Abstract 2360: GP350 containing exosomes as DNA vaccine carriers

Abstract

Abstract Background: Plasmid DNA vaccination is a safe and economical vaccine modality that has been demonstrated to elicit cellular and humoral immunity in preclinical models and human clinical trials. We have previously shown that enriched mature naive B cells, and not myeloid/DC lineages, are capable of expanding Ag specific CD8 T cells in vivo in mice, and in vitro with human cells. In this study, we sought a means to directly deliver plasmid DNA to B cells as a means to specifically activate this antigen-presenting cell type. Methods: Exosomes were isolated from EBV+ lymphoblastic cell lines (LCL) and from HEK293T cells that had been transfected to express the EBV protein GP350. Plasmid DNA was labeled with a fluorescent peptide nucleic acid (PNA) probe for detection by imaging and conventional cytometry. Exosomes were transfected with fluorescently labeled plasmid DNA and incubated with either human CD21 transgenic mouse splenocytes or human PBMC and assayed for uptake and activation by FACS. Plasmid DNA transfected exosomes were coincubated with human PBMC and evaluated for their ability to expand antigen-specific CD8+ T cells by different methods. Results: EBV LCL and HEK293T derived exosomes were successfully transfected with plasmid DNA as verified by image assisted flow cytometry. Transient transfection of HEK293T cells with plasmids encoding a transgene led to release of exosomes containing the transgene product. EBV LCL and HEK 293T-GP350 derived exosomes increased delivery of plasmid DNA to both human B lymphocytes and transgenic hCD21 mouse B lymphocytes, when compared to naked DNA alone, in an hCD21 dependent fashion. At 24h, plasmid DNA containing B lymphocytes exhibited increased activation and upregulation of CD80/86 costimulatory molecules. Further, human B lymphocytes treated with exosome-plasmid DNA complexes led to antigen mRNA production and expansion of Ag specific CD8 T cells without the need for APC subset enrichment. Studies comparing the immunogenicity of GP350-exosome mediated delivery versus naked DNA delivery are underway in different mouse models. Conclusion: GP350 containing exosomes can successfully increase delivery of plasmid DNA to B lymphocytes even in the presence of other phagocytic cells like macrophages or dendritic cells. This led to detectable antigen production and expansion of cognate Ag specific CD8 T cell expansion without the need for B cell enrichment. Studies examining in vivo immunogenicity of exosomal plasmid DNA delivery are underway, but results to date suggest this approach may be a simple method to boost vaccine efficacy through increased delivery of DNA directly to relevant antigen-presenting B cells. Citation Format: Viswa Teja Colluru, Douglas G. McNeel. GP350 containing exosomes as DNA vaccine carriers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2360.