Immunity elicited by natural infection or Ad26.COV2.S vaccination protects hamsters against SARS-CoV-2 variants of concern

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern have emerged and may pose a threat to both the efficacy of vaccines based on the original WA1/2020 strain and the natural immunity induced by infection with earlier SARS-CoV-2 variants. We investigated how mutations in the spike protein of circulating SARS-CoV-2 variants, which have been shown to partially evade neutralizing antibodies, affect natural and vaccine-induced immunity. We adapted a Syrian hamster model of moderate to severe clinical disease for two variant strains of SARS-CoV-2: B.1.1.7 (alpha variant) and B.1.351 (beta variant). We then assessed the protective efficacy conferred by either natural immunity from WA1/2020 infection or by vaccination with a single dose of the adenovirus serotype 26 vaccine, Ad26.COV2.S. Primary infection with the WA1/2020 strain provided potent protection against weight loss and viral replication in lungs after rechallenge with WA1/2020, B.1.1.7, or B.1.351. Ad26.COV2.S induced cross-reactive binding and neutralizing antibodies that were reduced against the B.1.351 strain compared with WA1/2020 but nevertheless still provided robust protection against B.1.351 challenge, as measured by weight loss and pathology scoring in the lungs. Together, these data support hamsters as a preclinical model to study protection against emerging variants of SARS-CoV-2 conferred by prior infection or vaccination.

Fig. 1.. SARS-CoV-2 challenge with variant strain viruses drives clinical disease in hamsters.

Groups of Syrian golden hamsters were challenged intranasally with WA1/2020, B.1.1.7, or B.1.351 variant challenge virus in 100 μl of volume using the indicated dose of each challenge stock. After challenge, hamsters were monitored for 14 days for clinical signs of disease. (A to C) Average relative body weight of each group is displayed as means ± SEM for hamsters challenged with WA1/2020 (A), B.1.1.7 (B), or B.1.351 (C) variant strain challenge stock (n = 5 to 6 hamsters per group). (D) A comparison of the peak weight loss across variant virus strains and challenge doses is shown. Horizontal lines in (D) indicate the group means.

Fig. 2.. Infection with WA1/2020 SARS-CoV-2 provides natural protection from homologous or heterologous strain rechallenge-induced weight loss.

(A) Hamsters (n = 18) were challenged on day 0 with 5 × 10⁴ TCID₅₀ (in 100 μl) of WA1/2020 SARS-CoV-2 challenge stock by the intranasal route and monitored for 35 days after challenge. Average relative body weight after primary challenge displayed as means ± SEM. (B) At week 5, hamsters were divided into three groups and rechallenged with 5 × 10⁴ TCID₅₀ of WA1/2020 (group 1, n = 6), B.1.1.7 (group 2, n = 5), or B.1.351 (group 3, n = 6) SARS-CoV-2. In addition, three groups of naïve hamsters (n = 6 per group) were challenged on study day 35 with the matched strains and doses (groups 4 to 6). (C) To allow comparison of weight loss after SARS-CoV-2 challenge or re-challenge on day 35, for the remainder of the study, hamster weights were normalized to the weight on study day 35. Average relative weight after primary challenge (open symbols) or rechallenge (closed symbols) is indicated as means ± SEM. (D) Peak weight loss over the span of study days 35 to 49 is shown. Maximum weight loss of each hamster is displayed, with group means indicated by horizontal lines. (E and F) At the terminal time point, day 49, hamsters were euthanized, and lung tissue was collected to quantify sgRNA (E) and gRNA (F) viral RNA. Log-transformed viral loads in individual hamsters, normalized per gram of lung tissue, are displayed. Horizontal lines indicate group means.

Fig. 3.. Characterization of Ad26.COV2.S-elicted variant RBD-specific binding and neutralizing antibodies.

Groups of hamsters (n = 10 per group) were immunized with 10¹⁰ viral particles of Ad26.COV2.S or a sham control (buffer only), and prechallenge humoral immune responses were quantified in serum. (A and B) Binding antibodies to WA1/2020, B.1.1.7, and B.1.351 RBD proteins were quantified by ELISA at weeks 0 (A) and 4 (B) after immunization. Horizontal lines indicate group geometric mean titer. (C and D) ECLAs were used to quantify binding to indicated variant strain RBD (C) and spike proteins (D). Horizontal lines indicate group geometric mean titer. (E) Pseudovirus (PV) neutralization assays were used to quantify neutralizing antibody (NAb) titers against pseudoviruses expressing SARS-CoV-2 spike protein specific for the WA1/2020, WA1/2020-D614G, B.1.1.7, or B.1.351 variant at week 4 after immunization. Data displayed are the NT50 values for each hamster; horizontal lines indicate group geometric mean titers. (F) Correlation analyses of binding and neutralizing titers for the indicated SARS-CoV-2 variant strains. Summary Spearman correlation results are displayed in the table. Statistics in (A) to (E) indicate the results of Kruskal-Wallis tests with Dunn’s multiple comparisons test (***P < 0.001; ****P < 0.0001). Horizontal dashed lines in (A) to (E) indicate the assay limits of quantitation.

Fig. 4.. Ad26.COV2.S protects hamsters from WA1/2020 or B.1.351 challenge–induced weight loss.

Groups of hamsters (n = 10 per group) were vaccinated with either 10¹⁰ viral particles of Ad26.CoV2.S or sham and then challenged with 5 × 10⁴ TCID₅₀ of either WA1/2020 or B.1.351 SARS-CoV-2 by the intranasal route at week 5. (A) Average relative body weight of each group is displayed as means ± SEM. (B) A comparison of the peak weight loss is shown across experimental groups with horizontal lines indicating the group means. (C and D) Hamsters were euthanized at day 14 after challenge to quantify sgRNA (C) and gRNA (D) in lung tissue. Horizontal lines indicate group means of log-transformed viral load data. Statistics shown are the results of Mann-Whitney tests comparing Ad26.COV2.S versus sham groups within each challenge strain. *P < 0.05; **P < 0.01; ***P < 0.001.