Protein-based SARS-CoV-2 spike vaccine booster increases cross-neutralization against SARS-CoV-2 variants of concern in non-human primates

Abstract

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants that partly evade neutralizing antibodies raises concerns of reduced vaccine effectiveness and increased infection. We previously demonstrated that the SARS-CoV-2 spike protein vaccine adjuvanted with AS03 (CoV2 preS dTM-AS03) elicits robust neutralizing antibody responses in naïve subjects. Here we show that, in macaques primed with mRNA or protein-based subunit vaccine candidates, one booster dose of CoV2 preS dTM-AS03 (monovalent D614 or B.1.351, or bivalent D614 + B.1.351 formulations), significantly boosts the pre-existing neutralizing antibodies against the parental strain from 177- to 370-fold. Importantly, the booster dose elicits high and persistent cross-neutralizing antibodies covering five former or current SARS-CoV-2 variants of concern (Alpha, Beta, Gamma, Delta and Omicron) and, unexpectedly, SARS-CoV-1. Interestingly, we show that the booster specifically increases the functional antibody responses as compared to the receptor binding domain (RBD)-specific responses. Our findings show that these vaccine candidates, when used as a booster, have the potential to offer cross-protection against a broad spectrum of variants. This has important implications for vaccine control of SARS-CoV-2 variants of concern and informs on the benefit of a booster with the vaccine candidates currently under evaluation in clinical trials.

Fig. 1. Kinetics of booster-neutralizing antibody responses (parental and Beta) in mRNA- or subunit-primed macaques.

a Schematic representation of the study schedule. In mRNA-primed cohort, 4 groups of 4 cynomolgus macaques were immunized intramuscularly with mRNA COVID-19 (D614) vaccine candidates on day 0 (D0) and on day 21 (D21). In subunit-primed cohort, 5 groups of 4–5 rhesus macaques were immunized intramuscularly with CoV2 preS dTM-AS03 (D614) vaccine candidates on D0 and D21. Both cohorts were boosted 7 months post-dose 1 with nonadjuvanted monovalent (B.1.351) CoV2 preS dTM (n = 4) or AS03-adjuvanted monovalent (D614 or B.1.351) (n = 5) or bivalent (D614 + B.1.351) CoV2 preS dTM (n = 5). Humoral immune responses were assessed at different timepoints throughout the study. b Pseudovirus-neutralizing antibody titers against the parental SARS-CoV-2 and c Beta variant were assessed at different timepoints after the priming phase and after the booster immunization in macaques. Individual macaque data are shown. Connecting lines indicate mean responses and horizontal dotted lines the limits of quantification of the assay. *timepoints relative to boosters. A human convalescent panel of sera (Human Conv. sera) (n = 93) was assayed against D614 and is plotted as a comparator. Dotted line represents the World Health Organization (WHO) International Standard for anti-SARS-CoV-2 immunoglobulin (human) NIBSC code: 20/136.

Fig. 2. Booster cross-neutralizing antibody responses against the current VOC and SARS-CoV-1 in the mRNA- and subunit-primed macaques.

Pseudovirus-neutralizing antibody assays against the parental SARS-CoV-2, variants of concern (Alpha, Beta, Gamma, Delta, and Omicron), and SARS-CoV-1 was assessed at day 14 after the booster injection in primed-macaques a mRNA-primed cohort (n = 4/group) and b protein subunit-primed cohort (n = 4 or 5/group). Individual macaque data are shown and are linked by connecting lines. Horizontal dotted lines indicate the limits of quantification of the assay.

Fig. 3. Booster immunization elicits an increase in functional antibody response in mRNA- and subunit-primed macaques.

Pseudovirus NAb/RBD-binding IgG ratio for parental D614G (a) and for Beta (b), post prime (D35) and 2 weeks post-boost (D224 or D216) for mRNA-primed cohort (n = 4/group) and subunit-primed cohort (n = 4–5/group). Individual animals are shown; bars indicate means.