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., Vm, Ψ). Despite compromised Ca2+ 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. See related Spotlight by Banuelos and Borges da Silva, p. 6.

Intracellular K + limits T cell exhaustion and preserves antitumor function.

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 (T Ex ) cell formation. Consistent with transcriptional and proteomic data suggesting a T Ex 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. Synopsis: High extracellular K + (↑[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.