Abstract
Simple SummaryPassive immunization with hyperimmune plasma from convalescent patients has been proposed as a potentially useful treatment for COVID-19. Nevertheless, its efficacy in patients with COVID-19 remains uncertain. Thus, the establishment and validation of standardized methods that predict the viral neutralizing (VN) activity of plasma against SARS-CoV-2 is of utmost importance to appraise its therapeutic value. Using an in-house quantitative ELISA test and two independent cohorts with a total of 345 donors, we found that plasma and serum from most convalescent donors contained IgG antibodies specific to the spike receptor-binding domain (RBD) of SARS-CoV-2, with varying concentrations which correlate with previous disease severity and gender. Anti-RBD IgG plasma concentration significantly correlated with the plasma/serum VN activity against SARS-CoV-2 in vitro.Several hundred millions of people have been diagnosed of coronavirus disease 2019 (COVID-19), causing millions of deaths and a high socioeconomic burden. SARS-CoV-2, the causative agent of COVID-19, induces both specific T- and B-cell responses, being antibodies against the virus detected a few days after infection. Passive immunization with hyperimmune plasma from convalescent patients has been proposed as a potentially useful treatment for COVID-19. Using an in-house quantitative ELISA test, we found that plasma from 177 convalescent donors contained IgG antibodies specific to the spike receptor-binding domain (RBD) of SARS-CoV-2, although at very different concentrations which correlated with previous disease severity and gender. Anti-RBD IgG plasma concentrations significantly correlated with the plasma viral neutralizing activity (VN) against SARS-CoV-2 in vitro. Similar results were found using an independent cohort of serum from 168 convalescent health workers. These results validate an in-house RBD IgG ELISA test in a large cohort of COVID-19 convalescent patients and indicate that plasma from all convalescent donors does not contain a high enough amount of anti-SARS-CoV-2-RBD neutralizing IgG to prevent SARS-CoV-2 infection in vitro. The use of quantitative anti-RBD IgG detection systems might help to predict the efficacy of the passive immunization using plasma from patients recovered from SARS-CoV-2.
Highlights
A new coronavirus responsible for severe acute respiratory syndrome (SARS), known as SARS-CoV-2, emerged in Wuhan, China in 2019 [1,2] and spread rapidly to the rest of the world
In this cohort we aimed to validate in a large number of samples a recently developed indirect ELISA that employed recombinant receptor-binding domain (RBD) produced in mammalian cells
Male patients presented significantly higher levels of RBD IgG than female patients (Figure 2D). These results indicate that the concentration of RBD IgG antibodies is increased in patients that had recovered from COVID-19 and required hospitalization and in male patients and, the application of this criterion might help to optimize donor selection and to improve the efficiency of passive immunization protocols for COVID-19
Summary
A new coronavirus responsible for severe acute respiratory syndrome (SARS), known as SARS-CoV-2, emerged in Wuhan, China in 2019 [1,2] and spread rapidly to the rest of the world. SARS-CoV-2 belongs to the family of human betacoronaviruses and it is the third member identified in this family causing a severe respiratory disease, behind the viruses SARS-CoV and Middle East respiratory syndrome (MERS) [3]. In contrast to SARS-CoV and MERS, which caused infections restricted to a limited number of countries, a few weeks after its identification SARS-CoV-2 had propagated all over the world, originating the pandemic known as coronavirus disease 19 (COVID-19). OD450 values were calculated by subtracting the background value from the OD values in RBD-coated wells. The limit of detection (LOD) was calculated using human negative plasma samples (collected before 2018) as mean + 3 × SD. Sensitivity and specificity were calculated using the 2 × 2 table method including the true positive, true negative, false positive, and false negative values using plasma samples collected before 2018 and plasma samples from convalescent donors
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