Validation of SARS-CoV-2 neutralization assay using VSV-based pseudovirus system

The gold standard for SARS-CoV-2 neutralization assays involves wild-type virus, which requires Biosafety Level 3 (BSL-3) containment. To improve safety and accessibility, pseudovirus-based neutralization assays utilizing non-replicating particles like Vesicular Stomatitis Virus (VSV) expressing the SARS-CoV-2 spike protein can be conducted under BSL-2 conditions. This study aimed to perform the analytical validation of a VSV-based pseudovirus system for SARS-CoV-2 using recombinant monoclonal antibody. Pseudo-VSV carrying SARS-CoV-2 Spike proteins were produced using LentiX-293T cells. The assay system was optimized for Multiplicity of Infection (MOI) and assessed for specificity, limit of quantification (LOQ), linearity, accuracy, and precision using the neutralizing mAb BD-604. The system was optimized at an MOI of 0.25. The assay proved highly specific, as mAb BD-604 showed clear neutralizing activity while mAb 1A9 did not. The limit of quantification (LOQ) was determined to be 125 ng of mAb BD-604, with a linear range of 125 - 1000 ng. The relative accuracy remained within the 80-120% range, and the precision (%CV) ranged from 1.92% to 13.57%. Additionally, the system successfully characterized variant-specific neutralization, revealing that BD-604 was effective against the Wuhan, Delta, and Omicron BA.1/BA.2 strains but lacked activity against the Omicron XBB.1.5 variant. This validated pseudo-VSV based SARS-CoV-2 neutralization assay is a valuable bioassay for evaluating neutralizing antibody potency against various SARS-CoV-2 strains in a BSL-2 environment, thus making it useful for vaccine and therapeutic development.