title: Platelet-derived MHC class I confers a pseudonormal phenotype to cancer cells that subverts the antitumor reactivity of natural killer immune cells.
abstract: Natural killer (NK) cells are cytotoxic lymphocytes that play an important role in tumor immunosurveillance, preferentially eliminating targets with low or absent expression of MHC class I and stress-induced expression of ligands for activating NK receptors. Platelets promote metastasis by protecting disseminating tumor cells from NK cell immunosurveillance, but the underlying mechanisms are not well understood. In this study, we show that tumor cells rapidly get coated in the presence of platelets in vitro, and circulating tumor cells of cancer patients display coexpression of platelet markers. Flow cytometry, immunofluorescent staining, confocal microscopy, and analyses on an ultrastructural level using immunoelectron microscopy revealed that such coating may cause transfer of MHC class I onto the tumor cell surface resulting in high-level expression of platelet-derived normal MHC class I. The resulting "phenotype of false pretenses" disrupts recognition of tumor cell missing self, thereby impairing cytotoxicity and IFN-γ production by NK cells. Thus, our data indicate that platelets, by conferring an unsuspicious "pseudonormal" phenotype, may enable a molecular mimicry that allows metastasizing tumor cells to downregulate MHC class I, to escape T-cell-mediated immunity without inducing susceptibility to NK cell reactivity.
authors: Department of Hematology and Oncology, Eberhard Karls University, Tuebingen, Germany.
authors: Theresa
authors: T
authors: Placke
authors: Melanie
authors: M
authors: Örgel
authors: Martin
authors: M
authors: Schaller
authors: Gundram
authors: G
authors: Jung
authors: Hans-Georg
authors: HG
authors: Rammensee
authors: Hans-Georg
authors: HG
authors: Kopp
authors: Helmut Rainer
authors: HR
authors: Salih
mesh_terms: D045744:Cell Line, Tumor; D005260:Female; D015395:Histocompatibility Antigens Class I / Q000097:blood / Q000276:immunology*; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology*; D009369:Neoplasms / Q000235:genetics / Q000276:immunology* / Q000473:pathology; D010641:Phenotype; D011971:Receptors, Immunologic / Q000276:immunology
chemical_list: D015395:Histocompatibility Antigens Class I; D011971:Receptors, Immunologic