Project Summary/Abstract Respiratory syncytial virus (RSV) is a leading cause of severe acute lower respiratory tract infection in infants and children worldwide. Bovine RSV (BRSV) is closely related to human RSV and a significant cause of morbidity in young cattle. BRSV infection in calves displays many striking similarities to HRSV infection in humans, and cattle are an outbred population that is naturally susceptible to BRSV infection. Therefore, BRSV infection in calves represents an excellent model for studying RSV infection and antiviral immunity in children. RSV is poorly immunogenic and this has been a complicating factor in the development of a safe and effective RSV vaccine. Polyanhydride nanovaccines have shown great promise as adjuvants and vaccine delivery vehicles in rodent models due to their ability to promote enhanced immunogenicity through both the route of administration and the ability to provide sustained antigen exposure. In a previously funded NIH grant, the polyanhydride nanovaccine platform was used to develop an efficacious, mucosal nanovaccine that incorporated the post-fusion F and G proteins from BRSV. Neonatal calves vaccinated with the BRSV-F/G nanovaccine develop virus-specific cellular and humoral immune responses in the mucosa, and demonstrate significant reductions in viral burden and disease-associated pathology. The overall objective of this application is to improve upon the established efficacy of the polyanhydride nanoparticle platform for use against RSV infection in the neonate, and to further characterize the mucosal immune responses that correlate with resistance to RSV infection. The experiments in Aim 1 build upon the established efficacy of the post-fusion F/G nanovaccine with the incorporation of additional toll like receptor agonists and modifications to the mucosal/parenteral inoculation regimen. The experiments in Aim 2 will determine the efficacy of a mucosal nanovaccine that incorporates the pre-fusion F and G proteins from BRSV, as well as characterize the antibody response towards the pre-fusion and post-fusion F protein in the respiratory tract of neonatal calves. The experiments in Aim 3 will determine the duration of immunity induced by polyanhydride nanoparticle vaccination, while determining the mucosal immune responses that correlate with long-term resistance to RSV infection in the calf. Much of our knowledge of RSV infection and immunity stems from studies in rodents and adult animals;; however, the experiments proposed here will study a natural host-pathogen interaction and will examine the response in the neonate, the same population commonly affected by severe RSV disease. We anticipate that these studies will have a positive impact by identifying a safe and efficacious vaccine for use in children and animals, and by determining the immune responses that are necessary for long-term resistance against RSV infection in the young.