Poster Presentation Melbourne Protein Group Student Symposium 2013

Investigating HCV escape mechanisms towards a broadly neutralising monoclonal antibody, MAb24 (#33)

Jun Gu 1 2 , Patricia Vietheer 1 , Yousef Alhammad 1 2 , Pantelis Poumbourios 1 2 , Heidi E Drummer 1 2 3
  1. Viral Fusion Laboratory, Burnet Institute, Melbourne, VIC , Australia
  2. Department of Microbiology, Monash University, Clayton, VIC, Australia
  3. Department of Microbiology and Immunology, University of Melbourne, Parkville, VIC, Australia

Hepatitis C virus (HCV) affects 200 million people worldwide.  It causes chronic liver diseases and is the main indicator for liver transplantation in developed countries.  Given its huge genetic diversity and high mutation rate, the development of a universal HCV vaccine is challenging.  Previous studies showed that HCV surface glycoprotein E2 interacts directly with its major host cell receptor CD81 and is the main target of antibody response.  Neutralizing antibodies targeting E2 can prevent infection both in vitro and in vivo.  Thus, generating an early broadly neutralizing antibody (brNAb) response against E2 will prevent the infection by diverse strains of HCV.

MAb24 is a mouse monoclonal brNAb elicited in response to immunization with Delta3TM, a lead vaccine candidate developed by our group that contains the highly conserved minimal core domain of E2.  Biochemical analyses indicate that MAb24 cross reacts with E2 from six major genotypes and inhibits E2-CD81 interaction.  Epitope mapping revealed that MAb24 recognises region that partially overlaps with previously characterized MAbs but also recognises distinct residues on E2.  Therefore, MAb24 has potential for as an immunotherapeutic agent. 

Antibodies of similar specificity to MAb24 can be elicited during natural HCV infection. In this study we used MAb24 to determine how HCV can escape antibody-mediated neutralization. The Huh 7.5 liver cell line was infected with cell culture derived HCV in the presence of a 90% neutralizing dose of MAb24 and serially passaged in the presence of MAb24 in vitro.  After 9 passages, MAb24 resistant virus was detected.  Sequencing of the viral cDNA revealed that escape to MAb24 involves acquisition of an N415D mutation, which is a direct change in the MAb24 epitope region and increases viral affinity for CD81. The escape mechanism may involve an increased ability of the virus to mediate cell-cell spread. In conclusion, we hope to better understand the specificity of brNAbs and the mechanism of viral escape. This will aid vaccine design.