Antigen Targeting to CD11b Allows Efficient Presentation of CD4+ and CD8+ T Cell Epitopes and In Vivo Th1-Polarized T Cell Priming

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Abstract
Bordetella pertussis adenylate cyclase (CyaA) is an invasive bacterial toxin that delivers its N-terminal catalytic domain into the cytosol of eukaryotic cells bearing the αMβ2 integrin (CD11b/CD18), such as myeloid dendritic cells. This allows use of engineered CyaA for targeted delivery of CD8+ T cell epitopes into the MHC class I pathway of APC and induction of robust and protective cytotoxic responses. In this study, we demonstrate that CyaA can efficiently codeliver both a CD8+ T cell epitope (OVA257–264) and a CD4+ T cell epitope (MalE100–114) into, respectively, the conventional cytosolic or endocytic routes of processing of murine bone marrow-derived dendritic cells. Upon CyaA delivery, a strong potentiation of the MalE100–114 CD4+ T cell epitope presentation is observed as compared with the MalE protein, which depends on CyaA interaction with its CD11b receptor and its subsequent clathrin-mediated endocytosis. In vivo, CyaA induces strong and specific Th1 CD4+ and CD8+ T cell responses against, respectively, the MalE100–114 and OVA257–264 epitopes. These results underscore the potency of CyaA for design of new vaccines.