Virus-neutralizing antibodies to hepatitis C virus.

For a long time, the lack of an appropriate cell culture system has hampered the study of neutralizing antibody responses against hepatitis C virus (HCV). However, the last decade has seen the development of several model systems that have significantly advanced our understanding of viral entry and antibody neutralization. Studies of acutely infected patients suggest that a strong and early production of neutralizing antibodies may contribute to control the virus during the acute phase of HCV infection and facilitate viral elimination by cellular immune responses. It also emerges that the early antibody response mainly targets hypervariable region 1 (HVR1) of the envelope glycoprotein E2. This host response can lead to viral escape from neutralization by rapid amino acid changes in this hypervariable region. In contrast, cross-reactive neutralizing antibodies seem to appear later during HCV infection, and several mechanisms contribute to reduce their accessibility to their cognate epitopes. These include the masking of major conserved neutralizing epitopes by HVR1, specific N-linked glycans and the lipid moiety of the viral particle. Other potential mechanisms of evasion from the neutralizing antibody response include a modulation by high-density lipoproteins and interfering antibodies as well as the capacity of the virus to be transferred by cell-to-cell contacts. Finally, the recent identification of several highly conserved neutralizing epitopes provides some opportunities for the design and development of vaccine candidates that elicit a protective humoral immune response.