Project Summary Severe asthma comprises ~10% of all asthma cases but accounts for a disproportionately high degree of asthma health care costs and causes substantial decrements in quality of life for patients. Clinically, this form of asthma is defined by inadequate symptom control despite treatment with high-dose inhaled corticosteroids combined with a long-acting β2-agonist (LABA) or leukotriene modifier. Persistent airway obstruction, increased urgent care utilization, and near-fatal events are also features of severe asthma. The “Type 2-high” (T2-high) form of severe asthma is a common severe asthma sub-type that is characterized by sputum eosinophilia, elevated fraction of exhaled nitric oxide, and increased serum periostin. While new, antibody- based treatment approaches for T2-high asthma have come online, these treatment approaches are only partially effective and do not sufficiently alleviate asthma symptoms and quality of life metrics. Thus, there is still an unmet need for new therapeutics for severe Type 2-high asthma. To address this need, we sought to create/identify a new model of severe T2-high asthma that could be used to identify and test new therapeutic approaches. We identified a strain from the Collaborative Cross mouse genetics reference population, namely CC011/UncJ (hereafter referred to as CC011), that develops extremely high levels of airway eosinophilia, total and HDM-specific IgE, and airway hyper-responsiveness after repeated house dust mite (HDM) allergen exposure (25 µg/treatment by intranasal administration, 3x/week for 5 weeks). Most impressively, CC011 mice consistently died after HDM exposure during weeks 3-4 of treatment, whereas there were no deaths among PBS treated CC011 mice or any other 30 CC strains tested. Importantly, steroid treatment did not ameliorate eosinophilic airway inflammation in this strain. Thus, CC011 represents a new model of severe, T2-high asthma. To further the utility of this of this model, the genetic and immunologic basis of this phenotype need to be determined. In the first aim, we will identify which cell types and pathways are integrally involved in CC011’s innate and adaptive immune responses to HDM. We will determine if allergic inflammation is T cell-dependent and if CD4+ Th2 cell priming is augmented in CC011 mice compared to BALB/cJ mice. We will investigate if airway epithelial cell-derived alarmins (IL-25, IL-33, TSLP, IL-1α/β) are increased in CC011 mice and whether neutralization of these cytokines ameliorates allergic inflammation. Finally, we will determine if allergen- induced expansion and activation of ILC2s are enhanced in CC011 mice. In the second aim, we will identify the genetic loci that harbor CC011’s susceptibility alleles using a quantitative trait locus mapping approach, and then leverage whole genome sequence data and gene expression data from CC011 and other strains to identify candidate genes. These candidate genes will become the focus of future investig...