Mechanisms of Immunologic Unresponsiveness to Hepatitis C Virus Infection

Andrea Cox, Ph.D.

Johns Hopkins University

Funded in December, 2005: $300000 for 3 years
LAY SUMMARY . ABSTRACT . BIOGRAPHY .

LAY SUMMARY

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Hepatitis C Virus Infection's Outcome May Depend on Immune T Cell Responses

This research will explore whether responses to Hepatitis C virus ("HepC") infection by a specific type of immune T cell, called "CD8 T" cells, determines whether the virus persists to cause cirrhosis or liver cancer, or whether it is cleared from the body.

Persistent HepC viral infection can cause death from liver failure or cancer. In the US, HepC results from use of contaminated needles passed among people injecting illicit drugs, blood transfusions with infected blood, transplantation of infected organs or tissues, and, rarely, from sexual transmission. HepC occurs in about one-quarter of people with HIV infection and has become a leading cause of death among this population. Moreover, HepC is the major cause of liver cancer in the US, and the incidence of this cancer has doubled in the last 20 years. Since HepC causes liver failure or cancer only if the infection persists, however, it is vital to improve methods for clearing it from the body.

The researchers hypothesize that the quality of anti-HepC responses by immune CD8 T cells determines whether or not HepC persists or is effectively eliminated from the body. They suspect that there are functional differences among CD8 T cells, emanating from genetic and environmental interactions, which render CD8 T cells in some people unable to recognize HepC infection. While the prevailing immunological view of chronic infection is that the virus mutates to escape CD8 T immune cell responses, the investigators are pursing the possibility that a malfunction also occurs in the way CD8 T cells respond to conserved parts of the virus. To test this hypothesis, they will study intravenous drug users with HepC infection. Typically, these individuals do not have symptoms of HepC, and about 78 percent of them develop persistent infection. The investigators will try to identify how the responses of CD8 T cells differ among those who develop persistent infection compared to those who do not.

Significance: This research could lead to methods to improve immunity against HepC virus infection among intravenous drug users, reducing their risk of eventual death from liver failure or the development of liver cancer caused by persistence of this infection.

ABSTRACT

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Mechanisms of Immunologic Unresponsiveness to Hepatitis C Virus Infection

Hepatitis C virus (HCV) infection is found in virtually every region of the world and an estimated 170 million persons are infected with HCV worldwide. HCV infection is found in 1-2% of the general population of most countries and may cause cirrhosis or hepatocellular carcinoma, but only if the infection persists. The underlying hypothesis for this proposal is that the quality of HCV-specific T cell responses, CD8 in particular, is a critical determinant of the outcome of HCV infection and that functional impairment of HCV-specific CD8 T cells leads to viral persistence. While we have demonstrated that viral escape mutations in T cell epitopes occur frequently with HCV immune evasion, a significant proportion of CD8 recognized HCV epitopes do not demonstrate escape mutations, even in patients who fail to clear HCV. It is thus likely that functional impairment of CD8 cells specific for non-escaped epitopes is an additional important factor in HCV persistence. We propose that a comprehensive comparative analysis of HCV-specific CD8 T cell phenotype and function among patients who clear HCV infection versus those that do not and between T cells recognizing epitopes that undergo substitution and those that do not will reveal specific molecular and cellular mechanisms of T cell unresponsiveness relevant to viral persistence.

Specifically, we aim:
1. To analyze the phenotype of HCV specific T cells via comprehensive FACS analysis of tetramer+ HCV specific CD8 T cells for the expression of cell surface receptors that have been shown to play important roles in regulating T cell function and responsiveness.
2. To perform a set of in vitro functional analyses assessing the capacity of HCV specific CD8 T cells to produce relevant effector cytokines and to perform killer functions and
3. To perform in vivo functional analysis of HCV specific CD8 T cells by engineering an in vivo cytotoxic lymphocyte (CTL) assay for functional analysis of tetramer+ HCV specific CD8 cells using adoptive transfer into RAG2-/-γc-/- mice. This system will allow us to directly analyze the in vivo functional effects of antibodies and/or cytokines targeted at potentially relevant cell membrane receptors, thereby linking phenotypic results from Aim 1 with functional results from Aims 2 and 3.

Using specific antagonist antibodies, candidate molecular determinants of CD8 T cell unresponsiveness will be interrogated in this novel in vivo system in which human T cells from patients are adoptively transferred into receptive immunodeficient mice. Outcomes of this interrogation will have direct translational relevance to the immunotherapy of chronic HCV infection.

INVESTIGATOR BIOGRAPHIES

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Andrea Cox, Ph.D.

Dr. Cox completed her B.A. and Ph.D. at the University of Virginia and medical school residency and an infectious disease fellowship at Johns Hopkins University. She currently holds a joint appointment as an Assistant Professor in the Departments of Medicine and Oncology at Johns Hopkins.

Her laboratory focuses on the immune response to hepatitis C, virus from the acute phase through clearance or persistence of the virus. She is particularly interested in how the virus evades the immune response to persist in the majority of hosts it infects. Her laboratory recently demonstrated that HCV immune evasion occurs via the selection of viral escape mutations in T cell epitopes in patients who develop persistent HCV infection. Current efforts are directed at elucidating the mechanisms underlying HCV evasion of the immune response so that those mechanisms can be reversed as immunotherapy for HCV.

Drew Pardoll received his B.S., M.D., and Ph.D. degrees from Johns Hopkins University. Except for a fellowship at the National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, he has remained at Hopkins as a resident, fellow, and faculty member. Currently Dr. Pardoll is the Seraph Professor of Oncology and holds joint appointments in Medicine, Pathology and Molecular Biology, and Genetics and is Director of the Cancer Immunology Program, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine. He is a member of numerous professional societies, scientific advisory boards, and National Institute of Health review groups and task forces.

The central goal of Dr. Pardoll's research program is the development of effective new cancer immunotherapy strategies based on understanding the molecular basis of immune recognition and regulation. In particular, he has developed genetically modified vaccines that selectively activate dendritic cells in the body to present tumor antigens to T cells. Dr. Pardoll's group has also discovered a number of costimulatory molecules as well as inhibitory molecules that modulate dendritic cell – T cell interactions and ultimately regulate the amplitude and quality of T cell responses. These insights can be integrated with the emerging understanding of cancer biology to ultimately define how the immune system interacts with tumor cells in a fashion that can be therapeutically manipulated. They can also be applied to the immunotherapy of chronic viral diseases that are precursors to cancer.