SARS-CoV-2 pseudovirus neutralization assay.

The SARS-CoV-2 pseudovirus neutralization titer was determined using a lentiviral SARS-CoV-2 pseudotyped virus as described in a previous study (59). Specifically, 100 μl of virus was incubated with mouse or hamster serum solutions for 1 h at 37°C, and the mixture was added to HEK293T cells expressing ACE2 in 96-well plates. At 72 h postinfection, supernatants were collected from each well for measurement of luciferase activity. Briefly, 20 μl of supernatant was transferred to a new 96-well plate and mixed with 20 μl of Gluc substrate (0.1 M Tris [catalog no. T6066; Millipore Sigma] pH 7.4, 0.3 M sodium ascorbate [catalog no. S1349; Spectrum], and 10 μM coelenterazine [catalog no. CZ2.5; GoldBio]). Luminescence was immediately read by a plate reader. A nonlinear regression of x-y analyses was performed and fitted with an inhibition curve. The 50% inhibitory concentration (IC₅₀) titer was calculated.