Chimeric RBD library: A novel strategy to develop a broad-spectrum Sarbecovirus vaccine 2778

Abstract Description The COVID-19 pandemic, driven by SARS-CoV-2, remains a major health challenge due to the virus’s rapid evolution and immune evasion. Current vaccines struggle against emerging variants, including the XBB variant—a recombinant of two BA.2 lineages—known for increased transmissibility and immune escape. To address this, we developed a chimeric receptor binding domain (RBD) library using five Sarbecoviruses (SARS-CoV, Delta, Omicron BA.2, Pangolin, and Bat coronaviruses). Utilizing PCR-based fragment amplification and golden-gate assembly, we generated a library of 3125 unique chimeric RBD variants, simulating natural recombination events. We identified 757 distinct chimeric RBDs, of which 134 candidates showed strong hACE2 binding in vitro. Immunization in mice with 87 selected constructs with high hACE-2-binding revealed 26 candidates with cross-neutralization against BA.4/5 pseudoviruses. Notably, the XE3 chimeric RBD induced higher neutralizing antibody levels against Omicron BA.4/5 than parental vaccines, suggesting broad-spectrum protection. This study demonstrates a promising strategy for next-generation vaccines targeting diverse Sarbecoviruses, enhancing future pandemic preparedness. Funding Sources Institute of Biomedical Sciences, Academia Sinica Topic Categories Vaccines and Immunotherapy (VAC)