DPP4 and lung disorder: Although the genetic approaches vary from complete replacement of murine DPP4 with human DPP4 [18], replacement of exons 10–12 in mouse Dpp4 with those of human DPP4 [19], or single amino acid changes at residues 288 and 330 to “humanize” murine DPP4 [11], these models have offered complementary insights into the viral and host factors that contribute to severe lung disease after MERS-CoV infection.