ChAdOx1 nCoV-19 protection against SARS-CoV-2 in rhesus macaque and ferret challenge models

Abstract

Vaccines against SARS-CoV-2 are urgently required, but early development of vaccines against SARS-CoV-1 resulted in enhanced disease after vaccination. Careful assessment of this phenomena is warranted for vaccine development against SARS CoV-2. Here we report detailed immune profiling after ChAdOx1 nCoV-19 (AZD1222) and subsequent high dose challenge in two animal models of SARS-CoV-2 mediated disease. We demonstrate in rhesus macaques the lung pathology caused by SARS-CoV-2 mediated pneumonia is reduced by prior vaccination with ChAdOx1 nCoV-19 which induced neutralising antibody responses after a single intramuscular administration. In a second animal model, ferrets, ChAdOx1 nCoV-19 reduced both virus shedding and lung pathology. Antibody titre were boosted by a second dose. Data from these challenge models on the absence of enhanced disease and the detailed immune profiling, support the continued clinical evaluation of ChAdOx1 nCoV-19.

Fig. 1. Antibody responses in rhesus macaques and ferrets following vaccination with ChAdOx1 nCoV-19.

a Anti-spike responses, ELISA, and neutralisation titres (PRNT₅₀) were measured in the serum and pseudoneutralisation titres (mVNT ID₅₀) in the plasma of rhesus macaque on days 0, 14, and 27 post vaccination. Data was analysed with a Friedman one-way anova and post hoc test. Responses in rhesus macaques vaccinated with PBS were below the limit of detection. b Anti-spike responses, ELISA and neutralisation titres measured in the serum and pseudoneutralisation titres measured in the plasma of ferrets following vaccination with ChAdOx1 nCoV-19 or ChAdOx1 GFP. Data were analysed by a one-way anova and post hoc test comparing all ChAdOx1 nCoV-19 vaccinated to all ChAdOx1 GFP at each relevant timepoint.

Fig. 2. T cell responses in rhesus macaques and ferrets following vaccination with ChAdOx1 nCoV-19.

Spike-specific T cell response in rhesus macaques (a) and ferrets (b) monitored by IFNγ ELISpot following vaccination and ICS (ferrets only). Response from ChAdOx1 nCoV-19 vaccinated NHPs was analysed with a Friedman one-way anova and post hoc test. Response in ferrets was analysed with a non-parametric one-way anova (Kruskal−Wallis) and post hoc Dunn’s multiple comparison test. A significant increase in the response compared to Day 0 was observed from day 14 onwards, with no statistically significant increase in the T cell response following booster vaccination. T cell responses in ferrets were measured by intracellular cytokine staining on day 28 post-vaccination and compared to responses measured by IFNγ ELISpot.

Fig. 3. Challenge of rhesus macaques with SARS-CoV-2.

a Representative CT scans of a vaccinated male (top panel), normal appearance at D5, unilateral mild abnormalities at D12, with peripheral ground-glass opacity (GGO) marked by yellow arrows, and PBS vaccinated female (lower panel) with bilateral disease on D5, mid-lobe GGO (yellow arrow), left lower lobe consolidated organising pneumonia pattern (red arrow), resolved by D12. The graph represents the total CT score representing disease severity. b Viral RNA quantitation in bronchoalveolar lavage fluid (BALF), nasal washes, and throat swabs. c RNA staining at day 7 (top) and day 13/14 (bottom) after challenge, the graph represents the quantification of viral RNA by ISH in the lung from all animals at 7 and 13/14 days after challenge. d. Histopathology at day 7 (top 2 panels), day 13/14 (bottom 2 panels) after challenge, and heatmap showing the relative frequency of histopathological abnormalities detected in different lung locations. Lines denote the size of the image, each line represents 100 μm.

Fig. 4. Challenge of ferrets with SARS-CoV-2.

a Quantification of virus RNA by PCR in nasal washes and throat swabs in ferrets vaccinated with ChAdOx1 nCoV-19 (black closed) or ChAdOx1 GFP controls (grey open) following challenge with SARS-CoV-2. The limit of quantification in the assay is indicated as a dotted line on the graph. b Histopathology was performed on lung sections of animals culled 1 week after challenge (day 6 or 7) (presented) or 2 weeks after challenge (days 13, 14, or 15) (Fig. S5). Lines denote the size of the images, each line represents 100 μm. Graphs represent the total histopathological score of each animal. Data points represent each animal, with bars denoting the median per group. Histopathological score data in each challenge was analysed with a two-way anova to determine the effect of vaccination and day of cull as independent variables; no difference between days was observed, a significant difference between groups was observed and is denoted on the graph.

Fig. 5. Immune responses following challenge with SARS-CoV-2.

a Immune responses following challenge of rhesus macaques with SARS-CoV-2 were measured in virus neutralisation assays and by IFNγ ELISpot. b Quantification of CD4⁺ and CD8⁺ T cells expressing HLA-DR and PD-1 prior to (day 0) and at days 3, 6−7 (7) and 13−14 post SARS-CoV-2 challenge of NHPs. Data in each graph was analysed with a two-way analysis of variance (repeated measure) and a post hoc Tukey test, p values indicate a significant difference (p < 0.05) within vaccine groups over time. c Quantification of NHP monocyte subpopulations determined by the expression of CD14 and CD16 by whole blood immunophenotyping flow cytometry assay. Bars show group medians with values measured in individual animals shown. Data in each graph was analysed with a two-way analysis of variance (repeated measure) and a post hoc Tukey test, p values indicate a significant difference (p < 0.05) within vaccine groups over time. d Antibody responses in ferrets following challenge were measured in the virus neutralisation assay. e To determine whether antibody responses impacted on the protection of ferrets from SARS-CoV-2 infection, a Pearson correlation analysis was performed comparing peak viraemia in each ferret to IgG ELISA Unit, neutralisation titre (PRNT₅₀), psuedoneutralisation titre (mVNT), or IFNγ ELISpot on the day of challenge, r² and p values are indicated on each graph.