CTSS and infection: Furthermore, cathepsin-mediated endosomal CoV entry appears to be less relevant in primary cells, organoids and in vivo models, where TMPRSS2 has been shown to mediate infection and spread of SARS-CoV-1 and the SARS-CoV-2 omicron variant [83–86], despite these viruses using the endosomal entry route in some cell lines.