Identification of Coccidioidomycosis Immunoreactive Peptides That Recall T-Cell Responses Indicating Past Exposure

Valley fever (VF) is a common cause of community-acquired pneumonia in the American Southwest. Diagnosis is challenging due to VF's similarities to other pulmonary diseases. The VF T-cell response is important to control the disease, and measuring this response holds promise as an improved diagnostic. We aim to identify of VF T-cell epitopes, and to develop disease and efficacy diagnostics for the clinic and vaccine trials.

We identified VF-specific T-cell epitopes by using their ability to bind the major histocompatibility complex (MHC) class II molecules and T-cell stimulation. We performed MHC binding prediction on known and unknown Coccidioides antigens and then empirically tested the predictions on unknown antigens with an in vitro multiplex MHC binding analysis. Peripheral blood mononuclear cells from patients with clinical Coccidioides infections and from endemic or nonendemic healthy controls were stimulated with the identified peptides and evaluated for immunologic memory responses.

A total of 108 Coccidioides peptides were identified by MHC class II binding. The 108 peptides (NAU108) were synthesized, pooled, and jointly evaluated for immunogenicity in VF-positive individuals. The peptides reactivated memory CD4+ T cells in VF-confirmed and endemic VF specimens when compared to nonendemic control samples as determined by activation marker and cytokine secretion.

This study identified peptides that, when pooled, had immunogenic properties in humans infected with Coccidioides that can be used to distinguish infected individuals from endemic area healthy controls or nonexposed individuals outside the endemic area. This approach holds relevance for the development of diagnostic assays for VF.