Mesenchymal Stem Cell-derived Extracellular Vesicles: Toward Cell-free Therapeutic Applications

Abstract

Mesenchymal stem (stromal) cells (MSCs) are multipotent cells with the ability to differentiate into several cell types, thus serving as a cell reservoir for regenerative medicine. Much of the current interest in therapeutic application of MSCs to various disease settings can be linked to their immunosuppressive and anti-inflammatory properties. One of the key mechanisms of MSC anti-inflammatory effects is the secretion of soluble factors with paracrine actions. Recently it has emerged that the paracrine functions of MSCs could, at least in part, be mediated by extracellular vesicles (EVs). EVs are predominantly released from the endosomal compartment and contain a cargo that includes miRNA, mRNA, and proteins from their cells of origin. Recent animal model-based studies suggest that EVs have significant potential as a novel alternative to whole cell therapies. Compared to their parent cells, EVs may have a superior safety profile and can be safely stored without losing function. In this article, we review current knowledge related to the potential use of MSC-derived EVs in various diseases and discuss the promising future for EVs as an alternative, cell-free therapy.

Figure 1

EVs origin and internalization. Origin of EVs are generally via (a) endocytosis or inward budding of plasma membrane that consist of lipid rafts and is mediated by clathrin-dependent or caveolae-dependent pathway, This gives rise to (b) early endosomes leading to the formation of numerous ILVs within a membrane maturing to MVBs. Finally MVBs fuse with plasma membrane releasing ILVs as exosomes. (c) Ectosomes are vesicles shed from the cell surface and (d) apoptotic bodies are also known as apobodies and are released by cells undergoing apoptosis. EVs are internalized by the target cells through several pathways including (e) endocytosis, (f) fusion, and (g) phagocytosis.

Figure 2

Potential clinical applications of EVs. Therapeutic benefits and mechanisms of action of MSC-derived EVs in: (a) various heart conditions, (b) kidney injury, (c) liver injury, (d) lung injury, and (e) wound healing.