Design and Evaluation of a Novel Recombinant Antigen for a T Cell-Based Vaccine Against Valley Fever 2260372

Introduction Valley Fever (VF) is a potentially fatal fungal disease caused by Coccidioides; however, no clinical vaccine exists. We previously created a recombinant Coccidioides antigen, rCpa1, with DRB1*04:01 (DR4) epitopes, but it is poorly expressed in E. coli. To enhance solubility and broaden HLA coverage, we removed 25 amino acids and incorporated three new DRB1*03:01 (DR3) epitopes, generating the rCpa5 antigen. We formulated rCpa5 with glucan-chitin particles (GCPs) as an adjuvant/delivery system. We hypothesize that GCP-rCpa5 can protect against VF by activating Th1/Th17 responses. Methods C57BL/6 (BL/6), DR4, and DR3 transgenic mice were vaccinated subcutaneously three times with GCP-rCpa5, and T cell epitopes were mapped by IFN-γ recall assays. Vaccinated and control mice were challenged intranasally to determine efficacy by survival (45 DPC) and fungal burden at 7 and 14 DPC. Lung T cell responses were profiled by intracellular cytokine assays. Additionally intramuscular and oropharyngeal vaccination routes were compared to identify the optimal route. Results The yield of the rCpa5 antigen was improved over 100-fold compared to rCpa1. We identified 14, 12, and 9 novel T cell epitopes within rCpa5 for BL/6, DR4, and DR3 mice, respectively. GCP-rCpa5 vaccination conferred 90% survival for BL/6 mice versus 10% in controls. Vaccinated DR4 mice showed a significant reduction in fungal burden in the lungs and spleen, with elevated Th1/Th17 responses compared to control mice. Comparable fungal clearance was observed across all three vaccination routes. Conclusion The rCpa5 antigen contains multiple epitopes for prevalent human MHC-II alleles and the GCP-rCpa5 vaccine is effective against Coccidioides infection for laboratory and humanized mice. Vaccine-induced protection is associated with mixed Th1/Th17 responses elicited by subcutaneous, oropharyngeal, and intramuscular vaccination. These data support that GCP-rCpa5 is protective and worthy of further development for clinical application.