Specific and off-target immune responses following COVID-19 vaccination with ChAdOx1-S and BNT162b2 vaccines-an exploratory sub-study of the BRACE trial

Abstract

Background: The COVID-19 pandemic led to the rapid development and deployment of several highly effective vaccines against SARS-CoV-2. Recent studies suggest that these vaccines may also have off-target effects on the immune system. We sought to determine and compare the off-target effects of the adenovirus vector ChAdOx1-S (Oxford-AstraZeneca) and modified mRNA BNT162b2 (Pfizer-BioNTech) vaccines on immune responses to unrelated pathogens.

Methods: Prospective sub-study within the BRACE trial. Blood samples were collected from 284 healthcare workers before and 28 days after ChAdOx1-S or BNT162b2 vaccination. SARS-CoV-2-specific antibodies were measured using ELISA, and whole blood cytokine responses to specific (SARS-CoV-2) and unrelated pathogen stimulation were measured by multiplex bead array.

Findings: Both vaccines induced robust SARS-CoV-2 specific antibody and cytokine responses. ChAdOx1-S vaccination increased cytokine responses to heat-killed (HK) Candida albicans and HK Staphylococcus aureus and decreased cytokine responses to HK Escherichia coli and BCG. BNT162b2 vaccination decreased cytokine response to HK E. coli and had variable effects on cytokine responses to BCG and resiquimod (R848). After the second vaccine dose, BNT162b2 recipients had greater specific and off-target cytokine responses than ChAdOx1-S recipients.

Interpretation: ChAdOx1-S and BNT162b2 vaccines alter cytokine responses to unrelated pathogens, indicative of potential off-target effects. The specific and off-target effects of these vaccines differ in their magnitude and breadth. The clinical relevance of these findings is uncertain and needs further study.

Funding: Bill & Melinda Gates Foundation, National Health and Medical Research Council, Swiss National Science Foundation and the Melbourne Children's. BRACE trial funding is detailed in acknowledgements.

Keywords: Cytokine; Heterologous immunity; Immunoregulation; Off-target; SARS-CoV-2; Vaccine.

Fig. 1

BCOS study schema. Blood samples were collected from participants prior to the first dose of a COVID-19 vaccination (V0), 28 (±3 days) after the first dose of a ChAdOx1-S (V1) and 28 (±3 days) after the second dose of ChAdOx1-S or BNT162b2 (V2). Created with BioRender.com.

Fig. 2

SARS-CoV-2-specific and off-target effects of ChAdOx1-S. Differences in immune responses 28 (±3 days) after the first (V1) or second (V2) dose of ChAdOx1-S compared to pre-vaccination (V0) samples. (a) Tukey boxplots and dot plot overlay depicting differences (V1/V2—V0) in log transformed anti-spike and anti-RBD IgG AUC (n = 80). Statistically significant differences before and after ChAdOx1-S vaccination were determined by paired-t test. (b–e) Volcano and Tukey boxplots (with dot plot overlay) depicting differences in (b and c) iSARS stimulation effect (iSARS—iVero response) (n = 55) and (d and e) BCG, C. albicans, E. coli, S. aureus and R848 stimulation effect (stimulant—nil) (n = 57–56) on whole blood cytokine responses. p-value for differences before (V0) and after the first dose of ChAdOx1-S vaccination (V1) were determined by Wilcoxon signed-rank test (WSR, squares) or sign-rank test (ST, circles) as indicated in Supplementary Table S4. (b & d) Volcano plots: Red line indicates p = 0.05 by WSR or ST. (a, c, e) Boxplots: centre lines indicate medians; box limits indicate 25th–75th percentiles; whiskers extend to 1.5 times the interquartile range from the 25th and 75th percentiles. Dots represent each individual participant with line colours representing direction of change relative to the previous datapoint (blue = increase, red = decrease, white = no change). (f) Spearman’s correlation coefficients of differences (V1–V0) in serum levels (IgG) and whole blood cytokine stimulation effect that showed change after ChAdOx1-S vaccination and had a p < 0.05 by WSR or ST. Unsupervised hierarchical clustering was done using Spearman’s correlation as the measure of similarity between cytokine–stimulant pairs. Red indicates a negative correlation, whereas blue indicates a positive correlation. The data shown are from participants with <10 missing paired results (n = 52). (g) Scatter plots of differences (V1—V0) in stimulation effect between cytokine–stimulant pairs. Correlation coefficient (R) and p-value determine by Spearman’s correlation. Purple line depicts regression line, grey indicates 95% confidence interval (CI). Abbreviations: auc, area under the curve; BCG or bcg, bacille Calmette Guérin; ca, C. albicans; ec, E. coli; Ig, immunoglobulin; iSARS (isars), γ-irradiated SARS-CoV-2; R848 or r848, resiquimod; RBD, receptor binding domain; sa, S. aureus; SE, stimulation effect, Th, T helper.

Fig. 3

SARS-CoV-2-specific and off-target effects of BNT162b2. Differences in immune responses 28 (±3 days) after the second (V2) dose of BNT162b2 compared to pre-vaccination (V0) samples. (a) Tukey boxplots and dot plot overlay depicting differences (V2—V0) in log transformed anti-spike and anti-RBD IgG AUC (n = 55). Statistically significant differences before and after BNT162b2 vaccination were determined by paired-t test. (b–e) Volcano and Tukey boxplots (with dot plot overlay) depicting differences in (b and c) iSARS stimulation effect (iSARS—iVero response) (n = 18) and (d and e) BCG, C. albicans, E. coli, S. aureus and R848 stimulation effect (stimulant—nil) (n = 19) on whole blood cytokine responses. p-value for differences before (V0) and after the first dose of BNT162b2 vaccination (V2) were determined by Wilcoxon signed-rank test (WSR, squares) or sign-rank test (ST, circles) as indicated in Supplementary Table S5. (b & d) Volcano plots: Red line indicates p = 0.05 by WSR or ST. (a, c, e) Boxplots: centre lines indicate medians; box limits indicate 25th–75th percentiles; whiskers extend to 1.5 times the interquartile range from the 25th and 75th percentiles. Dots represent each individual participant with line colours representing direction of change relative to the previous datapoint (blue = increase, red = decrease, white = no change). (f) Spearman’s correlation coefficients of differences (V2–V0) in serum levels (IgG) and whole blood cytokine stimulation effect that showed a change after BNT162b2 vaccination and had a p < 0.05 by WSR or ST. Unsupervised hierarchical clustering was done using Spearman’s correlation as the measure of similarity between cytokine–stimulant pairs. Red indicates a negative correlation, whereas blue indicates a positive correlation. The data shown are from participants with <10 missing paired results (n = 18). (g) Scatter plots of differences (V2—V0) in stimulation effect between cytokine–stimulant pairs. Correlation coefficient (R) and p-value determine by Spearman’s correlation. Green line depicts regression line, grey indicates 95% confidence interval (CI). Abbreviations: auc, area under the curve; BCG or bcg, bacille Calmette Guérin; ca, C. albicans; ec, E. coli; Ig, immunoglobulin; iSARS (isars), γ-irradiated SARS-CoV-2; R848 or r848, resiquimod; RBD, receptor binding domain; sa, S. aureus; SE, stimulation effect, Th, T helper.

Fig. 4

Comparison of SARS-CoV-2-specific and off-target in vitro immune responses following BNT162b2 and ChAdOx1-S vaccination. Forest plots depicting adjusted geometric mean ratios (GMR) and 95% confidence intervals for the effect of COVID-19 vaccine type on (a) serum IgG (n = 225) (b) iSARS-induced (n = 76–110) and (c and d) BCG (n = 37–115), C. albicans (n = 71–115), E. coli (n = 21–115), S. aureus (n = 70–115) and R848 (n = 24–115) -induced whole blood cytokine and chemokine responses 28 days after the second vaccination dose (V2). (c and d) A sub-set of (c) 7 chemokines and (d) 6 cytokines/growth factors are depicted, data for all cytokine–stimulant pairs are available in Supplementary Table S6. GMR > 1.0 indicates responses that were higher for BNT162b2-vaccinated compared to ChAdOx1-S-vaccinated participants. Abbreviations: BCG, bacille Calmette Guérin; GMR, geometric mean ratio; Ig, immunoglobulin; iSARS, γ-irradiated SARS-CoV-2; R848, resiquimod; RBD, receptor binding domain.