Neutralization Assay with SARS-CoV-1 and SARS-CoV-2 Spike Pseudotyped Murine Leukemia Virions

Background: Virus neutralization by antibodies is an important prognostic factor in many viral diseases. To easily and rapidly measure titers of neutralizing antibodies in serum or plasma, we developed pseudovirion particles composed of the spike glycoprotein of SARS-CoV-2 incorporated onto murine leukemia virus capsids and a modifed minimal murine leukemia virus genome encoding frefy luciferase. This assay design is intended for use in laboratories with biocontainment level 2 and therefore circumvents the need for the biocontainment level 3 that would be required for replication-competent SARS-CoV-2 virus. To validate the pseudovirion assay, we set up comparisons with other available antibody tests including those from Abbott, Euroimmun and Siemens, using archived, known samples. Results: 11 out of 12 SARS-CoV-2-infected patient serum samples showed neutralizing activity against SARS-CoV2-spike pseudotyped MLV viruses, with neutralizing titers-50 (NT50) that ranged from 1:25 to 1:1,417. Five historical samples from patients hospitalized for severe infuenza infection in 2016 tested negative in the neutralization assay (NT50<25). Three serum samples with high neutralizing activity against SARS-CoV-2/MLV pseudoviruses showed no detectable neutralizing activity (NT50