(396b) Surface Presentation of Adjuvants on Protein Nanoparticle Vaccines

Nanoparticle vaccines leverage the inherent immunogenicity of particulate matter to generate specific, adaptive immune responses to poorly immunogenic antigens. To examine the fundamental properties of effective nanoparticle vaccines, we have made nanoparticles directly from a crosslinked model antigen, ovalbumin (OVA), and examined the effects of nanoparticle size and coating on antigen uptake and processing, as well as dendritic cell (DC) inflammation and maturation. We observed that OVA nanoparticles enhance antigen uptake, experience attenuated endosomal acidification, and upregulate the DC maturation marker CD86 as compared to soluble protein. Dendritic cell inflammation was nanoparticle size- and coating-dependent. Small particles (270 nm) enhanced TNF-α production as compared to larger (350, 560 nm) nanoparticles, and 270 and 350 nm nanoparticles coated with an extra layer of OVA enhanced IL-1β production more than large coated nanoparticles, uncoated nanoparticles, or soluble OVA did. Based on these results, we have chosen coated, 270 nm nanoparticles as a platform for exploring other enhancements to nanoparticle vaccine adjuvancy.

In addition to coating with antigen, coating nanoparticles with molecular adjuvants can further enhance immunostimulation through several pathways. Molecular adjuvants can trigger immunostimulatory intracellular pathways, activate the extracellular complement system or target vaccines to specific cell types. Immunoglobulins can enhance immunity through all three of these mechanisms, and immunoglobulin G (IgG) and immunoglobulin M (IgM) have been identified as promising classes of adjuvants. Unlike traditional toll-like receptor ligands, such as flagellin, immunoglobulins are host-derived proteins, which greatly reduce the risk of an off-target immune response.

Building off of our prior work, we have coated OVA, flagellin, IgM, and IgG onto OVA nanoparticles. The activity of the coatings was confirmed by TLR-5/NFκB activation and complement activation studies in vitro for flagellin and immunoglobulin, respectively. Using an in vivo mouse immunization model, we examine the serum antibody responses and splenic T cell cytokine secretions in response to pathogen- and host-derived protein adjuvants. Our current work addresses three fundamental questions surrounding protein adjuvant use: (1) The benefit of antigen-adjuvant co-delivery, (2) The effectiveness of host-derived immunoglobulin in enhancing nanoparticle-based immune responses, and (3) Whether different immunoglobulin isotypes can trigger different types of adaptive immune responses. Our results contribute to current design strategies for molecular adjuvant incorporation onto nanoparticle vaccines.