Advanced ovarian cancer: exploiting exosomes to potentiate the anti-cancer immune response

Simone Pisano, Yajaira S. Jimenez, Gareth D. Healey, R. Steven Conlan, Bruna Corradetti

Advanced metastatic ovarian cancer (OC) accounts for over 75% of diagnosed ovarian malignancies. Despite advances in surgery and chemotherapy, OC remains the most frequent cause of death from a gynecologic malignancy, mainly due to diagnosis at late stage, recurrence, and resistance to chemotherapeutic agents. The high vessel permeability and compromised lymphatic drainage associated with advanced OC result in ascites buildup within the peritoneal cavity, which hinders delivery of cancer therapeutics to target sites and creates an immunosuppressive tumor micro-environment. To overcome transport barriers and boost the anti-cancer immune response we aimed at harnessing the potential of exosomes released by dendritic cells (DC)-based vaccines (Dex). Dex were collected from DC pulsed with whole tumor antigen lysates from an ovalbumin-overexpressing cancer cell line (ID8-OVA) and characterized in terms of yield and size distribution by Nanoparticle Tracking Analysis. Their biomolecular features, including the expression of MHC-II, co-stimulatory markers (CD80 and CD86) and the processed antigen OVA, were determined by flow cytometry and western blot and compared to parental cells. Functional assays were performed to demonstrate the effectiveness of Dex in activating the proliferation of OVA-specific T cells (isolated from OT-I mice) ex vivo. Dex biodistribution and efficacy in vivo was evaluated in a metastatic OC mouse model. Data obtained showed that Dex retain the biomolecular moieties of their parental cells. The presence of OVA on their surface was sufficient to activate an anti-tumor immune response as demonstrated in vitro. An increase in the percentage of CD8+ cells was shown by flow cytometry, concomitantly with the release of higher levels of interferon-g (IFN-g) detected by ELISpot. Dex preferentially accumulated in the metastatic nodules found across the peritoneal membrane, in abdominal organs (i.e., intestine, liver), and effectively penetrated into lymph nodes, where they activated an antitumor immune response. Our preliminary studies demonstrate that exosomes offer advantages over traditional cancer vaccines: i) due to their small size (30-150nm), they penetrate across lymphatic vessels and tumor interstitium to reach target organs, ii) exosomes derived from DC vaccines meet an immunosuppressive environment without losing their activity, iii) inflammatory cytokines in DC vaccine-derived exosomes will serve as chemo-attractants to entice T cell infiltration in target organs.

Authors declare no conflict of interest.

Acknowledgements:

BC acknowledges support through the Sêr Cymru II scheme, funded by the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement No. 663830, the Welsh European Funding Office (WEFO) under the European Regional Development Fund (ERDF) and Houston Methodist Research Institute. Additional support for the study was provided by the Golfers Against Cancer Foundation.