XCL1/glypican-3 fusion gene immunization generates potent antitumor cellular immunity and enhances anti-PD1 efficacy

Cancer vaccines can amplify existing antitumor responses or prime naive 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+DCs and human XCR1+CD141+DCs in vitro and promoted their IL-12 production. After subcutaneous mXcl1-GPC3 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 de novo 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 mXcl1-GPC3 plasmid starting six weeks, when malignant hepatocyte clusters formed, or 14 weeks, when liver tumor nodules developed, after diethylnitrosamine administration. mXcl1-GPC3 immunized mice displayed significantly inhibited tumor formation and growth compared to GPC3-immunized mice. After mXcl1-GPC3 immunization, mouse livers showed elevated production of IFNγ, granzyme B, IL-18, CCL5, CXCL19, Xcl1, and increased infiltration of GPC3-specific CD8+ T cells, activated NK cells and NKT cells. The antitumor effects of these immune cells were further enhanced by the administration of anti-PD1. Anti-HCC effects induced by hXCL1-GPC3 were confirmed in HCC-PDX model from three patients. Thus, XCL1-GPC3 might be a promising cancer vaccine to compensate for the deficiency of the checkpoint blockades in HCC immunotherapy.