Analysis of CD8+ T cell quality in Hepatitis C using novel MHC peptide tetramers.

Lead Research Organisation: University of Oxford
Department Name: Clinical Medicine

Abstract

Hepatitis C virus (HCV) infects nearly 200 million people worldwide. Once infected the body mounts an immune response, which is variably successful. Sometimes the immune response can clear the virus, however in most cases it fails to do so and the virus can then go on to cause severe liver damage. The quality of the immune response may determine the outcome of the infection. One aspect of the quality is how sensitive the key immune cells (T cells) are to low amounts of virus - the more sensitive cells might be more efficient in controlling the virus. We have developed new methods for measuring the quality of T cells in different people, including healthy volunteers receiving an experimental vaccine against HCV. We aim to create a panel of new tetramers, specially designed to identify the high and low quality cells in different donors, and look at how these correlate with the outcome of infection, or change over time. In doing this we hope to be able to better understand why some people clear the virus and others do not, and also to design better vaccines or immune treatments in the future.

Technical Summary

Background: Hepatitis C virus (HCV) sets up persistence in the majority of those infected. A minority, however, are able to control the virus long term. The innate and adaptive responses which determine this have been defined to some extent, but we still do not understand the detailed differences between successful and unsuccessful responses. CD8+ T cells have been shown to be important in control of HCV, and specific HLA alleles such as HLA B27 and A3 have been shown to be protective in certain cohorts. We propose to use MHC-peptide tetramers, fluorescent complexes which bind the T cell receptor (TCR) specifically, to define the CD8 dependence and TCR affinity of individual responses from HCV infected donors and controls.

Methodology: The Oxford lab have recently developed a set of tetrameric complexes which allow direct evaluation of the affinity of the T cells for peptide antigen (magic tetramers). This is achieved by modification of the CD8 binding site on MHC allowing identification of specific T cell subpopulations which are CD8 independent or hyper-dependent. This links closely with the triggering threshold for such cell populations in functional assays.

Design: The lab has identified cohorts of patients where such an approach can be exploited to identify the association between TCR affinity and clinical outcome. These include patients with chronic and acute infection, across a range of HLAs including patients with HLA-B27, the best defined protective allele. Functional assays will also be performed in concert with tetramer analyses.

Aims: I aim to use these tools and patients to define:
1. Changes in the quality (affinity) of responses over time in acute disease.
2. Differences in quality between different patient groups.
3. Differences in quality between different peptides/HLAs.
4. Differences in quality between different peptides/HLAs in a new cohort of healthy volunteers to be vaccinated with a novel HCV vaccine, designed specifically to elicit CD8+ T cells through novel viral vectors. (Funding for such a trial is already established and it is due to start in 2008 pending final regulatory approvals).

Opportunities: We aim to use novel tools to define the functionality of antiviral CD8+ T cells in relation to the outcome of persistent infection. This has implications for defining the outcome of HCV, its treatment and vaccination but also beyond this to other significant persistent viruses, including HBV and HIV, where the host-virus balance may hinge on similar aspects of T cell quality.

Publications

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Billerbeck E (2010) Analysis of CD161 expression on human CD8+ T cells defines a distinct functional subset with tissue-homing properties. in Proceedings of the National Academy of Sciences of the United States of America

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Walker LJ (2010) T cell sensitivity and the outcome of viral infection. in Clinical and experimental immunology

 
Description Analysis of microarray data from CD161++CD8+ T cells from cord blood and CD8aa T cells from adult peripheral blood 
Organisation University of Oxford
Department Wellcome Trust Centre for Human Genetics
Country United Kingdom 
Sector Academic/University 
PI Contribution We provided the raw data for this collaboration.
Collaborator Contribution Our collaborative partners provided bioinformatics expertise.
Impact Data from this collaboration is included in the paper currently pre-published in Blood (see previous section for details).
Start Year 2010
 
Description Study of CD161++CD8+ T cells in infants 
Organisation University of Cape Town
Country South Africa 
Sector Academic/University 
PI Contribution We used the samples to perform FACS analysis to study the CD161++CD8+ T cell subset.
Collaborator Contribution The collaboration provided samples from healthy infants to study.
Impact We have a paper pre-published online in Blood (see details in previous section) that has included data from this collaboration.
Start Year 2009
 
Description Study of Mucosal Associated Invariant T cells and their relationship to CD161++CD8+ T cells 
Organisation Marie Curie
Department Marie Curie Research Institute
Country United Kingdom 
Sector Academic/University 
PI Contribution We used the antibody provided to study the CD161++CD8+ T cell population.
Collaborator Contribution This collaboration provided an antibody against the MAIT cell T cell receptor (Va7.2), which was not commercially available at the time.
Impact The data obtained from this collaboration is included in the paper pre-published in Blood (see previous section for details).
Start Year 2010
 
Description Study of intra-hepatic CD161++CD8+ T cells 
Organisation University of Birmingham
Country United Kingdom 
Sector Academic/University 
PI Contribution We used the samples provided for FACS analysis of intra-hepatic CD161++CD8+ T cell populations
Collaborator Contribution This collaboration provided samples of liver derived lymphocytes.
Impact Data obtained from this collaboration is included in the paper which is pre-published in Blood (see previous section for details).
Start Year 2009
 
Description Study of peripheral and intra-hepatic CD161++CD8+ T cells in hepatitis C 
Organisation Harvard University
Department Department of Gastroenterology Harvard
Country United States 
Sector Academic/University 
PI Contribution We used the samples provided to study the CD161++CD8+ T cell population in the peripheral circulation and in the liver in chronic hepatitis C.
Collaborator Contribution This collaboration provided paired peripheral blood and intrahepatic lymphocyte samples for FACS analysis.
Impact Data obtained from this collaboration is in the paper currently pre-published in Blood (see previous section).
Start Year 2009