Identification and Mapping of HBsAg Loss-Related B-Cell Linear Epitopes in Chronic HBV Patients by Peptide Array

Massively-multiplexed epitope mapping techniques for viral antigen discovery

Following viral infection, viral antigens bind specifically to receptors on the surface of lymphocytes thereby activating adaptive immunity in the host. An epitope, the smallest structural and functional unit of an antigen, binds specifically to an antibody or antigen receptor, to serve as key sites for the activation of adaptive immunity. The complexity and diverse range of epitopes are essential to study and map for the diagnosis of disease, the design of vaccines and for immunotherapy. Mapping the location of these specific epitopes has become a hot topic in immunology and immune therapy. Recently, epitope mapping techniques have evolved to become multiplexed, with the advent of high-throughput sequencing and techniques such as bacteriophage-display libraries and deep mutational scanning. Here, we briefly introduce the principles, advantages, and disadvantages of the latest epitope mapping techniques with examples for viral antigen discovery.

Role of CXCR5+ CD8+ T cells in human hepatitis B virus infection

The replication of HBV in hepatocytes can be effectively inhibited by lifelong antiviral therapy. Because of the long-term presence of HBV reservoirs, the virus rebound frequently occurs once the treatment is stopped, which poses a considerable obstacle to the complete removal of the virus. In terms of gene composition, regulation of B cell action and function, CXCR5+ CD8+ T cells are similar to CXCR5+ CD4+ T follicular helper cells, while these cells are characterized by elevated programmed cell death 1 and cytotoxic-related proteins. CXCR5+ CD8+ T cells are strongly associated with progression in inflammatory and autoimmune diseases. In addition, CXCR5 expression on the surface of CD8+ T cells is mostly an indicator of memory stem cell-like failure in progenitor cells in cancer that are more responsive to immune checkpoint blocking therapy. Furthermore, the phenomena have also been demonstrated in some viral infections, highlighting the duality of the cellular immune response of CXCR5+ CD8+ T cells. This mini-review will focus on the function of CXCR5+ CD8+ T cells in HBV infection and discuss the function of these CD8+ T cells and the potential of associated co-stimulators or cytokines in HBV therapeutic strategies.

An Ideal Hallmark Closest to Complete Cure of Chronic Hepatitis B Patients: High-sensitivity Quantitative HBsAg Loss

In the era of antiviral therapy, the main goal of treatment has shifted from the persistent inhibition of hepatitis B virus (HBV) replication to the pursuit of serological clearance of HBs surface antigen (HBsAg). Based on the life cycle of HBV, HBsAg originates from covalently closed circular DNA (cccDNA) and integrated HBV DNA, thus reflecting their transcriptional activity. Complete HBsAg loss may mean elimination or persistent inactivity of the HBV genome including cccDNA and integrated HBV DNA. HBsAg loss improves the recovery of abnormal immune function, which in turn, may further promote the clearance of residual viruses. Combined with functional cure and the great improvement of clinical outcomes, the continuous seroclearance of high-sensitivity quantitative HBsAg may represent the complete cure of chronic hepatitis B (CHB). For many other risk factors besides HBV itself, patients with HBsAg loss still need regular monitoring. In this review, we summarized the evolution of CHB treatment, the origin of serum HBsAg, the pattern of HBsAg seroclearance, and the effect of HBsAg loss on immune function and disease outcomes. In addition, we discuss the significance of high-sensitivity HBsAg detection and its possibility as a surrogate of complete cure.

Longitudinal mapping of hepatitis B vaccine-induced B-cell linear epitopes in healthy individuals

The elimination of hepatitis B virus (HBV) infection is partially facilitated by the prophylactic HB vaccine. As the loss of seroprotection over time remains a conundrum for long-lasting protection, a comprehensive dynamic analysis of immunogenic targets of the HB vaccine will provide novel insights into the improvement and design of potential targets. In this study, 36 healthy subjects without prior history of hepatitis B infection and negative for hepatitis B surface antibody (anti-HBs) were enrolled. Participants were given a series of three doses of HB vaccine on a 0-, 1-, and 6-month schedule and longitudinally followed up. We systematically mapped 55 overlapping 15-mer peptides covering the small S protein of hepatitis B virus (SHBs) of vaccinees' serum samples at seven time points by performing an ELISA assay. Additionally, the frequencies and function dynamics of adaptive immune response were assessed by flow cytometry. We found that the SHBs peptide coverage presented an overall upward trend along with the vaccination progress, and the individual subpartition recognition was strongly correlated with the anti-HBs titers. Moreover, we identified one dominant epitope (S29) located on "a determinant region" associated with effective vaccine response. Besides, significant correlations between the proportion of plasmablasts and proliferating B cells and levels of anti-HBs were ascertained. Taken together, our data characterized the dynamics of HB vaccine-induced neutralizing antibodies against B-cell linear epitopes on SHBs and adaptive immune response, which will be constructive to develop the next-generation vaccine.