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

Nanoparticle vaccines displaying combinations of SARS-like betacoronavirus (sarbecovirus) receptor-binding domains (RBDs) could protect against SARS-CoV-2 variants and spillover of zoonotic sarbecoviruses into humans. Using a computational approach, we designed variants of SARS-CoV-2 RBDs and selected 7 natural sarbecovirus RBDs, each predicted to fold properly and abrogate antibody responses to variable epitopes. RBDs were attached to 60-mer nanoparticles to make immunogens displaying two (mosaic-2s), five (mosaic-5), or seven (mosaic-7) different RBDs for comparisons with mosaic-8b, which elicited cross-reactive antibodies and protected animals from sarbecovirus challenges. Naive and COVID-19 pre-vaccinated mice immunized with mosaic-7 elicited antibodies targeting conserved RBD epitopes, and their sera exhibited higher binding and neutralization titers against sarbecoviruses than mosaic-8b. Mosaic-2s and mosaic-5 elicited higher antibody potencies against some SARS-CoV-2 variants than mosaic-7. However, mosaic-7 elicited more potent responses against zoonotic sarbecoviruses and highly mutated Omicrons, supporting its use to protect against SARS-CoV-2 variants and zoonotic sarbecoviruses.