Luis Ontiveros‐Padilla

Currently licensed vaccine adjuvants offer limited mucosal immunity, which is needed to better combat respiratory infections such as influenza. Mast cells (MCs) are emerging as a target for a new class of mucosal vaccine adjuvants. Here, we developed and characterized a nanoparticulate adjuvant composed of an MC activator [mastoparan-7 (M7)] and a TLR ligand (CpG). This novel nanoparticle (NP) adjuvant was co-formulated with a computationally optimized broadly reactive antigen (COBRA) for hemagglutinin (HA), which is broadly reactive against influenza strains. M7 was combined at different ratios with CpG and tested for in vitro immune responses and cytotoxicity. We observed significantly higher cytokine production in dendritic cells and MCs with the lowest cytotoxicity at a charge-neutralizing ratio of nitrogen/phosphate = 1 for M7 and CpG. This combination formed spherical NPs approximately 200 nm in diameter with self-assembling capacity. Mice were vaccinated intranasally with COBRA HA and M7-CpG NPs in a prime–boost–boost schedule. Vaccinated mice had significantly higher antigen-specific antibody responses (IgG and IgA) in serum and mucosa compared with controls. Splenocytes from vaccinated mice had significantly increased cytokine production upon antigen recall and the presence of central and effector memory T cells in draining lymph nodes. Finally, co-immunization with NPs and COBRA HA induced influenza H3N2-specific HA inhibition antibody titers across multiple strains and partially protected mice from a challenge against an H3N2 virus. These results illustrate that the M7-CpG NP adjuvant combination can induce a protective immune response with a broadly reactive influenza antigen via mucosal vaccination.

Current FDA-approved influenza vaccines are limited by variable year to year efficacy, low immunogenicity, and poor stability outside of cold-chain storage. Polymeric microparticles can overcome many of these issues to provide an improved influenza vaccine platform. Here, an acetalated dextran microparticle platform was used to encapsulate a broadly active influenza COBRA immunogen and the adjuvant cGAMP. Microparticles were fabricated via the highly scalable electrospray method. Mice vaccinated with acetalated dextran microparticles loaded with COBRA and cGAMP produced antibodies with the ability to neutralize antigenically distinct influenza viruses. The microparticles also induced a potent cellular response against the COBRA immunogen. Finally, after storage for 3 months at 40°C or 6 months at 24°C, the microparticles produced as strong of an immune response as microparticles stored at -20°C for the same amount of time. Overall, acetalated dextran microparticles provide a promising platform for a broadly active influenza vaccine.