Low serum levels of the hepatitis B core-related antigen (HBcrAg) could be an early biomarker of a functional cure of a hepatitis B infection, according to new findings from a retrospective study.
A drop in HBcrAg predicted the seroclearance of hepatitis B surface antigen (HBsAg), the widely accepted measure of optimal liver-related outcomes in patient care and clinical trials, long before HBsAg levels actually fell.
“In a large retrospective cohort study of chronic hepatitis B patients, we found lower levels of HBcrAg were associated with higher probability of clearing HBsAg,” wrote Tai-Chung Tseng and coauthors at National Taiwan University Hospital in Taipei. “Reduction of HBcrAg developed 10 years before decline of HBsAg in patients with high HBsAg levels at baseline.”
Nearly 300 million people worldwide are estimated to be positive for the HBsAg antigen, a marker of active hepatitis B virus (HBV) infection. Chronic HBV puts individuals at greater risk of cirrhosis, hepatocellular carcinoma (HCC), and other liver complications.
Seroclearance of HBsAg is generally regarded as signaling a functional cure, because it is associated with low viral activity and good clinical outcomes. Patients with low HBsAg levels may transition to complete clearance, while those with levels of 1,000 IU/mL or higher rarely achieve clearance either spontaneously or through treatment.
As with HBsAg, higher serum levels of HBcrAg have been linked to a raised risk of adverse events, including increased viral activity and heightened risk of developing hepatitis B e antigen-negative hepatitis, cirrhosis, and HCC. Lower HBcrAg levels are associated with a greater likelihood of HBsAg seroclearance in chronic hepatitis B patients who discontinued antiviral therapy.
In a study published in Gastroenterology, researchers conducted a retrospective Taiwanese cohort study of 2,614 untreated patients with hepatitis B who underwent long-term follow-up at National Taiwan University Hospital. The median age was 38.2 years, and 60.6% were men. At baseline, 14.8% had HBsAg levels of less than 100 IU/mL, and 47.7% had HBcrAg levels less than 10,000 IU/mL. Most (77.5%) were infected with HBV genotype B. From stored serum samples, the researchers quantified levels of HBV DNA, HBsAg, and HBcrAg and evaluated the relationships with spontaneous HBsAg seroclearance.
Over an average follow-up of about 12 years, 465 patients cleared HBsAg, an incidence of 1.43% per year. Researchers stratified patients by levels of viral markers. Compared to those with the highest HBcrAg levels (> 100,000 IU/mL), lower levels of HBcrAg were associated with greater likelihood of HBsAg clearance.
Specifically, intermediate levels (10,000-99,999 IU/mL) were associated with nearly double the chance of HBsAg clearance (hazard ratio [HR], 1.95; 95% confidence interval [CI], 1.44-2.65), and the lowest levels (< 10,000 IU/mL) were associated with just over triple the chance of clearance (HR, 3.15; 95% CI, 2.45-4.05). These associations held up with multivariable analyses, and HBV DNA levels were not significantly associated with HBsAg clearance.
“Not surprisingly, HBsAg levels still serve as a better predictor than the other two biomarkers,” the authors wrote. “Notably, the HBsAg levels are more like a short-term predictor” (within 5 years).
For patients with higher HBsAg levels (> 1,000 IU/mL), it took a median of 16 years to achieve HBsAg clearance. A subanalysis of the 1,539 patients with HbsAg levels > 1,000 IU/mL found that only HBcrAg levels below 10,000 IU/mL predicted HBsAg seroclearance versus 100,000 U/mL or higher (adjusted HR, 1.95; 95% CI, 1.16-3.27).
HBsAg levels began to decline later, often between 5 and 9 years before HBsAg seroclearance occurs. However, HBcrAg levels became undetectable 10-14 years before HBsAg seroclearance. Among patients achieving undetectable levels of HBcrAg, the annual HBsAg seroclearance rate was higher in the second decade of follow-up than in the first decade (3.75% versus 0.97%).
HBcrAg levels reflect the transcriptional activity of covalently closed circular DNA (cccDNA), the authors noted, while HBsAg can come from cccDNA and HBV-DNA integrated into the host genome. Several novel hepatitis B therapies in development target cccDNA transcription, but it isn’t known if the strategy will result in HBsAg clearance.
In the discussion section, the authors speculated about the possible pathology and treatment implications for several chronic hepatitis B scenarios. For example, the finding that HBcrAg clearance usually precedes HBsAg clearance suggests that reduction of cccDNA transcription is a requirement for curing hepatitis B, the authors speculate, but it also suggests that add-on treatment may need to target HBsAg transcribed from the integrated viral genome for a functional cure.
The researchers noted several study limitations, including that the cohort included only Asians largely with HBV genotypes B or C and that “further validation from Caucasian patients infected with genotypes types A or D is mandatory.”
Tai-Chung Tseng disclosed financial conflicts with Fujirebio, Bristol-Myers Squibb, and Gilead Sciences. The remaining authors had no conflicts of interest. The study received grant support from several institutions, including National Taiwan University Hospital.
