Exosomes – Vehicles of Intercellular Signaling, Biomarkers, and Vectors of Cell Therapy.

Typical structure and content of exosomes. Exosomes are surrounded by a phospholipid bilayer and contain proteins, such as annexins, that are important for transport; tetraspanins for cell targeting; and other proteins, such as Alix and TSG101, that are involved in exosomal biogenesis from endosomes. Abbreviations: ERMs, ezrin/radixin/moesin proteins; FLOT1, flotillin 1; HSP, heat shock protein; MHC, major histocompatibility complex; Rab GDI, Rab GDP-dissociation inhibitor; RAP 1B, Ras-related protein 1B; TSG101, tumor susceptibility gene 101

Mesenchymal stem cells (MSCs), whose mechanism of action is predominantly paracrine, are being widely tested for the treatment of a variety of human diseases. No one factor has been proven sufficient to mediate the therapeutic effects of MSCs. However, exosomes-membrane vesicles secreted by many cells, including MSCs-are appealing candidates as vectors of their efficacy. Exosomes can transport and deliver a large cargo of proteins, lipids, and nucleic acids and can modify cell and organ function. In addition to their key role as vehicles of intercellular communication, exosomes are increasingly recognized as biomarkers and prognosticators of disease. Moreover, they have the potential to be used as vehicles of gene and drug delivery for clinical application. In this article, the author reviews the biogenesis of exosomes, their molecular composition, and their role as messengers of intercellular communication, focusing on their potential as therapeutic vectors for stem cell therapy.