Chronic hepatitis B (CHB) remains a formidable global health challenge, affecting over 250 million people and posing a significant risk for the development of cirrhosis and hepatocellular carcinoma (HCC). The persistence of the hepatitis B virus (HBV) is primarily driven by the covalently closed circular DNA (cccDNA), a stable mini-chromosome within the hepatocyte nucleus that serves as the template for viral transcription. As current nucleos(t)ide analogue (NA) therapies suppress viral replication but rarely eliminate cccDNA, there is a pressing need for non-invasive biomarkers that can accurately reflect the activity of this viral reservoir and predict clinical outcomes. This review synthesizes the growing evidence for two such promising biomarkers: serum HBV RNA and hepatitis B core-related antigen (HBcrAg). These markers offer a window into intrahepatic viral activity, enabling better monitoring of disease progression, treatment response, and risk stratification.
Serum HBV RNA: A Transcriptional Snapshot of cccDNA
Serum HBV RNA, first detected in 1996, is a heterogeneous population of viral transcripts, primarily composed of pregenomic RNA (pgRNA). Its molecular forms include full-length pgRNA, 3'-truncated pgRNA, splice variants, HBx transcripts, and recently discovered HBV-human chimeric RNAs. While research into the unique clinical significance of individual isoforms is emerging, the quantification of total serum pgRNA has proven most practical and informative. It serves as a direct transcriptional product of cccDNA, providing a non-invasive surrogate for intrahepatic cccDNA quantity and transcriptional activity. This correlation holds strong in both untreated patients and those undergoing NA therapy, where HBV RNA remains detectable even when HBV DNA is suppressed, offering a unique insight into the persistent transcriptional activity of the viral reservoir.
The clinical utility of serum HBV RNA is extensive:
Predicting Seroconversion: Dynamic changes in serum HBV RNA levels are powerful predictors of HBeAg and HBsAg seroconversion. Rapid declines in RNA levels are strongly associated with spontaneous and treatment-induced HBeAg seroconversion. Furthermore, low or undetectable RNA levels at the end of treatment are linked to higher rates of HBsAg clearance.
Guiding Treatment Cessation: A significant challenge in CHB management is determining when to safely stop NA therapy. Serum HBV RNA levels at the end of treatment are a key predictor of virological relapse. Patients with undetectable RNA have a substantially lower risk of relapse, and combining RNA negativity with low HBsAg levels further refines the identification of patients suitable for treatment cessation.
Assessing Liver Fibrosis: Serum HBV RNA levels show a strong correlation with the severity of liver necroinflammation and fibrosis, often outperforming traditional non-invasive indices like APRI and FIB-4. Notably, a rapid decline in RNA during treatment predicts subsequent histological regression of fibrosis.
Forecasting HCC Risk: Elevated serum HBV RNA levels are an independent risk factor for HCC development and are associated with poorer overall survival and higher recurrence rates post-resection in CHB patients. Interestingly, this relationship may be phase-dependent, as very advanced, poorly differentiated HCC can exhibit lower RNA levels, possibly due to a tumor-hostile microenvironment for viral replication.
HBcrAg: A Composite Marker of Viral Protein Production
HBcrAg is a novel composite biomarker that quantifies three viral proteins sharing an identical 149-amino-acid sequence: HBcAg, HBeAg, and the p22cr protein (a precore derivative). As these proteins are direct translational products of transcripts originating from cccDNA, HBcrAg serves as a robust serological proxy for intrahepatic cccDNA transcriptional activity.
The clinical applications of HBcrAg parallel and complement those of HBV RNA:
Correlation with cccDNA and Replicative Activity: HBcrAg demonstrates a superior and more consistent correlation with intrahepatic cccDNA levels than HBsAg or HBV DNA, a relationship that persists during long-term NA therapy. It also shows a strong correlation with HBV DNA, reflecting overall viral replicative activity.
Predicting Seroconversion and Relapse: Lower baseline or on-treatment HBcrAg levels are associated with a higher likelihood of HBeAg seroconversion and HBsAg loss. Crucially, both baseline and end-of-treatment HBcrAg levels are powerful independent predictors of virological relapse after stopping NAs, with specific cut-off values (e.g., <3.0-4.0 log U/mL) being incorporated into clinical guidelines to define low relapse risk.
Evaluating Liver Disease Progression: HBcrAg is a significant predictor of significant liver necroinflammation and fibrosis. Its diagnostic accuracy is high, with optimal cut-offs that vary based on HBeAg status. Furthermore, elevated HBcrAg levels are an independent risk factor for the progression to cirrhosis.
Stratifying HCC Risk: In both untreated and NA-treated patients, high serum HBcrAg levels are consistently associated with an increased risk of HCC development. Dynamic monitoring of HBcrAg can help identify patients with a continuously high oncogenic risk despite antiviral therapy.
Conclusion and Future Perspectives
Serum HBV RNA and HBcrAg have emerged as pivotal tools in the quest for precision medicine in CHB. They provide complementary, non-invasive means to assess the persistent transcriptional activity of the cccDNA reservoir, a parameter largely hidden from conventional markers like HBV DNA and HBsAg. Their ability to predict key clinical milestones—including seroconversion, treatment relapse, fibrosis progression, and HCC development—positions them to revolutionize patient management by enabling individualized treatment strategies and cessation guidelines.
Future efforts must focus on standardizing detection assays, establishing universally applicable cut-off values through large multicenter studies, and exploring the integration of these biomarkers into multi-parameter predictive models. By illuminating the "black box" of intrahepatic viral persistence, serum HBV RNA and HBcrAg are paving the way for a more informed and effective approach to curing chronic hepatitis B.
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The study was recently published in the Journal of Clinical and Translational Hepatology .
The Journal of Clinical and Translational Hepatology (JCTH) is owned by the Second Affiliated Hospital of Chongqing Medical University and published by XIA & HE Publishing Inc. JCTH publishes high quality, peer reviewed studies in the translational and clinical human health sciences of liver diseases. JCTH has established high standards for publication of original research, which are characterized by a study's novelty, quality, and ethical conduct in the scientific process as well as in the communication of the research findings. Each issue includes articles by leading authorities on topics in hepatology that are germane to the most current challenges in the field. Special features include reports on the latest advances in drug development and technology that are relevant to liver diseases. Regular features of JCTH also include editorials, correspondences and invited commentaries on rapidly progressing areas in hepatology. All articles published by JCTH, both solicited and unsolicited, must pass our rigorous peer review process.
