Adrenergic Stress Regulates The Exhausted Phenotype Of T Cells In The Tumor Microenvironment

We have shown previously that host adrenergic stress (model of standard ambient temperature-induced chronic stress) slows tumor progression by enhancing CD8+ T-cell activation and limiting the suppressive function of myeloid-derived suppressor cells in the tumor microenvironment (TME). We also found that reducing/blocking β-adrenergic receptor (β-AR) signaling significantly improves anti-tumor immune responses and efficacy of immune checkpoint immunotherapy. It has been reported that expression of immune checkpoint receptors (e.g. PD-1, TIM3, LAG3) is characteristic of exhausted T-cells and has been linked to failure of immune checkpoint inhibitors. Now we report that host adrenergic stress plays a previously unrecognized role in regulating T-cell exhaustion in the TME. In murine melanoma and colon cancer models, we found that propranolol (a pan β-AR blocker) significantly reduces the number of exhausted T-cells expressing immune checkpoint receptors in the TME and increases numbers of T-cells expressing effector cytokines. The overexpression of immune checkpoint receptors has also been associated with mitochondrial dysfunction. Our previous work shows that β-AR signaling during CD8+ T-cell activation in vitro impairs metabolic reprogramming. In new in vivo data, we observed that propranolol treatment increases both glycolysis and oxidative phosphorylation in tumor infiltrating CD8+ T-cells. Together these data suggest that β-AR signaling is a significant factor regulating the functional status of CD8+ T-cells in the TME. Blockade and/or reduction of adrenergic stress has the potential to improve anti-tumor immunity as well as the efficacy of immune checkpoint inhibitors.