs T cell adaptation, underscoring nutrient processing, in addition to availability, as a significant mediator of metabolism. The interplay between [K+]in and lysosomal pH highlights novel intervention points for genetic and pharmacologic interventions modulating T cell function in cancer immunotherapy. Citation Format: Robert L. Eil, Chelsea Jenkins, Jessica Briones, Matthew McWhorter, Alexandra Bartlett. High K+ in tumors impairs T cell effector activity via lysosomal acidification-induced autophagy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 906.