Defining protective immunity in hepatitis C virus infection, using novel ultra-sensitive techniques

Hepatitis C virus is a pandemic infection. Following infection with HCV the majority of individuals develop persistent infection associated with progressive liver disease and ultimately liver cirrhosis. The minority spontaneously eradicate the virus. The reasons as to why individuals have completely different clinical outcomes are currently unclear.

The best therapy to date for HCV infection is interferon- given in combination with ribavirin over 6-12 months. This therapy is effective in 45% of patients with genotype-1 HCV infection, but in 75% of genotype-3 infection. In the UK the majority of individuals are infected with therapy resistant genotype-1 HCV infection. The reasons for the dramatically different response rates between viral genoptypes is not known.

I plan to assess the role of the immune response, and in particular the T-lymphocyte response, in determining the resolution of HCV infection. I will assess this both in the context of spontaneous resolution and in the context of therapy. A better understanding of the factors which influence viral control is crucially important in directing future effective therapeutic and vaccination strategies.

Aims and relevance: Hepatitis C virus (HCV) infects 170 million people and is a significant cause of patient mortality and morbidity. My aim is to define those aspects of cellular immunity associated with viral control. This is essential for the development of future therapeutic strategies.

Scientific objectives and plan: My objectives are to study this in two distinct situations: (1) spontaneous control of virus following primary infection; (2) control of virus during drug therapy.
Following primary infection, 15% of individuals spontaneously control virus, whilst 85% develop persistent infection. Once persistent infection is established T-cell responses are clearly attenuated. However, previous work has shown that the quality of the T-cell response as well as the magnitude of the response is likely to play an important role in determining outcome. I plan to determine the qualitative aspects of the T-cell response in individuals with distinct clinical outcomes and to track the evolution of these responses and the virus during the primary phase of infection. I have established a collaboration with Dr. Paolo Fabris (Italy) who is providing sequential samples from patients with primary HCV infection.
My second objective is to study the cellular immune responses associated with viral control during combination therapy (pegylated-interferon- and ribavirin), having previously demonstrated that these drugs have immunomodulatory activity, in vitro and in vivo. During combination therapy, a sustained virological response is achieved in only 45% of genotype-1 patients treated for 12 months, but in 75% of genotype-3 patients treated for 6 months. Despite this fascinating observation, the host cellular response to genotype-3 infection is currently completely unknown. Since the viral sequences of these genotypes are very different they will present distinct T-cell epitopes. Thus, one explanation is that there is a different T-cell response to genotype-3 infection, which is preferentially enhanced by combination therapy. I plan to examine this hypothesis.

Design and collaborations: This will involve the use of techniques that I am proficient in (ELISpot matrix of genotype specific peptides to define HCV epitopes, panels of HLA class-I and HLA class-II tetramers, the technique of magnetic selection to identify rare populations of HCV specific T-cells, phenotypic analysis, cytokine secretion and cytotoxicity assays). Additionally I will develop techniques that are new to me. To do this I have set up the following collaborations; E. Holmes (Oxford) and Peter Simmonds (Edinburgh) -the analysis of viral evolution, V. Cerundolo (IMM, Oxford)-T-cell priming, A. Sewell (Oxford)-TCR affinity binding.