DPP4 and acute respiratory distress syndrome: In the MERS-CoV transgenic mouse model, through CRISPR/Cas9 to replace two amino acids at positions 288 and 330 in mouse dipeptidyl peptidase 4 (mDPP4) with their human counterparts enabled efficient MERS-CoV infection and replication in the lungs, with infected mice developing severe acute respiratory distress syndrome (ARDS)-like symptoms [58,59].