Platform technologies and human cell lines for the production of therapeutic exosomes

Abstract

Exosomes are extracellular vesicles secreted by most cell types and represent various biological properties depending on their producing cells. They are also known to be important mediators of intercellular communication. Recent data suggest that exosomes can mediate the therapeutic effects of their parental cells; hence, they have been in the spotlight as novel therapeutics. To develop and manufacture effective therapeutic exosomes, customized strategies are needed to use appropriate technologies for exosome engineering and to select suitable production cell lines. In this review, we provide an overview of currently available exosome engineering platform technologies for loading active pharmaceutical ingredient cargo and the types of human cells/cell lines that are being used as exosome-producing cells, particularly focusing on their characteristics, advantages, and disadvantages.

Keywords: HEK293; Therapeutic exosome; dendritic cells; exosome engineering technologies; human cells; stem cells.

Figure 1

Schema describing biogenesis of exosomes. Biogenesis of exosomes starts with the first invagination of plasma membrane of the producing cells, followed by the formation of early endosomes. Then, the cytosolic components (nucleic acids and proteins) are loaded into ILVs of the late endosomes through the second invagination. After the maturation of MVBs, some components undergo degradation by fusion with lysosomes, while others are secreted into the extracellular fluids as “exosome”. Exosomes enter the recipient cells via various mechanisms, such as endocytosis, phagocytosis, lipid raft, macropinocytosis, and direct fusion. After being taken up by the recipient cells, exosomes fuse with early endosomes and release their cargos into the intracellular area by disintegration. Other parts of the exosomes either are released back to the extracellular fluid by fusion with transmembrane or get degraded by lysosomes. ILVs: intraluminal vesicles; MVBs: multivesicular bodies.

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.