PROJECT SUMMARY/ABSTRACT - Canine Disease and Transplantation Model (Canine) Core Hematopoiesis is a complex process which is regulated by many internal and external factors. Numerous variables synergize or antagonize to influence differentiation and stem cell maintenance. These mechanisms that control the hematopoietic system are difficult to deconstruct into fundamental parts. Thus, hematopoietic stem cells are difficult to maintain in vitro, because the cells' responses to culture conditions are dictated by so many influences. The conclusions drawn from in vitro cell-based assays are then necessarily limited by the complexity of the system. There are many meritorious reasons to manipulate stem cells: correct a mutation, render them drug resistance, and control their antigenic profile to name a few. They can be modified for several purposes, but critically they must retain stem cell function. The only definitive assay for stem cell function is hematopoietic reconstitution following lethal conditioning. Therefore, animal model systems are used to reveal the fundamental biology of hematopoietic stem cells. However, no single animal model can fully recapitulate the human hematopoietic system, so we propose to offer the canine as a model to complement hematopoietic studies in mice. Canines address some of the key differences between mice and humans notably size, lifespan, and genetic diversity. Additionally, dogs have relatively large litters, which can be useful for histocompatibility and transplantation. This Canine Core will use engineered somatic mutations, spontaneous germline mutations, and develop canine biological reagents for non-malignant hematopoietic research. The accumulated knowledge of canine husbandry and stem cell transplantation, as well as existing facilities at Fred Hutch, make this Canine Core unique. In conjunction with the expertise of the other CCEH Cores, the entire breadth of an experiment can be completed. The Cell P&P core can isolate and store stem cells, these cells can be modified in the Tools core, the stem cell character can be verified in a canine-to- mouse transplant in the Xenografting Core, and the Canine Core can provide a large animal in vivo model to study the biology of stem cell modifications. Internal and external users of this core will be able to take advantage of decades of experience enriching stem cells, manipulating them, and assaying them in xenografts, as well as the 60 years of institutional experience with the canine model.