Engineered exosomes for targeted drug delivery. (A) Schematic diagram of production, acquisition, and re-administration of targeted self-exosomes for the delivery of genes. Reprinted with permission from Ref. [189]. Copyright 2011, Nature Publishing Group. (B) Schematic diagram of how the engineered exosomes are delivered and the process of chemo-photothermal synergistic tumor therapy. Reprinted with permission from Ref. [218]. Copyright 2018, Wiley. (C) Schematic diagram of construction and delivery of drug-loaded superparamagnetic nanoparticles-labeled exosomes. Reprinted with permission from Ref. [224]. Copyright 2016, American Chemical Society. (D) Schematic illustration of the design of functionalized exosomes for drug targeted delivery. Reprinted with permission from Ref. [225]. Copyright 2017, American Chemical Society.