Persistence of MERS-CoV-spike-specific B cells and antibodies after late third immunization with the MVA-MERS-S vaccine

Abstract

The Middle East respiratory syndrome (MERS) is a respiratory disease caused by MERS coronavirus (MERS-CoV). In follow up to a phase 1 trial, we perform a longitudinal analysis of immune responses following immunization with the modified vaccinia virus Ankara (MVA)-based vaccine MVA-MERS-S encoding the MERS-CoV-spike protein. Three homologous immunizations were administered on days 0 and 28 with a late booster vaccination at 12 ± 4 months. Antibody isotypes, subclasses, and neutralization capacity as well as T and B cell responses were monitored over a period of 3 years using standard and bead-based enzyme-linked immunosorbent assay (ELISA), 50% plaque-reduction neutralization test (PRNT50), enzyme-linked immunospot (ELISpot), and flow cytometry. The late booster immunization significantly increases the frequency and persistence of spike-specific B cells, binding immunoglobulin G1 (IgG1) and neutralizing antibodies but not T cell responses. Our data highlight the potential of a late boost to enhance long-term antibody and B cell immunity against MERS-CoV. Our findings on the MVA-MERS-S vaccine may be of relevance for coronavirus 2019 (COVID-19) vaccination strategies.

Trial registration: ClinicalTrials.gov NCT03615911.

Keywords: IgG ELISpot; IgG subclasses; MERS-CoV; MVA-MERS-S; immune persistence; late booster vaccination; long-term immunity; memory B cells; neutralizing antibodies; viral vector vaccine.

Conflict of interest statement

Declaration of interests The authors declare no competing interests.

Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.

Figures

Graphical abstract

Figure 1

Study design Study participants (n = 10) received two vaccinations wit MVA-MERS-S (V1 and V2) 28 days apart and a late third vaccination (V3) at 12 ± 4 months after prime. Blood was frequently sampled for up to 2 years after V3 at indicated time points (see also Table S1). Figure was created with BioRender.com.

Figure 2

MERS-CoV-S-specific humoral and T cell responses induced by three vaccinations with MVA-MERS-S (A) Longitudinal dynamics of S-specific IgG antibodies. Shown are the optical density (OD) values measured at 450–620 nm by ELISA. Data are represented as individual data points (mean of technical duplicates) and median ± interquartile range (IQR). (B) Neutralization activity of serum antibodies as measured by 50% plaque-reduction neutralization test (PRNT50). Data are represented as individual data points and median ± IQR. (C) Spearman correlation between S-specific IgG antibodies and serum neutralization activity. (D) T cell responses as measured by IFNγ ELISpot after stimulation with five overlapping peptide (OLP) pools (M1–M5), spanning the entire MERS-CoV-S amino acid sequence. Shown are the median values of spot forming units (SFUs; mean of technical triplicates) across all vaccinees (n = 10) for each OLP pool. Number of samples, median, and p values for each time point and all three assays are shown in Table S2.

Figure 3

Isotype and subclass distribution within vaccine-induced MERS-CoV-S-specific antibodies S1- (A) and S2- (B) specific responses of IgM, IgG1–4, and IgA1–2 at different time points after vaccination, displayed as fold changes of median fluorescence intensities (MFIs; measured by bead-based ELISA) compared with baseline values at V1:day 0. Data are represented as individual data points (mean of technical duplicates) and median ± IQR. Number of samples and median fold changes are shown in Table S3.

Figure 4

Longitudinal dynamics of MERS-CoV-S-specific IgG1 and IgG3 antibodies Vaccine-induced S1/S2-specific IgG1 (A) and IgG3 (B) are displayed as MFI, measured by bead-based multiplex ELISA. Data are represented as individual data points (mean of technical duplicates) and median ± IQR. LLD, lower limit of detection. Number of samples, median, and p values for each time point are shown in Table S4.

Figure 5

Antigen-specific B cell responses induced by MVA-MERS-S vaccination (A) Representative IgG ELISpot images of antigen-specific and control wells for PBMCs taken before the first (V1:day 0) and after the third vaccination (V3:day 14). (B) Frequencies of vaccine-induced S1/S2-specific B cells displayed as SFUs/106 PBMCs as determined by IgG ELISpot. Data are represented as individual data points (mean of technical duplicates) and median ± IQR. The dotted line indicates the cutoff value (6.6 SFUs/106 PBMCs). (C) p values as determined by Wilcoxon signed rank test (between time points) and Mann Whitney U test (between S1 and S2 responses). Number of samples, median, and p values for each time point are shown in Table S5.

Figure 6

Characterization of vaccine-induced memory B cells (A) Gating strategy for analysis of isotypes and MERS-CoV-S-specific cells within the memory B cell (MBC) population (representative contour plots belong to time point V3:day 14 from one study participant; gating strategy for identification of MBCs within whole PBMCs shown in Figure S2). (B) Longitudinal dynamics of antigen-specific MBCs induced by three vaccinations with MVA-MERS-S (V1, V2, and V3). Data are displayed as frequencies of S-specific cells within IgM+/IgG+/IgA+ MBCs. Boxplots indicate median ± IQR. Number of samples, median, and p values compared with V1:day 0 are shown in Table S6. (C) Resting, intermediate, atypical, and activated MBC phenotypes as identified by expression of CD21 and CD27 (top left panel). Representative plots are shown for one study participant at V3:day 0 and V3:day 14 and depict overlaid contour plots of total IgG+ MBCs and S-specific IgG+ MBCs (bottom left panel). Longitudinal distributions of phenotypes within the S-specific IgG+ MBC compartment are shown as mean values of all study participants.

Figure 7

Correlation between vaccine-induced antibody and B cell responses Correlation analysis of MERS-CoV-S1- (A) and -S2- (B) specific IgG1, IgG3, and ASBC responses at different time points after vaccinations 1, 2, and 3 (V1, V2, and V3). S-specific MBC responses were included into correlograms of both the S1 and S2 antigen. Positive correlations are shown in blue and negative correlations in red, as indicated by the color bar. Sample numbers included into correlation analysis are provided in Table S7.