Integration of hepatitis B virus DNA in chronically infected patients

Abstract Background: Hepatitis B virus (HBV) infection is the main risk factor for hepatocellular carcinoma (HCC) worldwide. Several factors contribute to the development of cancer. Integration of HBV DNA into the human genome may activate genes that promote, or disrupt genes that normally suppress, cell proliferation, and has been found in >80% of HBV-related HCC. Some studies have however failed to confirm an association between HCC and integration at putativeoncogenic sites, but instead found similar integrations in tumourous and non-tumourous tissue. Thus, the rate of integration during different stages of HBV infection, the mechanism for selection, and their role for the evolution of HCC remain unclear. Methods: We investigated liver biopsies from patients (n=75) in different stages of chronic HBV infection. Integration was searched by Alu-PCR, which combinesprimers specific for different regions of HBV (X, Core and S) with primers targeting Alusequences scattered in the human genome. Results: Integration was detected in 44of the patients (59 %), as an ampliconcontaining both human and HBV sequencesby AluPCR with one primer targeting any of the HBV regions. Thirty-oneintegrations were detectedwith an X region primer,26with a core region primerand only oneampliconwith an S region primer. A great majority of the HBV sequences were located upstream or downstream of the DR1-site. Roughly 60% of the HBV sequences were found in non-coding regions. Conclusion: Integrations of HBV DNA into the human genome appear to be a very frequent event that starts already during the early phases of infection.