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The human hepatitis B virus (HBV), that is causative for more than 240 million cases of chronic liver inflammation (hepatitis), is an enveloped virus with a partially double-stranded DNA genome. After virion uptake by receptor-mediated endocytosis, the viral nucleocapsid is transported towards the nuclear pore complex. In the nuclear basket, the nucleocapsid disassembles. The viral genome that is covalently linked to the viral polymerase, which harbors a bipartite NLS, is imported into the nucleus. Here, the partially double-stranded DNA genome is converted in a minichromosome-like structure, the covalently closed circular DNA (cccDNA). The DNA virus HBV replicates via a pregenomic RNA (pgRNA)-intermediate that is reverse transcribed into DNA. HBV-infected cells release apart from the infectious viral parrticle two forms of non-infectious subviral particles (spheres and filaments), which are assembled by the surface proteins but lack any capsid and nucleic acid. In addition, naked capsids are released by HBV replicating cells. Infectious viral particles and filaments are released via multivesicular bodies; spheres are secreted by the classic constitutive secretory pathway. The release of naked capsids is still not fully understood, autophagosomal processes are discussed. This review describes intracellular trafficking pathways involved in virus entry, morphogenesis and release of (sub)viral particles.

Macaque restricts hepatitis B virus (HBV) infection because its receptor homologue, NTCP (mNTCP), cannot bind preS1 on viral surface. To reveal how mNTCP loses the viral receptor function, we here solve the cryo-electron microscopy structure of mNTCP. Superposing on the human NTCP (hNTCP)-preS1 complex structure shows that Arg158 of mNTCP causes steric clash to prevent preS1 from embedding onto the bile acid tunnel of NTCP. Cell-based mutation analysis confirms that only Gly158 permitted preS1 binding, in contrast to robust bile acid transport among mutations. As the second determinant, Asn86 on the extracellular surface of mNTCP shows less capacity to restrain preS1 from dynamic fluctuation than Lys86 of hNTCP, resulting in unstable preS1 binding. Additionally, presence of long-chain conjugated-bile acids in the tunnel induces steric hindrance with preS1 through their tailed-chain. This study presents structural basis in which multiple sites in mNTCP constitute a molecular barrier to strictly restrict HBV. Here the authors look at why macaque is non-susceptible to hepatitis B virus by focusing on the protein structure of the host receptor homolog. They show that macaque-derived host receptor homolog has multiple structural defects against virus binding.

Glutamine cyclase, an enzyme involved in posttranslational modifications, is encoded by the glutaminyl-peptide cyclotransferase (QPCT) gene. Gene microarray analysis revealed that the QPCT gene was highly expressed in HepG2.2.15 cells compared with that in HepG2 cells. The serum expression level of the QPCT gene was detected by ELISA and was significantly greater in HBV-infected patients than in healthy controls. The mRNA and protein expression levels of the QPCT gene were markedly greater in the HBV-expressing cell lines (HepG2.2.15, and HepG2 and Huh7 cells transfected with the pBlu-HBV plasmid) than in the HepG2 and Huh7 cells. The levels of HBV pgRNA and HBV-DNA copy number, as well as the levels of HBeAg and HBsAg, also increased in the HepG2 and Huh7 cell lines cotransfected with the QPCT gene expression plasmid and the HBV 1.3-fold plasmid. Our study indicated that HBV can promote the expression of the QPCT gene, which in turn promotes the expression and replication of HBV.

Background: Gaps remain in the detection of nucleic acid test (NAT) yield and occult hepatitis B virus (HBV) infection (OBI) by current HBV surface antigen (HBsAg) assays. The lack of detection may be due to HBsAg levels below current assay detection limits, mutations affecting HBsAg assays or HBsAg levels, or the masking of HBsAg by antibody to HBsAg (anti-HBs). In this study, we evaluate the incremental detection of NAT yield and OBI from five diverse geographic areas by an improved sensitivity HBsAg assay and characterize the samples relative to the viral load, anti-HBs status, and PreS1–S2–S mutations. Included is a comparison population with HBV DNA levels comparable to OBI, but with readily detectable HBsAg (High Surface–Low DNA, HSLD). Methods: A total of 347 samples collected from the USA, South Africa, Spain, Cameroon, Vietnam, and Cote D’Ivoire representing NAT yield (HBsAg(−), antibody to HBV core antigen (anti-HBc)(−), HBV DNA(+), N = 131), OBI (HBsAg(−), anti-HBc(+), HBV DNA(+), N = 188), and HSLD (HBsAg(+), anti-HBc(+), HBV DNA(+), N = 28) were tested with ARCHITECT HBsAg NEXT (HBsAgNx) (sensitivity 0.005 IU/mL). The sequencing of the PreS1–S2–S genes from a subset of 177 samples was performed to determine the genotype and assess amino acid variability, particularly in anti-HBs(+) samples. Results: HBsAgNx detected 44/131 (33.6%) NAT yield and 42/188 (22.3%) OBI samples. Mean HBV DNA levels for NAT yield and OBI samples were lower in HBsAgNx(−) (50.3 and 25.9 IU/mL) than in HBsAgNx(+) samples (384.1 and 139.5 IU/mL). Anti-HBs ≥ 10 mIU/mL was present in 28.6% HBsAgNx(+) and 45.2% HBsAgNx(−) OBI, and in 3.6% HSLD samples. The genotypes were A1, A2, B, C, D, E, F, and H. There was no significant difference between HBsAgNx(−) and HBsAgNx(+) in the proportion of samples harboring substitutions or in the mean number of substitutions per sample in PreS1, PreS2, or S for the NAT yield or OBI (p range: 0.1231 to >0.9999). A total of 21/27 (77.8%) of HBsAgNx(+) OBI carried S escape mutations, insertions, or stop codons. HSLD had more PreS1 and fewer S substitutions compared to both HBsAgNx(−) and HBsAgNx(+) OBI. Mutations/deletions associated with impaired HBsAg secretion were observed in the OBI group. Conclusions: HBsAgNx provides the improved detection of NAT yield and OBI samples. Samples that remain undetected by HBsAgNx have exceptionally low HBsAg levels below the assay detection limit, likely due to low viremia or the suppression of HBsAg expression by host and viral factors.

Microalgae represent promising production factories for the light‐driven, cost‐effective production of recombinant proteins. The red microalga Porphyridium purpureum displays particularly favourable transgene expression properties due to the episomal maintenance of transformation vectors at high copy numbers in the nucleus. In this work, we explored the potential of Porphyridium purpureum to synthesise a candidate vaccine against Hepatitis B virus (HBV). We show high‐yield expression of an HBV chimeric surface antigen and efficient assembly of virus‐like particles (VLPs) in algal cells. We established a purification protocol for the VLPs and conducted vaccination studies in experimental animals. The results demonstrate that the alga‐produced HBV antigen elicits superior humoral and cellular immune responses compared to a commercial HBV vaccine produced in yeast. The antigen triggers virus‐neutralising antibodies against different HBV variants, including vaccine‐escape mutations that evade the immune response to current vaccines in humans. Our work establishes Porphyridium as a highly promising production platform for vaccines and other proteinaceous biopharmaceuticals.

Background Occult hepatitis B virus infection (OBI) carries high risk of transmissibility and pathogenicity. Mutations in the S gene are considered major contributors to OBI development. Our previous study identified the C138R mutation in the S gene of OBI patients. This study aimed to investigate the impact of the C138R mutation on HBsAg function and its mechanisms leading to OBI. Methods Full-length hepatitis B virus (HBV) plasmids (HBV 1.3, genotype B) and mutant plasmids (HBV C138R) were constructed, along with HA-tagged wild-type (sWT) and mutant (sC138R) S protein expression plasmids. The effects of the C138R mutation on HBsAg antigenicity, secretion, and dimer formation were evaluated through in vitro cell transfection and in vivo hydrodynamic tail vein injection in mice. Results The C138R mutation markedly reduced intra- and extracellular HBsAg levels without affecting HBV transcription, replication, or other viral protein expression. HA-tag assays indicated that this reduction resulted from impaired antigenicity. Several commercial ELISA kits results and HA levels in cell supernatants demonstrated that the C138R mutation also impaired HBsAg secretion. Similarly, the C107R mutation significantly decreased both HBsAg antigenicity and secretion. Non-reducing WB assays and Alphafold 3-based structural predictions revealed that the C138R mutation lead to the formation of aberrant HBsAg dimers. These findings were confirmed in the HBV mouse model. Conclusion The C138R mutation contributed to OBI by simultaneously impairing HBsAg antigenicity and secretion. Disruption of the disulfide bond between aa107 and aa138, resulting in the formation of structurally abnormal dimers, represented the primary mechanism underlying HBsAg dysfunction caused by this mutation.

The hepatitis B surface antigen (HBsAg) is a multifunctional glycoprotein composed of large (LHB), middle (MHB), and small (SHB) subunits. HBsAg isoforms have numerous biological functions during HBV infection—from initial and specific viral attachment to the hepatocytes to initiating chronic infection with their immunomodulatory properties. The genetic variability of HBsAg isoforms may play a role in several HBV-related liver phases and clinical manifestations, from occult hepatitis and viral reactivation upon immunosuppression to fulminant hepatitis and hepatocellular carcinoma (HCC). Their immunogenic properties make them a major target for developing HBV vaccines, and in recent years they have been recognised as valuable targets for new therapeutic approaches. Initial research has already shown promising results in utilising HBsAg isoforms instead of quantitative HBsAg for correctly evaluating chronic infection phases and predicting functional cures. The ratio between surface components was shown to indicate specific outcomes of HBV and HDV infections. Thus, besides traditional HBsAg detection and quantitation, HBsAg isoform quantitation can become a useful non-invasive biomarker for assessing chronically infected patients. This review summarises the current knowledge of HBsAg isoforms, their potential usefulness and aspects deserving further research.

Persistent hepatitis B virus (HBV) infection is established by the formation of an intranuclear pool of covalently closed circular DNA (cccDNA) in the liver. Very little is known about the intrahepatic distribution of HBV cccDNA in infected patients, particularly at the single-cell level. Here, we established a highly sensitive and specific ISH assay for the detection of HBV RNA, DNA, and cccDNA. The specificity of our cccDNA probe set was confirmed by its strict intranuclear signal and by a series of Southern blot analyses. Use of our in situ assay in conjunction with IHC or immunofluorescence uncovered a surprisingly mosaic distribution of viral antigens and nucleic acids. Most strikingly, a mutually exclusive pattern was found between HBV surface antigen-positive (HBsA-positive) and HBV DNA- and cccDNA-positive cells. A longitudinal observation of patients over a 1-year period of adeforvir therapy confirmed the persistence of a nuclear reservoir of viral DNA, although cytoplasmic DNA was effectively depleted in these individuals. In conclusion, our method for detecting viral nucleic acids, including cccDNA, with single-cell resolution provides a means for monitoring intrahepatic virological events in chronic HBV infection. More important, our observations unravel the complexity of the HBV life cycle in vivo.

Hepatitis B virus (HBV) exclusively infects hepatocytes and produces large amounts of subviral particles containing its surface antigen (HBsAg). T cell immunity is crucial for controlling and clearing HBV infection. However, the intercellular processes underlying HBsAg presentation to T cells are incompletely understood. Here, using preclinical mouse models, we show that, following HBsAg expression, the intrahepatic Batf3 + XCR1 + CCR7 - conventional dendritic cell subset cDC1 presents HBsAg by MHC-I cross-dressing, driving CD8 + T cell response. Meanwhile, upon HBsAg access to lymphoid tissues, B cells acquire HBsAg directly in the follicles of lymphoid tissues and initiate CD4 + T cell responses sequentially in the follicular and interfollicular regions, guided by chemoattractant receptors CCR5 and EBI2, respectively. Finally, we identify ALCAM, LFA-1, and CD80 as key co-stimulatory signals essential for optimal T cell responses. Thus, these findings reveal the roadmap of non-canonical antigen presentation that drives T cell immunity against HBsAg, advancing novel therapeutic strategies for chronic HBV infection. The mechanism of HBsAg antigen presentation to T cells during liver HBV infection is incompletely understood. Here, the authors show that in mice, intrahepatic type I dendritic cells acquire HBsAg by MHC-I complexes through cross-dressing for CD8 + T cell priming, whereas CD4 +  T cell responses rely on MHC-II-dependent antigen presentation by B cells in secondary lymphoid tissues.

A novel hepatitis B virus (HBV) strain (W29) was isolated from serum samples in the northwest of China. Phylogenetic and distance analyses indicate that this strain is grouped with a series of distinct strains discovered in Vietnam and Laos that have been proposed to be a new genotype I. TreeOrderScan and GroupScan methods were used to study the intergenotype recombination of this special group. Recombination plots and tree maps of W29 and these putative genotype I strains exhibit distinct characteristics that are unexpected in typical genotype C strains of HBV. The amino acids of P gene, S gene, X gene, and C gene of all genotypes (including subtypes) were compared, and eight unique sites were found in genotype I. In vitro and in vivo experiments were also conducted to determine phenotypic characteristics between W29 and other representative strains of different genotypes obtained from China. Secretion of HBsAg in Huh7 cells is uniformly abundant among genotypes A, B, C, and I (W29), but not genotype D. HBeAg secretion is low in genotype I (W29), whose level is close to genotype A and much lower than genotypes B, C, and D. Results from the acute hydrodynamic injection mouse model also exhibit a similar pattern. From an overview of the results, the viral markers of W29 (I1) in Huh7 cells and mice had a more similar level to genotype A than genotype C, although the latter was closer to W29 in distance analysis. All evidence suggests that W29, together with other related strains found in Vietnam and Laos, should be classified into a new genotype.