PROJECT SUMMARY / ABSTRACT Novel recombinant Rotavirus vaccine utilizing the probiotic microorganism Lactobacillus acidophilus Despite the worldwide licensure and availability of two rotavirus vaccines in 2006, it is estimated that rotavirus kills approximately 215,000 children each year. Children under the age of 5 in developing countries are significantly more likely to be affected by severe rotavirus disease as the currently available vaccines have lower efficacy (50-60%) as compared to developed nations (>85%). The ongoing morbidity and mortality as well as the risk posed by current live-attenuated vaccines, necessitate the development of a next generation human rotavirus vaccine. We have developed an orally-delivered, mucosal vaccine platform that employs Lactobacillus acidophilus. We have brought together innovative adjuvant and antigen-expression strategies in unique constructs with demonstrated potential to induce robust mucosal and systemic immune responses. This platform offers several important feasibility advantages as it employs a commensal designated as GRAS (generally regarded as safe) by the FDA, is inexpensive to produce, does not require cold-chain, and is needleless. We will utilize a novel CRISPR-Cas9 system adapted to L. acidophilus to engineer sophisticated vaccine constructs that will be tested using a homotypic mouse rotavirus challenge. Induction of homotypic and heterotypic neutralizing antibodies will be assessed using a novel, highly sensitive assay. We will assess vaccine strain colonization and potential off-target effects on the microbiome. Finally, we will perform a direct comparison of our rLA rotavirus vaccine against a human live attenuated vaccine in the gnotobiotic pig model using animals transplanted with human infant fecal microbiome. Efficacy against human rotavirus challenge will be determined. At the completion of these proposed studies, we aim to have a rLA construct ready to proceed toward human clinical trials.