Poxvirus MVA Expressing SARS-CoV-2 S Protein Induces Robust Immunity and Protects Rhesus Macaques From SARS-CoV-2

Abstract

Novel safe, immunogenic, and effective vaccines are needed to control the COVID-19 pandemic, caused by SARS-CoV-2. Here, we describe the safety, robust immunogenicity, and potent efficacy elicited in rhesus macaques by a modified vaccinia virus Ankara (MVA) vector expressing a full-length SARS-CoV-2 spike (S) protein (MVA-S). MVA-S vaccination was well tolerated and induced S and receptor-binding domain (RBD)-binding IgG antibodies and neutralizing antibodies against SARS-CoV-2 and several variants of concern. S-specific IFNγ, but not IL-4, -producing cells were also elicited. After SARS-CoV-2 challenge, vaccinated animals showed a significant strong reduction of virus loads in bronchoalveolar lavages (BAL) and decreased levels in throat and nasal mucosa. Remarkably, MVA-S also protected macaques from fever and infection-induced cytokine storm. Computed tomography and histological examination of the lungs showed reduced lung pathology in MVA-S-vaccinated animals. These findings favor the use of MVA-S as a potential vaccine for SARS-CoV-2 in clinical trials.

Keywords: COVID-19; MVA vaccine; SARS-CoV-2; efficacy; immunogenicity; rhesus macaques; safety; spike.

Figure 1

Immunization schedule in rhesus macaques. (A) Rhesus macaques (n = 6 per group) were immunized at weeks 0 and 4 by the intramuscular (i.m.) route with two doses of 2 × 10⁸ PFUs of MVA-S vaccine or control MVA-WT virus, as indicated (blue arrow). At week 8, all animals were challenged intranasally plus intratracheally with 1 × 10⁶ TCID₅₀ of SARS-CoV-2 (red arrow). At different timepoints before and after challenge, diverse types of samples were taken, as indicated by arrowheads. All animals were sacrificed at days 15 or 16 post-challenge (black arrow). (B) Body temperature increase after the first (left) and second (right graph) immunization. Averages and standard error of the mean (SEM) (shaded area) are presented per group. Body temperature was recorded every 15 min. Normal 24-h body temperature before immunization (mean of 8–14 days before immunization) was subtracted from post immunization body temperature of each individual animal.

Figure 2

MVA-S elicited SARS-CoV-2-specific binding IgG antibodies. ELISA IgG antibody titers to SARS-CoV-2 S protein (A), and RBD (B) in time, and IgG antibody titers at 14 days post-challenge as measured by array analysis to S1 domain (C) and ectodomain (D) of the S protein from several coronaviruses (common cold α [229E, NL63] or β [OC43, HKU1] coronaviruses; SARS-CoV-2, SARS-CoV-1, and MERS) of MVA-S (red) and MVA-WT (black) immunized macaques. Each animal is represented by a symbol. Mean and SEM are shown in columns for each group of animals. Significant differences between the groups are indicated in the graph by a horizontal line and p-value (Mann–Whitney test).

Figure 3

MVA-S vaccination induced SARS-CoV-2 neutralizing antibodies. SARS-CoV-2 neutralizing NT₅₀ antibody titers to SARS-CoV-2 strain MAD6 (having the D614G mutation) (A), VSV-luciferase recombinant viruses pseudotyped with SARS-CoV-2 Spike_614G (B), alpha (C), beta (D), gamma (E), and delta (F) VOC at different timepoints, and live SARS-CoV-2 D614G and VOC alpha, beta, and delta (G). Horizontal dotted line indicates level of neutralizing antibody titers measured in a human convalescent sera standard (NIBSC 20/136) (A). Each animal is represented by a symbol. Mean and SEM are shown in columns for each group of animals. Significant differences between the groups are indicated in the graph by a horizontal line and p-value (Mann–Whitney test).

Figure 4

SARS-CoV-2-specific cell immune responses are induced by MVA-S. S-specific IFN-γ (A) and IL-4 (B) cell responses (directed against pp1 and pp2 peptide pools) 2 weeks post second immunization (Week 6) and 2 weeks post-challenge (day 14 pc) of MVA-S (red) and MVA-WT (black) immunized individual macaques, as measured by ELISpot assay. Each animal is represented by a symbol. Mean and SEM are shown in columns for each group of animals. Significant differences between the groups are indicated in the graph by a horizontal line and p-value (Mann–Whitney test).

Figure 5

Control of SARS-CoV-2 replication by MVA-S vaccine candidate. (A) SARS-CoV-2 sgmRNA load (copies/ml) in lung (BAL), throat, and nose of MVA-S (red) and MVA-WT (black) immunized macaques (symbols) at different days post-challenge. Averages and SEM per group are indicated by lines with shaded areas. (B) Total SARS-CoV-2 sgmRNA load in BAL, throat and nose of MVA-S (red) and MVA-WT (black) immunized animals over time, as measured by the area under the curve (AUC). Individual animals (symbols), averages, and SEM are shown in columns and bars for each group of animals. Significant differences between the groups are indicated in the graph by a horizontal line and p-value (Mann–Whitney test). (C) Correlation between total sgmRNA SARS-CoV-2 load in BAL and neutralizing antibody titers measured at week 6 against the SARS-CoV-2 MAD6 strain (having the D614G mutation in the S protein) in animals immunized with MVA-S. The correlation was calculated by Pearson correlation test on log-transformed data. The black line represents interpolated data, as a linear curve.

Figure 6

Immunization with MVA-S reduced lung pathology. (A) Body temperature increase after SARS-CoV-2 challenge. Averages and SEM (shaded area) are represented per group. Body temperature was recorded every 15 min. Normal 24-h body temperature before challenge (mean of 7 days) was subtracted from post-challenge body temperature of each individual animal. Body temperature changes caused by sedation procedures are not included. (B) CT scores of MVA-S vaccinated (red) and MVA-WT control (black) animals at days 0, 2, 7, and 15/16 post SARS-CoV-2 challenge. Individual animals (symbols), averages, and SEM are shown in columns and bars for each group of animals. Maximum score per timepoint is 35. (C) Lung pathology score. Shown is the total pathology score as well as the scores for perivascular inflammatory infiltrates, peribronchiolar inflammatory infiltrates, alveolar cellular exudate, and alveolar septal inflammatory cells of MVA-S-vaccinated (red) and MVA-WT control (black) animals. Scores for animal r10067 (vaccinated with MVA-S) were excluded because this animal showed non-specific vascular congestion, caused by the pentobarbital used for euthanasia. The maximum total score is 336, and the maximum score per individual parameter is 28. Significant differences between the groups are indicated in the graph by a horizontal line and p-value (Mann–Whitney test). (D) Lung histopathology. Lung histopathology on day 15 after infection. Shown is H&E staining on left middle lung lobe of animal r15067 (control MVA-WT) and animal r10003 (MVA-S). Original magnification ×50.

Figure 7

Control of SARS-CoV-2-induced cytokine storm by MVA-S vaccine candidate. (A) IL-6, CXCL10, CXCL11, CCL11, CCL2, and CCL4 levels in serum of MVA-S (red) and MVA-WT (black) groups in time. Horizontal dotted line indicates lower limit of detection. At day -14, the sample of one MVA-WT animal is missing. (B) IL-6, CXCL10, CXCL11, CCL11, IL-8, and CXCL9 levels in BAL of MVA-S (red) and MVA-WT (black) groups in time. All data are shown relative to the day of challenge (day 0, study day 56). Levels of individual values (indicated by different symbols) in time are shown. No measurements were performed on day of challenge, but data obtained at day 14 before challenge are shown.