Researchers use genetically engineered tumor cell-derived exosomes for adjuvant co-delivery of cancer immunotherapy

For cancer immunotherapy via tumor antigen vaccination in combination with an adjuvant, major challenges include the identification of a particular tumor antigen and efficient delivery of the antigen as well as adjuvant to antigen-presenting cells. In this study, Kyoto University researchers proposed an efficient exosome-based tumor antigens-adjuvant co-delivery system using genetically engineered tumor cell-derived exosomes containing endogenous tumor antigens and immunostimulatory CpG DNA. Murine melanoma B16BL6 cells were transfected with a plasmid vector encoding a fusion streptavidin (SAV; a protein that binds to biotin with high affinity)-lactadherin (LA; an exosome-tropic protein) protein, yielding genetically engineered SAV-LA-expressing exosomes (SAV-exo). SAV-exo were combined with biotinylated CpG DNA to prepare CpG DNA-modified exosomes (CpG-SAV-exo). Fluorescent microscopic observation revealed the successful modification of exosomes with CpG DNA by SAV-biotin interaction. CpG-SAV-exo showed efficient and simultaneous delivery of exosomes with CpG DNA to murine dendritic DC2.4 cells in culture. Treatment with CpG-SAV-exo effectively activated DC2.4 cells and enhanced tumor antigen presentation capacity. Immunization with CpG-SAV-exo exhibited stronger in vivo antitumor effects in B16BL6 tumor-bearing mice than simple co-administration of exosomes and CpG DNA. Thus, genetically engineered CpG-SAV-exo is an effective exosome-based tumor antigens-adjuvant co-delivery system that will be useful for cancer immunotherapy.

Schematic representation of the preparation of CpG DNA-modified exosomes

exosomes

A plasmid DNA encoding a fusion protein of streptavidin (SAV), N-terminal secretion signal of lactadherin (LA) and C1C2 domain of LA (SAV-LA) was constructed. SAV–LA expressing exosomes (SAV-exo) were collected from the culture supernatants of B16BL6 cells transfected with the plasmid DNA. CpG DNA-modified exosomes (CpG-SAV-exo) were prepared by mixing SAV-exo and biotinylated CpG DNA.

Morishita M, Takahashi Y, Matsumoto A, Nishikawa M, Takakura Y. (2016) Exosome-based tumor antigens-adjuvant co-delivery utilizing genetically engineered tumor cell-derived exosomes with immunostimulatory CpG DNA. Biomaterials 111:55-65.[Epub ahead of print]. [abstract]

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