Antibody-dependent enhancement of SARS-CoV-2, the impact of variants and vaccination

Abstract

This study characterized antibody-dependent enhancement (ADE) in serum samples from individuals exposed to SARS-CoV-2 via infection or vaccination and evaluated its association with SARS-CoV-2 variants (Wuhan and Omicron), MERS-CoV, and NL63. ADE assays were performed on sera from SARS-CoV-2-infected patients (n = 210) with varying disease severity and vaccinated individuals (n = 225) who received adenovirus vector, inactivated virus or mRNA vaccines. ADE was assessed using pseudoviruses (PVs) in BHK cells expressing FcgRIIa. Neutralizing antibody levels, total IgG, IgG subclasses, and complement activation were analyzed using ELISA and neutralization assays. ADE was observed in 6.2% of infection samples (primarily severe cases) and 5.3% of vaccinated samples (adenovirus-vector and inactivated virus groups). ADE-positive samples showed reduced neutralizing activity, while total IgG and IgG subclasses did not differ significantly between ADE-positive and negative samples. Complement activation was elevated in severe cases but did not correlate clearly with ADE. Notably, MERS-CoV PV induced ADE in a subset of infected samples, but no ADE was detected for NL63. ADE was observed in SARS-CoV-2-infected individuals, particularly in severe cases, and in those vaccinated with adenovirus-vector and inactivated virus vaccines, but not with mRNA vaccines. Cross-reactivity leading to ADE was detected for MERS-CoV but not for NL63. ADE was associated with reduced neutralizing antibody activity and elevated complement activation in severe infections, though the specific role of complement in ADE remains unclear. These findings highlight the need to investigate the mechanisms underlying ADE and its implications for vaccine design and post-infection immunity against respiratory viruses.

Keywords: ADE; SARS-CoV2; Virology; immunology; variants.

Figure 1.

ADE of SARS-CoV-2 in COVID-19 infected serum samples; ADE in samples from ICU patients; TP1 (a), TP2 (b), and TP3 (c); severe non-ICU patients; TP1 (d), TP2 (e); mild infection; TP1 (f). ADE is indicated as significantly higher luminescence signals between serum dilutions of SARS-CoV-2 infected and control samples. Statistical analysis was performed using unpaired t test and the significance is indicated by **(p value 0.0022, <0.0001, 0.0312, 0.0247).

Figure 2.

ADE of SARS-CoV-2 in COVID-19 vaccinated serum samples: Adenovirus vector vaccine; Dose 1(a), Dose 2 (b) and Dose 3 (c). Inactivated virus vaccine; Dose 1 (d), Dose 2 (e) and Dose 3 (f). mRNA Vaccine; Dose 1(g), Dose 2(h) and Dose 3 (i). ADE (higher luminescence) was reported as luciferase activity inside cells upon uptake of the SARS-CoV-2 PV via the Fc-RIIa receptor. Statistical analysis was performed using unpaired t test, significance is indicated by **, * and p value = 0.0294, 0.0024, 0.0321, 0.0011, 0.0053 and 0.0401.

Figure 3.

ADE of SARS-CoV-2 omicron, hCoV and MERS-Cov in SARS-CoV-2 infection and/or vaccination samples. ADE positive and negative samples from SARS-CoV-2 infected (all three TPs) and vaccinated (all three doses) were analyzed for ADE of SARS-CoV-2 omicron, NL63 and MERS-CoV PVs using BHK-FcgRIIa cells. ADE of SARS-CoV-2 omicron (a), NL63 (b), and MERS-CoV (c) in SARS-CoV-2 infection samples. ADE of SARS-CoV-2 omicron (d), NL63 (e), and MERS-CoV (f) in SARS-CoV-2 vaccination samples. Difference in luminescence of ADE positive and control samples were analyzed using unpaired t test, significance is indicated by **, * (p value = 0.0015 and 0.0428).

Figure 4.

IgG Subtypes and neutralization in ADE positive and negative samples against different SARS-CoV-2 variants and hCoV (NL63). Levels of IgG subtypes (IgG1–4) were measured against SARS-CoV-2 RBD (a) and S1 (b) antigens. Statistical significance was determined using a one-way ANOVA. Panel (c) shows neutralization of pseudoviruses (PVs) using HEK293T cells expressing ACE2. Samples were categorized into ADE-positive and ADE-negative groups for each PV, with further classification into infected and vaccinated subgroups. The analysis included 13 ADE-positive samples from four ICU patients (collected across three timepoints), one severe non-ICU patient (one timepoint), and 12 ADE-positive samples from vaccinated individuals across three different vaccine doses. Statistical comparisons were performed using unpaired t-tests, and significance was indicated by * for p-values <0.05.

Figure 5.

Association between ADE and neutralization in ADE-positive (a) (n = 9) and ADE-Negative (b) (n = 11) samples. Percentage of virus uptake (ADE) were calculated as (luminescence of serum dilutions/luminescence of pre-pandemic control) *100. Similarly, percentage neutralization was calculated as (luminescence of serum dilutions/luminescence of non-serum control) *100. Average of percent virus uptake and percent neutralization for all samples at designated dilutions were calculated and plotted accordingly.

Figure 6.

Association of ADE with serum complements in SARS-CoV-2 infection samples. Serum complement levels in ADE positive and negative samples from ICU, severe non-ICU and mild infection patients. Complements including C1q (a), C3 (b), C3a (c) and C5a (d) are analyzed using statistical analysis: unpaired t test and the significance is indicated by ** and ***.