ABSTRACT Plasmacytoid dendritic cells (pDCs) and pDC-related cells are developmentally related innate immune cells capable of performing multiple functions essential for successful antiviral immune responses, including type I interferon secretion and T cell activation. The identity, i.e., development and function, of pDCs and pDC-related cells is controlled by the precise interaction of transcription factors (TFs). Tight regulation of transcriptional programs is essential to promote the appropriate response to pathogens while avoiding damage to healthy tissues. Thus, it is critical to unravel the transcriptional regulation of pDCs and pDC-related cells. Using a high- dimensional unbiased approach, we have recently discovered two conserved TFs that are specific and highly active in pDCs and pDC-related cells but not in other DC subsets. In two specific aims, we propose to explore the role of these TFs in determining the development and function of pDCs and pDC-related cells. To achieve our goal, we will take advantage of novel conditional knockout mouse models, transcription factor- overexpressing human cell lines, and high-dimensional approaches already established in our lab. We anticipate that findings from this proposal will bring into light novel mechanisms of transcriptional regulation that result in the positive outcome of innate immune responses against viruses. Importantly, our integrated approach will incorporate analyses of both mouse and human DCs; thus, it can reveal features that are conserved between species. This proposal has the potential to impact the rational design of therapeutic strategies by exploring regulatory programs determining the identity of key antiviral innate cells.