Immunogenicity of prime-boost protein subunit vaccine strategies against SARS-CoV-2 in mice and macaques

Abstract

SARS-CoV-2 vaccines are advancing into human clinical trials, with emphasis on eliciting high titres of neutralising antibodies against the viral spike (S). However, the merits of broadly targeting S versus focusing antibody onto the smaller receptor binding domain (RBD) are unclear. Here we assess prototypic S and RBD subunit vaccines in homologous or heterologous prime-boost regimens in mice and non-human primates. We find S is highly immunogenic in mice, while the comparatively poor immunogenicity of RBD is associated with limiting germinal centre and T follicular helper cell activity. Boosting S-primed mice with either S or RBD significantly augments neutralising titres, with RBD-focussing driving moderate improvement in serum neutralisation. In contrast, both S and RBD vaccines are comparably immunogenic in macaques, eliciting serological neutralising activity that generally exceed levels in convalescent humans. These studies confirm recombinant S proteins as promising vaccine candidates and highlight multiple pathways to achieving potent serological neutralisation.

Current vaccine strategies for SARS-CoV-2 focus on eliciting neutralising antibodies to the spike protein (S), but differences in immunogenicity of full-length S versus receptor binding domain (RBD) only aren’t fully understood. Here, the authors show immunogenicity of different prime-boost strategies with S and/or RBD in mice and macaques.