HCA519/TPX2: a potential T-cell tumor-associated antigen for human hepatocellular carcinoma

Abstract

Ahmed M Aref,1–3 Neil T Hoa,3 Lisheng Ge,3 Anshu Agrawal,4 Maria Dacosta-Iyer,5,6 Nils Lambrecht,5,6 Yi Ouyang,5,6 Andrew N Cornforth,7 Martin R Jadus5,6,8 1Biological Science Department, Modern Sciences and Arts University, Faculty of Dentistry, Cairo, Egypt; 2Southern California Institute for Research and Education, Veterans Affairs Medical Center, Long Beach, CA, USA; 3Research Health Care Group, Veterans Affairs Medical Center Long Beach, CA, USA; 4Department of Medicine, Division of Basic and Clinical Immunology, University of California, Irvine, CA, USA; 5Pathology and Laboratory Medicine Department, Veterans Affairs Medical Center Long Beach, CA, USA; 6Department of Pathology and Laboratory Medicine, University of California, Irvine, CA, USA; 7California Stem Cells, Inc., CA, USA; 8Neuro-Oncology Program, Chao Comprehensive Cancer Center, University of California, Irvine, CA, USA Background: Immunotherapy for human hepatocellular cancer (HCC) is slowly making progress towards treating these fatal cancers. The identification of new antigens can improve this approach. We describe a possible new antigen, hepatocellular carcinoma-associated antigen-519/targeting protein for Xklp-2 (HCA519/TPX2), for HCC that might be beneficial for T-cell specific HCC immunotherapy. Methods: HCC was studied for the expression for 15 tumor-associated antigens considered useful for immunotherapy within three HCC cell lines (HepG2, Hep3B, and PLC/PRF/5), lymphocytes, non-cancerous livers, and clinical HCC. The expression of tumor antigenic precursor proteins (TAPPs) messenger RNA was first screened by reverse transcriptase quantitative real-time polymerase chain reaction. Results: Four antigens (alpha fetoprotein, aspartyl/asparaginyl β-hydroxylase, glypican-3 and HCA519/TPX2) proved to be the best expressed TAPPs within the HCC specimens by molecular analyses. HCA519/TPX2 was detected by intracellular cell flow cytometry within HCC cell lines by using a specific antibody towards this TAPP. This antibody also detected the protein within primary HCCs. We synthesized two HCA519/TPX2 peptides (HCA519464–472 and HCA519351–359) which can bind to human leukocyte antigen (HLA)-A*0201. Dendritic cells pulsed with these peptides stimulated cytolytic T lymphocytes (CTLs). These killer T-cells lysed HLA-A*0201+ T2 cells exogenously loaded with the correct specific peptide. The CTLs killed HepG2 (HLA-A2+ and HCA519+), but not the Hep3B and PLC/PRF/5 cell lines, which are HCA519+ but HLA-A2-negative. In silico analysis reveals that HCA519/TPX2 has the inherent ability to bind to a very wide variety of HLA antigens. Conclusion: HCA519/TPX2 is a viable immunotarget that should be further investigated within HCC patients. Keywords: tumor immunity, cytolytic T-cells, HLA-A2, HCA519/TPX2