CTSL and infection: Accordingly, out of the seven known human CoVs, only SARS-CoV and SARS-CoV-2 have conserved CTSL cleavage sites at T259 and Y636, indicating that CTSL cleavage is crucial for the infection process of SARS-CoV/SARS-CoV-2 and life cycle (Zhao et al., 2022a).