BNT162b2 mRNA Vaccine-Induced Immune Response in Oral Fluids and Serum

Abstract

Objectives: The COVID-19 vaccine is currently being administered worldwide to address the ongoing pandemic. Although these vaccines have proven effective in preventing severe disease, the level of immunity required to prevent respiratory mucosal infection remains less well understood. Therefore, it is desirable to develop a noninvasive screening strategy such as oral fluid to monitor secreted antibodies longitudinally as potential surrogates of mucosal immunity.

Methods: We evaluated the anti-spike protein antibodies in gingival crevicular fluid (GCF) and saliva and compared them to immune responses in the blood of 50 healthy health care workers following 2 doses of intramuscular Pfizer/BioNTech-BNT162b2 vaccine.

Results: The antibodies to SARS-CoV-2 spike and subdomain proteins (RBD, S1, S2, and NTD) were significantly higher in serum than oral fluids but showed a greater detection rate and higher median titres in GCF than saliva. For all tested SARS-CoV-2 antigens, IgG in GCF (as opposed to saliva) showed a more significant and stronger correlation with IgG in serum. Serum-neutralising antibodies (Nab) titres also displayed a significant and stronger correlation with anti-spike protein and their subdomains in GCF than saliva. Interestingly, the time post-second dose of vaccine and sex had a similar influence on IgG in serum and GCF. However, interferon (IFN)-γ-producing T-cell responses showed no association with SARS-Cov-2 IgG antibodies in serum, GCF, or saliva and neutralisation antibodies in serum. The correlation matrix of all measured parameters grouped serum and GCF IgG parameters separately from salivary IgG parameters indicating that GCF better represents the humoural response in serum than saliva.

Conclusions: Within limitations, we propose that GCF could be a less invasive alternative to serum and more appropriate than saliva to detect antibody responses by current COVID-19 vaccines if the GCF collection procedure could be standardised. Further research is needed to investigate the suitability of GCF for community immune surveillance for vaccines.

Keywords: COVID-19 vaccines; Gingival crevicular fluid; Immunity; Saliva.

Fig. 1

IgG responses to SARS-CoVgcf-2 S-protein and its subdomains in gingival crevicular fluid (GCF), saliva, and serum samples. IgG-specific to spike (S) protein (A), RBD (B), S1 (C), S2 (D), and NTD (E) of SARS-CoV-2 (ancestral strain) were measured using a bead-based Luminex immunoassay. Humoural responses between groups were statistically compared using Mann–Whitney U tests, and all P values >.05 are marked on the graph. ****P < .0001, ***.001 < P < .001, **.01 < P < .001, *.05 < P < .01.

Fig. 2

Correlation between SARS-CoV-2–specific IgG-binding titres in serum and oral fluids. IgG titres between serum and oral fluids (ie, gingival crevicular fluid [GCF] or saliva) were compared using Spearman correlation analysis for the SARS-CoV-2 antigens, spike (A), RBD (B), S1 (C), S2 (D), and NTD (E) proteins.

Fig. 3

Correlations between antibody responses and interferon (IFN)-γ T-cell responses. Correlation analysis of vaccine-induced SARS-CoV-2–specific IFN-γ cellular responses in blood-derived peripheral blood mononuclear cells were compared to binding IgG in serum (A), gingival crevicular fluid (GCF) (B), and saliva (C) and to serum-neutralizing antibodies (D).

Fig. 4

SARS-CoV-2–neutralizing antibody activity in serum, gingival crevicular fluid (GCF), and saliva. A, Neutralizing antibodies against the ancestral strain of SARS-CoV-2 was assessed in samples using the surrogate virus neutralisation assay. B–D, The correlation of neutralizing antibodies in serum with binding IgG in serum (B), GCF (C), or saliva (D). Neutralizing antibodies were compared amongst serum, GCF, and saliva using Mann–Whitney U tests, whilst correlation analyses between IgG and surrogate virus neutralisation test (sVNT) were compared using Spearman correlation. E, Correlation matrix with hierarchical clustering analysis of all measured immune parameters. Four hierarchical clusters are marked with green squares.