Host susceptibilities and entry processes of SARS-CoV-2 Omicron variants using pseudotyped viruses carrying spike protein

The zoonotic potential has been well studied for SARS-CoV-2 and its earlier variants, but the information for Omicron variants and SARS-CoV is lacking. In this study, we generated lentivirus-based pseudoviruses carrying spike protein (S) of SARS-CoV-2, parental and Omicron variants including BA.1.1, BA.4/5, XBB.1 and JN.1 to assess the entry into cells expressing human or animal ACE2 including dogs, cats and white-tailed deer. Using these pseudoviruses, along with pseudoviruses carrying S of MERS-CoV and SARS-CoV, we assessed the protease processing of these various S through western blotting, entry/inhibition assays, and fusion assays. The results showed that overall, pseudotyped viruses carrying each S of SARS-CoV-2 Omicron strains efficiently entered cells expressing human or animal ACE2 comparably (BA.1.1 and JN.1) or better (BA.4/5 and XBB.1) than those with parental strain. In addition, the entries of pseudotyped viruses carrying S of SARS-CoV were also efficient the cells expressing human or animal ACE2. The presence of TMPRSS2 significantly increased the entry of all tested pseudoviruses including those with S of MERS-CoV, SARS-CoV and SARS-CoV-2, with BA.1.1, JN1, and XBB.1 Omicron having the largest fold increase. When cathepsin inhibitors were examined to assess their inhibitory effects on entry of parental and Omicron variants, they were significantly less effective in the entry of Omicron variants compared to parent strain, suggesting Omicron strains do not depend on the endosomal route compared to parental strain.