The acute respiratory distress syndrome (ARDS) is a common and devastating complication of sepsis that is characterized by flooded lungs, need for mechanical ventilation, and severely low blood oxygen levels. ARDS inflicts a very high mortality yet pharmacoprevention or pharmacotherapy options are lacking. In addition, the risk for ARDS is incompletely explained by clinical factors suggesting that individual risk factors may be important. We previously identified and replicated a genetic variant in the angiopoietin-2 gene (ANGPT2) that strongly associated with ARDS risk. We demonstrated that carriers of the ARDS-associated genetic variant exhibited a higher proportion of full-length angiopoietin-2 (ANG2) isoform in plasma, suggesting to us that some patients are genetically predisposed to develop ARDS via the ANGPT2 gene, and that this risk may be mediated by changes in plasma expression of ANG2. We used genetic regulation of plasma ANG2 during sepsis, in a Mendelian Randomization analysis, to demonstrate that plasma ANG2 has a causal effect on the risk of ARDS. Thus our long term objectives are to identify subjects who will benefit from anti-ANG2 therapy and to develop compounds that effectively antagonize ANG2 as an early ARDS treatment. For this application, we will identify and validate thresholds of plasma ANG2 that objectively increase or decrease ARDS risk using classification and regression tree (CART) methodology on 2 large cohorts of critically ill patients with sepsis who are carefully phenotyped for ARDS. The output will be plasma thresholds that might help to include or exclude subjects for a future precision trial of anti-ANG2 therapy targeted to those likely to benefit. We will enact Mendelian Randomization analysis to test whether the true effect of day 0 and day 2 plasma ANG2 towards ARDS mortality is causal, because this could inform the utility of anti-ANG2 therapy for prevention alone versus for prevention and treatment. Finally, we will use a novel platform known as ex vivo lung perfusion (EVLP), whereby lungs declined for transplantation are ventilated and perfused in a highly controlled environment, to test whether 2 drugs that mimic ANG1 to activate the TIE2 receptor achieve an improved phosphoTIE2/TIE2 ratio and improved oxygenation and lung compliance after a one-time dose. The multidisciplinary team of investigators and consultants to enact these aims include 2 EVLP experts, 2 epidemiologists with expertise in lung injury prediction and molecular subphenotyping, a nanomedicine pharmacologist with expertise in rational drug design, and the PI, a translational scientist who first identified a link between ANGPT2 variation, plasma protein expression, and ARDS risk. Completion of these aims will provide key data to inform a future precision anti-ANG2 trial for ARDS, including who should be enrolled, whether the trial should focus on ARDS prevention or treatment, and which drug(s) to test.