Intracellular K⁺ Limits T-cell Exhaustion and Preserves Antitumor Function

T cells are often compromised within cancers, 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. To alleviate K+-mediated T-cell dysfunction, we pursued genetic means to lower intracellular K+. CD8(+) T cells robustly and dynamically express the Na+/K+ ATPase, among other K+ transporters. CRISPR-Cas9-mediated disruption of the Atp1a1 locus lowered intracellular K+ and elevated the resting membrane potential (i.e., V-m, psi). Despite compromised Ca(2+ )influx, Atp1a1-deficient T cells harbored tonic hyperactivity in multiple signal transduction cascades, along with a phenotype of exhaustion in mouse and human CD8(+) T cells. Provision of exogenous K+ restored intracellular levels in Atp1a1-deficient T cells and prevented damaging levels of reactive oxygen species (ROS), and both antioxidant treatment and exogenous K+ prevented Atp1a1-deficient T-cell exhaustion in vitro. T cells lacking Atp1a1 had compromised persistence and antitumor activity in a syngeneic model of orthotopic murine melanoma. Translational application of these findings will require balancing the beneficial aspects of intracellular K+ with the ROS-dependent nature of T-cell effector function.