Notably, SARS-CoV-2 is thought to enter host cells via two distinct pathways: one moderated by serine protease TMPRSS2 at the cell surface and the other moderated by cysteine protease cathepsin L in the endosome.24 Accordingly, the development of protease inhibitors can be a potential target for treating COVID-19. This evidence concerns the gene CTSL and COVID-19.