Multivalent display of a recombinant Ag2/PRA-CSA protein on the surface of highly immunogenic bacteriophage VLPs as a novel approach to elicit protective immune responses against Coccidioides fungi - PROJECT SUMMARY Coccidioidomycosis or valley fever is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. Historically, these fungi grow in alkaline soil in the dry southwest of the US, Northern Mexico, Central and South America. Recently, the fungi have expanded their geographical distribution to eastern Washington, Oregon, and Utah. Within the last 20 years, coccidioidomycosis cases have increased by >71% in the US. Sixty percent of people infected with the fungi do not get sick; however, 40% of humans infected with the fungi get sick; infection is associated with shortness of breath, cough, pneumonia, fever, etc. Seniors >65 years, diabetic patients and smokers are at a higher risk of developing severe pulmonary complications from infections. In addition to this, infection of individuals with a depressed immune system can lead to disseminated infection to other parts of the body. Currently, Coccidioides infections are treated with anti-fungal drugs; however, treatment is associated with serious side effects. Unfortunately, there are no approved vaccines to protect humans against these fungal infections. Coccidioides posadasii Δcps1, is promising live-attenuated candidate vaccine against Coccidioides infection. Nevertheless, this candidate vaccine cannot be used in individuals with a depressed cell-mediated immunity and are more vulnerable to disseminated infections. Protein antigens against valley fever is a better alternative to live-attenuated vaccines: i) they are very safe; ii) their antigenic targets are well-defined and are very specific; iii) they are very easy to produce in large quantities. Two protein antigens (antigen 2 or proline rich antigen, Ag2/PRA, and Coccidioides-specific antigen, CSA), have been shown to protect against Coccidioides infection. However, protein antigens are poorly immunogenic. Different approaches have been used to enhance the immunogenicity of protein antigens. Nevertheless, these approaches are time consuming, very challenging and require large doses of antigens with multiple immunizations. To overcome these challenges, we covalently displayed, multivalently, Ag2/PRA-CSA from Coccidioides posadasii on two highly immunogenic bacteriophage virus-like particle (VLP) platforms (MS2 and PP7). Immunization with Ag2/PRA-CSA coupled to VLPs have several advantages compared to previous Coccidioides vaccine approaches: i) our VLPs serve as a delivery platform; ii) they contain T cell epitopes; iii) they serve as adjuvant (our VLPs encapsidate single-stranded RNA, which is a ligand for toll-like receptor (TLR 7/8) and activate Th1 responses; iv) they are immunogenic at low doses. VLPs have been used as a platform to display T cell epitopes from infectious agents and cancer. However, they have never be explored to develop a candidate vaccine against fungi. In this proposal, we plan to assess the immunogenicity of Ag2/PRA-CSA displayed on phage VLPs in the presence of exogenous adjuvant, zymosan (a TLR2/6 ligand that promotes differentiation of Th cells to Th17 cells). The goal is to stimulate multiple signaling pathways on immune cells (Th1 & Th17) that are associated with Coccidioides protection. Our hypothesis is that immunization with Ag2/PRA-CSA antigen displayed multivalently on bacteriophage VLP platforms in combination with zymosan will elicit robust protective innate and T cell responses compared to immunization with Ag2/PRA-CSA not displayed on the platform.
