Immunomodulatory effects of exosomes: promising candidates in immunotherapy

Abstract

Exosomes are type of extracellular vesicles secreted from almost all cell types and carry numerous biological molecules such as nucleic acids, protein and lipids. They mediate many cellular processes including cellular communication and immune responses. Accumulating evidence suggests that these vesicles play a key role in the pathogenesis of inflammatory diseases, infectious diseases and many malignancies. The significant role of exosomes in cellular level also describe their intriguing potential in cancer therapeutics. The primary aim of this thesis is to identify the immunomodulatory roles of distinct exosome species and extend the knowledge of exosome utilization in immunotherapy. The exosomes purified from i) RAW264.7 (murine macrophage-like), ii) EG7 (murine T cell lymphoma), and iii) HUH7 (human hepatocellular carcinoma) had distinct characteristics as well as immunomodulatory features upon murine splenocyte stimulation either alone or in combination with poly(I:C) (a TLR3 ligand), R848(a TLR7/8 ligand), and CpG ODN(a TLR9 ligand). Strikingly, these cell line-derived exosomes displayed changing internalization kinetics by immune cells. Furthermore, the involvement of exosomes in the liver disease progression in the course of Hepatitis B virus (HBV) infection, cirrhosis and hepatocellular carcinoma (HCC) was investigated. As a result of patients’ exosome stimulation assays with healthy peripheral blood mononuclear cells (PBMCs) and murine splenocytes, patient plasma-derived exosomes had inflammatory effects correlated with the severity of liver damage suggesting that these exosomes might have a pathological role in liver disease progression and/or pathogenesis. In the final part, we used a dehydration-rehydration technique enabling external loading of desired Toll-like receptors (TLR) ligand within exosome and liposome. We developed a robust therapeutic vaccine delivery system in which injection of therapeutic vaccine to tumor burden animals enhanced anti-tumor activity and prolonged survival of HCC xenografts. In summary, this approach could broaden the immunotherapeutic utility of exosomes in the clinic.