Generation and characterization of a humanized mouse model of Crohn’s disease Crohn’s-disease (CD) and ulcerative colitis (UC) are the two major forms of inflammatory bowel disease (IBD), a chronic inflammatory disorder that affects an estimated 3 million Americans. The etiopathogenesis of CD is distinctive for each patient and involves a complex interaction between genetic factors, the immune system, the gut microbiota and other environmental factors. Mouse models of IBD have been invaluable in providing critical mechanistic insights into its complex etiopathogenesis and in indicating new potential therapeutic targets. However, it has been particularly difficult to translate advances in our understanding of IBD pathogenesis into novel therapies that prove successful in the clinic. A major obstacle is that mice and humans, despite their similarities, have fundamental differences in their intestinal physiology and, crucially, in the function of their immune system. A second problem is that the vast majority of mouse models of IBD recapitulate aspects of the natural history of UC but not the unique pathology of CD. Not surprisingly, notable examples of clinical trials that failed in CD patients were originally guided by mouse models of colitis at the preclinical level. One inviting avenue for pre-clinical testing is humanized mouse modeling, where human hematopoietic stem cells (HSCs) are engrafted into immunodeficient mice and a human immune system develops in the mouse host. Humanized mouse models allow to study the function of human immune cells in vivo without directly involving human patients. Despite recent progress in the humanization of the immune system in mice, the development of humanized models of IBD is lagging behind and has been limited to the chemical induction of colitis upon transfer of human CD4+ T-cells. Translational animal models that faithfully recapitulate human CD pathology have been lacking. In this project we aim to develop the first humanized mouse model of CD. For this purpose we will integrate two state-of-the-art mouse models: a genetic mouse model that specifically resembles the pathological and mechanistic features of human CD and the MISTRG6 humanized model which supports the most comprehensive humanization of the immune system achieved to date, including not only T, B and NK cells, but also myeloid populations crucial in CD such as macrophages and neutrophils. Major goals of this pilot project are to 1) generate these mice by CRISPR/Cas9 engineering and optimize the humanization of their immune system and 2) determine the kinetics of humanized Crohn’s pathogenesis and thoroughly characterize its phenotypic aspects at the level of tissue pathology and intestinal immune responses. This humanized system will be an important and unique preclinical/translational tool for the CD research community. It will reveal pathways employed by human immune cells to drive CD pathogenesis and also enable future studies assessing th...