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Clinical Trial
. 2020 Dec 1;130(12):6366-6378.
doi: 10.1172/JCI142804.

COVID-19 survival associates with the immunoglobulin response to the SARS-CoV-2 spike receptor binding domain

Massimiliano Secchi  1 , Elena Bazzigaluppi  1 , Cristina Brigatti  1 , Ilaria Marzinotto  1 , Cristina Tresoldi  1 , Patrizia Rovere-Querini  1   2 , Andrea Poli  1 , Antonella Castagna  1   2 , Gabriella Scarlatti  1   2 , Alberto Zangrillo  1   2 , Fabio Ciceri  1   2 , Lorenzo Piemonti  1   2 , Vito Lampasona  1
Affiliations
Clinical Trial

COVID-19 survival associates with the immunoglobulin response to the SARS-CoV-2 spike receptor binding domain

Massimiliano Secchi et al. J Clin Invest. .

Abstract

BACKGROUNDSerological assays are of critical importance to investigate correlates of response and protection in coronavirus disease 2019 (COVID-19), to define previous exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in populations, and to verify the development of an adaptive immune response in infected individuals.METHODSWe studied 509 patients confirmed to have COVID-19 from the San Raffaele Hospital of Milan and 480 samples of prepandemic organ donor sera collected in 2010-2012. Using fluid-phase luciferase immune precipitation (LIPS) assays, we characterized IgG, IgM, and IgA antibodies to the spike receptor binding domain (RBD), S1+S2, nucleocapsid, and ORF6 to ORF10 of SARS-CoV-2, to the HCoV-OC43 and HCoV-HKU1 betacoronaviruses spike S2, and the H1N1Ca2009 flu virus hemagglutinin. Sequential samples at 1 and 3 months after hospital discharge were also tested for SARS-CoV-2 RBD antibodies in 95 patients.RESULTSAntibodies developed rapidly against multiple SARS-CoV-2 antigens in 95% of patients by 4 weeks after symptom onset and IgG to the RBD increased until the third month of follow-up. We observed a major synchronous expansion of antibodies to the HCoV-OC43 and HCoV-HKU1 spike S2. A likely coinfection with influenza was neither linked to a more severe presentation of the disease nor to a worse outcome. Of the measured antibody responses, positivity for IgG against the SARS-CoV-2 spike RBD was predictive of survival.CONCLUSIONThe measurement of antibodies to selected epitopes of SARS-CoV-2 antigens can offer a more accurate assessment of the humoral response in patients and its impact on survival. The presence of partially cross-reactive antibodies with other betacoronaviruses is likely to impact on serological assay specificity and interpretation.TRIAL REGISTRATIONCOVID-19 Patients Characterization, Biobank, Treatment Response and Outcome Predictor (COVID-BioB). ClinicalTrials.gov identifier: NCT04318366.FUNDINGIRCCS Ospedale San Raffaele and Università Vita Salute San Raffaele.

Keywords: Adaptive immunity; COVID-19; Immunoglobulins; Immunology; Influenza.

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Conflict of interest statement

Conflict of interest: The authors have declared that no conflict of interest exists.

Figures

Figure 1
Figure 1. Flow diagram of patients characterized in the study.
All patients included in the study had a confirmed SARS-CoV-2 infection as defined by a positive RT-PCR from a nasal/throat swab and/or signs, symptoms, and radiological findings suggestive of COVID-19 pneumonia.
Figure 2
Figure 2. Kinetics of SARS-CoV-2 spike RBD antibody development.
Antibody levels in COVID-19 patient (n = 575) and control (n = 480) sera were stratified by the symptom duration (weeks 1, 2, 3, ≥4) at serum sampling and by IgM, IgA, IgG immunoglobulin class (A–C, respectively). For each assay and time point are shown the percentage and count of antibody positive sera, the arbitrary units measured in each sample (circles), their probability density estimate (with the half violin plots upscaled to maximum width for better visualization), a box plot showing median, IQR, and whiskers extending to 1.96 times the median. The dashed vertical lines correspond to the threshold for positivity. Fill colors correspond to an antibody-positive (magenta) or -negative (light blue) score. A schematic depiction of the recombinant antigen is shown on top.
Figure 3
Figure 3. Assay performance of the SARS-CoV-2 spike RBD LIPS in COVID-19.
Antibody levels in COVID-19 patient (n = 575) and control (n = 480) sera were stratified by symptom duration (weeks 1, 2, 3, ≥4) at serum sampling and IgM, IgA, IgG immunoglobulin class. Left panels: ROC curve analysis of LIPS assays measuring either IgM, IgA, or IgG at 1 week to 4 weeks or later after symptom onset. Shown are the total ROC-AUC and the pAUC95. Middle panels: Venn diagrams of spike RBD antibody-positive or -negative score combinations (shown as count and percentages) for different immunoglobulin classes at the same time points. Right panels: ROC-AUC, pAUC95, sensitivity, specificity, positive, and negative predictive values of an algorithm combining results from IgG and IgM immunoglobulin class–specific LIPS assays at the same time points.
Figure 4
Figure 4. SARS-CoV-2 spike RBD antibody titer after hospital discharge.
The line plots show the titer of IgG (orange), IgM (purple), and IgA (blue) according to time from development of symptom onset in sequential samples from the same patients (n = 35). Samples were collected at baseline and at follow-up visits 1 and 3 month after hospital discharge. The dashed lines indicate the cutoff of the IgG and IgM (black) and IgA (blue) assays.
Figure 5
Figure 5. Hazard ratios for death, ICU admission, and nasopharyngeal swab SARS-CoV-2 viral RNA RT-PCR negativization in patients with COVID-19.
The forest plots show the corresponding hazard ratios for each variable at the time of antibody sampling. The univariable Cox regression analysis was adjusted for sex and age and stratified for the duration of symptoms at serum sampling. Antibody positivity was considered as a time-dependent covariate. Dots represent the HR, filled dots indicate P < 0.05.
Figure 6
Figure 6. Multivariable hazard ratios for anti–SARS-CoV2 spike antibodies and time to death or to swab RT-PCR negativization in patients with COVID-19.
(A) Forest plots of hazard ratios for time to death obtained with 2 models of multivariable Cox regression analysis using SARS-CoV-2 RBD IgG-positive score and the shown variables measured at the time of antibody sampling. (B) Forest plot of the hazard ratio of a multivariable model for time to nasopharyngeal swab SARS-CoV-2 RNA RT-PCR negativization based on SARS-CoV-2 S1+S2 IgA-positive score and the shown variables. A higher hazard ratio corresponds to a decreased time to swab negativization. The multivariable Cox regression analysis was adjusted for sex and age and stratified for the duration of symptoms at serum sampling. Antibody positivity was considered as a time-dependent covariate. Dots represent the HR, filled dots indicate P < 0.05.
Figure 7
Figure 7. HCoV-OC43 and HUK1 S2 IgG antibodies in patients with COVID-19.
(A, B) Kinetics of HCoV-OC43 and HKU1 S2 IgG expansion in COVID-19 (n = 575) and control (n = 480) sera stratified by the duration of symptoms at serum sampling. For each sample are shown the measured arbitrary units (circles), the probability density estimate (with the half violin plot upscaled to maximum width for better visualization), box plot displaying median, IQR, and whiskers extending to 1.96 times the IQR. Fill colors correspond to AU greater than 66th (light blue), greater than 33rd (purple), or less than 33rd (orange) percentile in patients with COVID-19. Shown are the percentages and count of subjects with AU greater than the 66th percentile. (C) Correlation of SARS-CoV-2, HCoV-OC43, and HCoV-HKU1 spike IgG in symptomatic COVID-19 sera. Shown are the linear regression (black lines) of log-transformed AU (circles), its 95% CI (gray areas), and its coefficients. (D) Dumbbell plot of IgG binding reduction in a selection of symptomatic and paucisymptomatic patients with COVID-19. LIPS using the indicated HCoV-OC43 and SARS-CoV-2 antigens were performed with (orange fill) or without (light blue fill) competition with untagged SARS-CoV-2 S1+S2 protein.
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