Project Summary Over the past twenty years, six coronaviruses (CoV) have emerged or expanded their geographic range. The emergent human CoVs with the greatest global impact (SARS-CoV-1, SARS-CoV-2, and MERS-CoV) belong to the Sarbecovirus and Merbecovirus subgenera within the Betacoronavirus genus of the Coronaviridae family. Many zoonotic high-risk Sarbecoviruses and Merbecoviruses are poised for human emergence events because they can bind human ACE2 and DPP4 entry receptors and infect human cells in culture. Given the historical outbreaks of CoVs, coupled with the recent emergence of SARS-CoV-2 and its destabilizing consequence on global health and economy, there is an urgent need to develop vaccines capable of broad protection against existing and future Sarbecoviruses and Merbecoviruses. Thus, the overarching goal of this P01 proposal is to generate viral-vectored vaccines that induce broad cross-protective humoral and cellular immunity to Sarbecoviruses and Merbecoviruses with pandemic potential, especially those viruses at high risk for zoonotic emergence into human populations. Project 3 will use antigen and epitope designs from Projects 1 and 2 to create vaccine platforms that generate cross-reactive immune responses against Sarbecoviruses and Merbecoviruses with pandemic potential. We will use several spike (S), RBD, and non-structural protein antigens that can be administered as part of a polyvalent formulation to induce broad B and T cell immunity. Project 3 will perform parallel and iterative engineering of an intranasally delivered chimpanzee adenoviral vectored virus (ChAd) and an intramuscularly delivered live-attenuated vesicular-stomatitis virus (VSV) displaying or producing optimized antigens. Antigens and vaccines that show immune responses of the highest magnitude and greatest cross-reactivity (determined with Core A) will be tested in in naïve, virus-immune, and mRNA vaccinated mice to determine how pre-existing immunity to SARS-CoV-2 impacts the immunogenicity of our more broadly targeting CoV vaccines. Vaccines showing optimal B and T cell immunogenicity (breadth, magnitude, and function) will be prioritized for mouse and hamster challenge studies in Core B with multiple Sarbecoviruses and Merbecoviruses. Our proposal is a proof-of-principle for product development. We envision generating at least one vaccine that induces broad-spectrum immunity to multiple CoV of concern.