Production and titration of SARS-CoV-2 pseudovirus
A pseudovirus strain of SARS-Cov-2 Omicron BA.1 and BA.5 variants were constructed with more than 32 mutations in the S protein. Pseudoviruses of the prototype was also constructed. The SARS-CoV-2 pseudovirus was prepared by transfecting 293T cells with S protein expression plasmids. And G*ΔG-VSV (Kerafast, Boston, MA) was added by providing genomes of VSV. Following collection and filtering, the pseudotyped viruses were titered on Vero cells (8). Briefly described, the pseudotyped viruses were diluted from 1:10 to 1:7290 by three-fold serial dilutions, and mixed with Vero cells (2x104 / well) in 96-well plates. The mixture was incubated at 37°C, 5% CO2 for 24 h. The chemiluminescence signals were collected using the Britelite plus reporter gene assay system (PerkinElmer, Waltham, MA). The 50% tissue culture infective dose (TCID50) was calculated using the Reed-Muench method.