DPP4 and COVID-19: DPP4, the MERS-CoV receptor, is also suggested to influence SARS-CoV-2 cell entry, but the evidence for this is less direct, mainly based on similarities between MERS-CoV and SARS-CoV-2 [138], several computational binding studies between DPP4 and SARS-CoV-2 spike protein with differing results [139–141], and studies indicating DPP4 inhibitor drugs might have a positive effect on COVID-19 outcomes in certain patient groups [138, 142].