Project Summary Recent successes using nanoparticles encapsulating mRNA payload for COVID-19 vaccination have energized the field of exosomes as novel vaccine agents. Exosomes (40-180nm), extracellular vesicles of the size of a virus and shed by all cells, are actively studied in viral biology. The reported use of exosomes to improve immunogenicity of vaccines (including SARS-Cov) may result from their enhanced stability in vivo, tropism for immune cells, enhanced uptake and antigen processing, and unique, virus-like presentation of a conformationally intact antigen on their surface, a feature recognized as essential for SARS CoV-2 spike glycoprotein (SC2S) antigenicity. Further, exosomes present with the unique property to deliver a siRNA/ASO therapeutic payload (TP), a strategy developed at MDACC for pancreatic cancer and FDA approved for Phase I trial (NCT03608631). Leveraging our good manufacturing practices (GMP) certified clinical grade exosomes platform, our recent efforts in engineering and testing exosomes presenting with surface SC2S protein aimed to yield a vaccine designed to be readily interchangeable to other SARS, past or future. The engineered exosomes, ExoVAX-SC2S, present SC2S on their surface and encapsulate mRNA for the spike protein. In this administrative supplement, we will test the efficacy of ExoVAX-SC2S in eliciting B- and T cell immunity as well as long term antibody production in Baboons. The species is best suited for testing this novel vaccine approach due to its symptomatic presentation to SARS CoV-2 and a similar antibody repertoire as humans. The administrative supplement coalesces the expertise of Simmons and Kalluri laboratories to accomplish the proposed studies.