Resistance to chemotherapy remains a major obstacle for the effective treatment of oral squamous cell carcinoma (OSCC).Evidence for the involvement of exosomes as important regulators of cisplatin chemoresistance in OSCC is still poorly understood.Our objective of this study was to explore the roles for exosomes in modulating key cellular pathways mediating response to chemotherapy.We first developed the cisplatin-resistant cell lines (HSC-3-R and SCC-9-R) and found that the conditioned media from cisplatin-resistant OSCC cells enhanced the chemoresistance of parental OSCC cell.The release of exosomes was blocked by inhibitor (GW4869) and exosomes were found to be involved in the chemoresistance of parental OSCC cell transferred from resistant cells.The exosomes derived from resistant cells and parental cells were isolated.Then,the isolated exosomes were characterized and quantified by electron microscopy,qNano analysis,and weste blot analysis.Exosomes derived from cisplatin-resistant OSCC cells were found to enhance the chemoresistance of OSCC cell and decrease the DNA damage signaling in response to cisplatin.It was also found that exosomes derived from cisplatin-resistant OSCC cells transferred miR-21 to OSCC parental cells and induced cisplatin resistance by targeting phosphatase and tensin homolog and programmed cell death 4.Furthermore,the roles of cisplatin-resistant OSCC cells-derived exosomes in vivo were confirmed by subcutaneous xenograft mouse model.Collectively,the results suggest that exosomes released from cisplatin-resistant OSCC cells transmit miR-21 to induce cisplatin resistance of OSCC cells.