**6. Vaccines for histoplasmosis**

The creation of vaccination strategies for clinically relevant fungi has been a longsought ambition for investigators, even with the difficulties assigned to these organisms' complex eukaryotic cells and their similarity to human proteins. Preventing or diminishing the severity of histoplasmosis through targeted vaccine development is then deemed to be an important scientific breakthrough [54, 55].

Glucan particles (GPs) are hollow, porous microspheres with an average diameter of 2–4 μm, derived from baker's yeast (*Saccharomyces cerevisiae*) purified cell walls and composed of 1,3-D-glucan and trace sums of chitin [56]. They are considered innovative and promising vaccine delivery systems, due to the possibility of encapsulating, transporting, delivering, and releasing protein antigens in their inner void cavity. In addition, the GPs delivery system retains the intrinsic immunostimulatory properties of 1,3-D-glucan on the surface. This polysaccharide functions as a ligand for receptor-mediated cell uptake by phagocytic cells bearing β-glucan receptors, for example, macrophages and dendritic cells in the immune system. Hence, GPs act as antigen-presenting phagocytic cells-selective-targeted delivery systems with adjuvant properties [55, 56].

A recent preclinical study was able to produce an extract from *H. capsulatum* yeast cells with the ability to convene protective immunity when encapsulated in GPs [21]. Succinctly, the GP vaccine consisted of *Histoplasma* alkaline extract, mouse serum albumin, and yeast RNA complexed with the glucan cells. Overall, the developed alkaline extract packaged in GP conferred vaccine-induced immunity, along with a reduced fungal burden by roughly 80% and improved survival in mice [56].

These data overlooks GP as useful vaccine delivery vehicles and may serve as a platform for the identification of proteins to include in GPs that both enhance protective immunity and modify immune responses to the agent [21]. On the other hand, this opens doors to the development of new GP nanoparticle-loaded formulations, which take advantage not only from the drug encapsulation assets of NPs but also from the macrophage-targeting properties of GPs [56].

Another ground-breaking study combining immunoproteomic and immunopeptidomic methods was able to map *H. capsulatum* peptide epitopes for the first time using murine dendritic cells and macrophages. After selecting and synthesizing the four most promising peptides, the incorporation into GPs took place. Efficient induction of CD4+ and CD8+ T lymphocytes was observed, as well as a production

stimulation of IFN-γ, IL-17, and IL-2. The selected epitopes are derived from enolase (a heat shock protein 60) and the ATP-dependent molecular chaperone HSC82, which share a great degree of similarity with proteins expressed by other clinically relevant pathogenic fungi. Ergo, the authors preconize these promiscuous epitopes as the steppingstone for the creation of a multi-epitope peptide vaccine against histoplasmosis and other fungi [54].
