Project Abstract Diseases of the lung vasculature, including capillary leak syndrome/acute respiratory distress syndrome (ARDS), inhalation injury, primary pulmonary hypertension, and the novel coronavirus disease-19 (COVID-19), are difficult to study due to the lack of functional ex vivo models. Conventional culture systems are typically limited in their ability to represent human pathophysiology for the study of disease and drug mechanisms. The overall objective of this proposal is to develop an experimental platform that mimics the pulmonary microvasculature, and that can simulate native cellular phenotypes and functions in vitro, during normal homeostasis and during disease states such as severe inflammation, and sepsis. The lung microvascular niche characteristics, such as paracrine factors, hemodynamics, and extracellular matrix composition are all of pivotal importance for regulating endothelial maturation and maintaining vascular homeostasis. Whole organ decellularization opens a door to provide a construct that recapitulates the substrate structure and components of an entire vascular tree. Additionally, leveraging single-cell RNA-seq (scRNAseq), we developed computational tools to identify the paracrine signals in human distal lungs. In this study, I will leverage these tools to identify novel, important locally acting soluble factors in a functional lung microvascular niche to improve pulmonary microvascular maturation in acellular lung scaffolds. During the K99 phase of this proposal, I will first leverage our published scRNAseq computational tools to evaluate the scRNAseq dataset on native adult human lungs. I will determine a group of important and novel soluble factors that could improve endothelial maturation. Then, I will rationally iterate on our endothelial repopulated lung platform with the addition of relevant soluble factors derived from the native microvascular milieu. During the R00 phase, I will use the vascular platform established in prior aims and start to develop a disease modeling system to study the impact of inflammation for drug testing. This work will lead to the creation of a novel platform which, unlike previous microvascular platforms, specifically resembles many physiological aspects of the native lung environment. Such a platform could be used for pulmonary vascular disease modeling and drug testing.