Mechanisms underlying delayed loss of HBeAg and HBV DNA following HBsAg seroclearance in PEG-IFNα treated patients of chronic hepatitis B.

Abstract

Background & aims: A notable proportion of CHB patients undergoing PEG-IFNα based therapy experience lagged serum HBeAg and/or HBV DNA disappearance in patients achieving HBsAg loss. In this study, we explored the molecular mechanisms behind this clinical phenomenon, offering novel insights into the sustainability of chronic HBV infection.

Methods: Two independent clinical cohorts were enrolled to validate this phenomenon. Then comprehensive analysis was performed using public datasets, coupled with a series of molecular biology experiments.

Results: Approximately 17-20% CHB patients underwent PEG-IFNα based therapy experienced seroclearance of HBsAg, while serum HBeAg and/or HBV DNA remained positive. These patients are more prone to serum HBsAg reappearance compared to those achieving complete virological response. Analysis of public datasets revealed that compared to the PC/BCP, the SP1/SP2 promoter displayed more pronounced inhibitory epigenetic modifications in HBeAg-negative patients and SP1/SP2 in-frame mutation peaked in immune active patients. In vitro experiments demonstrated that introduced SP1/SP2 inactive mutations would enhance PC/BCP transcriptional activity by a mechanism known as adjacent transcriptional interference. Furthermore, the deletion of L-HBsAg facilitated intracellular cccDNA replenishment.

Conclusion: This study elucidates that under IFNα treatment and low viral load, transcriptional suppression of SP1/SP2 promoters through mutations and/or epigenetic changes would favour the maintenance of sustain chronic HBV infection, via enhancing the transcription activity of BCP to promote cccDNA replenishment.

Impact and implications: In clinical practice with IFNα antiviral treatment for CHB patients, a "paradoxical" phenomenon is observed where serum HBsAg disappears while HBV DNA or/and HBeAg remains at low positive levels, with delayed disappearance. Our study confirms this clinical phenomenon using two independent clinical cohorts and explores the potential mechanisms behind the persistence of chronic HBV infection under IFNα treatment and low viral load. Transcriptional suppression of SP1/SP2 promoters through mutations and/or epigenetic changes supports the maintenance of chronic HBV infection by enhancing the transcriptional activity of the BCP, which in turn promotes cccDNA replenishment.

HighlightsApproximately 20% of patients with CHB who have just achieved HBsAg loss under IFNα treatment show positive serum HBV DNA and/or HBeAg.During disease progression, in frame indel mutations accumulate in the HBV genome's SP1 and SP2 promoters, with epigenetic modifications contributing to their suppression.In frame indel mutations in the HBV genome's SP1 and SP2 promoters inhibit the transcription of HBV S mRNA and promote the transcription of 3.5 kb HBV RNA.The loss of L-HBs and envelop proteins leads to an increase in intracellular cccDNA, promoting the maintenance of chronic infection.