Relation between viral fitness and immune escape within the hepatitis C virus protease

Gut. 2006 Feb;55(2):266-74. doi: 10.1136/gut.2005.072231. Epub 2005 Aug 16.

Abstract

Background: The hepatitis C virus (HCV) mutates within human leucocyte antigen (HLA) class I restricted immunodominant epitopes of the non-structural (NS) 3/4A protease to escape cytotoxic T lymphocyte (CTL) recognition and promote viral persistence. However, variability is not unlimited, and sometimes almost absent, and factors that restrict viral variability have not been defined experimentally.

Aims: We wished to explore whether the variability of the immunodominant CTL epitope at residues 1073-1081 of the NS3 protease was limited by viral fitness.

Patients: Venous blood was obtained from six patients (four HLA-A2+) with chronic HCV infection and from one HLA-A2+ patient with acute HCV infection.

Methods: NS3/4A genes were amplified from serum, cloned in a eukaryotic expression plasmid, sequenced, and expressed. CTL recognition of naturally occurring and artificially introduced escape mutations in HLA-A2-restricted NS3 epitopes were determined using CTLs from human blood and genetically immunised HLA-A2-transgenic mice. HCV replicons were used to test the effect of escape mutations on HCV protease activity and RNA replication.

Results: Sequence analysis of NS3/4A confirmed low genetic variability. The major viral species had functional proteases with 1073-1081 epitopes that were generally recognised by cross reactive human and murine HLA-A2 restricted CTLs. Introduction of mutations at five positions of the 1073-1081 epitope prevented CTL recognition but three of these reduced protease activity and RNA replication.

Conclusions: Viral fitness can indeed limit the variability of HCV within immunological epitopes. This helps to explain why certain immunological escape variants never appear as a major viral species in infected humans.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Disease
  • Adult
  • Animals
  • Cytotoxicity, Immunologic
  • Epitopes, T-Lymphocyte / immunology
  • Female
  • Genes, Viral
  • Genetic Variation / immunology
  • HLA-A2 Antigen / metabolism
  • Hepacivirus / genetics*
  • Hepacivirus / immunology
  • Hepatitis C / immunology*
  • Hepatitis C / virology
  • Hepatitis C, Chronic / immunology
  • Hepatitis C, Chronic / virology
  • Humans
  • Immune Tolerance*
  • Immunodominant Epitopes / genetics
  • Immunodominant Epitopes / immunology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Middle Aged
  • Mutation
  • Peptide Fragments / immunology
  • RNA, Viral / genetics
  • T-Lymphocytes, Cytotoxic / immunology
  • Viral Nonstructural Proteins / genetics*
  • Viral Nonstructural Proteins / immunology
  • Virus Replication / genetics
  • Virus Replication / immunology

Substances

  • Epitopes, T-Lymphocyte
  • HLA-A2 Antigen
  • Immunodominant Epitopes
  • NS3 protein, hepatitis C virus
  • Peptide Fragments
  • RNA, Viral
  • Viral Nonstructural Proteins