Abstract
Extracellular vesicles (EVs) released from tissues can be found in human biofluids. EVs reflect the phenotypic state of their cell of origin, carrying informative molecular biomarkers within and between tissues, and represent a promising target for liquid biopsy. However, the heterogeneity of EVs in their surface composition, luminal content, biogenesis and cellular origin poses a challenge for selective enrichment and validation of origin-specific EVs from the complex pool of circulating EVs. Another obstacle for translating EVs into liquid biopsy applications is the wide variety of separation and characterization methods, many of which lack standardization and reproducibility. In this review, we summarize current knowledge on tissue-specific EVs, highlighting their potential as indicators of tissue health and disease, as well as the existing challenges and limitations. From the existing literature, we identify a compelling need for better validation and reproducibility studies to support the development of tissue-specific EV applications. Identifying reliable tissue-enriched biomarkers, in particular, will be required to enable further insights into the physiology and pathology of EV source tissues. We also propose some considerations to address future guidelines on the topic. Together, these approaches will help to establish EV liquid biopsy applications as a keystone of translational medicine.