Mannoprotein Cig1 Contributes to the Immunogenicity of a Heat-Killed F-box Protein Fbp1Cryptococcus neoformansVaccine Model

Currently, no fungal vaccine exists for clinical use while fungal infections are responsible for over 1.5 million deaths every year. Our previous studies identified aCryptococcus neoformansmutant strainfbp1Δ as a potential vaccine candidate. This mutant strain contains a deletion of the F-box protein Fbp1, a key subunit of the SCF E3 ligase complex necessary for ubiquitin-mediated proteolysis. Vaccination with heat-killedfbp1Δ (HK-fbp1)can elicit protection againstC. neoformansparental strain and its sibling speciesC. gattiiin an interferon gamma (IFN-γ) dependent Type 1 immune response. However, we have yet to decipher the immunogenic factor(s) expressed by thefbp1Δ mutant that are responsible for the induction of the protective immune response. In this study, we have identified that capsule plays an important role in HK-fbp1vaccine mediated protection, as acapsular HK-fbp1cells showed diminished protection against wild type challenge. Additionally, our studies have shown that Cytokine Inducing Glycoprotein 1 (Cig1), a GPI anchored mannoprotein, is regulated by Fbp1 and contributes to the immunogenicity of HK-fbp1. Deletion of Cig1 in thefbp1Δ background resulted in decreased recruitment of anti-fungal effector T cells and diminished production of protective inflammatory cytokines by the host. Furthermore, loss of Cig1 in thefbp1Δ mutant resulted in reduced protection in vaccination survival studies at lower vaccine inoculum doses compared to HK-fbp1. In aggregate, these findings demonstrate Cig1 is an antigen contributing to the immunogenicity of HK-fbp1that may be utilized to further optimize the HK-fbp1fungal vaccine as a tool in the arsenal against invasive fungal infections.