Mucosal antibody responses following Vaxzevria vaccination

Abstract

Mucosal antibodies play a key role in protection against breakthrough COVID-19 infections and emerging viral variants. Intramuscular adenovirus-based vaccination (Vaxzevria) only weakly induces nasal IgG and IgA responses, unless vaccinees have been previously infected. However, little is known about how Vaxzevria vaccination impacts the ability of mucosal antibodies to induce Fc responses, particularly against SARS-CoV-2 variants of concern (VoCs). Here, we profiled paired mucosal (saliva, tears) and plasma antibodies from COVID-19 vaccinated only vaccinees (uninfected, vaccinated) and COVID-19 recovered vaccinees (COVID-19 recovered, vaccinated) who both received Vaxzevria vaccines. SARS-CoV-2 ancestral-specific IgG antibodies capable of engaging FcγR3a were significantly higher in the mucosal samples of COVID-19 recovered Vaxzevria vaccinees in comparison with vaccinated only vaccinees. However, when IgG and FcγR3a engaging antibodies were tested against a panel of SARS-CoV-2 VoCs, the responses were ancestral-centric with weaker recognition of Omicron strains observed. In contrast, salivary IgA, but not plasma IgA, from Vaxzevria vaccinees displayed broad cross-reactivity across all SARS-CoV-2 VoCs tested. Our data highlight that while intramuscular Vaxzevria vaccination can enhance mucosal antibodies responses in COVID-19 recovered vaccinees, restrictions by ancestral-centric bias may have implications for COVID-19 protection. However, highly cross-reactive mucosal IgA could be key in addressing these gaps in mucosal immunity and may be an important focus of future SARS-CoV-2 vaccine development.

Keywords: COVID-19; SARS-CoV-2; Vaxzevria; antibodies; saliva; tears.

Figure 1

COVID‐19 recovered Vaxzevria vaccinees displayed enhanced IgA and FcγR responses in saliva and tear fluid. Paired saliva and plasma samples were collected pre‐ and post‐ Vaxzevria vaccination from vaccinated only (a) and COVID‐19 recovered (b) individuals at the indicated time‐points. Saliva (c) and plasma (d) antibody isotype and subclass responses from both cohorts against the various SARS‐CoV‐2 spike antigens were compiled into respective radar plots. To transform the data into percentages for use in the radar plots (c, d), the median of each cohort/timepoint's antigen‐specific MFI was divided by the antigen‐specific MFI in the 99th percentile for that detector (99th percentile was chosen to minimize the impact of outliers on the data transformation). IgA, total IgG and FcγR3a saliva (e) and tear (f) antibody features from COVID‐19 recovered individuals after their second Vaxzevria vaccination are also illustrated in respective bar graphs. Statistical significance was calculated using the Friedman test followed by Dunn's test for multiple comparisons and where significant or trending significance, P‐values are reported (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001).

Figure 2

Cross‐reactive salivary IgA avoids vaccination‐induced ancestral‐centric bias. Bar graphs describe salivary (a–c) and plasma (d–f) inhibition of RBD‐ACE2 interactions against the ancestral wildtype (WT) SARS‐CoV‐2 or the VoCs (α, Alpha; δ, Delta; β, Beta; ο BA.1, Omicron BA.1; ο BA.2, Omicron BA.2) by vaccinated only (a, d) and COVID‐19 recovered individuals (b, c, e, f), respectively. The number of individuals with detectable responses above the arbitrary 20% assay threshold (dotted line) at either timepoint are listed under the bar graphs in their respective colors. Significant differences between both timepoints were calculated using the two‐tailed Mann–Whitney U‐test, followed by Bonferroni‐Dunn's test for multiple comparisons. Bar graphs also show the salivary (g) and tear (h) FcγR3a responses against WT SARS‐CoV‐2 or the VoCs in COVID‐19 recovered individuals after their second Vaxzevria vaccination. Fold changes listed above the bar graphs were calculated for post dose 2 Vaxzevria responses (purple) over their respective pre‐vaccination responses (gray) for each antigen. The number of individuals with detectable responses above the assay threshold (median responses from COVID‐19 unvaccinated, uninfected healthy controls; dotted line) at either timepoint were listed under the bar graphs in their respective colors. Significant differences between both timepoints were calculated using the two‐tailed Mann–Whitney U‐test, followed by Bonferroni‐Dunn's test for multiple comparisons. Heat maps illustrate the VoC‐specific Spike Trimer salivary (i) and plasma (j) antibody responses post‐mRNA booster and post‐ Vaxzevria vaccination (dose 1 or 2) for both vaccinated only and COVID‐19 recovered cohorts respectively. The median antibody response for each VoC spike was described as a fold change to the wildtype spike. Statistical significance was calculated using Friedman's test followed by Dunn's test for multiple comparisons. Bar graphs show the salivary IgA responses against WT SARS‐CoV‐2 or the VoCs in COVID‐19 recovered individuals after their first (k) and second (l) Vaxzevria vaccines. Fold changes listed above are calculated against that for the WT SARS‐CoV‐2. WT SARS‐CoV‐2 salivary IgA responses from COVID‐19 unvaccinated and uninfected healthy controls are shown by the dotted line. Where significant, P‐values are reported (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001).