Clinical, laboratory, and temporal predictors of neutralizing antibodies against SARS-CoV-2 among COVID-19 convalescent plasma donor candidates

Abstract

BACKGROUNDSARS-CoV-2-specific antibodies may protect from reinfection and disease, providing rationale for administration of plasma containing SARS-CoV-2-neutralizing antibodies (nAbs) as a treatment for COVID-19. Clinical factors and laboratory assays to streamline plasma donor selection, and the durability of nAb responses, are incompletely understood.METHODSPotential convalescent plasma donors with virologically documented SARS-CoV-2 infection were tested for serum IgG against SARS-CoV-2 spike protein S1 domain and against nucleoprotein (NP), and for nAb.RESULTSAmong 250 consecutive persons, including 27 (11%) requiring hospitalization, who were studied a median of 67 days since symptom onset, 97% were seropositive on 1 or more assays. Sixty percent of donors had nAb titers ≥1:80. Correlates of higher nAb titers included older age (adjusted OR [AOR] 1.03 per year of age, 95% CI 1.00-1.06), male sex (AOR 2.08, 95% CI 1.13-3.82), fever during illness (AOR 2.73, 95% CI 1.25-5.97), and disease severity represented by hospitalization (AOR 6.59, 95% CI 1.32-32.96). Receiver operating characteristic analyses of anti-S1 and anti-NP antibody results yielded cutoffs that corresponded well with nAb titers, with the anti-S1 assay being slightly more predictive. nAb titers declined in 37 of 41 paired specimens collected a median of 98 days (range 77-120) apart (P < 0.001). Seven individuals (2.8%) were persistently seronegative and lacked T cell responses.CONCLUSIONnAb titers correlated with COVID-19 severity, age, and sex. SARS-CoV-2 IgG results can serve as useful surrogates for nAb testing. Functional nAb levels declined, and a small proportion of convalescent individuals lacked adaptive immune responses.FUNDINGThe project was supported by the Frederick National Laboratory for Cancer Research with support from the NIAID under contract number 75N91019D00024, and was supported by the Fred Hutchinson Joel Meyers Endowment, Fast-Grants, a New Investigator award from the American Society for Transplantation and Cellular Therapy, and NIH contracts 75N93019C0063, 75N91019D00024, and HHSN272201800013C, and NIH grants T32-AI118690, T32-AI007044, K08-AI119142, and K23-AI140918.

Keywords: Adaptive immunity; Immunoglobulins; Infectious disease; Virology.

Figure 1. Study design and participants.

Figure 2. Distribution of nAb titers in convalescent subjects (n = 250).

Values on the x axis represent the dilution factor of serum that yielded a 50% reduction in SARS-CoV-2 infection of Vero E6 cells.

Figure 3. Relationship between serum measurements of anti–SARS-CoV-2 antibodies.

Levels of anti–SARS-CoV-2 IgG antibodies specific for S1 (Euroimmun; EU) (A) or of anti–SARS-CoV-2 IgG antibodies specific for NP (Abbott) expressed as z scores (B) are shown relative to nAb titers obtained from the same samples. Each symbol represents the initial specimen from one person. (C) Anti–SARS-CoV-2 S1 IgG levels (EU) relative to anti–SARS-CoV-2 nucleocapsid protein (NP) IgG levels (Abbott). The dotted lines indicate the positivity threshold (z score of 3) for both EU and Abbott assay results. Colored circles indicate discordant results between the Euroimmun and Abbott assays. Blue circles represent samples with negative z score results (<3.0) by Euroimmun and positive z score results (≥3.0) by Abbott. Conversely, red circles represent samples with positive results (z ≥ 3.0) by Euroimmun and negative results (z < 3.0) by Abbott.

Figure 4. Individual antibody levels obtained at various time points after symptom resolution from 41 persons recovered from PCR-positive SARS-CoV-2 infection and with an initial nAb titer of 1:40 or greater.

The same 41 persons are represented in each graph. Red lines correspond to hospitalized participants (n = 7). Neutralization assay (A), Euroimmun (anti-S1) IgG assay (B), and Abbott (anti-NP) IgG assay (C) results as a function of time since resolution of symptoms. Each line connects 2 results from a single participant.