Antitumor therapeutic vaccination induces immunosuppressive dendritic cells. Mus musculus

Vaccination induces immunostimulatory signals which are often accompanied by regulatory mechanisms such as IL-10, which control T-cell activation and inhibit vaccine-dependent antitumor therapeutic effect. Thus, here we characterized IL-10-producing cells treated with therapeutic vaccines. Although several cell subsets produced IL-10 irrespective of treatment, an early vaccine-dependent induction of IL-10 was detected in dendritic cells (DC). IL-10 production defined a DC population characterized by a poorly mature phenotype, lower expression of T-cell stimulating molecules and upregulation of PD-L1. These IL-10+ DC showed impaired in vitro T-cell stimulatory capacity, which was rescued by incubation with IL-10R and PD-L1-inhibiting antibodies. In vivo IL-10 blockade during vaccination decreased the proportion of IL-10+ DC and improved their maturation, without modifying PD-L1 expression. Similarly, PD-L1 blockade did not affect IL-10 expression, suggesting independent regulation of these molecules. Interestingly, vaccination combined with simultaneous blockade of IL-10 and PD-L1 induced stronger immune responses, resulting in a higher therapeutic efficacy in tumor-bearing mice. These results show that vaccine-induced immunoregulatory DC with dual expression of IL-10 and PD-L1 impair priming of antitumor immunity, suggesting that therapeutic vaccination protocols may benefit from combined targeting of these molecules. Overall design: Vert-X mice (n=10) were immunized with OVA + Imiquimod and two day later spleens were harvested an pooled. Splenic IL-10+ and IL-10- DC from pooled material were purified by using anti-CD11c-conjugated magnetic beads followed by staining with CD11c-APC antibodies and separation with a FACSAria flow cytometer according to their expression of IL-10 (GFP). Gene expression in IL-10+ and IL-10- DC was compared.