ChAdOx1 and MVA based vaccine candidates against MERS-CoV elicit neutralising antibodies and cellular immune responses in mice - PubMed (original) (raw)

. 2017 Jun 27;35(30):3780-3788.

doi: 10.1016/j.vaccine.2017.05.032. Epub 2017 Jun 1.

Eriko Padron-Regalado 2, Craig P Thompson 3, Alexandra Kupke 4, Daniel Wells 2, Megan A Sloan 2, Keith Grehan 5, Nigel Temperton 5, Teresa Lambe 2, George Warimwe 2, Stephan Becker 4, Adrian V S Hill 2, Sarah C Gilbert 2

Affiliations

ChAdOx1 and MVA based vaccine candidates against MERS-CoV elicit neutralising antibodies and cellular immune responses in mice

Naif Khalaf Alharbi et al. Vaccine. 2017.

Abstract

The Middle East respiratory syndrome coronavirus (MERS-CoV) has infected more than 1900 humans, since 2012. The syndrome ranges from asymptomatic and mild cases to severe pneumonia and death. The virus is believed to be circulating in dromedary camels without notable symptoms since the 1980s. Therefore, dromedary camels are considered the only animal source of infection. Neither antiviral drugs nor vaccines are approved for veterinary or medical use despite active research on this area. Here, we developed four vaccine candidates against MERS-CoV based on ChAdOx1 and MVA viral vectors, two candidates per vector. All vaccines contained the full-length spike gene of MERS-CoV; ChAdOx1 MERS vaccines were produced with or without the leader sequence of the human tissue plasminogen activator gene (tPA) where MVA MERS vaccines were produced with tPA, but either the mH5 or F11 promoter driving expression of the spike gene. All vaccine candidates were evaluated in a mouse model in prime only or prime-boost regimens. ChAdOx1 MERS with tPA induced higher neutralising antibodies than ChAdOx1 MERS without tPA. A single dose of ChAdOx1 MERS with tPA elicited cellular immune responses as well as neutralising antibodies that were boosted to a significantly higher level by MVA MERS. The humoral immunogenicity of a single dose of ChAdOx1 MERS with tPA was equivalent to two doses of MVA MERS (also with tPA). MVA MERS with mH5 or F11 promoter induced similar antibody levels; however, F11 promoter enhanced the cellular immunogenicity of MVA MERS to significantly higher magnitudes. In conclusion, our study showed that MERS-CoV vaccine candidates could be optimized by utilising different viral vectors, various genetic designs of the vectors, or different regimens to increase immunogenicity. ChAdOx1 and MVA vectored vaccines have been safely evaluated in camels and humans and these MERS vaccine candidates should now be tested in camels and in clinical trials.

Keywords: Adenoviral vector; ChAdOx1; Coronavirus; Immunogenicity; MERS-CoV; MVA; Poxviral vector; Prime boost; Vaccination; Vaccine.

Copyright © 2017. Published by Elsevier Ltd.

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Figures

Fig. 1

Fig. 1

Construction of MERS-CoV vaccine candidates. (A) Schematic representation of ChAdOx1 and MVA based vaccines, each encodes the same MERS-CoV spike gene (Genbank accession number:

KJ650098.1

). The S gene was inserted into the E1 region of ChAdOx1 genome or into the F11L locus of MVA genome (see Section 2). tPA: Human tissue plasminogen activator (tPA) signal peptide sequence. IE CMV: The human cytomegalovirus major immediate early promoter. mH5 and F11: Poxviral promoters. LHA: left homology arm sequence. RHA: right homology arm sequence. (B) The expression of spike transgene, cloned into a plasmid vector, was confirmed by transfection s an African green monkey kidney cell line (Vero cells) and immunostaining. (C) Untransfected cells control. Green colour represents detection of the spike protein. Blue colour represents nuclei by staining nucleic acid with DAPI. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Fig. 2

Antibody responses to ChAdOx1 MERS vaccine candidates. BALB/c mice (n = 6) were immunised intramuscularly with 1 × 108 IU ChAdOx1 MERS that either encodes or lacks tPA signal peptide upstream of the antigen sequence. A control group of mice were immunised with ChAdOx1 expressing eGFP instead of MERS-CoV S gene (given at 1 × 108 IU intramuscularly). Serum samples were collected at 14 and 28 days post immunisation (d.p.i.). S1-binding antibodies were measured by ELISA (A) and neutralisation activity of the antibodies were confirmed by MERS-CoV pseudotyped viral particles (MERSpp) neutralisation assay (B) or neutralisation assay (C). Individual data points (representing individual mice) are shown with line as the median. Data are representative of two independent experiments. Statistical significance by Kruskal–Wallis test is shown.

Fig. 3

Fig. 3

Cellular immune responses to ChAdOx1 MERS vaccine candidate. BALB/c mice (n = 6) were immunised with intramuscularly with 1 × 108 IU ChAdOx1 MERS that encodes tPA signal peptide upstream of the antigen sequence. Twenty-eight days post-immunisation, IFN-γ ex vivo ELISpot (A) or Intracellular Cytokine Staining (ICS (B)), were performed to determine the percentage of splenic IFN-γ secreting CD4+ and CD8+ after in vitro re-stimulation with a MERS-CoV S-specific peptide. Individual data points (representing individual mice) are shown with line as the median (A) or error bars as the SD (B). Data are representative of two independent experiments.

Fig. 4

Fig. 4

Humoral and cellular immunogenicity of heterologous ChAdOx1 MERS and MVA MERS vaccination. BALB/c mice (n = 6) were immunised intramuscularly with 1 × 108 IU ChAdOx1 MERS that encodes tPA signal peptide upstream of the antigen sequence. At 28 d.p.i. mice were boosted intramuscularly with 1 × 106 pfu MVA MERS. MVA MERS vaccine candidates utilise either the mH5 or F11 promoter for transgene expression. Serum samples were collected at 28 (post-prime) and 42 (post-boost) d.p.i. S1-binding antibodies were measured by ELISA (A) and neutralisation activity of serum antibodies at 42 d.p.i. were confirmed by MERSpp neutralisation assay (B). At 42 d.p.i, IFN-γ ex vivo ELISpot (C) or Intracellular Cytokine Staining (ICS (D)) were performed to determine the percentage of CD8+ IFN-γ+ splenocytes after in vitro re-stimulation with a MERS-CoV S-specific peptide. ICS of splenocytes re-stimulated with MVA-specific peptides (F(G)2 and E3) was also performed (E and F). Individual data points (representing individual mice) are shown with line as the median. Data are representative of two independent experiments. Statistical significance by Kruskal–Wallis test is shown. Symbols are closed squares (■) for ChAdOx1 prime responses, open circles (○) for mH5-MVA boost responses, and closed circles (●) for F11-MVA boost responses.

Fig. 5

Fig. 5

Humoral and cellular immunogenicity of homologous MVA MERS vaccination. BALB/c mice (n = 6) were immunised intramuscularly with 1 × 106 pfu MVA MERS, in a homologous prime-boost vaccination with three-weeks interval between vaccination. MVA MERS vaccine candidates utilise either the mH5 or F11 promoter for transgene expression. Serum samples were collected at 21 (post-prime) and 42 (post-boost) d.p.i. S1-binding antibodies were measured by ELISA (A) and neutralisation activity of serum antibodies at 42 d.p.i. were confirmed by MERSpp neutralisation assay (B). At 42 d.p.i splenocytes were processed and re-stimulated with a MERS-CoV S-specific peptide (CD8+ T cell specific) for IFN-γ ex vivo ELISpot (C). ICS of splenocytes re-stimulated with MVA-specific peptides (F(G)2 and E3) was also performed (D and E) as was performed in Fig. 4. Individual data points (representing individual mice) are shown with line as the median. Data are representative of two independent experiments. Statistical significance by Kruskal–Wallis test is shown. Symbols are open circles (○) for mH5-MVA and closed circles (●) for F11-MVA.

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