ACE2 and COVID-19: Attractive features of this model epithelium included (i) histological and molecular fidelity to normal small airway epithelial cell physiology41,43; (ii) a normal male karyotype, 46 X/Y41–43; (iii) cell specific expression of COVID-19-related genes including ACE2, ADAM10 and ADAM17, TMPRSS2, FURIN and CTSL43; and (iv) our preliminary data demonstrating functional expression of CFTR chloride channels and CFTR protein in differentiated epithelia40.