Designed mosaic nanoparticles enhance cross-reactive immune responses in mice.

1Using computational methods, we designed 60-mer nanoparticles displaying SARS-like betacoronavirus (sarbecovirus) receptor-binding domains (RBDs) by () creating RBD sequences with 6 mutations in the SARS-COV-2 WA1 RBD that were predicted to retain proper folding and abrogate antibody responses to variable epitopes (mosaic-2s; mosaic-5), and () selecting 7 natural sarbecovirus RBDs (mosaic-7). These antigens were compared with mosaic-8b, which elicits cross-reactive antibodies and protects from sarbecovirus challenges in animals. Immunizations in naïve and COVID-19 pre-vaccinated mice revealed that mosaic-7 elicited higher binding and neutralization titers than mosaic-8b and related antigens. Deep mutational scanning showed that mosaic-7 targeted conserved RBD epitopes. Mosaic-2s and mosaic-5 elicited higher titers than homotypic SARS-CoV-2 Beta RBD-nanoparticles and increased potencies against some SARS-CoV-2 variants than mosaic-7. However, mosaic-7 elicited more potent responses against zoonotic sarbecoviruses and highly mutated Omicrons. These results support using mosaic-7 to protect against highly mutated SARS-CoV-2 variants and zoonotic sarbecoviruses with spillover potential.