Candida auris Bloodstream Infection Induces Upregulation of the PD-1/PD-L1 Immune Checkpoint Pathway in an Immunocompetent Mouse Model

Candida auris is a globally spreading yeast pathogen causing bloodstream infections with high mortality in critically ill patients. The inherent antifungal drug resistance of most C. auris isolates and threat of multidrug-resistant strains create a need for adjunct immunotherapeutic strategies. While C. albicans candidemia was shown to induce immune paralysis and activation of inhibitory immune checkpoints, in vivo data on host responses to C. auris bloodstream infection are lacking as is an immunocompetent murine infection model to study the immunopathology and immunotherapy of C. auris sepsis. Therefore, herein, we developed an immunocompetent C. auris sepsis model by intravenously infecting C57BL/6 mice with 1.5 × 108 to 8 × 108 yeast cells of aggregate-forming (AR-0384) and nonaggregative (AR-0381) C. auris reference isolates. Both isolates caused reproducible, inoculum-dependent increasing morbidity, mortality, and fungal burden in kidney tissue. Notably, morbidity and mortality outcomes were partially decoupled from fungal burden, suggesting a role of additional modulators of disease severity such as host immune responses. Flow cytometric analyses of splenic immune cells revealed significant upregulation of the programmed cell death protein 1 (PD-1) on T cells and its ligand PD-L1 on macrophages from mice infected with C. auris AR-0384 compared to uninfected mice. PD-L1 expression on macrophages from AR-0384-infected mice strongly correlated with fungal tissue burden (Spearman's rank correlation coefficient ρ = 0.95). Altogether, our findings suggest that C. auris sepsis promotes a suppressive immune phenotype through PD-1/PD-L1 induction, supporting further exploration of PD-1/PD-L1 blockade as an immunotherapeutic strategy to mitigate C. auris candidiasis. IMPORTANCE Health authorities consider Candida auris to be one of the most serious emerging nosocomial pathogens due to its transmissibility, resistance to disinfection procedures, and frequent antifungal drug resistance. The frequency of multidrug-resistant C. auris isolates necessitates the development of novel therapeutic platforms, including immunotherapy. However, in vivo data on host interactions with C. auris are scarce, compounded by the lack of reliable immunocompetent mammalian models of C. auris candidemia. Herein, we describe a C. auris sepsis model in immunocompetent C57BL/6 mice and demonstrate reproducible and inoculum-dependent acute infection with both aggregate-forming and nonaggregative reference isolates from different clades. Furthermore, we show that C. auris sepsis induces upregulation of the PD-1/PD-L1 immune checkpoint pathway in infected mice, raising the potential of a therapeutic benefit of immune checkpoint blockade. Our immunocompetent model of C. auris sepsis could provide a facile preclinical platform to thoroughly investigate immune checkpoint blockade and combination therapy with antifungals.