CD4 and Airway obstruction: Allergen-activated CD4 T cells play a critical role in orchestrating acute disease features such as recruitment of eosinophils, airway inflammation, and mucus production, that ultimately leads to airway obstruction in asthma patients (2, 3). As importantly, it is believed that long-lived populations of lung-localized CD4 memory T cells, also referred to as tissue-resident memory T cells or Trm (4–7), might be responsible for persisting disease, and are the cell type that initiates periodic exacerbations of lung inflammation upon encounter with airborne allergens.