Blockade of β-adrenergic receptor signaling improves cancer vaccine efficacy through its effect on naive CD8+ T-cell priming

{beta}-adrenergic receptor ({beta}-AR) signaling, by acting directly on tumor cells and angiogenesis, has been showed to exert pro-tumoral effects. Growing evidence also suggests that {beta}-AR expressed by immune cells affect the associated anti-tumor immune response. However, how and where {beta}-AR signaling impinges the anti-tumor immune response is still unclear. Using a mouse model of vaccine-based immunotherapy, we show here that propranolol, a non-selective {beta}-blocker, strongly improved the efficacy of the vaccine by enhancing the frequency of CD8+ T lymphocytes infiltrating the tumor (TILs). However, propranolol had no obvious effect on the reactivity of CD8+ TILs, a result further strengthened by ex-vivo experiments showing that these cells are insensitive to AR signaling triggered by adrenaline or noradrenaline. In contrast, we show that naive CD8+ T cell activation was strongly inhibited by {beta}-AR signaling and that the beneficial effect of propranolol mainly occurred during their initial priming phase. We also demonstrate that the differential sensitivity of CD8+ TILs and naive CD8+ T cells is related to their activation status since in vitro-activated CD8+ T cells behaved similarly to CD8+ TILs, both exhibiting a down-regulation of the {beta}2-AR expression. These results reveal that the initial priming phase of the anti-tumor response in the tumor-draining lymph node is a decisive part of the suppressive effect of {beta}-AR signaling on the CD8+ T-cell response against cancer. These findings provide a rationale for the strategic use of clinically available {beta}-blockers in patients to improve cancer immunotherapies such as anti-cancer vaccination strategies.