Engineering extracellular vesicles for disease therapy

Extracellular vesicles (EVs), as natural nanoscale delivery carriers, exhibit tremendous application potential owing to their excellent biocompatibility and low immunogenicity. However, native EVs suffer from two major bottlenecks, namely insufficient targeting capability and low loading efficiency of therapeutic molecules, which severely hinder their clinical translation. This framework distinguishes three complementary strategy categories: endogenous loading (intervention at the donor cell stage), exogenous engineering (intervention after EV separation), and in situ in vivo engineering (intervention within the living body). Together, these strategies delineate the technological evolution from ex vivo manipulation to in vivo programming. We thoroughly compare the technical principles, application scenarios, and limitations of each strategy, and highlight their representative preclinical applications in models of neurological disorders, cancer, and autoimmune diseases. In particular, this review focuses on two key frontiers: the synergistic mechanisms of combined multi-strategy approaches and the unique potential of in situ in vivo engineering as a next-generation translational platform. Finally, we provide forward-looking perspectives on the critical challenges facing different strategies in clinical translation, including scalable production for endogenous loading, quality control for exogenous engineering, and safety and precision control for in situ engineering, aiming to offer a systematic reference for the rational design of engineered EVs.