Hidden allies: how extracellular vesicles drive biofilm formation, stress adaptation, and host-immune interactions in human fungal pathogens

Abstract

Pathogenic fungi pose a significant threat to human health, especially given the rising incidence of invasive fungal infections and the emergence of drug-resistant strains. This requires the development of vaccines and the advancement of antifungal strategies. Recent studies have focused on the roles of fungal extracellular vesicles (EVs) in intercellular communication and host-pathogen interactions. EVs are nanosized, lipid membrane-bound particles that facilitate the transfer of proteins, lipids, and nucleic acids. Here, we review the multifaceted functions of EVs produced by different human fungal pathogens, highlighting their importance in the response of fungal cells to different environmental cues and their interactions with host immune cells. We summarize the current state of research on EVs and how leveraging this knowledge can lead to innovative approaches in vaccine development and antifungal treatment.

Keywords: biofilms; drug resistance; extracellular vesicles; fungal pathogens; immunity; stress response.

Fig 1

The role of fungal EVs in antifungal resistance. (A and D) In S. cerevisiae and C. auris, caspofungin treatment leads to increased EV production. Complementation assays using wild-type EVs can restore the caspofungin susceptibility of cell wall defective mutants in S. cerevisiae and increase resistance to amphotericin B in C. auris. (B and C) In C. albicans and C. tropicalis, EVs contribute to drug resistance, biofilm formation, and the production of the biofilm extracellular matrix. Inhibitors of the vesicular trafficking pathway, such as turbinmicin, decrease biofilm biomass and EV production in C. albicans. In C. tropicalis, complementation with biofilm-derived EVs increases drug resistance and biofilm biomass. (E) In C. neoformans, fluconazole exposure decreases EV yield. Serial passaging in the absence of antifungal pressure restores EV production and drug susceptibility. Illustration created with BioRender.

Fig 2

Fungal EVs modulate and interact with the host immune system. The table shows changes in cytokine expression, nitric oxide secretion, or phenotype transitions when specific immune cell types are stimulated with EVs isolated from different pathogenic fungi. Arrows indicate increases or decreases relative to no EV treatment. Empty spaces indicate that the respective immune responses have not been evaluated for EVs produced by those respective species. BMDM = bone marrow derived macrophages; BMDN = bone marrow derived neutrophils; PBMC = peripheral blood mononuclear cells; PMN = polymorphonuclear neutrophils. Illustration created with BioRender.

Fig 3

Animal immunization with fungal EVs protects against subsequent fungal infection. G. mellonella larvae treated with EVs derived from A. fumigatus, A. flavus, or C. albicans prior to fungal infection showed increased survival rates and reduced fungal burdens. A protective effect of fungal EV treatment prior to fungal infection was also observed in murine studies. Immunization with EVs derived from A. fumigatus and C. albicans increased fungal clearance, reduced fungal burdens in multiple organs, and showed synergistic effects with antifungals. While pre-treatment of mice with C. neoformans EVs enhanced survival in a cryptococcosis infection model, immunization with S. brasiliensis EVs increased the fungal load of skin lesions caused by this fungus. Illustration created with BioRender.