title: Merkel cell polyomavirus-specific CD8⁺ and CD4⁺ T-cell responses identified in Merkel cell carcinomas and blood.
abstract: OBJECTIVE
  Merkel cell polyomavirus (MCPyV) is prevalent in the general population, integrates into most Merkel cell carcinomas (MCC), and encodes oncoproteins required for MCC tumor growth. We sought to characterize T-cell responses directed against viral proteins that drive this cancer as a step toward immunotherapy.
  
  
  METHODS
  Intracellular cytokine cytometry, IFN-γ enzyme-linked immunospot (ELISPOT) assay, and a novel HLA-A*2402-restricted MCPyV tetramer were used to identify and characterize T-cell responses against MCPyV oncoproteins in tumors and blood of MCC patients and control subjects.
  
  
  RESULTS
  We isolated virus-reactive CD8 or CD4 T cells from MCPyV-positive MCC tumors (2 of 6) but not from virus-negative tumors (0 of 4). MCPyV-specific T-cell responses were also detected in the blood of MCC patients (14 of 27) and control subjects (5 of 13). These T cells recognized a broad range of peptides derived from capsid proteins (2 epitopes) and oncoproteins (24 epitopes). HLA-A*2402-restricted MCPyV oncoprotein processing and presentation by mammalian cells led to CD8-mediated cytotoxicity. Virus-specific CD8 T cells were markedly enriched among tumor infiltrating lymphocytes as compared with blood, implying intact T-cell trafficking into the tumor. Although tetramer-positive CD8 T cells were detected in the blood of 2 of 5 HLA-matched MCC patients, these cells failed to produce IFN-γ when challenged ex vivo with peptide.
  
  
  CONCLUSIONS
  Our findings suggest that MCC tumors often develop despite the presence of T cells specific for MCPyV T-Ag oncoproteins. The identified epitopes may be candidates for peptide-specific vaccines and tumor- or virus-specific adoptive immunotherapies to overcome immune evasion mechanisms in MCC patients.
authors: Department of Medicine/Dermatology, University of Washington, Seattle, Washington 98109, USA.
authors: Jayasri G
authors: JG
authors: Iyer
authors: Olga K
authors: OK
authors: Afanasiev
authors: Christopher
authors: C
authors: McClurkan
authors: Kelly
authors: K
authors: Paulson
authors: Kotaro
authors: K
authors: Nagase
authors: Lichen
authors: L
authors: Jing
authors: Joshua O
authors: JO
authors: Marshak
authors: Lichun
authors: L
authors: Dong
authors: Joseph
authors: J
authors: Carter
authors: Ivy
authors: I
authors: Lai
authors: Erik
authors: E
authors: Farrar
authors: David
authors: D
authors: Byrd
authors: Denise
authors: D
authors: Galloway
authors: Cassian
authors: C
authors: Yee
authors: David M
authors: DM
authors: Koelle
authors: Paul
authors: P
authors: Nghiem
mesh_terms: D000818:Animals; D000957:Antigens, Viral, Tumor / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D019556:COS Cells; D015266:Carcinoma, Merkel Cell / Q000097:blood / Q000276:immunology* / Q000821:virology; D002522:Chlorocebus aethiops; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D059871:HLA-A24 Antigen / Q000276:immunology; D006801:Humans; D007371:Interferon-gamma / Q000096:biosynthesis / Q000276:immunology; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology; D059965:Merkel cell polyomavirus / Q000276:immunology*; D010455:Peptides / Q000276:immunology; D027601:Polyomavirus Infections / Q000097:blood / Q000276:immunology* / Q000821:virology; D012878:Skin Neoplasms / Q000097:blood / Q000276:immunology* / Q000821:virology; D014412:Tumor Virus Infections / Q000097:blood / Q000276:immunology* / Q000821:virology
chemical_list: D000957:Antigens, Viral, Tumor; D018984:Epitopes, T-Lymphocyte; C438506:HLA-A*24:02 antigen; D059871:HLA-A24 Antigen; D010455:Peptides; D007371:Interferon-gamma