S protein is cleaved at the S1/S2 site by furin and subsequent at the S2’ site by TMPRSS2, triggering an irreversible and extensive conformational change to mediate membrane fusion.32–34 Besides, inside the endosome, a pH-dependent endosomal protease cathepsin L can facilitate the cleavage and proteolytical activation of S protein for fusion within the endosomal membrane.35 Inhibition of these proteases, particularly TMPRSS2,36 might constitute a treatment option to treat COVID-19. The gene discussed is PROS1; the disease is COVID-19.