Neutralizing activity to SARS-CoV-2 of convalescent and control plasma used in a randomized controlled trial

Abstract

Background: There are limited data on the neutralizing activity of convalescent plasma (CP) administered in randomized controlled trials (RCT) of COVID-19 infection. Study Design and Methods: As part of an RCT, CP was collected per FDA guidelines from individuals recovered from COVID-19 infection. CP donors had to have ≥145 optical density (OD) units (ideal target ≥300) using a semiquantitative, immunochromatographic test for IgG antibody to the nucleocapsid protein (NP) of SARS-CoV-2 (typical range 0–500 OD units). A random subset of samples [14 control plasma, 12 CP “medium-anti-NP” (145–299 OD units), and 13 CP “high” anti-NP (≥300 OD units)] were tested for neutralizing antibodies using an established viral luciferase antibody inhibition assay to detect the infection of SARS-CoV-2 pseudovirus that encoded spike protein (SARS2-Strunc) on a human immunodeficiency virus 1 vector (NL43dEnvNanoLuc), using ACE2-expressing 293 T cells. The titer needed to neutralize 50% of viral activity (NT50) was calculated. Results: The uptake of SARS-CoV-2 pseudovirus by 293TACE2 cells was inhibited by pretreatment with CP compared to control CP (p 1:80 in 100% of randomly selected samples, using a conservative approach that excluded non-specific binding. Discussion: Plasma from donors screened using an immunochromatographic test for IgG antibody to SARS-CoV-2 NP exhibited neutralizing activity meeting FDA's minimum standard in all randomly selected COVID-19 CP units.