PROJECT SUMMARY/ABSTRACT The chikungunya virus (CHIKV) is a single-stranded, positive sense RNA alphavirus which is transmitted to humans by the bite of a mosquito. Infection with this virus causes a debilitating arthralgia and results in death in some people. The virus has acquired mutations in the envelope proteins (E1 and E2) that have allowed for increased transmission by mosquitos to humans in over 40 countries, making this a great concern for public health. There is no current vaccine or specific anti-viral therapy for this disease. The goal of our proposal is to develop novel adjuvant formulations for use with a CHIKV virus-like particle (VLP) vaccine expressing key CHIKV antigens, E1 and E2. The adjuvants will contain a synthetic toll-like receptor (TLR) 4 agonist (SLA) and/or a retinoic acid-inducible gene I protein (RIG-I)-like receptor agonist (5'ppp-dsRNA). We first plan to test the stability and compatibility of each of these agonist formulations (containing an oil-in-water emulsion, liposomes, or Alum) with the CHIKV VLP. Those adjuvants that are compatible with the CHIKV VLP antigen will be tested for immunogenicity in the C57BL/6 mouse model. Immunogenicity of these vaccine candidates will be assessed following either a prime or boost immunization. The vaccine candidates will be down-selected using a defined rank-based selection criteria: (1) antibody responses (enhanced neutralizing antibody titers and increased IgG2c:IgG1 ratios); (2) increased B cell and antigen-specific bone marrow plasma cell responses; (3) Increased germinal center responses (and enhanced Tfh cells); (4) increased CD4+ TH1 polyfunctional cytokine responses (including IFN-?, TNF and IL-2); and (5) increased CD8+ T cell responses. In our last Aim we plan to test the efficacy of these vaccine candidates in the arthritic C57BL/6 mouse model, and in a partial type-I IFN receptor deficient mouse model (A129; IFN-?/?R+/-). Finally, we will test two lead CHIKV vaccine candidates in a passive antibody transfer study, where antibodies from immunized mice will be transferred into the lethal AG129 CHIKV infection model (AG129 lack both type 1 and type 2 IFN receptors) to determine whether these antibodies are protective.