Exosomes are lipid bilayer-enclosed, nano-sized extracellular vesicles (EVs) which contain fingerprints of the cells that produce them, e.g., nucleic acids, proteins and lipids. Based on the close relationship of EVs including exosomes to various physiological and pathogenic conditions, EVs are expected to be applied to a wide range of diseases as diagnostic or therapeutic tools. Since EVs are known to exhibit diverse tissue distribution depending on their cell of origin and their subtypes, it is quite important to understand the tissue distribution properties of individual EVs. Therefore, researchers have been trying to elucidate the tissue distribution of EVs and to control it to increase the therapeutic potential of EVs as well as to expand their application as delivery vehicles for various pharmaceuticals, including low molecular weight compounds, proteins, and nucleic acids. In this review, we focus on small EVs with a diameter of about 100 nm, which include exosomes, and discuss about their tissue distribution, including their labeling methods, and approaches and technologies how to control it.

There are various molecules in our body fluids, and liquid biopsy is attracting attention as a new testing method for diagnosis using these molecules as clues about cancer. In recent years, extracellular vesicles, including exosome, have been attracting attention as a resource to expand the scope of liquid biopsy. Cells pack various molecules as messages into exosomes and secrete them. In this review, we will discuss how to read these messages from exosomes, how to use them for cancer diagnosis, and their potential.

Exosomes, lipid bilayer vesicles secreted from almost all cells, have emerged as a novel signal mediator of cell-to-cell communication. Lipids are essential components of exosomes to outline the boundaries of exosomes and to sequester their components from the external environment. Additionally, recent studies have suggested that exosomal lipids engage in exosome formation, uptake, and signal transduction to receiver cells. Lipids consisting of exosomal membrane are similar to those of cellular membrane, but some lipids seem to be actively enriched in exosomes, indicating a selective lipid loading system during exosome formation. Despite the importance and intriguing biological functions, the lipid composition of exosomes is less studied than other components due to technical difficulties. Here I summarize current knowledge and limitations of lipid studies of exosomes.