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. 2020 May 20;eabc6284.
doi: 10.1126/science.abc6284. Online ahead of print.

DNA Vaccine Protection Against SARS-CoV-2 in Rhesus Macaques

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Free PMC article

DNA Vaccine Protection Against SARS-CoV-2 in Rhesus Macaques

Jingyou Yu et al. Science. .
Free PMC article

Abstract

The global COVID-19 pandemic caused by the SARS-CoV-2 virus has made the development of a vaccine a top biomedical priority. In this study, we developed a series of DNA vaccine candidates expressing different forms of the SARS-CoV-2 Spike (S) protein and evaluated them in 35 rhesus macaques. Vaccinated animals developed humoral and cellular immune responses, including neutralizing antibody titers comparable to those found in convalescent humans and macaques infected with SARS-CoV-2. Following vaccination, all animals were challenged with SARS-CoV-2, and the vaccine encoding the full-length S protein resulted in >3.1 and >3.7 log10 reductions in median viral loads in bronchoalveolar lavage and nasal mucosa, respectively, as compared with sham controls. Vaccine-elicited neutralizing antibody titers correlated with protective efficacy, suggesting an immune correlate of protection. These data demonstrate vaccine protection against SARS-CoV-2 in nonhuman primates.

Figures

Fig. 1
Fig. 1. Construction of candidate DNA vaccines against SARS-CoV-2.
(A) Six DNA vaccines were produced expressing different SARS-CoV-2 Spike (S) variants: 1) full-length (S), 2) deletion of the cytoplasmic tail (S.dCT), 3) deletion of the transmembrane domain and cytoplasmic tail reflecting the soluble ectodomain (S.dTM), 4) S1 domain with a foldon trimerization tag (S1), 5) receptor-binding domain with a foldon trimerization tag (RBD), and a 6) prefusion stabilized soluble ectodomain with deletion of the furin cleavage site, two proline mutations, and a foldon trimerization tag (S.dTM.PP). Open square depicts foldon trimerization tag; red lines depict proline mutations. (B) Western blot analyses for expression from DNA vaccines encoding S (lane 1), S.dCT (lane 2), S.dTM (lane 3), and S.dTM.PP (lane 4) in cell lysates and culture supernatants using an anti-SARS polyclonal antibody (BEI Resources). (C) Western blot analyses for expression from DNA vaccines encoding S1 (lane 1) and RBD (lane 2) in cell lysates using an anti-SARS-CoV-2 RBD polyclonal antibody (Sino Biological).
Fig. 2
Fig. 2. Humoral immune responses in vaccinated rhesus macaques.
Humoral immune responses were assessed following immunization by (A) binding antibody ELISA, (B) pseudovirus neutralization assays, and (C) live virus neutralization assays. (D) Comparison of pseudovirus neutralization titers in vaccinated macaques (all animals and S / S.dCT groups), a cohort of 9 convalescent macaques, and a cohort of 27 convalescent humans from Boston, United States who had recovered from SARS-CoV-2 infection. (E) S- and RBD-specific antibody-dependent neutrophil phagocytosis (ADNP), antibody-dependent complement deposition (ADCD), antibody-dependent monocyte cellular phagocytosis (ADCP), and antibody-dependent NK cell activation (IFN-γ secretion, CD107a degranulation, and MIP-1β expression) are shown. Radar plots show the distribution of antibody features across the vaccine groups. The size and color intensity of the wedges indicate the median of the feature for the corresponding group (blue depicts antibody functions, red depicts antibody isotype/subclass/FcγR binding). The principal component analysis (PCA) plot shows the multivariate antibody profiles across groups. Each dot represents an animal, the color of the dot denotes the group, and the ellipses shows the distribution of the groups as 70% confidence levels assuming a multivariate normal distribution. Red bars reflect median responses. Dotted lines reflect assay limit of detection.
Fig. 3
Fig. 3. Cellular immune responses in vaccinated rhesus macaques.
Cellular immune responses were assessed at week 5 following immunization by (A) IFN-γ ELISPOT assays and (B) IFN-γ+ and (C) IL-4+ intracellular cytokine staining assays for CD4+ and CD8+ T cells in response to pooled S peptides. Red bars reflect median responses.
Fig. 4
Fig. 4. Viral loads in rhesus macaques challenged with SARS-CoV-2 virus.
Rhesus macaques were challenged by the intranasal and intratracheal route with 1.2 × 108 VP (1.1 × 104 PFU) SARS-CoV-2. (A) Log10 sgmRNA copies/ml or copies/swab (limit 50 copies) were assessed in bronchoalveolar lavage (BAL) and nasal swabs (NS) in sham controls at multiple timepoints following challenge. (B) Log10 sgmRNA copies/ml in BAL and (C) log10 sgmRNA copies/swab in NS in vaccinated animals at multiple timepoints following challenge. (D) Summary of peak viral loads in BAL and NS following challenge. Peak viral loads occurred variably on day 1-4 following challenge. Red lines reflect median viral loads. P-values indicate two-sided Mann-Whitney tests.
Fig. 5
Fig. 5. Immune correlates of protection.
Correlations of (A) pseudovirus NAb titers and (B) live NAb titers prior to challenge with log peak sgmRNA copies/ml in BAL or log peak sgmRNA copies/swab in nasal swabs following challenge. Red lines reflect the best-fit relationship between these variables. P and R values reflect two-sided Spearman rank-correlation tests. (C) The heat map (top panel) shows the Spearman and Pearson correlations between antibody features and log10 peak sgmRNA copies/ml in BAL (*q < 0.05, **q < 0.01, ***q < 0.001 with Benjamini-Hochberg correction for multiple testing). The bar graph (bottom left panel) shows the rank of the Pearson correlation between cross-validated model predictions and data using the most predictive combination or individual antibody features for partial least square regression (PLSR) and random forest regression (RFR). The correlation heatmap (bottom right panel) represents pairwise Pearson correlations between features across all animals. (D) The heat map (top panel) shows the difference in the means of the z-scored features between the completely protected and partially protected animals (**q < 0.01 with Benjamini-Hochberg correction for multiple testing). The dot plots show differences in log10 NAb titers, RBD-specific ADCD responses, S-specific ADCD responses, and RBD-specific ADCP responses between the completely protected and partially protected animals. P-values indicate two-sided Mann-Whitney tests.

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