PROJECT ABSTRACT Dendritic cells (DCs) are immune sentinel cells that can be activated by innate stimuli to orchestrate adaptive immune responses. Conventional DCs (cDCs) efficiently present and cross-present antigens to prime T cell responses, whereas plasmacytoid DCs (pDCs) rapidly produce type I interferon (IFN-α/β, IFN-I) and other cytokines in response to pathogen-derived nucleic acids. Recent studies revealed an intricate topological organization of the genome into topologically associated domains (TADs) established through cohesin- mediated loop extrusion and demarcated by binding sites of transcription factor CTCF. CTCF/cohesin- mediated chromatin architecture is thought to control cell type-specific gene expression programs, thereby facilitating cell differentiation and function. However, the topological chromatin landscapes of DCs and their role in DC differentiation and function are poorly understood. The overall goal of the project is to characterize the chromatin architecture in DCs and elucidate the chromatin-level control of DC function. In Aim 1, we will examine the role of CTCF/cohesin-mediated regulation in the differentiation of DC subsets. In Aim 2, we will analyze the role of cohesin in DC function, including cytokine responses and antigen presentation. In Aim 3, we will analyze the architecture of the locus encoding IFN-I genes, and the role of chromatin in the control of interferon production in DCs. Collectively, these results would provide novel insights into the role and mechanism of chromosomal organization in the regulation of DC differentiation and function.