Exosomes are small vesicles with an average diameter of 100 nm that are produced by many, if not all, cell types. Exosome cargo includes lipids, proteins, and nucleic acids arranged specifically in the endosomes of donor cells. Exosomes can transfer the donor cell components to target cells and can affect cell signaling, proliferation, and differentiation. Important new information about exosomes' remote communication with other cells is rapidly being accumulated. Recent data indicates that the results of this communication depend on the donor cell type and the environment of the host cell. In the field of cancer research, major questions remain, such as whether tumor cell exosomes are equally taken up by cancer cells and normal cells and whether exosomes secreted by normal cells are specifically taken up by other normal cells or also tumor cells. Furthermore, we do not know how exosome uptake is made selective, how we can trace exosome uptake selectivity, or what the most appropriate methods are to study exosome uptake and selectivity. This review will explain the effect of exosome source and the impact of the donor cell growth environment on tumor and normal cell interaction and communication. The review will also summarize the methods that have been used to label and trace exosomes to date.
Keywords: exosomes; liquid biopsy; nanoparticle (NPs); normal cell-derived exosomes; tumor cell-derived exosomes.