Not All EVs Are Equal: Functional Heterogeneity of Extracellular Vesicles in Neuroregenerative Therapies

Extracellular vesicles (EVs) are increasingly being investigated as cell-free therapies for neurological diseases. However, their clinical application remains limited by biological and functional heterogeneity. EVs should therefore not be considered as a single, uniform therapeutic product defined only by their cell of origin, size, or conventional vesicle classification. EV composition and activity are influenced by extrinsic factors, including donor and tissue source, culture conditions, and isolation procedures, as well as by intrinsic mechanisms of vesicle biogenesis and selective cargo loading. Some vesicles may have beneficial therapeutic effects, whereas others may show little biological activity or act on unintended cellular targets. For this reason, EVs may be better classified according to biological function rather than only physical properties or cellular origin. A functionality-based classification could improve potency assessment, dose selection, reproducibility, and the development of consistent EV-based products. EV properties can be modulated by selecting appropriate parental cells, modifying culture conditions, or using genetic or metabolic engineering to alter EV production and cargo. Single-vesicle approaches can reveal differences between EV subpopulations and identify those responsible for specific biological effects. Overall, understanding EV heterogeneity may provide a rational basis for developing reproducible and disease-specific EV therapies for neurological and neurodegenerative disorders.