We compared this autocleavage seen in transfected 293T cells, to that seen in several epithelial cell lines that naturally express endogenous ACE2 and TMPRSS2 [24]: the human lung cell line, Calu-3, and the human colorectal adenocarcinoma cell line, Caco-2, both of which are extensively used for SARS-CoV-2 research. Here, TMPRSS2 is linked to colorectal adenocarcinoma.