Usefulness of a novel oncofetal antigen, Glypican-3, for diagnosis and immunotherapy of hepatocellular carcinoma

We identified glypican-3 (GPC3), as a novel oncofetal antigen, overexpressed specifically in hepatocellular carcinoma (HCC) and melanoma in humans by utilizing genome-wide cDNA microarray analyses of HCC tissues and normal fetal and adult tissues. We also found that GPC3 is a novel tumor marker for HCC and melanoma, and that the pre-immunization of BALB/c mice with dendritic cells pulsed with the H-2K(d)-restricted mouse GPC3 298-306 (EYILSLEEL) peptide prevented the growth of tumor expressing mouse GPC3. Because of similarities in the binding peptide motifs between H-2K(d) and HLA-A24 (A(*)2402), the H-2K(d)-restricted GPC3 298-306 peptide thus seemed to be useful for the immunotherapy of HLA-A24(+) patients with HCC and melanoma. We investigated whether the GPC3 298-306 peptide could induce GPC3 reactive CTLs from the peripheral blood mononuclear cells (PBMCs) of HLA-A24 (A(*)2402)(+) HCC patients. In addition, we used HLA-A2.1 (HHD) transgenic mice (Tgm) to identify the HLA-A2 (A(*)0201)-restricted GPC3 epitopes to expand the applications of GPC3 based immunotherapy to the HLA-A2(+) HCC patients. We found that the GPC3 144-152 (FVGEFFTDV) peptide could induce peptide-reactive CTLs in HLA-A2.1 (HHD) Tgm without inducing autoimmunity. In 5 out of 8 HLA-A2(+) GPC3(+) HCC patients, the GPC3 144-152 peptide-reactive CTLs were generated from PBMCs by in vitro stimulation with the peptide and the GPC3 298-306 peptide-reactive CTLs were also generated from PBMCs in 4 of 6 HLA-A24(+) GPC3(+) HCC patients. The inoculation of these CTLs reduced the human HCC tumor mass implanted into NOD/SCID mice. We have recently started a phase I clinical trial of GPC3 peptide vaccine-based immunotherapy of patients with advanced HCC. We have also succeeded in inhibition of growth of tumors expressing mouse GPC3 by immunization of mice with dendritic cells differentiated in vitro from mouse embryonic stem cells and pulsed with the GPC3 peptides. Our study raises the possibility that these GPC3 peptides may therefore be applicable to cancer immunotherapy for a large number of patients with HCC and melanoma.