Table 3.

The road forward

Need	Rationale	Action
Increased sensitivity of biomarker assays	Measurement of HBV replication below the current limit of detection, particularly in patients who are treated; improved sensitivity will enable prediction of off-treatment remission and cure (sustained response), particularly as serum does not always reflect liver pathology	Diagnostic companies should be encouraged to develop highly sensitive HBV DNA assays; improved sensitivity will also assist in the detection of OBI
Extrapolation of assays to different patient cohorts	The clinical value of current and emerging biomarkers needs to be assessed in different patient cohorts, including their ability to define phases of HBV natural history	Patient cohorts should include different ethnic groups, HBV (sub)genotypes, higher representation of women, individuals with HIV co-infection, pregnant and lactating people, and children; although these markers can reflect cccDNA transcription in the liver, more understanding is required on the factors regulating their expression
Combination of assays	It is unclear at present how best to combine biomarkers; there is no ‘silver bullet’ and determining how to integrate multiple markers and their kinetics presents major challenges	Combining HBcrAg, HBsAg and pgRNA levels predicts sustained response following treatment cessation in some settings; although these markers might reflect cccDNA transcription in the liver, more understanding is required on the factors regulating their expression; technical validation of different biomarkers for different treatment modalities in clinical trials is under way or planned; collaborations between multiple clinical trial sites is recommended to obtain sufficient statistical power; a viral biomarker composite score similar to the REACH-B175 might assist clinical decision-making; biomarkers could be combined to generate the score and to predict outcomes such as which patients would benefit from stopping therapy
Development of core-specific biomarkers	As HBcrAg represents multiple antigens, with HBeAg predominating, a specific core antigen biomarker would be a useful surrogate marker of cccDNA activity as its level is not affected by the presence of basal core promoter and/or precore mutants or peripheral clearance (for example, HBcAg or HBeAg antibodies) being contained in virions	Development of a core-specific biomarker is under way
Correlation of expression of biomarkers in liver and plasma/serum	It is unclear how accurately HBV serum biomarkers reflect the liver	Further studies in animal models and humans are required to correlate circulating markers with the intrahepatic environment
Definition of disease progression and treatment response	Biomarkers of treatment response and disease progression are needed	A panel of biomarkers is needed to enable clinicians to identify patients who could cease therapy with a lower risk of relapse; biomarkers of HCC are needed, particularly those that can replace or complement ultrasonography for HCC detection; issues around access to these assays must be improved, particularly in resource-limited settings
Development of immunological markers	Immunological markers are not as well developed as virological markers	Currently available immunological markers largely measure liver inflammation whereas, ideally, these biomarkers should predict the activity of immune targeting drugs and, ultimately, off-treatment response; to date, measuring cytokines and chemokines in the periphery has been of limited value as they are only present at the time of inflammation
Further studies on FNA	FNA (also known as needle biopsy)	Understanding the contribution of the relatively few hepatocytes within the FNA and how this correlates with the ‘gold standard’ liver biopsy from both an immunological and virological perspective; as FNAs are a very small representation of a large organ, with inherent risks in terms of sampling error, performing FNAs in large patient populations might be necessary; identifying suitable clinical trial sites with the necessary expertise for collection, processing and storage, and providing training for sites lacking expertise; ideal conditions for the storage of FNAs have not been defined

cccDNA, covalently closed circular DNA; FNA, fine-needle aspiration; HCC, hepatocellular carcinoma; HBcAg, hepatitis B core antgen; HBcrAg, hepatitis B core-related antigen; HBeAg, hepatitis B e antigen; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; HIV, human immunodeficiency virus; OBI, occult hepatitis B virus infection; pgRNA, pre-genomic RNA.