title: COX-2 inhibition improves immunotherapy and is associated with decreased numbers of myeloid-derived suppressor cells in mesothelioma. Celecoxib influences MDSC function.
abstract: BACKGROUND
  Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature cells that accumulates in tumour-bearing hosts. These cells are induced by tumour-derived factors (e.g. prostaglandins) and have a critical role in immune suppression. MDSC suppress T and NK cell function via increased expression of arginase I and production of reactive oxygen species (ROS) and nitric oxide (NO). Immune suppression by MDSC was found to be one of the main factors for immunotherapy insufficiency. Here we investigate if the in vivo immunoregulatory function of MDSC can be reversed by inhibiting prostaglandin synthesis by specific COX-2 inhibition focussing on ROS production by MDSC subtypes. In addition, we determined if dietary celecoxib treatment leads to refinement of immunotherapeutic strategies.
  
  
  METHODS
  MDSC numbers and function were analysed during tumour progression in a murine model for mesothelioma. Mice were inoculated with mesothelioma tumour cells and treated with cyclooxygenase-2 (COX-2) inhibitor celecoxib, either as single agent or in combination with dendritic cell-based immunotherapy.
  
  
  RESULTS
  We found that large numbers of infiltrating MDSC co-localise with COX-2 expression in those areas where tumour growth takes place. Celecoxib reduced prostaglandin E2 levels in vitro and in vivo. Treatment of tumour-bearing mice with dietary celecoxib prevented the local and systemic expansion of all MDSC subtypes. The function of MDSC was impaired as was noticed by reduced levels of ROS and NO and reversal of T cell tolerance; resulting in refinement of immunotherapy.
  
  
  CONCLUSIONS
  We conclude that celecoxib is a powerful tool to improve dendritic cell-based immunotherapy and is associated with a reduction in the numbers and suppressive function of MDSC. These data suggest that immunotherapy approaches benefit from simultaneously blocking cyclooxygenase-2 activity.
authors.affiliation: Department of Pulmonary Medicine, Erasmus MC Rotterdam, The Netherlands.
authors.forename: Joris D
authors.initials: JD
authors.lastname: Veltman
authors.forename: Margaretha E H
authors.initials: ME
authors.lastname: Lambers
authors.forename: Menno
authors.initials: M
authors.lastname: van Nimwegen
authors.forename: Rudi W
authors.initials: RW
authors.lastname: Hendriks
authors.forename: Henk C
authors.initials: HC
authors.lastname: Hoogsteden
authors.forename: Joachim G J V
authors.initials: JG
authors.lastname: Aerts
authors.forename: Joost P J J
authors.initials: JP
authors.lastname: Hegmans
mesh_terms: D000818:Animals; D015153:Blotting, Western; D000068579:Celecoxib; D051546:Cyclooxygenase 2 / Q000737:chemistry / Q000378:metabolism*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology*; D003713:Dendritic Cells / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D015232:Dinoprostone / Q000378:metabolism; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D007108:Immune Tolerance; D007124:Immunoenzyme Techniques; D007167:Immunotherapy; D008654:Mesothelioma / Q000201:enzymology / Q000276:immunology* / Q000628:therapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D022423:Myeloid Cells / Q000276:immunology* / Q000473:pathology / Q000637:transplantation; D009569:Nitric Oxide / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology
chemical_list: D052246:Cyclooxygenase 2 Inhibitors; D011720:Pyrazoles; D017382:Reactive Oxygen Species; D013449:Sulfonamides; D009569:Nitric Oxide; D051546:Cyclooxygenase 2; D000068579:Celecoxib; D015232:Dinoprostone
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