Toward HCV vaccine - Structural studies of HCV E2 envelop glycoprotein that facilitate rational design of HCV vaccine

Netanel Tzarum ^1,5 Linling He ^1,2 Fang Chen ² Erick Gian ² Jannick Prentoe ³ Elias Augestad ³ Leopold Kong ¹ Steven K.H. Foung ⁴ Jens Bukh ³ Jiang Zhu ^1,2 Ian A. Wilson ¹ Mansun Law ²

¹Department of Integrative Structural and Computational Biology, The Scripps Research Institute, USA
²Department of Immunology and Microbiology, The Scripps Research Institute, USA
³Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
⁴Department of Pathology, Stanford University School of Medicine, USA
⁵The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel

Infecting 1-2% of the world population, hepatitis C virus (HCV) is a major health burden that leads to ~500,000 deaths and an estimated 1.5-2 million new infections annually. Direct-acting antivirals effectively treat HCV infection (cure rate of >95%) but face major issues making the development of effective vaccination approaches critical to prevent HCV spread. A major challenge in HCV vaccine development is how to elicit a broadly protective immune response to overcome the high genetic diversity. Broadly neutralizing antibodies (bnAbs) targeting HCV E1 and E2 envelope (Env) glycoproteins help to define conserved neutralizing epitopes and can assist the design of new vaccine immunogens to overcome viral variability. For this purpose, we determined the crystal structures of HCV E2 core (E2c) fragment in complex with a panel of bnAbs that were isolated from infected patients and non-human primate immunization experiments. Structural analysis of our novel structures indicated that cross-neutralization of HCV by this group of bnAbs is mediated by their binding to highly conserved hydrophobic surface that overlaps with the CD81 receptor binding site. Structural based design of the E2c resulted in improved antigens that demonstrate greater antigenicity and thermostability. Crystal structures of the optimized E2 cores with human bnAbs revealed how our design stabilizes E2 without altering key neutralizing epitopes. Displaying of the optimized E2 cores on self-assembling nanoparticles resulted in enhanced antigenicity and more effective elicitation of nAbs response in mice immunization experiments, assessing their potential as HCV vaccine candidates for eliciting a broadly neutralizing B-cell response.