Quantitative Assessment of shRNA Loading and Delivery Efficiency of Engineered Extracellular Vesicles

RNA interference (RNAi) therapeutics enable selective silencing of disease-associated genes. Yet, their clinical application remains largely confined to the liver due to extrahepatic delivery constraints of current platforms such as GalNAc conjugates and lipid nanoparticles. Extracellular vesicles (EVs) offer an attractive alternative delivery strategy owing to their biocompatibility, ability to traverse biological barriers, and amenability to engineering. However, EV-mediated RNA delivery is limited by inefficient endogenous RNA loading and poor cytosolic release following uptake. Here, we establish a modular EV-based platform that addresses both challenges by integrating enhanced endogenous shRNA loading with fusogen-mediated cytosolic delivery. Using Argonaute 2 (AGO2)-assisted loading, we substantially increase shRNA copy numbers per vesicle (up to 3.7 copies/EV) and enable quantitative, molecule-resolved assessment of delivery potency. Engineered EVs achieve robust and reproducible shRNA-mediated gene silencing with picomolar IC50 values across multiple cell types and induce significant target knockdown in the mouse brain following intracerebral administration. Together, these findings demonstrate that coordinated engineering of shRNA loading and cytosolic release can overcome key limitations of EV-mediated small RNA delivery.