ACE2 and lung adenocarcinoma: We screened several commonly used cell lines for ACE2 and TMPRSS2 mRNA, and only four demonstrated notable expression of ACE2: HepG2 (hepatoma), Caco-2 (colonic adenocarcinoma), Calu-3 (lung adenocarcinoma), and Vero E6 (monkey kidney epithelia) (Figure 1A).