The use of exosomes in clinical settings is progressively becoming a reality, as clinical trials testing exosomes for diagnostic and therapeutic applications are generating remarkable interest from the scientific community and investors. Exosomes are small extracellular vesicles secreted by all cell types playing intercellular communication roles in health and disease by transferring cellular cargoes such as functional proteins, metabolites and nucleic acids to recipient cells. An in-depth understanding of exosome biology is therefore essential to ensure clinical development of exosome based investigational therapeutic products.
University College London researchers summarize the most up-to-date knowledge about the complex biological journey of exosomes from biogenesis and secretion, transport and uptake to their intracellular signaling. They delineate the major pathways and molecular players that influence each step of exosome physiology, highlighting the routes of interest, which will be of benefit to exosome manipulation and engineering. They highlight the main controversies in the field of exosome research: their adequate definition, characterization and biogenesis at plasma membrane. The researchers also delineate the most common identified pitfalls affecting exosome research and development. Unravelling exosome physiology is key to their ultimate progression towards clinical applications.
 Exosomes are generated through the formation of ILVs in the late endocytic pathway and  gets secreted via exocytosis from the plasma membrane. Upon reaching the target recipient cell,  exosomes either interact with the surface molecules of recipient cell to induce downstream signalling or  fuse with the plasma membrane to release their contents into cytosol or  get internalised via various routes.  Upon internalisation, exosomes are addressed in the early endosome, then late endosomes or MVBs and undergo multiple fates.  The exosome contents can get released into the nucleus or ER,  leak into cytosol or  get degraded in the lysosomes.  Another possibility include release back to the extracellular space through the recycling endosome. ILV: Intraluminal Vesicles; EE: Early Endosomes, RE: Recycling endosomes, MVB: Multivesicular Bodies, ER: Endoplasmic Reticulum