TMPRSS2 and infection: Alternative Vero cells have been modified to more closely resemble the human epithelia., e.g., Vero human signaling lymphocytic activation molecule (hSLAM) cells that express the hSLAM (14), and Vero E6-ACE2-TMPRSS2 (VAT) cells-Vero E6 expressing both human angiotensin-converting enzyme 2 (ACE2), the major receptor of SARS-CoV-2, and transmembrane serine protease 2 (TMPRSS2), which cleaves the viral S protein priming it for cellular infection (15).