An E. coli-produced single-chain variable fragment (scFv) targeting hepatitis B virus surface protein potently inhibited virion secretion

Antiviral Res. 2019 Feb;162:118-129. doi: 10.1016/j.antiviral.2018.12.019. Epub 2018 Dec 30.

Abstract

Hepatitis B virus (HBV) envelopes as well as empty subviral particles carry in their lipid membranes the small (S), middle (M), and large (L) surface proteins, collectively known as hepatitis B surface antigen (HBsAg). Due to their common S domain all three proteins share a surface-exposed hydrophilic antigenic loop (AGL) with a complex disulfide bridge-dependent structure. The AGL is critical for HBV infectivity and virion secretion, and thus represents a major target for neutralizing antibodies. Previously, a human monoclonal antibody (mAb) targeting a conformational epitope in the AGL, IgG12, exhibited 1000-fold higher neutralizing activity than hepatitis B immune globulin (HBIG). Here we designed a single-chain variable fragment (scFv) homolog of IgG12, G12-scFv, which could be efficiently produced in soluble form in the cytoplasm of E. coli SHuffle cells. Independent in vitro assays verified specific binding of G12-scFv to a conformational S epitope shared with IgG12. Despite 20-fold lower affinity, G12-scFv but not an irrelevant scFv potently neutralized HBV infection of susceptible hepatoma cells (IC50 = 1.8 nM). Strikingly, low concentrations of G12-scFv blocked virion secretion from HBV producing cells (IC50 = 1.25 nM) without disturbing intracellular viral replication, whereas extracellular HBsAg was reduced only at >100-fold higher though still nontoxic concentration. The inhibitory effects correlated with S binding specificity and presumably also G12-scFv internalization into cells. Together these data suggest G12-scFv as a highly specific yet easily accessible novel tool for basic, diagnostic, and possibly future therapeutic applications.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Neutralizing
  • Escherichia coli
  • Hep G2 Cells
  • Hepatitis B Surface Antigens / immunology*
  • Hepatitis B virus / drug effects*
  • Hepatitis B virus / physiology
  • Humans
  • Inhibitory Concentration 50
  • Single-Chain Antibodies / biosynthesis
  • Single-Chain Antibodies / immunology*
  • Single-Chain Antibodies / pharmacology*
  • Virion / drug effects*
  • Virion / physiology
  • Virus Replication / drug effects

Substances

  • Antibodies, Neutralizing
  • Hepatitis B Surface Antigens
  • Single-Chain Antibodies