DPP4 and diabetes mellitus: Although DPP-4 does not function as the receptor in SARS-CoV-2 infections, DPP-4 inhibitors (DPP-4is), one of the new oral therapies for diabetes characterized by neutral weight and few adverse effects, is now used to improve insulin secretion as a treatment for T2DM [8], and researchers have speculated on whether DPP-4 inhibitors (DPP-4i) play a role in protecting against COVID-19 and their use as therapeutic drugs to improve outcomes in patients with COVID-19 and type 2 diabetes (T2DM) [9, 10].