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Figure 1. Examples of practical applications of BEVs and the potential impact of heterogeneity in their production and activities. (This figure was created using Figdraw). The figure shows examples of four application areas of BEVs and how their heterogeneity affects these applications. Vaccine manufacturing: An example is the direct use of BEVs derived from Neisseria meningitidis in vaccine production. Another example involves using BEVs as a vector for heterologous antigens. In this case, proteins from group A and B streptococci are fused with E. coli OmpA guide sequences, which are then expressed in the lumen of E. coli-derived BEVs, resulting in BEVs containing proteins from group A and B streptococci for use in vaccine production. Inflammation and immune response: The ability of LEV to promote the differentiation of monocytes into M2 macrophages in human THP-1 cells has been shown to play a role in anti-inflammation responses. Tumor imaging: BEVs were labeled with Cy7. In vivo fluorescence imaging showed that in addition to the high levels of BEV aggregation observed at the tumor site, different levels of BEV aggregation were also detected in the spleen, liver, heart, kidneys, lungs, and intestines. Drug delivery: The figure highlights two key aspects of drug delivery using BEVs - drug loading and biosafety. The drug loading section demonstrates that creating a pH gradient and adding cholesterol to drug-loaded vesicles can greatly improve the encapsulation efficiency of DOX. The biosafety section shows that LPS on the surface of BEVs can affect the human nervous system and cause heat generation, raising potential safety concerns in drug delivery applications. BEVs: Bacterial extracellular vesicles; LEV: BEVs derived from Lactobacillus plantarum; Cy7: a fluorescent dye; DOX: doxorubicin; LPS: lipopolysaccharides; DOX: doxorubicin; M2: macrophages: alternatively activated macrophages.