title: Highly active microbial phosphoantigen induces rapid yet sustained MEK/Erk- and PI-3K/Akt-mediated signal transduction in anti-tumor human gammadelta T-cells.
abstract: BACKGROUND
  The unique responsiveness of Vgamma9Vdelta2 T-cells, the major gammadelta subset of human peripheral blood, to non-peptidic prenyl pyrophosphate antigens constitutes the basis of current gammadelta T-cell-based cancer immunotherapy strategies. However, the molecular mechanisms responsible for phosphoantigen-mediated activation of human gammadelta T-cells remain unclear. In particular, previous reports have described a very slow kinetics of activation of T-cell receptor (TCR)-associated signal transduction pathways by isopentenyl pyrophosphate and bromohydrin pyrophosphate, seemingly incompatible with direct binding of these antigens to the Vgamma9Vdelta2 TCR. Here we have studied the most potent natural phosphoantigen yet identified, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), produced by Eubacteria and Protozoa, and examined its gammadelta T-cell activation and anti-tumor properties.
  
  
  RESULTS
  We have performed a comparative study between HMB-PP and the anti-CD3epsilon monoclonal antibody OKT3, used as a reference inducer of bona fide TCR signaling, and followed multiple cellular and molecular gammadelta T-cell activation events. We show that HMB-PP activates MEK/Erk and PI-3K/Akt pathways as rapidly as OKT3, and induces an almost identical transcriptional profile in Vgamma9(+) T-cells. Moreover, MEK/Erk and PI-3K/Akt activities are indispensable for the cellular effects of HMB-PP, including gammadelta T-cell activation, proliferation and anti-tumor cytotoxicity, which are also abolished upon antibody blockade of the Vgamma9(+) TCR Surprisingly, HMB-PP treatment does not induce down-modulation of surface TCR levels, and thereby sustains gammadelta T-cell activation upon re-stimulation. This ultimately translates in potent human gammadelta T-cell anti-tumor function both in vitro and in vivo upon transplantation of human leukemia cells into lymphopenic mice,
  
  
  CONCLUSIONS
  The development of efficient cancer immunotherapy strategies critically depends on our capacity to maximize anti-tumor effector T-cell responses. By characterizing the intracellular mechanisms of HMB-PP-mediated activation of the highly cytotoxic Vgamma9(+) T-cell subset, our data strongly support the usage of this microbial antigen in novel cancer clinical trials.
authors.affiliation: Molecular Immunology Unit, Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
authors.forename: Daniel V
authors.initials: DV
authors.lastname: Correia
authors.forename: Francisco
authors.initials: F
authors.lastname: d'Orey
authors.forename: Bruno A
authors.initials: BA
authors.lastname: Cardoso
authors.forename: Telma
authors.initials: T
authors.lastname: Lança
authors.forename: Ana R
authors.initials: AR
authors.lastname: Grosso
authors.forename: Ana
authors.initials: A
authors.lastname: deBarros
authors.forename: Leila R
authors.initials: LR
authors.lastname: Martins
authors.forename: João T
authors.initials: JT
authors.lastname: Barata
authors.forename: Bruno
authors.initials: B
authors.lastname: Silva-Santos
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D017252:CD3 Complex / Q000378:metabolism; D045744:Cell Line, Tumor; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D011756:Diphosphates / Q000276:immunology; D004705:Endocytosis / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D008024:Ligands; D008213:Lymphocyte Activation / Q000187:drug effects; D051379:Mice; D016513:Mice, SCID; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D018716:Molecular Mimicry / Q000187:drug effects; D009369:Neoplasms / Q000276:immunology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000276:immunology*; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: C443995:4-hydroxy-3-methylbut-2-enyl pyrophosphate; D000942:Antigens, Bacterial; D017252:CD3 Complex; D011756:Diphosphates; D007376:Interleukin-2; D008024:Ligands; D016692:Receptors, Antigen, T-Cell, gamma-delta; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases