| Summary: | Programmed death-ligand 1 (PD-L1) and its receptor programmed cell death protein 1 (PD-1) modulate antitumor immunity and are major targets of checkpoint blockade immunotherapy. However, clinical trials of anti-PD-L1 and anti-PD-1 antibodies in breast cancer demonstrate only modest efficacy. Furthermore, specific PD-L1 contributions in various tissue and cell compartments to antitumor immunity remain incompletely elucidated. Here we show that PD-L1 expression is markedly elevated in mature adipocytes versus preadipocytes. Adipocyte PD-L1 prevents anti-PD-L1 antibody from activating important antitumor functions of CD8+ T cells in vitro. Adipocyte PD-L1 ablation obliterates, whereas forced preadipocyte PD-L1 expression confers, these inhibitory effects. Pharmacologic inhibition of adipogenesis selectively reduces PD-L1 expression in mouse adipose tissue and enhances the antitumor efficacy of anti-PD-L1 or anti-PD-1 antibodies in syngeneic mammary tumor models. Our findings provide a previously unappreciated approach to bolster anticancer immunotherapy efficacy and suggest a mechanism for the role of adipose tissue in breast cancer progression.
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