Hepatitis B Virus RNA Profiles in Liver Biopsies by Digital Polymerase Chain Reaction

Replication of hepatitis B virus (HBV) originates from covalently closed circular DNA (cccDNA) and involves reverse transcription of pregenomic RNA (pgRNA), which is also called core RNA and encodes the capsid protein. The RNA coding for hepatitis B surface antigen (HBsAg) in the envelope of viral or subviral particles is produced from cccDNA or from HBV DNA integrated into the host genome. Because only cccDNA can generate the core and the 3' redundancy regions of HBV RNA, we aimed to clarify to what extent such HBV integrations are expressed by quantifying the different HBV RNA species in liver tissue. Digital droplet polymerase chain reaction (ddPCR) was employed to quantify six HBV RNA targets in 76 liver biopsies from patients with chronic infection, comprising 14 who were hepatitis B e antigen (HBeAg) positive and 62 who were HBeAg negative. In patients who were HBeAg negative, HBV RNA from the S RNA region was >1.6 log₁₀ units higher than in the core and 3' redundancy regions (P < 0.0001), indicating that >90% of S RNA was integration derived. HBeAg-negative samples showed 10 times lower levels of pgRNA (5' core) compared with core RNA (3' part of core; P < 0.0001), suggesting that a large proportion of core RNA might have a downstream shift of the transcription starting point. In multiple regression analysis, HBV DNA levels in serum were most strongly dependent on pgRNA. Conclusion: In patients who were HBeAg negative, integration-derived S RNA seemed to predominate and a large proportion of the core RNA lacked the 5' part. Because this part comprises the down-regulator of transcription 1 sequences, which are necessary for virus production (plus strand translocation), the finding might help to explain the low level of HBV DNA in serum that frequently is observed in patients with chronic HBV infection who are HBeAg negative.