title: Tetramer enrichment reveals the presence of phenotypically diverse hepatitis C virus-specific CD8+ T cells in chronic infection.
abstract: Virus-specific CD8(+) T cells are rarely detectable ex vivo by conventional methods during chronic hepatitis C virus (HCV) infection. In this study, however, we were able to detect and characterize HCV-specific CD8(+) T cells in all chronically HCV genotype 1a-infected, HLA-A*02:01-positive patients analyzed by performing major histocompatibility complex (MHC) class I tetramer enrichment. Two-thirds of these enriched HCV-specific CD8(+) T-cell populations displayed an effector memory phenotype, whereas, surprisingly, one-third displayed a naive-like phenotype despite ongoing viral replication. CD8(+) T cells with an effector memory phenotype could not expand in vitro, suggesting exhaustion of these cells. Interestingly, some of the naive-like CD8(+) T cells proliferated vigorously upon in vitro priming, whereas others did not. These differences were linked to the corresponding viral sequences in the respective patients. Indeed, naive-like CD8(+) T cells from patients with the consensus sequence in the corresponding T-cell epitope did not expand in vitro. In contrast, in patients displaying sequence variations, we were able to induce HCV-specific CD8(+) T-cell proliferation, which may indicate infection with a variant virus. Collectively, these data reveal the presence of phenotypically and functionally diverse HCV-specific CD8(+) T cells at very low frequencies that are detectable in all chronically infected patients despite viral persistence.
  
  
  OBJECTIVE
  In this study, we analyzed CD8(+) T-cell responses specific for HLA-A*02:01-restricted epitopes in chronically HCV-infected patients, using MHC class I tetramer enrichment. Importantly, we could detect HCV-specific CD8(+) T-cell populations in all patients. To further characterize these HCV-specific CD8(+) T-cell populations that are not detectable using conventional techniques, we performed phenotypic, functional, and viral sequence analyses. These data revealed different mechanisms for CD8(+) T-cell failure in HCV infection, including T-cell exhaustion, viral escape, and functional impairment of naive-like HCV-specific CD8(+) T cells.
authors.affiliation: Department of Medicine II, University Hospital Freiburg, Freiburg, Germany Faculty of Biology, University of Freiburg, Freiburg, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Nitschke
authors.affiliation: Department of Medicine II, University Hospital Freiburg, Freiburg, Germany Faculty of Biology, University of Freiburg, Freiburg, Germany Spemann Graduate School of Biology and Medicine, University of Freiburg, Freiburg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Flecken
authors.affiliation: Department of Medicine II, University Hospital Freiburg, Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Schmidt
authors.affiliation: Institute of Infection and Immunity, Cardiff University School of Medicine, Cardiff, United Kingdom.
authors.forename: Emma
authors.initials: E
authors.lastname: Gostick
authors.affiliation: Institute of Transfusion Medicine, University Hospital Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Marget
authors.affiliation: Department of Medicine II, University Hospital Freiburg, Freiburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Neumann-Haefelin
authors.affiliation: Department of Medicine II, University Hospital Freiburg, Freiburg, Germany.
authors.forename: Hubert E
authors.initials: HE
authors.lastname: Blum
authors.affiliation: Institute of Infection and Immunity, Cardiff University School of Medicine, Cardiff, United Kingdom.
authors.forename: David A
authors.initials: DA
authors.lastname: Price
authors.affiliation: Department of Medicine II, University Hospital Freiburg, Freiburg, Germany robert.thimme@uniklinik-freiburg.de.
authors.forename: Robert
authors.initials: R
authors.lastname: Thimme
mesh_terms: D000328:Adult; D000368:Aged; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D049109:Cell Proliferation; D005260:Female; D016174:Hepacivirus / Q000276:immunology*; D019698:Hepatitis C, Chronic / Q000276:immunology*; D006801:Humans; D007156:Immunologic Memory; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D055815:Young Adult