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Figure 2. Platform technologies for therapeutic exosomes can be categorized into three subtypes. (A) Naïve exosomes are isolated from different types of cultured cells including stem cells and immune cells. The major limitation of this method is the control over type and amount of cargo molecules. (B) The direct cargo-loading method uses ex vitro stimulations after exosome isolation. Limitations with this method include exosome stability, productivity, and the size of the cargo molecules. (C) In the indirect cargo-loading method, selected and specific macromolecules can be loaded into exosomes by engineering producer cells. Currently, this technique is not only used for loading therapeutic macromolecules but also for targeting specific tissues and organs.