Lymphatic Transport and Immune Activation Effect by Locally Administered Extracellular Vesicles from Saccharomyces cerevisiae as Biocompatible Vaccine Adjuvants

The yeast strain Saccharomyces cerevisiae is an eukaryotic organism that has been widely used for the production of fermented foods. Most cells secrete extracellular vesicles (EVs), small particles composed of lipid membranes. Elucidating the role of EVs as a new intercellular communication system and developing novel EV-based therapies have attracted the increased attention of researchers. Although recent studies have reported the secretion of EVs from S. cerevisiae, their in vivo fate and subsequent EV-mediated biological responses in the host are unclear. In this study, we characterized both the biodistribution of locally (intradermally and subcutaneously) administered Saccharomyces cerevisiae-derived EVs (S-EVs) and the EV-mediated immune responses to evaluate their potential use as biocompatible vaccine adjuvants. S-EVs were round but heterogeneous in size and contained glucan, DNA, and RNA. Their mean particle sizes and zeta potentials were approximately 177.5 nm and −14.6 mV, respectively. We provided evidence that locally administered S-EVs were delivered to the lymph nodes, mainly reaching the B-cell zone. Measurement of host immune reactions revealed that administration of S-EVs increased the expression of cytokine (tumor necrosis factor (TNF)-α) and costimulatory molecules (CD40, CD80, CD86), which are indicators of immune activation. Especially, subcutaneously injected S-EVs showed potent adjuvanticity, indicating that subcutaneous administration of S-EVs is the desirable approach for achieving effective immune stimulation. These findings will facilitate the development of novel EV-based immunotherapies.