mRNA delivery of mosaic-8 pan-sarbecovirus RBD vaccines elicits distinct antibody epitope signatures

Protein-based mosaic-8 nanoparticles displaying eight SARS-like betacoronavirus (sarbecovirus) receptor-binding domains (RBDs) elicited broadly cross-reactive antibodies that could protect from zoonotic spillovers. Here, we extend the mosaic-8 concept to mRNA by encoding membrane-bound RBD quartets (four linked RBDs) as dual quartet RBD-mRNA and dual quartet RBD-EABR-mRNA, the latter leveraging ESCRT- and ALIX-binding region (EABR) technology for display on cell surfaces and secreted virus-like particles. Compared with protein-based mosaic-8, mRNA-encoded mosaic-8 induced equivalent or enhanced antibody breadth, neutralization potencies, and conserved epitope targeting, while eliciting enhanced T cell responses and more balanced IgG subclass profiles consistent with potentially superior Fc effector functions. Finally, systems serology-polyclonal epitope mapping (SySPEM) revealed distinct IgG-subclass-specific epitope signatures across mRNA, EABR-mRNA, and protein vaccines, demonstrating that the mode of antigen display can shape epitope recognition. Successful conversion of a multivalent protein vaccine to mRNA platforms informs the design of broadly protective vaccines and advances mosaic-8 toward clinical development.