Hepatitis B virus (HBV) DNA integration in patients with occult HBV infection and hepatocellular carcinoma

Background & aims: Hepatitis B virus (HBV) DNA integration in the host genome is a major mechanism responsible for the etiopathogenetic role exerted by HBV in hepatocellular carcinoma (HCC) development. Extensive analyses evaluating viral integration in HBV surface antigen (HBsAg) negative patients with occult HBV infection (OBI) have not yet been performed. The aim of this study was to investigate and characterize HBV DNA integration in HCC tissues from OBI patients.

Methods: Tumour DNA extracts from 69 HCC patients (49 HBsAg-negative with occult infection diagnosed by HBV DNA detection in tumour tissues; 10 HBsAg-positive and 10 HBsAg-negative/OBI-negative as control groups) were examined by Alu-PCR technique to reveal HBV DNA integration into the host genome. The molecular characterization of the virus-genome junctions was performed by cloning and sequencing analyses.

Results: Integrated HBV DNA was detected in 37/49 (75.5%) OBI-positive HCC samples, in 8/10 (80%) HBsAg-positive and in 0/10 OBI-negative HCC samples. Nine of 37 (24.3%) integrated viral sequences from OBI-positive cases were inside human genome coding regions and in the remaining cases the localization at intergenic level was frequently adjacent to coding genes. Concerning viral integrants in OBI cases, X gene sequences were found in 14 cases, preS/S sequences in 13, Core sequences in 7, and Polymerase gene sequences in three cases.

Conclusions: In analogy to what occurs in HBsAg-positive cases, HBV DNA integration is highly prevalent in OBI-related HCCs, it mainly involves X and preS/S viral genomic regions and it frequently occurs at the level of regulatory and functional genes.