Coronavirus disease 2019 (COVID-19) is a clinical syndrome caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). BNT162b2 (Pfizer, USA) and mRNA 1273 (Moderna) vaccines were the first messenger RNA (mRNA)-based vaccines ever approved. In both vaccines, a mRNA sequence determines the structure and assembly of the immunogen, the SARS-CoV-2 spike (S) glycoprotein. In this study, the Australian authors investigated cytokine responses to heterologous pathogens, Toll-like receptor agonists andSARS-CoV-2 antigens in children aged 5 to 11 years vaccinated with two doses of the BNT162b2 mRNA COVID-19 vaccine.
Of note, a recent study that investigated SARS-CoV-2 spike subunit 1 (S1)–specific and receptor-binding domain (RBD)-specific immunoglobulin (Ig) G subclasses in children 5 to 11 years of age has found an increase in IgG4 levels specific for S1 and RBD one year after the BNT162b2 vaccination. IgG4, as the least abundant IgG subclass in humans, has some unique structural and functional features that lead to it being described as a “blocking” and “anti-inflammatory” antibody that cannot activate antibody-dependent immune effector responses. https://discovermednews.com/elevated-igg4-children-after-mrna-bnt162b2-vaccination/
SARS-CoV-2 is an enveloped, positive-sense, single-stranded RNA virus. Its genome encodes four structural proteins, namely the spike (S), envelope (E), nucleocapsid (N), and membrane (M) protein. The S protein is a glycosylated homotrimer with each monomer composed of subunits S1 and S2, separated by host cell proteases. The S1 domain comprises the N-terminal domain (NTD), the receptor binding domain (RBD) with a receptor binding motif (RBM), and two C-terminal domains.
About the study
The study included 29 children from a single-arm clinical trial called COSI BAIR, which is part of Melbourne Infant Study: BCG for Allergy and Infection Reduction (MIS BAIR). MIS BAIR) is a randomized controlled trial investigating whether neonatal BCG vaccination can protect children from infections, allergies, and asthma in childhood. Neonates were randomly assigned to receive or not receive the BCG vaccine in the first ten days of life. Participants from both groups were recruited for the COSI BAIR study. All participants included in the COSI BAIR trial received two doses of the BNT162b2 vaccine, 8 weeks apart.
The age limit was five to eleven years. The exclusion criteria were hypersensitivity to the BNT162b2, previous COVID-19 vaccination, previous COVID-19 confirmed by polymerase chain reaction or SARs-CoV-2, clinically significant illness, and receipt of BCG vaccine outside the MIS BAIR trial.
The paired blood samples were taken from participants, the first was taken immediately before the first BNT162b2 vaccination, and the second 28 days after the second vaccination. The samples from eight children were taken 6 months after the second BNT162b2 vaccination. The whole blood stimulation assay was used to investigate in vitro cytokine responses to heterologous stimulants, such as SARS-CoV-2 antigens, Toll-like receptor agonists, and killed pathogens like heat-killed (HK) Haemophilus influenzae type B, HK Listeria monocytogenes, BCG, HK Staphylococcus aureus, HK Escherichia coli, HK Candida albicans and hepatitis B virus surface antigen.
A cytokine assay was employed to analyze 27 pro-inflammatory and anti-inflammatory cytokines and chemokines in supernatants, including eotaxin, basic fibroblast growth factor basic (FGF), granulocyte-colony stimulation factor (G‐CSF), granulocyte-macrophage colony-stimulating factor (GM‐CSF), interferon-γ (IFN‐γ), interleukin (IL)‐1β, IL‐1rα, IL‐2, IL‐4, IL‐5, IL‐6, IL‐7, IL‐8, IL‐9, IL‐10, IL‐12(p70), IL‐13, IL‐15, IL‐17, IFN-γ-induced protein (IP‐10), monocyte chemoattractant protein (MCP‐1), macrophage inflammatory protein (MIP)‐1α, MIP‐1β, platelet-derived growth factor-BB (PDGF‐BB), RANTES, tumor necrosis factor-α (TNF‐α) and vascular endothelial growth factor (VEGF).
The SARS-CoV-2 S protein, the S1 and S2 subunits, and RBD were quantified by ELISA.
Results
Cytokine responses in children vaccinated with the BNT162b2 one month after the second vaccination
Cytokine and chemokine responses to bacterial, fungal, viral, and Toll-like receptor agonist stimulation showed a general decrease at 28 days after the second dose of the BNT162b2 vaccine compared to responses before the vaccination. The largest decreases were observed for IFN-γ and MCP-1.
A stimulation with BCG, H. influenzae, S. aureus, hepatitis B antigen, poly (I: C), and R848 decreased the responses of IL-6, IL-15, and IL-17. Stimulation with L. monocytogenes decreased the responses of IL-15, TNF-α, and IP-10, whereas H. Influenzae and S. aureus decreased the response of IL-8.
RANTES was the only analyte that increased in response to heterologous stimulants (L. monocytogenes and C. albicans) 28 days after the second dose of the BNT162b2 vaccine.
These results demonstrated decreased responses of inflammatory cytokines (IFN-γ, MCP-1, IL-6, IL-8, and IL-15) to heterologous pathogen stimulation after BNT162b2 vaccination.
In contrast, cytokine and chemokine responses to SARS-CoV-2-specific stimuli showed an increase at 28 days after the second dose of the BNT162b2 vaccine compared to the responses before the vaccination. The largest increases were observed in IL-6, IL-15, GM-CSF, IL-10, IL-12p70, IL-2, and IL-13, as well as of chemokines MIP-1β and RANTES to stimulation with irradiated SARS-CoV-2, S1 and S2 subunits. The responses of TNF-α, G-CSF, PDGF-BB, VEGF, FGF-basic, IL-4, IL-17, and IP-10 increased following stimulation with the S1 and S2 subunits.
MCP-1 was the only analyte that decreased after the stimulation with SARS-CoV-2-specific N protein or irradiated SARS-CoV-2.
Of note, the BCG status had a negligible or no effect on cytokine responses after the BNT162b2 vaccination in participants who did not receive the BCG vaccination in the MIS BAIR trial.
Cytokine responses in children vaccinated with the BNT162b2 up to six months after the second vaccination
This analysis included eight children with blood samples taken before the first vaccination and 6 months after the second BNT162b2 vaccination who remained negative for the SARS-CoV-2 N protein.
Their results demonstrated a sustained decrease in cytokine response to viral stimulants, but not to bacterial stimulants six months after the second BNT162b2 vaccination compared to response before the vaccination.
The responses of IL-6, IL-15, TNF-α, GM-CSF, PDGF-BB, VEGF, FGF-basic, IL-10, IFN-γ, IL-2, IL-4, IL-5, IL-9, IL-13, and eotaxin decreased after hepatitis B antigen and poly (I: C) stimulation. Hepatitis B antigen stimulation decreased the responses of IL-1β, IL-12p70, IL-17, and MIP-1β, whereas Poly (I: C) stimulation decreased the responses of IL-1ra, IL-7, and MIP-1α.
C. albicans stimulation decreased the responses of MCP-1 and eotaxin but increased the responses of IL-1β, IL-1ra, IL-8, FGF-basic, IL-12p70, IL-8, and MIP-1.
Bacterial stimulations, like BCG, E. coli, H. influenza, and L. monocytogenes increased the response of IL-8. Stimulation with E. coli and H. influenzae increased the responses of TNF-α and G-CSF. BCG stimulation increased the response of RANTES but decreased the response of IP-10. The response of IL-1β was markedly increased with R848 stimulation.
Importantly, the responses of most cytokines and chemokines, like IL-1β, IL-1ra, IL-6, G-CSF, GM-CSF, VEGF, FGF-basic, IFN-γ, IL-2, IL4, IL-5, IL-17, MIP-1α, and MIP-1β to SARS-CoV-2-specific stimuli remained higher six months after the second BNT162b2 vaccination. Also, stimulation with the SARS-CoV-2 N protein increased the responses of 22/27 cytokines and chemokines.
The correlation between SARS-CoV-2-specific immunity and heterologous cytokine responses
Titers of anti-S protein and anti-RBD total IgG antibodies were evaluated before the first vaccination and 28 days and 6 months after the second vaccination. All participants had robust anti-S protein and anti-RBD IgG antibody titers 28 days after the second BNT162b2 vaccination, and these titers positively correlated. However, the titer of anti-RBD IgG antibody did not correlate with a cytokine response to heterologous stimulation.
Conclusion
This study demonstrated that cytokine responses to heterologous pathogens, Toll-like receptor agonists, and SARS-CoV-2 antigens were altered in children aged 5 to 11 years vaccinated with two doses of the BNT162b2 mRNA COVID-19 vaccine. These effects persisted for up to six months after their second vaccination.
It should be noted that a decrease in immune response to other pathogens makes children more susceptible to other infections. Accordingly, the authors concluded that these findings highlight the need for further investigation and consideration of vaccination policy.
This article was published in the Frontiers in Immunology.
Journal Reference
Noé A, Dang TD, Axelrad C, Burrell E, Germano S, Elia S, Burgner D, Perrett KP, Curtis N and Messina NL (2023) BNT162b2 COVID-19 vaccination in children alters cytokine responses to heterologous pathogens and Toll-like receptor agonists. Front. Immunol. 14:1242380. (Open Access) https://doi.org/10.3389/fimmu.2023.1242380
