IL-10 expression defines an immunosuppressive dendritic cell population induced by antitumor therapeutic vaccination

// Diana Llopiz 1, 2 , Marta Ruiz 1, 2 , Stefany Infante 1 , Lorea Villanueva 1 , Leyre Silva 1, 2 , Sandra Hervas-Stubbs 1, 2 , Diego Alignani 2, 3 , Elizabeth Guruceaga 2, 4 , Juan J. Lasarte 1, 2 , Pablo Sarobe 1, 2 1 Program of Immunology and Immunotherapy, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain 2 IdiSNA, Instituto de Investigacion Sanitaria de Navarra, Pamplona, Spain 3 Cytometry Unit, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain 4 Bioinformatics Unit, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain Correspondence to: Pablo Sarobe, email: psarobe@unav.es Keywords: dendritic cells, therapeutic vaccination, IL-10, PD-L1, immunoregulation Received: September 14, 2016      Accepted: November 22, 2016      Published: December 01, 2016 ABSTRACT Vaccination induces immunostimulatory signals that are often accompanied by regulatory mechanisms such as IL-10, which control T-cell activation and inhibit vaccine-dependent antitumor therapeutic effect. Here we characterized IL-10-producing cells in different tumor models 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. 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 IL- 10 + DC impair priming of antitumor immunity, suggesting that therapeutic vaccination protocols may benefit from combined targeting of inhibitory molecules expressed by this DC subset.