title: Route of administration of the TLR9 agonist CpG critically determines the efficacy of cancer immunotherapy in mice.
abstract: BACKGROUND
  The TLR9 agonist CpG is increasingly applied in preclinical and clinical studies as a therapeutic modality to enhance tumor immunity. The clinical application of CpG appears, however, less successful than would be predicted from animal studies. One reason might be the different administration routes applied in most mouse studies and clinical trials. We studied whether the efficacy of CpG as an adjuvant in cancer immunotherapy is dependent on the route of CpG administration, in particular when the tumor is destructed in situ.
  
  
  RESULTS
  In situ tumor destruction techniques are minimally invasive therapeutic alternatives for the treatment of (nonresectable) solid tumors. In contrast to surgical resection, tumor destruction leads to the induction of weak but tumor-specific immunity that can be enhanced by coapplication of CpG. As in situ tumor destruction by cryosurgery creates an instant local release of antigens, we applied this model to study the efficacy of CpG to enhance antitumor immunity when administrated via different routes: peritumoral, intravenous, and subcutaneous but distant from the tumor. We show that peritumoral administration is superior in the activation of dendritic cells, induction of tumor-specific CTL, and long-lasting tumor protection. Although the intravenous and subcutaneous (at distant site) exposures are commonly used in clinical trials, they only provided partial protection or even failed to enhance antitumor responses as induced by cryosurgery alone.
  
  
  CONCLUSIONS
  CpG administration greatly enhances the efficacy of in situ tumor destruction techniques, provided that CpG is administered in close proximity of the released antigens. Hence, this study helps to provide directions to fully benefit from CpG as immune stimulant in a clinical setting.
authors.affiliation: Department of Tumor Immunology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Stefan
authors.initials: S
authors.lastname: Nierkens
authors.forename: Martijn H
authors.initials: MH
authors.lastname: den Brok
authors.forename: Thijs
authors.initials: T
authors.lastname: Roelofsen
authors.forename: Jori A L
authors.initials: JA
authors.lastname: Wagenaars
authors.forename: Carl G
authors.initials: CG
authors.lastname: Figdor
authors.forename: Theo J
authors.initials: TJ
authors.lastname: Ruers
authors.forename: Gosse J
authors.initials: GJ
authors.lastname: Adema
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D045744:Cell Line, Tumor; D045142:Cross-Priming / Q000187:drug effects; D003713:Dendritic Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D004333:Drug Administration Routes; D007109:Immunity / Q000187:drug effects; D016219:Immunotherapy, Adoptive; D007267:Injections; D008198:Lymph Nodes / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000276:immunology*; D009838:Oligodeoxyribonucleotides / Q000008:administration & dosage* / Q000494:pharmacology / Q000627:therapeutic use*; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology; D051217:Toll-Like Receptor 9 / Q000819:agonists*; D016896:Treatment Outcome
chemical_list: D000951:Antigens, Neoplasm; C408982:CPG-oligonucleotide; D009838:Oligodeoxyribonucleotides; D051217:Toll-Like Receptor 9