Convalescent plasma donors show enhanced cross-reactive neutralizing antibody response to antigenic variants of SARS-CoV-2 following immunization

Abstract

Background: The therapeutic benefit of convalescent plasma (CP) therapy to treat COVID-19 may derive from neutralizing antibodies (nAbs) to SARS-CoV-2. To investigate the effects of antigenic variation on neutralization potency of CP, we compared nAb titers against prototype and recently emerging strains of SARS-CoV-2, including Delta and Omicron, in CP donors previously infected with SARS-CoV-2 before and after immunization.

Methods and materials: Samples were assayed from previously SARS-CoV-2 infected donors before (n = 17) and after one (n = 43) or two (n = 71) doses of Astra-Zeneca or Pfizer vaccinations. Ab titers against Wuhan/wild type (WT), Alpha, Beta, and Delta SARS-CoV-2 strains were determined by live virus microneutralization assay while titers to Omicron used a focus reduction neutralization test. Anti-spike antibody was assayed by Elecsys anti-SARS-CoV-2 quantitative spike assay (Roche).

Results: Unvaccinated donors showed a geometric mean titer (GMT) of 148 against WT, 80 against Alpha but mostly failed to neutralize Beta, Delta, and Omicron strains. Contrastingly, high GMTs were observed in vaccinated donors against all SARS-CoV-2 strains after one vaccine dose (WT:703; Alpha:692; Beta:187; Delta:215; Omicron:434). By ROC analysis, reactivity in the Roche quantitative Elecsys spike assay of 20,000 U/mL was highly predictive of donations with nAb titers of ≥1:640 against Delta (90% sensitivity; 97% specificity) and ≥1:320 against Omicron (89% sensitivity; 81% specificity).

Discussion: Vaccination of previously infected CP donors induced high levels of broadly neutralizing antibodies against circulating antigenic variants of SARS-CoV-2. High titer donations could be reliably identified by automated quantitative anti-spike antibody assay, enabling large-scale preselection of high-titer convalescent plasma.

Keywords: COVID-19; Delta; Omicron; SARS-CoV-2; antibody neutralization; antigenic variants; convalescent plasma; vaccination.

FIGURE 1

Comparison of neutralizing antibody titers against each SARS‐CoV‐2 strain in plasma from infected, prevaccinated individuals with those receiving 1 or 2 doses of vaccine obtained by microneutralization assay (A) and focus reduction neutralization assay (B). Median values of reactivity and fold change from reactivity to the WT strain are shown under each graph. Further comparisons of fold‐changes in reactivity after immunization with 1 or 2 vaccine doses are shown along links. Statistical comparisons of antibody levels induced by different SARS‐CoV‐2 strains used the Spearman rank correlation test (p values <.05 shown in bold).

FIGURE 2

Time course of neutralizing antibody levels to each SARS‐CoV‐2 strain in sequential samples from pre‐ and post‐vaccinated subjects (time intervals and totals listed in Table S1); gray lines indicate results from subjects with samples collected pre‐ and post‐single vaccine does, or between dose 1 and dose 2 vaccinations.

FIGURE 3

(A) Associations between neutralizing antibody titers to each SARS‐CoV‐2 strain by microneutralization assay (x‐axis panels) and in the Roche Elecsys assay (y‐axis). Samples collected prevaccination and after 1 or 2 vaccination doses are plotted separately (see key). Neutralizing antibody titer values have been jittered by ±1.2 fold to avoid overlapping points. Datapoints lines of best fit of log transformed values from both assays were separately plotted for samples collected pre‐ and post‐vaccination; R ² and p values shown. (B) Receiver operating characteristic (ROC) analysis to evaluate the predictive value of the Roche S quantitative assay for neutralizing antibody titers of 1:640 and 1:320 against Delta and Omicron. The sensitivity and specificity of chosen Roche antibody levels to predict high titer convalescent donations containing a minimum neutralizing antibody titer of 1:640 or 1:320 against Delta and Omicron variants is tabulated to the right.