In the US, RSV infects nearly 100% of children, and total associated hospital charges are estimated at approximately $2.5 billion dollars. Infants are most susceptible to severe RSV-related disease in the first six months of life. During this time, infants mount poorly protective antibody-mediated immunity on their own upon RSV infection or vaccination. Rather they veer toward Th2-type responses, which can cause disease- or vaccine- enhanced severity upon re-infection, and subsequent wheezing throughout childhood and into their teens. In recent years, promising maternal RSV vaccine candidates have progressed to clinical trials, but the window of protection to the infant remains limited to the half-life of the maternally-derived antibody (~1 month) or moderately longer if the mother is breast feeding. An RSV vaccine that protects infants beyond the first month of life or ameliorates the course of their respiratory disease, will (i) reduce the frequency of infant hospitalizations, (ii) improve the quality of life for infants, families, communities, and populations, and (iii) lessen disease burden on the US economy. In this multiple PI project, we seek to optimize and characterize a nanoparticle-based intranasal RSV vaccine platform with intrinsic adjuvant properties. The biodegradable biotin-nanoparticle system (referred to as bNP) functions as an antigen carrier and immune activator. Coupling antigen delivery and adjuvant properties into a single physical entity will enhance the capacity to overcome the inherent immunosuppressive environment of mucosal tissues. The particle system has a tunable design in which the dose of the antigen can be varied without remanufacturing. To ensure a Th-1 type response, we will use a variant RSV prefusion protein (preF) engineered to lock in the native conformation as the cargo antigen. We hypothesize that preF sterically stabilized on bNP (preF-bNP) will activate antigen-presenting cells to induce important correlates of protection, including RSV-specific Th1-dominant T cell response, CD8 resident memory T cells, and neutralizing antibody. Three specific aims are proposed. In Aim 1 we will optimize display of preF on bNP and capacity of the formulation to activate antigen presenting cells. In Aim 2 we will determine preF-bNP uptake kinetics into antigen presenting cells and preF-bNP-induced immunity in vivo, including resident memory T cells. In Aim 3 we will establish the safety and efficacy of intranasal preF-bNP in an RSV mouse model. Successful completion of the studies will lead pave the way for advancing a novel RSV vaccine formulation for generating safe and protective RSV immunity in young children.