Pharmacokinetics of high-titer anti-SARS-CoV-2 human convalescent plasma in high-risk children

Abstract

BACKGROUNDWhile most children who contract COVID-19 experience mild disease, high-risk children with underlying conditions may develop severe disease, requiring interventions. Kinetics of antibodies transferred via COVID-19 convalescent plasma early in disease have not been characterized.METHODSIn this study, high-risk children were prospectively enrolled to receive high-titer COVID-19 convalescent plasma (>1:320 anti-spike IgG; Euroimmun). Passive transfer of antibodies and endogenous antibody production were serially evaluated for up to 2 months after transfusion. Commercial and research ELISA assays, virus neutralization assays, high-throughput phage-display assay utilizing a coronavirus epitope library, and pharmacokinetic analyses were performed.RESULTSFourteen high-risk children (median age, 7.5 years) received high-titer COVID-19 convalescent plasma, 9 children within 5 days (range, 2-7 days) of symptom onset and 5 children within 4 days (range, 3-5 days) after exposure to SARS-CoV-2. There were no serious adverse events related to transfusion. Antibodies against SARS-CoV-2 were transferred from the donor to the recipient, but antibody titers declined by 14-21 days, with a 15.1-day half-life for spike protein IgG. Donor plasma had significant neutralization capacity, which was transferred to the recipient. However, as early as 30 minutes after transfusion, recipient plasma neutralization titers were 6.2% (range, 5.9%-6.7%) of donor titers.CONCLUSIONConvalescent plasma transfused to high-risk children appears to be safe, with expected antibody kinetics, regardless of weight or age. However, current use of convalescent plasma in high-risk children achieves neutralizing capacity, which may protect against severe disease but is unlikely to provide lasting protection.Trial registrationClinicalTrials.gov NCT04377672.FundingThe state of Maryland, Bloomberg Philanthropies, and the NIH (grants R01-AI153349, R01-AI145435-A1, K08-AI139371-A1, and T32-AI052071).

Keywords: COVID-19; Immunoglobulins; Infectious disease.

Figure 1. Study flow diagram.

Figure 2. SARS-CoV-2 antibody pharmacokinetics and neutralization capacity in donors and recipients of COVID-19 convalescent plasma.

(A) Commercial ELISA assays were used to measure SARS-CoV-2 anti-nucleocapsid protein IgG/IgM/IgA (Bio-Rad) and anti-spike IgG (Euroimmun) titers of donor and recipient plasma prior to plasma administration (n = 13 pairs of donors and recipients). S/C, signal-to-cutoff ratio. (B and C) Indirect ELISAs were used to measure IgG antibody levels against spike or spike receptor binding domain (RBD) in 3-fold serial dilution starting at 1:20. Results are presented as AUC values on a logarithmic scale (n = 12 donors and n = 13 recipients for all time points other than 30 minutes, for which n = 9). (D) Microneutralization assay was performed on each plasma sample in 2-fold serial dilutions starting at 1:20. Results are presented as AUC values on a logarithmic scale (n = 12 donors and n = 13 recipients for all time points other than 30 minutes, for which n = 9). (E) Plaque reduction neutralization test (PRNT₅₀) was performed on plasma from 5 recipients (recipients 9–13) and 4 donors (donors 9 and 11–13) in 2-fold serial dilutions starting at 1:10. Results are presented as AUC values on a logarithmic scale. A 2-tailed Mann-Whitney U test was used to compare donor to recipient titers and recipient titers before and 30 minutes after transfusion. The corresponding P values are shown.

Figure 3. Kinetics of transferred and endogenous pan-coronavirus antibodies.

Plasma from 4 recipients (R1–R4) was subjected to VirScan, a phage-display library of epitopes from various coronaviruses, including SARS-CoV-2. Fold change (FC) was measured for antibody subsets in recipient plasma (each line represents a single antibody subset): donor antibodies (red) and endogenous antibodies (blue). Note that participants R1, R2, and R4, who developed SARS-CoV-2 infection, demonstrate endogenous antibody production. However, participant R3, who remained asymptomatic and SARS-CoV-2 PCR negative throughout the study period, did not develop an endogenous response.

Figure 4. Transfer of pan-coronavirus immunodominant antibodies.

Plasma from 4 donor-recipient pairs (R1–R4) were subjected to VirScan, a phage-display library of epitopes from various coronaviruses, including SARS-CoV-2 and the 4 endemic coronaviruses (NL63, OC43, 229E, and HKU1). (A) Donor and recipient convalescent antibody reactivities to SARS-CoV-2 spike protein. (B) The number of antibodies targeting pan-coronavirus immunodominant epitopes is presented for each group. Only antibodies unique to each group are shown. Immunodominant epitopes were previously defined (17): receptor binding domain (RBD), S1/S2 cleavage site (CS), fusion peptide (FP), heptad repeat (HR), and nucleocapsid protein (N).