Presence and short-term persistence of SARS-CoV-2 neutralizing antibodies in COVID-19 convalescent plasma donors

Abstract

Background: In March 2020, the Food and Drug Administration (FDA) approved use of COVID-19 convalescent plasma (CCP) as an investigational new drug for treatment of COVID-19. Since then, collection of CCP from COVID-19-recovered patients has been implemented in donor centers nationwide. Children's Hospital Colorado rapidly put into practice a CCP collection protocol, necessitating development and implementation of assays to evaluate SARS-CoV-2 antibodies in CCP units.

Study design and methods: We evaluated 87 units of CCP collected from 36 donors over two to four sequential donations using both antigen-binding assays for SARS-CoV-2 nucleoprotein and spike antigens and a live virus focus reduction neutralization test (FRNT₅₀ ).

Results: Our data show that the majority of donors (83%) had a FRNT₅₀ titer of at least 80, and 61% had a titer of at least 160, which met the FDA's criteria for acceptable CCP units. Additionally, our data indicate that analysis of antibodies to a single SARS-CoV-2 antigen is likely to miss a percentage of seroconverters; however, these individuals tend to have neutralizing antibody titers of less than 80. There was considerable variability in the short-term, sustained antibody response, measured by neutralizing antibody titers, among our donor population.

Conclusion: The correlation of neutralizing activity and antigen-binding assays is necessary to qualify CCP for therapeutic use. Since SARS-CoV-2 antibody levels decline in a percentage of donors, and such a decline is not detectable by current qualitative assays implemented in many laboratories, robust, quantitative assays are necessary to evaluate CCP units best suited for therapeutic infusion in COVID-19 patients.

Keywords: FFP transfusion; Regulatory and QA; blood component preparations.

FIGURE 1

Comparison of reciprocal FRNT₅₀ titer with either anti‐N IgG (A) or anti‐S1‐RBD IgG (B). Data are the mean and 95% CIs for each group of FRNT₅₀ titers. N = 86 for FRNT50 vs anti‐N antibodies and N = 84 for FRNT₅₀ vs anti‐S1‐RBD antibodies. *P < .05, **P < .001, and ***P < .0001 using Welchʼs test for unequal variance

FIGURE 2

Comparison of anti‐N IgG (OD450, x‐axis), anti‐S1‐RBD IgG (ratio, y‐axis), and FRNT₅₀ reciprocal titer (relative size of bubble, larger bubbles correspond to higher titers). Eighty‐five samples were compared for correlation among anti‐N, anti‐S1‐RBD, and neutralizing antibody titers. Two samples with the highest FRNT₅₀ titers (red circles) also had the highest S1‐RBD ratios and moderately high levels of anti‐N1. Three samples with the highest anti‐N OD₄₅₀ values had FRNT₅₀ values of approximately 200 (purple circles), while five samples (green circles) had FRNT50 values of approximately 1000 but had varying levels of anti‐N and anti‐S1‐RBD. Dashed lines indicate cutoff values for OD₄₅₀ and ratios above which 90% of FRNT₅₀ values were 80 or greater [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

FRNT₅₀ titers in CCP donors (A) and FRNT₅₀ titers grouped by sequential CCP donations (B). Eighty‐seven samples were analyzed for FRNT₅₀ titers. Data are grouped by FRNT50 titer and the number of samples in each group is indicated (A). FRNT₅₀ titers correlated with CCP collection time point. The difference between groups was considered significant (P < .05) using Welchʼs test for unequal variances. ns, not significant [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 4

Change in FRNT₅₀ titers over two sequential donations. FRNT₅₀ titer increased or remained relatively unchanged (A, n = 17 donors). FRNT₅₀ titers decreased from the initial to the second donation (B, n = 7). Fold increase from initial donation for donors with two sequential donations (C, n = 24)

FIGURE 5

Change in FRNT₅₀ titer over three or four sequential donations. (A) FRNT titers over the course of three or four donations for individual donors. (B) Fold increase from initial donation. n = 12