title: Neutrophil degranulation and immunosuppression in patients with GBM: restoration of cellular immune function by targeting arginase I.
abstract: OBJECTIVE
  The source of glioblastoma (GBM)-associated immunosuppression remains multifactorial. We sought to clarify and therapeutically target myeloid cell-derived peripheral immunosuppression in patients with GBM.
  
  
  METHODS
  Direct ex vivo T-cell function, serum Arginase I (ArgI) levels, and circulating myeloid lineage populations were compared between patients with GBM and normal donors or patients with other intracranial tumors. Immunofunctional assays were conducted using bulk and sorted cell populations to explore the potential transfer of myeloid cell-mediated immunosuppression and to identify a potential mechanism for these effects. ArgI-mediated immunosuppression was therapeutically targeted in vitro through pharmacologic inhibition or arginine supplementation.
  
  
  RESULTS
  We identified a significantly expanded population of circulating, degranulated neutrophils associated with elevated levels of serum ArgI and decreased T-cell CD3ζ expression within peripheral blood from patients with GBM. Sorted CD11b(+) cells from patients with GBM were found to markedly suppress normal donor T-cell function in coculture, and media harvested from mitogen-stimulated GBM peripheral blood mononuclear cell (PBMC) or GBM-associated mixed lymphoid reactions showed ArgI levels that were significantly higher than controls. Critically, T-cell suppression in both settings could be completely reversed through pharmacologic ArgI inhibition or with arginine supplementation.
  
  
  CONCLUSIONS
  These data indicate that peripheral cellular immunosuppression in patients with GBM is associated with neutrophil degranulation and elevated levels of circulating ArgI, and that T-cell function can be restored in these individuals by targeting ArgI. These data identify a novel pathway of GBM-mediated suppression of cellular immunity and offer a potential therapeutic window for improving antitumor immunity in affected patients.
authors.affiliation: Department of Neurosurgery, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA.
authors.forename: Trisha R
authors.initials: TR
authors.lastname: Sippel
authors.forename: Jason
authors.initials: J
authors.lastname: White
authors.forename: Kamalika
authors.initials: K
authors.lastname: Nag
authors.forename: Vadim
authors.initials: V
authors.lastname: Tsvankin
authors.forename: Marci
authors.initials: M
authors.lastname: Klaassen
authors.forename: B K
authors.initials: BK
authors.lastname: Kleinschmidt-DeMasters
authors.forename: Allen
authors.initials: A
authors.lastname: Waziri
mesh_terms: D001119:Arginase / Q000037:antagonists & inhibitors / Q000502:physiology*; D001120:Arginine / Q000627:therapeutic use; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000276:immunology*; D015550:Cell Degranulation; D002478:Cells, Cultured; D005909:Glioblastoma / Q000188:drug therapy* / Q000201:enzymology / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance; D007111:Immunity, Cellular; D058990:Molecular Targeted Therapy / Q000379:methods*; D009504:Neutrophils / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D001120:Arginine; D001119:Arginase