Plenty of immune cells infiltrate into the tumor microenvironment (TME) during tumor progression, in which myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells with immunosuppressive activity. Tumor cells and stromal cells facilitate the activation and expansion of MDSCs in TME via intercellular communication, and expanded MDSCs suppress anti-tumor immune responses through direct and indirect mechanisms. Currently, exosomes, which are a kind of extracellular vesicles (EVs) that can convey functional components, are demonstrated to participate in the local and distal intercellular communication between cells. Numerous studies have supposed that tumor-derived exosomes (TEXs), whose assembly and release can be modulated by TME, are capable of modulating the cell biology of MDSCs, including facilitating their activation, promoting the expansion, and enhancing the immunosuppressive function. Therefore, in this review, we mainly focus on the role of TEXs in the cell-cell communication between tumor cells and MDSCs, and discuss their clinical applications.

MicroRNAs (miRNAs) are a class of short, single-stranded, noncoding RNAs, with a length of about 18–22 nucleotides. Extracellular vesicles (EVs) are derived from cells and play a vital role in the development of diseases and can be used as biomarkers for liquid biopsy, as they are the carriers of miRNA. Existing studies have found that most of the functions of miRNA are mainly realized through intercellular transmission of EVs, which can protect and sort miRNAs. Meanwhile, detection sensitivity and specificity of EV-derived miRNA are higher than those of conventional serum biomarkers. In recent years, EVs have been expected to become a new marker for liquid biopsy. This review summarizes recent progress in several aspects of EVs, including sorting mechanisms, diagnostic value, and technology for isolation of EVs and detection of EV-derived miRNAs. In addition, the study reviews challenges and future research avenues in the field of EVs, providing a basis for the application of EV-derived miRNAs as a disease marker to be used in clinical diagnosis and even for the development of point-of-care testing (POCT) platforms.

Exosomes are membrane nanovesicles carrying molecular information that may reflect the biological and genetic characteristics of their parent cells. Numerous studies have demonstrated the potential of exosomes as noninvasive cancer biomarkers. Hence, specific detection of cancer cell-derived exosomes is of significant importance. Here, we developed a fluorescence assay for the determination of gastric cancer exosomes based on branched rolling circle amplification (BRCA) and an aptamer to target specific exosomes. The designed padlock probe was cyclized after incubation with an aptamer binding with the target exosome. BRCA was triggered by adding a second primer and the resulting long tandem double-stranded DNA product was detected using SYBR Green I as the fluorescent dye. This method demonstrated a high specificity for target exosomes with a detection limit of 4.27 × 10⁴ exosomes per mL. Moreover, plasma from gastric cancer patients was tested to verify the clinical applicability of this assay. Our results demonstrated that this aptamer-based biosensor may show potential for the early diagnosis of gastric cancer.