Characterization of dual DNA polymerase knockout strains of Candida albicans with live whole-cell vaccine competence

Systemic candidiasis inflicts ~1.2 million deaths annually worldwide. Despite its severity, an approved antifungal vaccine remains an unmet human need. In a quest to design a live-whole cell vaccine, we characterized and demonstrated the vaccine potential of two dual DNA polymerase-defective strains of Candida albicans. While the deletion of POL32 in a hyper-virulent rad30ΔΔ strain attenuated the virulence, the deletion of RAD30 in an avirulent pol32ΔΔ did not revert to a hypervirulence phenotype. Both the dual polymerase-defective strains replicate transiently in the host and trigger immune responses to prevent reinfections in mice by employing a concerted involvement of innate, adaptive, and trained immunity. The cellular and molecular depletion in immunized mice suggested the role of B- and T-cells, neutrophils, and macrophages in antifungal immunity. Altogether, our results confirmed that Pol32 is a true virulence factor and intravenous vaccination with these attenuated strains could prevent systemic candidiasis in the preclinical models without evident safety concerns; thus, these candidate strains have enormous translational potential to fully develop as antifungal vaccines.