Dominant mutations of hepatitis B virus variants in hepatoma accumulate in B-cell and T-cell epitopes of the HBx antigen

Hepatitis B virus (HBV) X gene, encoding a pleotropic transactivator of HBx protein, has been associated with the development of hepatocellular carcinoma (HCC). Molecular information on liver-derived HBV variants isolated from HCC among Taiwanese population was studied. Amplification of the HBV X genes of 20 HCC patients in high stringency with HBV specific primers was observed. The resulting amplified HBV X genes were purified and individually-cloned into pUC-T vector. Sequences of the eight liver-derived X gene were aligned and compared with the wild type, the ayw HBV serotype. Results indicate that the HBx protein of variants were found predominantly within the regions of amino acid positions 26–45 in N-terminus, and positions 87, 88, 116, 118, 119, 127 and 144. Sequences from six out of the eight variants were found to be identical. These accumulated sequence mutations among the eight HBx variants were found to coincide within the B-cell epitopes (positions 29–48), particularly in the HBx proline and serine rich (PSR) domain, and the T-cell epitopes regions (positions 116–127). These frequent mutations of HBV variants, rather than subtype-specific polymorphic sites, may be involved in immunoevasion.