CTSB and COVID-19: The next drug for the treatment of COVID-19 has been examined heretofore: IFN type I, IFN type III, remdesivir, camostat mesylate [a cofactor transmembrane protease serine 2 (TMPRSS2) inhibitor], E-64d (an inhibitor of the endosomal cysteine proteases cathepsin B and L), and a library of FDA-approved drugs (the Prestwick collection) (Han et al., 2021; Huang et al., 2020; Lamers et al., 2021).