Deciphering the mechanisms that allow the induction of strong immune responses is crucial to developing efficient vaccines against infectious diseases and cancer. Based on the discovery that the adenylate cyclase from Bordetella pertussis binds to the CD11b/CD18 integrin, we developed a highly efficient detoxified adenylate cyclase-based vector (CyaA) capable of delivering a large variety of Ags to the APC. This vector allows the induction of protective and therapeutic immunity against viral and tumoral challenges as well as against transplanted tumors in the absence of any added adjuvant. Two therapeutic vaccine candidates against human papilloma viruses and melanoma have been developed recently, based on the CyaA vector, and are currently in clinical trials. We took advantage of one of these highly purified vaccines, produced under good manufacturing practice-like conditions, to decipher the mechanisms by which CyaA induces immune responses. In this study, we demonstrate that CyaA binds both human and mouse CD11b(+) dendritic cells (DCs) and induces their maturation, as shown by the upregulation of costimulatory and MHC molecules and the production of proinflammatory cytokines. Importantly, we show that DCs sense CyaA through the TLR4/Toll/IL-1R domain-containing adapter-inducing IFN-β pathway, independent of the presence of LPS. These findings show that CyaA possesses the intrinsic ability to not only target DCs but also to activate them, leading to the induction of strong immune responses. Overall, this study demonstrates that Ag delivery to CD11b(+) DCs in association with TLR4/Toll/IL-1R domain-containing adapter-inducing IFN-β activation is an efficient strategy to promote strong specific CD8(+) T cell responses.

Centre National de la Recherche Scientifique Unité Mixte de Recherche 3528 Paris F 75015 France

Division of Gene Therapy and Hepatology Centre for Applied Medical Research University of Navarra Pamplona 31008 Spain

INSERM U1041 Paris F 75015 France

Institut Pasteur Unité de Biochimie des Interactions Macromoléculaires Paris F 75015 France

Institut Pasteur Unité de Régulation Immunitaire et Vaccinologie Paris F 75015 France

Institute of Microbiology of the Academy of Sciences of the Czech Republic Verejna Vyzkumna Instituce Videnska 1083 142 20 Prague Czech Republic

Unité Mixte de Recherche 7355 Université d'Orléans Centre National de la Recherche Scientifique Laboratoire Immunologie et Neurogénétique Expérimentales et Moléculaires Orléans 45071 France