CD44+ and CD133+ Extracellular Vesicles as Future Potential Targets in Gastrointestinal Tumor

Extracellular vesicles (EVs) are small nanometric particles surrounded by a lipid bilayer and actively secreted by different cell types. EVs play a key role in cell-to-cell communication, and the vast array of biomolecules that EVs transport reflects the molecular profile of the originating cells. In cancer, EVs are key components of the tumor microenvironment (TME); meanwhile once released into the peripheral circulation, EVs can travel systemically and transmit signals beyond the primary tumor site, making EVs ideal candidates for liquid biopsy. Notably, EVs can be isolated from a blood sample and analyzed to obtain real-time information on tumor biology, enabling early diagnosis, monitoring of treatment response, and evaluation of disease evolution, with high sensitivity and specificity. This review examines the biological significance and clinical utility of EVs expressing the stemness-associated glycoproteins CD44 and CD133 in gastrointestinal (GI) malignancies. Cancer stem cells (CSCs) expressing these surface markers are known to exhibit enhanced tumorigenic potential, metastatic capacity, and therapy resistance. In particular, we focus on the increasing evidence that EVs enriched in CD44+ and CD133+ populations play critical roles in key aspects of tumor progression in cholangiocarcinoma, pancreatic, colorectal, and gastric cancers. Following internalization by recipient cells, CD44+ and CD133+ EVs drive phenotypic reprogramming, foster more aggressive cellular states, and promote chemoresistance by delivering specific molecular cargo. Mechanistically, CD44 isoforms, particularly CD44v6 and CD44v9, activate key oncogenic signaling pathways, including Wnt/β-catenin and phosphoinositide 3-kinase (PI3K)/serine/threonine kinase AKT (AKT). In parallel, CD133-enriched EVs help maintain stemness and contribute to TME reorganization, thereby facilitating tumor progression. Despite ongoing challenges in EV isolation and standardization, EVs positive for stemness markers show great potential as liquid biopsy analytes for noninvasive disease monitoring, prognostic evaluation, and patient stratification. This review summarizes the expanding body of knowledge on cancer stem cell (CSC)-derived EVs in GI tumors, underscoring the potential of these particles for early diagnosis, prognosis, and the development of targeted therapies to overcome treatment resistance.