In the past decade, extracellular vesicles
(EVs) have emerged as a key cell-free strategy for the
treatment of a range of pathologies, including cancer,
myocardial infarction, and inflammatory diseases. Indeed,
the field is rapidly transitioning from promising in vitro
reports toward in vivo animal models and early clinical
studies. These investigations exploit the high physicochemical
stability and biocompatibility of EVs as well as their
innate capacity to communicate with cells via signal
transduction and membrane fusion. This review focuses
on methods in which EVs can be chemically or biologically
modified to broaden, alter, or enhance their therapeutic
capability. We examine two broad strategies, which have
been used to introduce a wide range of nanoparticles, reporter systems, targeting peptides, pharmaceutics, and functional
RNA molecules. First, we explore how EVs can be modified by manipulating their parent cells, either through genetic or
metabolic engineering or by introducing exogenous material that is subsequently incorporated into secreted EVs. Second,
we consider how EVs can be directly functionalized using strategies such as hydrophobic insertion, covalent surface
chemistry, and membrane permeabilization. We discuss the historical context of each specific technology, present
prominent examples, and evaluate the complexities, potential pitfalls, and opportunities presented by different reengineering
strategies.