Extracellular vesicles as drug delivery systems: Why and how?

Over the past decades, a multitude of synthetic drug delivery systems has been developed and introduced to the market. However, applications of such systems are limited due to inefficiency, cytotoxicity and/or immunogenicity. At the same time, the field of natural drug carrier systems has grown rapidly. One of the most prominent examples of such natural carriers are extracellular vesicles (EVs). EVs are cell-derived membranous particles which play important roles in intercellular communication. EVs possess a number of characteristics that qualify them as promising vehicles for drug delivery. In order to take advantage of these attributes, an in-depth understanding of why EVs are such unique carrier systems and how we can exploit their qualities is pivotal. Here, we review unique EV features that are relevant for drug delivery and highlight emerging strategies to make use of those features for drug loading and targeted delivery.