T cell cross priming (the initiation of CD8+ T cell responses to antigen that are not expressed by dendritic cells, DCs) requires the phagocytosis of antigens by DCs and their presentation on MHC class I molecules, a process referred to as “cross presentation”. Here, we propose a series of integrated approaches to address the most fundamental mechanisms of cross presentation and explore the use of this process for translational purposes in human cancer.This proposal will pursue three main objectives:1) To analyze the mechanisms of control of antigen cross presentation and phagocytic functions in DCs. We will use genome wide screens and conditional KO mice, associated to quantitative assays for phagosomal functions and cross presentation, to investigate the molecular mechanisms of cross presentation in vitro and in vivo.2) To study the epigenetic programing of cross presentation during the ontogeny of mouse DC subpopulations. We will define a “cross presentation gene signature” that will be validated by systematic gene silencing in vitro and we will analyze the epigenetic basis of control of cross presentation-related genes developing DCs.3) To investigate the regulation of cross presentation in human primary DCs and to develop translational approaches in cancer. We will study cross presentation and phagosome functions in primary human DC subpopulations and its regulation by innate receptors for the development of original immunomodulation and vaccination strategies. We will explore the use of DCs cross presentation abilities in solid tumor infiltrating DCs and their use for prognosis in cancer.The results of this project will unravel fundamental mechanisms of phagocytosis and its control by innate signals in mice and humans. The proposal also aims at defining new possible strategies for cancer treatment and prognosis.