Cryptococcus extracellular vesicles properties and their use as vaccine platforms

Abstract

Whereas extracellular vesicle (EV) research has become commonplace in different biomedical fields, this field of research is still in its infancy in mycology. Here we provide a robust set of data regarding the structural and compositional aspects of EVs isolated from the fungal pathogenic species Cryptococcus neoformans, C. deneoformans and C. deuterogattii . Using cutting‐edge methodological approaches including cryogenic electron microscopy and cryogenic electron tomography, proteomics, and flow cytometry, we revisited cryptococcal EV features and suggest a new EV structural model, in which the vesicular lipid bilayer is covered by mannoprotein‐based fibrillar decoration, bearing the capsule polysaccharide as its outer layer. About 10% of the EV population is devoid of fibrillar decoration, adding another aspect to EV diversity. By analysing EV protein cargo from the three species, we characterized the typical Cryptococcus EV proteome. It contains several membrane‐bound protein families, including some Tsh proteins bearing a SUR7/PalI motif. The presence of known protective antigens on the surface of Cryptococcus EVs, resembling the morphology of encapsulated virus structures, suggested their potential as a vaccine. Indeed, mice immunized with EVs obtained from an acapsular C. neoformans mutant strain rendered a strong antibody response in mice and significantly prolonged their survival upon C. neoformans infection.

Extracellular Vesicles from Fusarium graminearum Contain Protein Effectors Expressed during Infection of Corn

“…Similarly, C. neoformans EVs contain proteins with SUR7 domains [6] suggesting that SUR7 is a conserved protein marker of fungal EVs.…”

“…They are produced by cells from all three domains of life [4] and have different biological functions and cargo, composed mostly of protein, nucleic acids, and carbohydrates. EVs have been identified in more than 20 yeasts and filamentous fungal species, although EVs from human pathogens such as Candida albicans [5], and Cryptococcus neoformans [6] are the best characterized.…”

Gene Expression of Diverse Cryptococcus Isolates during Infection of the Human Central Nervous System

“…Other notable functions include several proteins linked to environmental responses or interactions. For instance, other highly expressed genes, including CFO1 , BLP2 , BLP4 , CDA1 , and the glyoxal oxidase gene, also encode membrane-bound proteins which have been discovered in extracellular vesicles produced by this yeast and shown to participate in the export of virulence factors ( 32 ). The quorum-sensing gene CQS1/QSP1 is required for full virulence and is also highly expressed ( 33 ).…”

Extracellular Vesicles From Paracoccidioides brasiliensis Can Induce the Expression of Fungal Virulence Traits In Vitro and Enhance Infection in Mice

“…Differences in the vEV and aEV cargo, especially at the membrane surface, are likely to explain the present results. Rizzo et al (2021) obtained partial protection in preliminary experiments based on adjuvant-free intraperitoneal mice inoculations of cryptococcal EVs from an acapsular mutant and the dose was calculated as protein concentration. Vargas et al (2020) obtained 100% survival of immunosuppressed mice infected with C. albicans using three doses (as sterol concentration) of EVs alone or inoculated with adjuvant via the intraperitoneal route.…”

“…Additionally, the current fungal EV literature results on the protective role of EVs in vivo can vary with the fungal model and the experimental protocols: while fungal EVs were able to vaccinate mice against C. albicans and C. neoformans infection ( Vargas et al., 2015 ; Vargas et al., 2020 ; Rizzo et al., 2021 ), they enhanced subcutaneous infection with Sporothrix brasiliensis in mice ( Ikeda et al., 2018 ). In the cryptococcosis model, the mortality of mice treated with fungal EV-stimulated macrophages increased upon infection with C. neoformans ( Zhang et al., 2021 ).…”