Appearance of tolerance-induction and non-inflammatory SARS-CoV-2 spike-specific IgG4 antibodies after COVID-19 booster vaccinations

Abstract

Background: Understanding the characteristics of the humoral immune responses following COVID-19 vaccinations is crucial for refining vaccination strategies and predicting immune responses to emerging SARS-CoV-2 variants.

Methods: A longitudinal analysis of SARS-CoV-2 spike receptor binding domain (RBD) specific IgG antibody responses, encompassing IgG subclasses IgG1, IgG2, IgG3, and IgG4 was performed. Participants received four mRNA vaccine doses (group 1; n=10) or two ChAdOx1 nCoV-19 and two mRNA booster doses (group 2; n=19) in Bangladesh over two years.

Results: Findings demonstrate robust IgG responses after primary Covishield or mRNA doses; declining to baseline within six months. First mRNA booster restored and surpassed primary IgG responses but waned after six months. Surprisingly, a second mRNA booster did not increase IgG levels further. Comprehensive IgG subclass analysis showed primary Covishield/mRNA vaccination generated predominantly IgG1 responses with limited IgG2/IgG3, Remarkably, IgG4 responses exhibited a distinct pattern. IgG4 remained undetectable initially but increased extensively six months after the second mRNA dose, eventually replacing IgG1 after the 3rd/4th mRNA doses. Conversely, initial Covishield recipients lack IgG4, surged post-second mRNA booster. Notably, mRNA-vaccinated individuals displayed earlier, robust IgG4 levels post first mRNA booster versus Covishield counterparts. IgG1 to IgG4 ratios decreased with increasing doses, most pronounced with four mRNA doses. This study highlights IgG response kinetics, influenced by vaccine type and doses, impacting immunological tolerance and IgG4 induction, shaping future vaccination strategies.

Conclusions: This study highlights the dynamics of IgG responses dependent on vaccine type and number of doses, leading to immunological tolerance and IgG4 induction, and shaping future vaccination strategies.

Keywords: COVID-19; IgG; IgG4; antibody; booster; tolerance; vaccine.

Figure 1

IgG Antibody responses after two primary and two booster COVID-19 vaccination. RBD-specific IgG was analyzed in serum samples after four mRNA doses (A, C) and two primary Covishield and two booster mRNA doses (B, D) at different time intervals. Different doses of vaccine administration time points are indicated below the graphs. Samples were collected before vaccination (Pre-V), 1 month, 2/3 Months, 6 months, 12 months, 18 months, and 24 months after the first vaccination. Fold increase was calculated 1 month post-vaccination IgG conc. vs pre-vaccination IgG conc. for each dose as indicated in Figures (C, D). Each symbol represents one individual, and bars indicate geometric mean values. Symbols without any color represent participants who got infected before or after vaccination. Statistical analysis was performed between pre and post-vaccination using the Kruskal-Wallis test. ^*P <0.05, ^**P <0.01, ^***P <0.001, ns, not significant; P >0.05.

Figure 2

Kinetics of IgG subclasses after receiving COVID-19 mRNA vaccines as both primary and booster. RBD-specific IgG1 (A), IgG2 (B), IgG3 (C) and IgG4 (D) were analyzed in serum samples after four mRNA doses at different time intervals. Different doses of vaccine administration time points are indicated below the graphs. Samples were collected before vaccination (Pre-V), 1 month, 2/3 Months, 6 months, 12 months, 18 months, and 24 months after the first vaccination. Symbols without any color represent participants who got infected before or after vaccination. Statistical analysis was performed between pre and post-vaccination antibody titer using the Kruskal-Wallis test. **P <0.01, ***P <0.001, ns, not significant; P >0.05.

Figure 3

Kinetics of IgG subclasses after receiving COVID-19 vaccine Covishield as primary and mRNA as booster. RBD-specific IgG1 (A), IgG2 (B), IgG3 (C) and IgG4 (D) were analyzed in serum samples after two Covishield and two mRNA doses at different time intervals. Different doses of vaccine administration time points are indicated below the graphs. Samples were collected before vaccination (Pre-V), 1 month, 2/3 Months, 6 months, 12 months, 18 months, and 24 months after the first vaccination. Symbols without any color represent participants who got infected before or after vaccination. Statistical analysis was performed between pre and post-vaccination antibody titer using the Kruskal-Wallis test. **P <0.01, ***P <0.001, ns, not significant; P >0.05.

Figure 4

Comparison between IgG1 and IgG4 subclasses after four different doses of COVID-19 vaccines. RBD-specific IgG1 and IgG4 antibodies (mean+SEM) are shown in line graphs after four mRNA doses (A) and two primary Covishield and two booster mRNA doses (C). IgG1 to IgG4 ratio was measured in individual participants one month after each vaccine dose are shown in graph (B, D). Each symbol represents one individual, and bars indicate geometric mean values. Statistical analysis was performed between pre and post-vaccination antibody titer using the Kruskal-Wallis test. **P <0.01, ***P <0.001, ns, not significant; P >0.05.