Humoral Immune Responses in Patients with Severe COVID-19: A Comparative Pilot Study between Individuals Infected by SARS-CoV-2 during the Wild-Type and the Delta Periods

Abstract

Since the onset of the COVID-19 pandemic, humanity has experienced the spread and circulation of several SARS-CoV-2 variants that differed in transmissibility, contagiousness, and the ability to escape from vaccine-induced neutralizing antibodies. However, issues related to the differences in the variant-specific immune responses remain insufficiently studied. The aim of this study was to compare the parameters of the humoral immune responses in two groups of patients with acute COVID-19 who were infected during the circulation period of the D614G and the Delta variants of SARS-CoV-2. Sera from 48 patients with acute COVID-19 were tested for SARS-CoV-2 binding and neutralizing antibodies using six assays. We found that serum samples from the D614G period demonstrated 3.9- and 1.6-fold increases in RBD- and spike-specific IgG binding with wild-type antigens compared with Delta variant antigens (p < 0.01). Cluster analysis showed the existence of two well-separated clusters. The first cluster mainly consisted of D614G-period patients and the second cluster predominantly included patients from the Delta period. The results thus obtained indicate that humoral immune responses in D614G- and Delta-specific infections can be characterized by variant-specific signatures. This can be taken into account when developing new variant-specific vaccines.

Keywords: COVID-19; SARS-CoV-2; variants of concern; virus neutralization.

Figure 1

The dynamics of the spread of SARS-CoV-2 variants in Moscow population during the period from May 2020 to April 2023. Numbers of confirmed COVID-19 cases (A). Relative prevalence of SARS-CoV2 VOCs. Brackets denote the two periods of infection, D614G and Delta, in the study groups. (B) showed a succession of different SARS-CoV-2 genetic variants.

Figure 2

RBD- and S-binding activity of sera from patients with COVID-19 infected during the D614G and Delta periods. (A) Levels of serum IgG against WT, Delta, and BA.1 RBD, measured by ELISA. (B) Levels of serum IgG against WT, Delta, and BA.1 S protein, measured by mELISA. Dotted lines indicate the cut-off value for differentiating a positive response from a background response in the pre-pandemic samples from healthy donors (HD). ** p < 0.01, * p < 0.05.

Figure 3

Neutralization antibody titers (ID₅₀ values) against SARS-CoV-2 variants for sera from COVID-19 patients infected in the D614G and Delta period. (A) Neutralization of VLPs pseudotyped with the S protein from WT, Delta, and BA.1 Omicron variants. (B) Antibody-mediated blocking of ACE2-Alexa488 binding to HEK293 cells transiently transfected with S protein from WT, Delta, and BA.1 Omicron variants evaluated in fcVNA. (C) Antibody-mediated blocking of ACE2-HRP binding with RBD from WT, Delta, and BA.1 Omicron variants evaluated in sVNA.

Figure 4

IFN-γ expression by NK cells in ADNKA. Plates were coated with wild-type (left panel) or Delta (right panel) RBD. NK cells were cultivated on plates in the presence of serum samples (dilution 1:40) from patients infected during D614G and Delta periods.

Figure 5

Hierarchical cluster (A) and principal component analysis (B) of serum samples from patients hospitalized with COVID-19 during D614G and Delta period. (A) Columns denote patients with their IDs. Rows correspond to immune response variables. Dendrograms on the top illustrate the clustering of patients. Immune response measurement values are color-coded according to the key shown on the right. (B) Principal component analysis of patients with COVID-19. Patient IDs are shown. D614G- and Delta-period clusters are indicated by the ovals. Results are shown for individual samples (symbols) from D614G period (n = 26) and Delta period (n = 19) patients.