Abstract 6534: Antigen specific antitumor effect induced by antigen-electroporated, natural killer T cell ligand-loaded dendritic cells
Authors: Watanabe Akihiro , Yamashita Kimihiro , Arimoto Akira , Sugita Yutaka , Fukuoka Eiji , Kamigaki Takashi , Takimoto Rishu , Kakeji Yoshihiro 
Published: September 2020

Background: Invariant natural killer T (iNKT) cells have been shown as an ideal immunotherapeutic target of which the activation via α-galactosylceramide (α-Gal) conjugated with the MHC class I- like CD1d molecule induces both innate and adaptive immune system. With transfection of antigen information, α-Gal loaded CD1d expressing cells can act as a vector to enhance the antigen specific immune responses. Though transfection of antigen information coded as mRNA is popular, the process of extracting mRNA or identifying tumor peptide is sometimes too complicated. Electroporation (EP) has been reported as a way to induce substances easily into cells. We applied EP to deliver the antigen into the vector for iNKT cell activation just as a simple procedure. In this study, we aimed to show a feasibility of EP as a method to deliver the antigen into α-Gal loaded dendritic cells (DCs), a naturally CD1d expressing vector, in terms of inducing antigen specific antitumor responses.

Methods: DCs were generated from bone marrow of C57BL/6 mice. Ovalbumin (OVA) was electroporated to DCs as a tumor model antigen. To load α-Gal, DCs were cultured with α-Gal for 48 hours. We compared the antitumor responses of α-Gal loaded DCs with or without electroporated OVA in C57BL/6 mice. In subcutaneous tumor model, mice were prophylactically administered each type of DCs intravenously followed by subcutaneous injection of EG7, which is OVA induced EL4, thymoma (n = 5, respectively). We evaluated the tumor size and the survival rate. We also evaluated the antitumor responses of which EP density of OVA can induce efficient antitumor response.

Results: With electroporated OVA, tumors didn't grow in mice administered α-Gal loaded DCs whereas tumors in mice administered α-Gal loaded DCs without electroporated OVA aggressively progressed (P &lt; 0.05). In mice administered α-Gal loaded DCs with electroporated OVA, no death was observed during the whole observation period. Survival rate was significantly better for mice administered α-Gal loaded DCs with electroporated OVA than those administered α-Gal loaded DCs without electroporated OVA (P &lt; 0.05). The α-Gal loaded DCs also induce more memory progenitor cells than control group (P &lt; 0.01).

Conclusion: α-Gal loaded DCs with electroporated OVA showed significantly higher rate of tumor rejection and longer survival in the mice model inoculated OVA-induced tumor comparing to α-Gal loaded DCs without electroporated OVA. EP was feasible as a way to deliver the antigen into the vector which induced antigen specific antitumor responses. We are trying to show the activity of antigen-specific cytotoxic T lymphocytes following the administration of α-Gal loaded DCs with electroporated antigen.

Citation Format: Akihiro Watanabe, Kimihiro Yamashita, Akira Arimoto, Yutaka Sugita, Eiji Fukuoka, Takashi Kamigaki, Rishu Takimoto, Yoshihiro Kakeji. Antigen specific antitumor effect induced by antigen-electroporated, natural killer T cell ligand-loaded dendritic cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6534.