A Role for B Cells to Transmit Hepatitis C Virus Infection

Hepatitis C virus (HCV) is highly variable and transmits through infected blood to establish a chronic liver infection in the majority of patients. Our knowledge on the infectivity of clinical HCV strains is hampered by the lack of in vitro cell culture systems that support efficient viral replication. We and others have reported that HCV can associate with and infect immune cells and may thereby evade host immune surveillance and elimination. To evaluate whether B cells play a role in HCV transmission, we assessed the ability of B cells and sera from recent (<2 years) or chronic (≥ 2 years) HCV patients to infect humanized liver chimeric mice. HCV was transmitted by B cells from chronic infected patients whereas the sera were non-infectious. In contrast, B cells from recently infected patients failed to transmit HCV to the mice, whereas all serum samples were infectious. We observed an association between circulating anti-glycoprotein E1E2 antibodies and B cell HCV transmission. Taken together, our studies provide evidence for HCV transmission by B cells, findings that have clinical implications for prophylactic and therapeutic antibody-based vaccine design.

HVR1-mediated antibody evasion of highly infectious in vivo adapted HCV in humanised mice

OBJECTIVE

HCV is a major cause of chronic liver disease worldwide, but the role of neutralising antibodies (nAbs) in its natural history remains poorly defined. We analysed the in vivo role of hypervariable region 1 (HVR1) for HCV virion properties, including nAb susceptibility.

DESIGN

Analysis of HCV from human liver chimeric mice infected with cell-culture-derived prototype genotype 2a recombinant J6/JFH1 or HVR1-deleted variant J6/JFH1_ΔHVR1 identified adaptive mutations, which were analysed by reverse genetics in Huh7.5 and CD81-deficient S29 cells. The increased in vivo genomic stability of the adapted viruses facilitated ex vivo density analysis by ultracentrifugation and in vivo neutralisation experiments addressing the role of HVR1.

RESULTS

In vivo, J6/JFH1 and J6/JFH1_ΔHVR1 depended on single substitutions within amino acids 867-876 in non-structural protein, NS2. The identified A876P-substitution resulted in a 4.7-fold increase in genomic stability. In vitro, NS2 substitutions enhanced infectivity 5-10-fold by increasing virus assembly. Mouse-derived mJ6/JFH1_A876P and mJ6/JFH1_ΔHVR1/A876P viruses displayed similar heterogeneous densities of 1.02-1.1 g/mL. Human liver chimeric mice loaded with heterologous patient H (genotype 1a) immunoglobulin had partial protection against mJ6/JFH1_A876P and complete protection against mJ6/JFH1_ΔHVR1/A876P. Interestingly, we identified a putative escape mutation, D476G, in mJ6/JFH1_A876P. This mutation in hypervariable region 2 conferred 6.6-fold resistance against H06 IgG in vitro.

CONCLUSIONS

The A876P-substitution bridges in vitro and in vivo studies using J6/JFH1-based recombinants. We provide the first in vivo evidence that HVR1 protects cross-genotype conserved HCV neutralisation epitopes, which advocates the possibility of using HVR1-deleted viruses as vaccine antigens to boost broadly reactive protective nAb responses.

Genome-scale Arabidopsis promoter array identifies targets of the histone acetyltransferase GCN5

We have assembled approximately 20 000 Arabidopsis thaliana promoter regions, compatible with functional studies that require cloning and with microarray applications. The promoter fragments can be captured as modular entry clones (MultiSite Gateway format) via site-specific recombinational cloning, and transferred into vectors of choice to investigate transcriptional networks. The fragments can also be amplified by PCR and printed on glass arrays. In combination with immunoprecipitation of protein-DNA complexes (ChIP-chip), these arrays enable characterization of binding sites for chromatin-associated proteins or the extent of chromatin modifications at genome scale. The Arabidopsis histone acetyltransferase GCN5 associated with 40% of the tested promoters. At most sites, binding did not depend on the integrity of the GCN5 bromodomain. However, the presence of the bromodomain was necessary for binding to 11% of the promoter regions, and correlated with acetylation of lysine 14 of histone H3 in these promoters. Combined analysis of ChIP-chip and transcriptomic data indicated that binding of GCN5 does not strictly correlate with gene activation. GCN5 has previously been shown to be required for light-regulated gene expression and growth, and we found that GCN5 targets were enriched in early light-responsive genes. Thus, in addition to its transcriptional activation function, GCN5 may play an important role in priming activation of inducible genes under non-induced conditions.