**3. The role of the extracellular vesicles in human health**

Extracellular vesicles are released by many different cell types and organisms. The role of the EVs is mediated by the signals transmitted through them by the protein, lipids, and nucleic acids that are part of the EVs cargo. The release of the EVs to the environment allows the emitting cell to send messages to sites close or even far from the origin. These vesicles are able to transport biological information through

the system with cell targeting properties, making them as great candidates for drug delivery systems [31–33]. EVs are naturally secreted by human cells and they are not strange for the system, avoiding the negative response by the immune cells. The use of EVs as drug delivery systems is focused on improving their ability to reach the target recipient cells and deliver the content, controlling the purity of EV preparation, and analyzing the best administration routes. The challenges are prolonging their circulating and improving targeting. The use of EVs as drug delivery systems is being studied for several disorders, including cancer, infectious diseases, brain disorders, liver diseases, and among others [34–37]. However, this field is still in the early stage of development with great potential for future applications, but also with big challenges to attempt [38].

More applications for EVs have been described. The specific cargo of the EVs makes them useful in the discovery of biomarkers for clinical diagnosis. Because EVs are secreted from almost all cells, they are found in various body fluids, making them easy to collect and analyze and playing a critical role in diagnosis of several conditions, such as cancer, Alzheimer's, epilepsy, and liver diseases [37, 39–42]. EVs participate in pathogenesis and can also be used as diagnosis or vaccines [33, 35, 43]. Last novel applications for EVs include using their signaling properties to repair injured muscle or use them as biomarkers for male infertility or pregnancy-related disorders [44–46].
