Vaccine Based on Dendritic Cells Electroporated with an Exogenous Ovalbumin Protein and Pulsed with Invariant Natural Killer T Cell Ligands Effectively Induces Antigen-Specific Antitumor Immunity.

(1) Background: Cancer vaccines are administered to induce cytotoxic CD8 T cells (CTLs) specific for tumor antigens. Invariant natural killer T (iNKT) cells, the specific T cells activated by α-galactosylceramide (α-GalCer), play important roles in this process as they are involved in both innate and adaptive immunity. We developed a new cancer vaccine strategy in which dendritic cells (DCs) were loaded with an exogenous ovalbumin (OVA) protein by electroporation (EP) and pulsed with α-GalCer. (2) Methods: We generated bone marrow-derived DCs from C57BL/6 mice, loaded full-length ovalbumin proteins to the DCs by EP, and pulsed them with α-GalCer (OVA-EP-galDCs). The OVA-EP-galDCs were intravenously administered to C57BL/6 mice as a vaccine. We then investigated subsequent immune responses, such as the induction of iNKT cells, NK cells, intrinsic DCs, and OVA-specific CD8 T cells, including tissue-resident memory T (T) cells. (3) Results: The OVA-EP-galDC vaccine efficiently rejected subcutaneous tumors in a manner primarily dependent on CD8 T cells. In addition to the OVA-specific CD8 T cells both in early and late phases, we observed the induction of antigen-specific T cells in the skin. (4) Conclusions: The OVA-EP-galDC vaccine efficiently induced antigen-specific antitumor immunity, which was sustained over time, as shown by the T cells.