In this study, the Australian authors investigated the heterologous and specific immunological effects of vaccination in children aged 5 to 11 years who received two doses of BNT162b2 COVID-19 vaccine (Pfizer, USA). The results showed that SARS-CoV-2 mRNA vaccine alters cytokine responses to heterologous stimulants (killed pathogens, Toll-like receptor agonists, and SARS-CoV-2 antigens) in children, and that these effects can persist for up to six months after vaccination.
About the study
The COSI BAIR was a single-arm clinical trial in which all participants received two doses of BNT162b2 vaccine (Pfizer, USA), 8 weeks apart. COSI BAIR participants were a subgroup of the Melbourne Infant Study: BCG for Allergy and Infection Reduction (MIS BAIR) randomized controlled trial. The aim of the MIS BAIR study was to investigate 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 10 days of life. Participants from both groups were recruited for the COSI BAIR study.
The age limit for COSI BAIR study was five to eleven years. The exclusion criteria were hypersensitivity to BNT162b2, previous receipt of a COVID-19 vaccine, previous COVID-19 confirmed by polymerase chain reaction, clinically significant illness, and receipt of BCG vaccine outside the MIS BAIR trial.
The study included 29 children, aged 5 to 11 years, with paired blood samples. The first blood sample was taken immediately before the first BNT162b2 vaccination, and the second blood sample was taken 28 days after the second BNT162b2 vaccination. The samples from eight children were taken 6 months after the second BNT162b2 vaccination. A whole blood stimulation assay was used to investigate in vitro cytokine responses to heterologous stimulants. The stimulants included 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, hepatitis B virus surface antigen, and HK Candida albicans.
The supernatants were analyzed using a cytokine assay, which enabled the detection of 27 pro-inflammatory and anti-inflammatory cytokines and chemokines. The analysis included 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), regulated upon activation, normal T cell expressed and secreted (RANTES), tumor necrosis factor-α (TNF‐α) and vascular endothelial growth factor (VEGF).
The SARS-CoV-2 spike (S) protein and receptor-binding domain (RBD) were quantified by ELISA.
Results one month following a second vaccination with BNT162b2
At 28 days following a second BNT162b2 vaccination, cytokine and chemokine responses to bacterial, fungal and viral stimulation, as well as to Toll-like receptor agonists stimulation, showed a general decrease 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 stimulation 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 BNT162b2 vaccine.
These results demonstrated that SARS-CoV-2 mRNA vaccination in children decreased the responses of inflammatory cytokines (IFN-γ, MCP-1, IL-6, IL-8 and IL-15) to heterologous bacterial, fungal and viral re-stimulation.
In contrast, the response of most cytokines and some chemokines to SARS-CoV-2-specific stimuli was increased at 28 days after the second vaccination compared to the response before the vaccination. The largest increases were observed in the responses of 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 irradiated SARS-CoV-2 and S1 and S2 subunit stimulation. The responses of TNF-α, G-CSF, PDGF-BB, VEGF, FGF-basic, IL-4, IL-17, and IP-10 increased following S1 and S2 stimulation.
MCP-1 was the only analyte that decreased following the SARS-CoV-2-specific stimulation (with nucleocapsid protein or irradiated SARS-CoV-2).
Of note, the analysis of participants who did not receive the BCG vaccination in the MIS BAIR trial revealed that the BCG status had a negligible or no effect on cytokine responses after BNT162b2 vaccination.
Results six months following the second BNT162b2 vaccination
The eight children who had samples before the first BNT162b2 vaccination and 6 months after the second BNT162b2 vaccination, and who remained negative for SARS-CoV-2 nucleocapsid protein, were included in this analysis.
Six months after the second BNT162b2 vaccination, there were sustained decreases in cytokine responses to viral stimulants, but not to bacterial stimulants 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, MIP-1. Bacterial stimulations, like BCG, E. coli, H. influenzae and L. monocytogenes increased the response of IL-8. Stimulation with E. coli and H. influenzae increased the responses of TNF-α, IL-1ra and G-CSF. BCG stimulation increased response of RANTES, but decreased response of IP-10.
The response of IL-1β was markedly increased with R848 stimulation.
Six months following the second BNT162b2 vaccination, the responses to SARS-CoV-2-specific stimuli 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, remained higher. Also, stimulation with the SARS-CoV-2 nucleocapsid protein increased the responses of 22/27 cytokines and chemokines.
The correlation between SARS-CoV-2-specific immunity and heterologous cytokine responses
Anti-S protein and anti-RBD total IgG antibody titers were measured in all participants before the first BNT162b2 vaccination and 28 days and 6 months after the second BNT162b2 vaccination. All participants with paired samples had robust anti-S protein and anti-RBD IgG antibody titers 28 days after the second BNT162b2 vaccination. Anti-S protein IgG antibody titer and the anti-RBD IgG antibody titer were positively correlated 28 days after the second BNT162b2 vaccination. However, the anti-RBD IgG antibody titer and cytokine response to heterologous stimulation did not correlate, suggesting that the observed changes in cytokine responses to heterologous stimulants were not related to the specific antibody response to the vaccine.
In summary, these results suggest that SARS-CoV-2 mRNA vaccine alters cytokine responses to heterologous stimulants in children, and that these effects can persist for up to six months after vaccination. Decreased immune response to other pathogens makes children more susceptible to other infections. These data highlight the need for further investigation and consideration of heterologous effects in vaccination policy, given their extensive public health implications.
This article was published in the Frontiers in Immunology.
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