Table 3.

Challenges of TDEVs in constructing drug-carrying systems.

Aspects	Challenges	Solutions
Cell culture	Large-scale cultivation costs are high.	Choose the appropriate parental cell and culture method 5.
	There are many impurities in the culture solution that are not easy to separate 2.	Closely monitor gene stability and the influence of contaminants during the cultivation process.
Method of isolation	The biological environment in which TDEVs exist may contain other impurities, such as cell debris, which affect purity. Further interfere with the determination, or cause the quality of the preparation to decrease 6.	Should be extracted multiple times, or combined with different methods of extraction and purification. Try to purify to remove interfering substances.
	The content of TDEVs is small and the concentration is low. It takes more cost to extract the required amount 7.	Improve the efficiency of the extraction method and choose a method with a relatively high sensitivity.
	Excessive operation time or some extraction methods based on the surface components of TDEVs may destroy the integrity of TDEVs.	Choose the appropriate method according to the needs of DDS construction, sample type, impurity type, etc 8.
Drug loading method	The drug loading process involves damage to the vesicle membrane, or changes in certain physical and chemical properties, which may affect the safety of the preparation 198.	During the drug loading process, attention should be paid to changes in membrane proteins to avoid causing immune reactions. Conduct comprehensive clinical trials to ensure its safety.
	Due to the biological function of TDEVs in cancer progression, it may promote the occurrence and development of tumors.	Design a DDS whose therapeutic effect is greater than that of cancer promotion, and conduct experiments to verify that the DDS is mainly therapeutic.
Transport and storage	Higher temperatures may cause structural damage to the vesicles and reduce the effective load 199.	Store below -80℃.
Targeting	Insufficient targeting, the accumulation of drugs at the tumor site cannot reach an effective concentration.	Fully consider factors such as tumor cells and cell activity in the tumor microenvironment, tissue homing ability, immunogenicity, and carcinogenicity, and select appropriate parental cells. In addition, surface modification can also improve the targeting of DDS.
	The protective effect of biological barriers.	Construct DDS that can pass through biological barriers and overcome its hindrance in drug delivery. However, care should be taken to avoid its accumulation in the barrier and produce toxic side effects 200.
	There is an accumulation of drugs in non-tumor areas.	Choose appropriate drugs and DDS construction methods to reduce side effects.
	The introduction of a large number of exogenous EVs may affect the signal transduction function of endogenous EVs, leading to disorder of information transmission.	Conduct comprehensive clinical trials to ensure its safety.