CD8+ T-cell response promotes evolution of hepatitis C virus nonstructural proteins

Area of Science:

• Virology
• Immunology
• Genetics

Background:

• Hepatitis C virus (HCV) develops mutations to evade CD8+ T-cell responses.
• The population-level impact of this viral evolution remains unclear.
• A 1977-1978 outbreak of HCV genotype 1b provided a unique dataset to study viral adaptation.

Purpose of the Study:

• To investigate the role of CD8+ T-cell escape mutations in Hepatitis C virus evolution.
• To identify specific viral regions and host genetic factors (HLA class I) associated with HCV adaptation.
• To assess the extent of immune pressure on HCV at a population level.

Main Methods:

• Sequencing of HCV nonstructural protein coding regions (NS3-NS5B) from 78 patients.
• Mapping mutations relative to known CD8+ T-cell epitopes.
• Developing statistical methods to detect reproducible selection pressure linked to HLA class I alleles.

Main Results:

• Higher frequency of mutations within CD8+ T-cell epitopes compared to outside, especially in NS3/4A and NS5B.
• Identification of 6 new CD8+ T-cell epitopes confirmed in vitro.
• Reproducible mutations within epitopes correlated with shared HLA alleles, indicating population-level immune pressure.
• Statistical evidence for selection in 18 epitopes, with 14 restricted by HLA-B alleles.

Conclusions:

• HLA class I-associated selection pressure, particularly from HLA-B alleles, drives Hepatitis C virus evolution in nonstructural proteins (NS3/4A, NS5B).
• HCV adaptation to CD8+ T-cell responses occurs at the population level.
• Understanding this adaptation is crucial for developing effective Hepatitis C virus vaccines.