Specific Anti-SARS-CoV-2 Humoral and Cellular Immune Responses After Booster Dose of BNT162b2 Pfizer-BioNTech mRNA-Based Vaccine: Integrated Study of Adaptive Immune System Components

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), is modifying human activity all over the world with significant health and economic burden. The advent of the SARS-CoV-2 pandemic prompted the scientific community to learn the virus dynamics concerning transmissibility, epidemiology, and usefulness of vaccines in fighting emerging health hazards. Pieces of evidence suggest that the first and second doses of mRNA vaccines induce a significant antibody response in vaccinated subjects or patients who recovered from SARS-CoV-2 infection, demonstrating the importance of the previously formed memory. The aim of this work has been to investigate the effects of BNT162b2 Pfizer-BioNTech mRNA-based vaccine booster dose in a cohort of 11 uninfected immunocompetent (ICs), evaluating the humoral and cellular responses, with more carefulness on memory B and T cells. Our findings underscore the potential benefit of the third dose of mRNA vaccine on the lifespan of memory B and T cells, suggesting that booster doses could increase protection against SARS-CoV-2 infection.

Keywords: B cells; BNT162b2; SARS-CoV-2; T cells; booster dose; mRNA vaccine.

Figure 1

Kinetic of total anti-SARS-CoV-2 IgG and IgA serum antibodies levels in seronegative recipients (ICs n=11) of Pfizer-BioNTech BNT162b2 mRNA-based vaccination. The evaluation of both serum antibodies was conducted at three weeks (T1) and nine months (T2) after the second dose, and three weeks after the booster dose (T3). In Figure (A) anti-SARS-CoV-2 S1/S2 IgG levels and in (B) anti-SARS-CoV-2 S1 IgA levels. The dotted lines correspond to IgG (> 15.0 AU/mL) and IgA (>1.1 Ratio) cut-off, respectively. The significance was determined using Tukey’s multiple comparisons test. One-way ANOVA, ***p=0.0002; ****p<0.0001, ns, not significant.

Figure 2

SARS-CoV-2-specific memory B cells in seronegative recipients (ICs n=11) of Pfizer-BioNTech BNT162b2 mRNA-based vaccination before (T2) and after (T3) the booster dose. (A) Percentage (%) of SARS-CoV-2 specific B cells before and after the booster dose. (B) Comparison amid T2 and T3 of percentage (%) positive cell to surface immunoglobulin isotypes, IgG, IgA, and IgM. (C) Representative flow cytometry plots (one subject) showing memory B-cell subpopulations. The significance was determined using Wilcoxon matched-pairs test (A) and Sidak’s multiple comparisons test (B), one-way ANOVA, **p=0.0021.

Figure 3

Comparison of QuantiFERON SARS-CoV-2 antigen tube (Ag minus Nil) response, express as IFN-γ (IU/ml), in seronegative subjects (ICs n=11) before (T2) and after (T3) the booster dose of the Pfizer-BioNTech BNT162b2 mRNA-based vaccine. (A) QFN-SARS-CoV-2 Ag1-Nil responses; (B) Ag2-Nil responses; (C) Ag3-Nil responses. The dotted lines, in each graph, correspond to IFN-γ cutoff (0.2 IU/ml). (D) Correlation between IFN-γ-ELISpot and IFN-γ-QFN responses of each specific antigen (Ag1 contains CD4+ epitopes derived from the S1 subunit of the spike protein; Ag2 contains CD4+ and CD8+ epitopes from the S1 and S2 subunits of the spike protein; and Ag3 contains CD4+ and CD8+ epitopes from S1 and S2, plus immunodominant CD8+ epitopes derived from the whole genome). (E) Graphic comparison of IFN-γ-ELISpot and IFN-γ-QFN responses of all subjects studied. The significance was determined using Wilcoxon matched-pairs test, *p = 0.0332 (A–C) and Pearson correlation, *p=0.0332; **p=0.0021; ***p=0.0002.

Figure 4

Activation-induced memory (AIM)-T cell detection in seronegative recipients (ICs n=11) of Pfizer-BioNTech BNT162b2 mRNA-based vaccination at T3. (A) Comparing of percentage (%) of AIM-T cells in Nil tubes to SARS-CoV-2 antigen using specific marker CD137/OX-40, CD69/CD40L, CD137/CD69 (CD40L is uniquely expressed on activated CD4 T cells; CD69 is an activation marker of both CD4 and CD8 T cells; CD137 and OX-40, both belonging to the TNF receptor superfamily, are also markers of Ag-specific CD8 and CD4 T cells, respectively. In combinations, CD137/OX-40 and CD69/CD40L identify Ag-specific CD4 T cells, while CD137/CD69 identifies Ag-specific CD8 T cells). (B) Representative flow cytometry plots (one subject) showing AIM-T cell subpopulations stimulated or not (Nil) with SARS-CoV-2 antigen and the positive control (Mitogen). The significance was determined using Wilcoxon matched-pairs test, **p = 0.0021; ***p = 0.0002.