ACE2 and tongue squamous cell carcinoma: Since the ACE2 gene expression in the tongue squamous cell carcinoma cell line HSC3 and the TMPRSS2 gene expression in the human glioma cell line LN319 were established by a microarray, HSC3 and LN319 were used as experimental controls of the RT‐PCR analysis for the ACE2 and TMPRSS2 gene expression in the human tissue specimens.