Middle East respiratory syndrome coronavirus (MERS-CoV) is a novel virus that emerged in 2012, causing acute respiratory distress syndrome (ARDS), severe pneumonia-like symptoms, and multi-organ failure, with a case fatality rate of ~36%. Limited clinical studies indicate that humans infected with MERS-CoV exhibited pathology consistent with late stages of ARDS, which is reminiscent of disease observed in patients infected with SARS coronavirus. Models of MERS-CoV-induced severe respiratory disease have been difficult to achieve, and small animal models traditionally used to investigate viral pathogenesis (mouse, hamster, guinea pig, and ferret) are naturally resistant to MERS-CoV. Therefore, we used CRISPR/Cas9 to modify the mouse genome to encode two human amino acids (288 and 330) in the dipeptidyl peptidase 4 receptor, making mice susceptible to MERS-CoV replication. Serial MERS-CoV passage in these engineered mice was then used to generate a mouse-adapted virus that replicated efficiently within the lungs, and evoked symptoms indicative of severe acute respiratory distress syndrome (ARDS), including decreased survival, extreme weight loss, decreased pulmonary function, pulmonary hemorrhage, and pathological signs indicative of end stage lung disease. Importantly, therapeutic countermeasures comprising MERS-CoV neutralizing antibody treatment or a MERS-CoV spike protein vaccine protected engineered mice against MERS-CoV-induced ARDS
