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

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.

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.

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.

HCA519/TPX2 is a viable immunotarget that should be further investigated within HCC patients.