Table 2 Commonly used technique for the production of engineered Exos
From: Beneficial and challenges of exosome application in ischemic heart disease
Modification Type | Methodology | Description | Advantages | Limitations |
|---|---|---|---|---|
Interior modifications | Pre-isolation approaches | Modifications are done on donor cells before Exo isolation | Simple, and direct loading | Loading efficiency↓ |
Post-isolation approaches | Incorporating of target molecules after Exo isolation | Loading efficiency↑ | Injury to Exo integrity↑ | |
(a) Passive loading [177] | Isolated Exos are incubated with target compounds and these compounds are loaded into the Exos after membrane diffusion | Easy, and protect the Exo structure | Loading efficiency↓ | |
(a1) Active loading [178] | The Exo membrane is temporarily permeabilized to permit the cargo loading | Loading efficiency↑ | Needs complex protocols and instruments | |
(a2) Electroporation [179] | Induces pores in the Exo membrane | Loading efficiency↑ | Aggregation and possible injury to Exo integrity↑ | |
(a3) Extrusion [180] | The combination of Exos and target compounds is extruded through a membrane | Loading efficiency↑ | Needs extrusion instrument | |
Repeated freezing and thawing help the loading of target molecules into Exos | Applicable for sensitive and fragile compounds | Time-consuming, and the possibility of endogenous cargo loss, reduces the Exo number, and increases the Exo size | ||
(a5) Chemical transfection [182] | Using chemicals such as surfactants, pores are induced in the Exo membrane for cargo entry | Simultaneously various compounds can be loaded | Injury to Exo integrity↑ | |
Surface Modifications | Genetic engineering of donor cells [183] | Genetic modification of donor cells is done to up-/down-regulate specific molecules on the Exo surface | Applicable for enhanced delivery purposes | Needs complex and sophisticated gene editing approaches |
Direct manipulation | Direct modification is done on isolated Exos | Targeting delivery↑ | Injury to Exo integrity↑ | |
(a1) Covalent binding via click chemistry [184] | Covalent bonds are generated between target molecules and Exo surface | Specificity↑ | Needs specific chemical reactions and alters Exo integrity | |
(a2) Non-covalent approaches [185] | Approaches such as receptor-ligand binding or electrostatic interactions are applied | Simple | Stability of reaction↓ | |
(a3) Hybridization with fusogenic liposomes [186] | Exos and liposomes combination are used to increase delivery efficiency | Internalization rate↑ | Complexity↑ and requires two vesicle types | |
(a4) Direct hydrophobic component loading [187] | Incorporation of hydrophobic drugs onto Exos | Targeting delivery↑ | Only hydrophobic compounds can be used |