CTSB and type 2 diabetes mellitus: Our computational investigations have shown that the FDA approved DPP4 inhibitor linagliptin, along with two other DPP4 inhibitors gemigliptin and evogliptin which are marketed in the Republic of Korea to treat type-2 diabetes, have the potential to inhibit the SARS-CoV-2 Mpro viral cysteine protease by reversible, noncovalent binding suggesting their repurposing in treating COVID-19 infections.