Final Report Summary - SKINIMMUNITY (The Role of Langerhans Cells in T-Cell Priming During Intradermal Naked DNA Immunization) Plasmid DNA and lentiviral vectors are potent vaccine modalities that effectively induce cellular immune responses. Following intradermal immunisation, dendritic cells (DCs) migrate from the skin to the draining lymph nodes (LN) in order to present vector-encoded antigen to T cells for their specific activation. Skin DCs can be divided into at least three subsets: epidermal Langerhans cells (LCs), langerin-positive dermal DCs (Ln+ dDCs) and langerin-negative dermal DC (dDCs). The precise role of each DC subset in skin immunisation remains controversial and appears to depend on the nature of the infectious agent or vector employed. In this study we employed plasmid DNA and lentiviral vectors to dissect the role of skin DC following intradermal immunisation. We characterised the role of each skin DC subsets following immunisation with plasmid DNA (Elnekave-M et al. 2010 Journal of Immunology) and lentivectors (Furmanov-K et al. 2010 Journal of Immunology). We demonstrated that the noted vaccine modalities differentially activated skin DCs for induction of antigen-specific CD8+ T cells. While langerin-expressing DCs (i. e. LCs and/or Ln+ dDCs) were crucial for plasmid DNA-mediated immunity, these cells were negligible during immunisation with lentivectors as dDCs were the subset presenting antigen to T cells. We further analyzed DC function in the described experimental setting. First, we characterised the origin and function of newly recruited LCs during inflammatory response generated by plasmid DNA immunisation, and found a unique role for LCs and their epidermal precursors in immune induction. In another project, we provided a novel explanation for the inability of lentivectors to activate efficiently memory T cells following boosting intradermal immunisation. We demonstrated that lentivectors trigger exceptionally slow kinetics of antigen expression in the skin, while optimal activation of lentivector-induced T cells relays on durable expression of the antigen. These qualities hamper secondary responses, since lentivector-encoded antigen is rapidly cleared by primary cytotoxic T cells that limit its presentation by skin DCs. Finally, we extended our research to DCs of the oral mucosa. We used plasmid DNA to dissect the role of oral DCs in distinct niches of the oral cavity (the buccal versus the lining mucosa). Our results indicate that each oral mucosal tissue engaged different subsets of DCs for T-cell immune induction (Nudel-I et al. 2011 journal of Immunology). Taken together, the data generated by the above studies should increase our understating on the immunological mechanisms involve in genetic immunisation. We hope that this knowledge will be translated in future vaccine studies in order to modulate skin immunity and to improve vaccine efficacy.