Characterization of a novel monoclonal antibody targeting epitope II within hepatitis C virus E2 envelope glycoprotein

Infections with hepatitis C virus (HCV) represent a worldwide health burden and a prophylactic vaccine is still not available. Liver transplantation (LT) is often the only option for patients with HCV-induced end-stage liver disease. However, the liver graft becomes infected by circulating virus, resulting in accelerated progression of liver disease. Although the efficacy of HCV treatment has improved significantly, immune compromised LT-patients and patients with advanced liver disease remain difficult to treat. As an alternative approach, interfering with viral entry could prevent infection of the donor liver. In the present study, we describe the full characterization of the human monoclonal antibody (mAb) 2A5 raised against the HCV envelope. Results of GNA binding ELISA showed high affinity of mAb2A5 towards HCV envelope glycoproteins E1E2 of different strains. mAb2A5 efficiently cross-neutralized HCVpp and HCVcc from all genotypes and completely protected humanized mice from genotypes 1a and 4a challenge. Partial protection from genotypes 1b and 6a was achieved however sequence analysis of E1E2 from non-protected mice did not reveal resistance. Epitope mapping using a synthetic peptide library and alanine mutants of full length E1E2 identified the E2-region spanning amino acids 434 to 446 (epitope II) as the predominant contact domain. In addition, the binding activity was completely lost against denatured E1E2 indicating a conformation-dependent epitope. Interestingly, competition ELISA showed no interference with the binding activity of the murine mAb AP33 that target epitope I in the E2 protein. Finally, sequence alignment revealed highly conserved residues critical for mAb binding among different HCV genotypes. In conclusion, mAb2A5 shows potent anti-HCV neutralizing activity and could hence provide an effective strategy to prevent HCV recurrence in chronically infected HCV LT-patients. In addition, the detailed identification of the neutralizing epitope can be applied for the design of prophylactic HCV vaccines with cross-protection activity.