mRNA delivery of genetically encoded mosaic-8 pan-sarbecovirus RBD vaccines

Global health remains threatened by spillovers of zoonotic SARS-like betacoronaviruses (sarbecoviruses) that could be mitigated by a pan-sarbecovirus vaccine¹. We described elicitation of potently neutralizing and cross-reactive anti-sarbecovirus antibodies by mosaic-8 nanoparticles (NPs) displaying eight different sarbecovirus spike receptor-binding domains (RBDs) as 60 copies of eight individual RBDs^2-6 (mosaic-8 RBD-NPs) or 30 copies of two "quartets," each presenting four tandemly-arranged RBDs⁷ (dual quartet RBD-NPs). To facilitate manufacture of a broadly protective mosaic-8 vaccine, we generated membrane-bound RBD quartets that can be genetically encoded and delivered via mRNA: dual quartet RBD-mRNA and dual quartet RBD-EABR-mRNA, which utilizes ESCRT- and ALIX-binding region (EABR) technology that promotes immunogen presentation on cell surfaces and circulating enveloped virus-like particles (eVLPs)⁸. Immunization with mRNA immunogens elicited equivalent or improved binding breadths, neutralization potencies, T cell responses, and targeting of conserved RBD epitopes across sarbecoviruses, demonstrating successful conversion of protein-based mosaic-8 RBD vaccines to mRNA formats. Systems serology⁹ showed that the mRNA vaccines elicited balanced IgG subclass responses with increased Fcγ receptor-binding IgGs, consistent with potentially superior Fc effector functions. A new technique, Systems Serology-Polyclonal Epitope Mapping (SySPEM), revealed distinct IgG-subclass-specific epitope targeting signatures across mRNA and protein-based vaccine modalities. These results demonstrate successful conversion of mosaic-8 RBD-NPs to mRNA or EABR-mRNA vaccines that provide easy manufacturing and enhanced protection from future pandemic sarbecovirus outbreaks.