Cellular Immunity in COVID-19 Convalescents with PCR-Confirmed Infection but with Undetectable SARS-CoV-2–Specific IgG

Abstract

O ne promising therapeutic option to treat se- verely ill patients with coronavirus disease is the use of convalescent plasma (CP) of donors who recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (1-3). When searching for potential CP donors with PCR-confirmed SARS-CoV-2 infection, we observed that 17% of those who volunteered had either borderline or negative results (ratio <1.1) to a SARS-CoV-2 IgG ELISA. We decided to follow up with these volunteers by repeating antibody tests and by assessing T-cell immunity by enzyme-linked immunospot (ELISpot) assay for interferon- (IFN-).