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 1-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 by using antigen coding mRNA or tumor peptide is common, 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 as a simple method to deliver the antigen into the vector for iNKT cell activation.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 and innate immunity.

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 24 hours before cultured with LPS. 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). We evaluated the tumor size and the survival rate. We also evaluated the innate immunity which induced by α-Gal loaded DCs with or without electroporated OVA.

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 < 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 < 0.05). On the other hand, α-Gal loaded DCs with or without electroporated OVA showed no difference in inducing NK cells. But, they either induced more NK cells than α-Gal unloaded DCs(P < 0.05).

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. Also, EP didn't impair the ability of inducing innate immunity. 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, Kouta Yamada, Kyosuke Agawa, Takashi Kamigaki, Rishu Takimioto, Yoshihiro Kakeji. Antigen electroporated DC loaded with NKT-cell ligand induces the antigen specific antitumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 698.