The immune context of tumors has significant prognostic value and is predictive of responsiveness to several forms of therapy, including immunotherapy. We report here that CD8+ T cell frequency and functional orientation within the tumor microenvironment is regulated by β2-adrenergic receptor (β-AR) signaling in host immune cells. We used three strategies - physiologic (manipulation of ambient thermal environment), pharmacologic (β-blockers), and genetic (β2-adrenergic receptor knockout mice) to reduce adrenergic stress signaling in two widely studied preclinical mouse tumor models. Reducing β-AR signaling facilitated conversion of tumors to an immunologically active tumor microenvironment with increased intra-tumoral frequency of CD8+ T cells with an effector phenotype and decreased expression of PD-1, in addition to an elevated effector CD8+ T cell to CD4+ regulatory T cell ratio (IFN-γ+CD8+:Treg). Moreover, this conversion significantly increased the efficacy of anti-PD-1 checkpoint blockade. These data highlight the potential of adrenergic stress and norepinephrine-driven β-adrenergic receptor signaling to regulate the immune status of the tumor microenvironment and supports the strategic use of clinically available β-blockers in patients to improve responses to immunotherapy.

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Synopsis: T-cell exhaustion impacts immunotherapy efficacy. How T-cell exhaustion is regulated remains incompletely understood. Here, the sympathetic stress response is shown to regulate the development of T-cell exhaustion by modulating CD8 + T-cell metabolism and function in the TME.

Highlights d Tumor progression increases the expression of b2-AR on MDSCs d b2-AR signaling increases fatty acid oxidation and oxidative phosphorylation in MDSCs d b2-AR signaling in MDSCs increases autophagy-mediated PGE2 production

Stress in patients and pre-clinical research animals plays a critical role in disease progression Activation of the sympathetic nervous system (SNS) by stress results in secretion of the catecholamines epinephrine (Epi) and norepinephrine (NE) from the adrenal gland and sympathetic nerve endings. Adrenergic receptors for catecholamines are present on immune cells and their activity is affected by stress and the accompanying changes in levels of these neurotransmitters. In this short review, we discuss how this adrenergic stress impacts two categories of immune responses, infections and autoimmune diseases. Catecholamines signal primarily through the β2-adrenergic receptors present on innate and adaptive immune cells which are critical in responding to infections caused by pathogens. In general, this adrenergic input, particularly chronic stimulation, suppresses lymphocytes and allows infections to progress. On the other hand, insufficient adrenergic control of immune responses allows progression of several autoimmune diseases.