<i>XCL1</i> / <i>Glypican-3</i> Fusion Gene Immunization Generates Potent Antitumor Cellular Immunity and Enhances Anti–PD-1 Efficacy

Abstract

Cancer vaccines can amplify existing antitumor responses or prime naïve T cells to elicit effector T-cell functions in patients through immunization. Antigen-specific CD8⁺ T cells are crucial for the rejection of established tumors. We constructed XCL1-GPC3 fusion molecules as a liver cancer vaccine by linking the XCL1 chemokine to glypican-3 (GPC3), which is overexpressed in hepatocellular carcinoma (HCC). Cells expressing XCL1-GPC3 chemoattracted murine XCR1⁺CD8α⁺ dendritic cells (DC) and human XCR1⁺CD141⁺ DCs <i>in vitro</i> and promoted their IL12 production. After subcutaneous <i>mXcl1-GPC3</i> plasmid injection, mXCL1-GPC3 was mainly detected in CD8α⁺ DCs of mouse draining lymph nodes. XCL1-GPC3-targeted DCs enhanced antigen-specific CD8⁺ T-cell proliferation and induced the <i>de novo</i> generation of GPC3-specific CD8⁺ T cells, which abolished GPC3-expressing tumor cells in mouse and human systems. We immunized a murine autochthonous liver cancer model, with a hepatitis B background, with the <i>mXcl1-GPC3</i> plasmid starting at 6 weeks, when malignant hepatocyte clusters formed, or at 14 weeks, when liver tumor nodules developed, after diethylnitrosamine administration. <i>mXcl1-GPC3</i>-immunized mice displayed significantly inhibited tumor formation and growth compared with <i>GPC3</i>-immunized mice. After <i>mXcl1-GPC3</i> immunization, mouse livers showed elevated production of IFNγ, granzyme B, IL18, CCL5, CXCL19, and <i>Xcl1</i> and increased infiltration of GPC3-specific CD8⁺ T cells, activated natural killer (NK) cells, and NKT cells. The antitumor effects of these immune cells were further enhanced by the administration of anti-PD-1. Anti-HCC effects induced by hXCL1-GPC3 were confirmed in an HCC-PDX model from 3 patients. Thus, XCL1-GPC3 might be a promising cancer vaccine to compensate for the deficiency of the checkpoint blockades in HCC immunotherapy.