To identify the sensitive cells to the SARS-CoV-2 infection, angiotensin-converting enzyme 2 (ACE2) (NM_021804.2), furin (NM_001289823.1), type II transmembrane serine protease (TMPRSS2) (NM_001135099.1), cathepsin L (NM_001912.5), and empty vector pcDNA3.1 (MN996867) were studied for their assistance in virus infections. Here, CTSL is linked to viral infectious disease.