Inhibition of pseudovirus entry by SARS-CoV-2 RBD protein was carried out, as previously described, with some modifications.31 Briefly, SARS-CoV-2 RBD protein at serial dilutions was incubated with hACE2/293T target cells for 1 h at 37 °C. After removing medium containing the protein, the cells were infected with SARS-CoV-2 pseudovirus. SARS-CoV RBD and MERS-CoV RBD, as well as SARS-CoV pseudovirus and MERS-CoV pseudovirus, were used as controls. Fresh medium was added 24 h later, and the cells were lysed and analyzed, as described above. The 50% inhibitory concentration (IC50) of the RBD protein was calculated using the CalcuSyn computer program, as described above.