Intracellular K+ limits T cell exhaustion and preserves antitumor function

Abstract

The cancer-killing activity of T cells is often compromised within tumors, allowing disease progression. We previously found that intratumoral elevations in extracellular K+ related to ongoing cell death constrained CD8+ T cell Akt-mTOR signaling and effector function (1,2). To alleviate K+ mediated T cell suppression, we pursued genetic means to lower intracellular K+. Transcriptomic analysis of CD8+ T cells demonstrated the Na+/K+ ATPase to be robustly and dynamically expressed. CRISPR-Cas9 mediated deletion of the catalytic alpha subunit of the Na+/K+ ATPase lowered intracellular K+ but produced tonic hyperactivity in multiple signal transduction cascades along with the acquisition of co-inhibitory receptors and terminal differentiation in mouse and human CD8+ T cells. Mechanistically, Na+/K+ ATPase disruption led to ROS accumulation due to depletion of intracellular K+ in T cells. Antioxidant treatment or high K+ media prevented Atp1a1 deficient T cells from exhausted T (TEx) cell formation. Consistent with transcriptional and proteomic data suggesting a TEx cell phenotype, T cells lacking Atp1a1 had compromised persistence and antitumor activity in a syngeneic model of orthotopic murine melanoma. Translational application of these findings will include efforts to lower intracellular K+ while limiting ROS accumulation within tumor specific T cells. SynopsisHigh extracellular K+ ({uparrow}[K+]e) is found within tumors and suppresses T cell effector function. Collier et al. find that deletion of the Na+/K+ ATPase in T cells lowers intracellular K+ and promotes ROS accumulation, tonic signal transduction and T cell exhaustion owing to ROS accumulation. Engineering T cell ion transport is an important consideration for cancer immunotherapy.