Even under a cutoff of less than 2000 IU/ml HBV DNA, infected patients have an increased risk of developing hepatocellular carcinoma. This is probably due to the integration of the hepatitis B virus (HBV) into the human genome, as researchers explained at the International Liver Congress (ILC) 2019 in Vienna.
Patients infected with the hepatitis B virus are not necessarily healthy even if the surface antigen HBsAg is lost. HBV has the ability to integrate its DNA into the genome of the human liver cell. Current study data show that this can occur not only in the acute phase of the disease but also in HBeAg-negative chronic (i.e. HBsAg-positive) hepatitis B with a low HBV DNA titer. This is important as these patients are not necessarily treated at present. In her presentation, Dr. Romina Salpini from the University of Rome emphasized that the data available on the intrahepatic HBV reservoir in the HBeAg-negative phase of the disease is currently sparse. This also applies to the integration of the virus into the human genome. And this is clinically significant since virus integration into human DNA increases the risk of disease progression and hepatocellular carcinoma even without manifest hepatitis.
A study carried out by several groups in Italy and Great Britain now closes this evidence gap. The study included 40 HBeAg-negative patients and therapy naïve patients who had been under observation for at least two years prior to inclusion. The patients were stratified into three groups according to their viral load: Group 1 with HBV-DNA <2000 IU/ml (n=8), group 2 with HBV-DNA 2000-20 000 IU/ml (n=14) and group 3 with HBV-DNA >20 000 IU/ml (n=18).
Based on a liver biopsy, the hepatic HBV reservoir including cccDNA and pgRNA was quantified in these patients. The viral DNA integrated into the human genome was detected by whole exome sequencing (WES). All three patient groups showed cases of virus integration into the genome ("integration events"). The prevalence of genomic virus integration in regions relevant for gene replication was 35.4% across the study population. Patients with pronounced viremia (group 3) with a prevalence of integration events of 55.6% were most affected. But even in the two groups with a lower viral load, "integration events" often occurred, namely 25% in group 1 and 14.3% in group 2.
This is not only relevant for virus replication. Of the 17 different integration events identified, 11 concerned the region coding for the HBx protein responsible for the transcription and regulation of HBV. Three concerned the HBs antigen/polymerase (pol) encoding region and three the HBV core encoding region. "11 out of 17 HBV integration events occurred in introns that are important for RNA splicing and mRNA production," said Salpini, "but in six individuals HBV integration took place in human genes that regulate cell proliferation, and some of these genes are also involved in hepatocarcinogenesis or important for lipid metabolism or drug metabolism.
The antiviral and inflammatory activity of the cell is also influenced by affected genes." Salpini: "These data show how complex the HBV infection is. And they also suggest that even patients who, according to current recommendations, do not need to be candidates for therapy, may be affected by disease progression and increased cancer risk. Thus, our study could have implications for the management of patients with chronic HBV infection in the future. In any case, it shows that HBeAg-negative hepatitis B is by no means easy to control and will not be."
Sources:
1. Gong DY et al.: Role and functional domain of hepatitis B virus X protein in regulating HBV transcription and replication in vitro and in vivo. Viruses 2013; 5: 1261-71
2. Salpini R et al.: The integration of hepatitis B virus into the human genome is a common event in the setting of HBeAg negative disease: implications for the treatment and management of CHB. ILC 2019, GS-17
3. International Liver Congress (ILC) of the European Association for the Study of the Liver (EASL), 11 April 2019, Vienna