Sodium chloride in the tumor microenvironment enhances T cell metabolic fitness and cytotoxicity

The efficacy of antitumor immunity is associated with the metabolic state of cytotoxic T cells, which is highly amenable to perturbation by the tumor microenvironment. It is therefore of tremendous interest to bypass immunosuppressive signaling in the tumor microenvironment and to identify factors that augment T cell immunometabolism, cytotoxic effector functions and eventually tumor killing. Whether ionic signals serve as aberrant immune signals and influence the adaptive human antitumor immune response is still largely unexplored. We demonstrate a significant enrichment of sodium in solid tumors of breast cancer patients, which leaves a transcriptomic imprint on intratumoral immune cells. Sodium chloride (NaCl) enhanced the activation state and effector functions of human CD8+ memory T cells. These functional alterations were associated with improved metabolic fitness, in particular with an increase in glycolysis and oxidative phosphorylation and overall nutrient uptake. These NaCl-induced effects translated into increased tumor cell killing in vitro and in a tumor mouse model in vivo. We therefore propose NaCl as a positive regulator of acute antitumor immunity, which could be harnessed for ex vivo conditioning of adoptively transferred T cells in the future. Overall design: For scRNA-seq, a library of human CD8+CD45RA–CD45RO+ cells that were stimulated with anti-CD3 and anti-CD28 monoclonal antibodies for 3 days in high and low NaCl conditions was constructed with Chromium Next GEM Single Cell 5' Reagents v.2 (Dual Index) (10x Genomics, Inc.). The library was sequenced on an Illumina NovaSeq 6000 Sequencing System (Flow Cell Type S4) according to the manufacturer's instructions, with 150-bp, paired-end, dual-indexing sequencing (sequencing depth: 20,000 read pairs per cell).