title: Focal radiation therapy combined with 4-1BB activation and CTLA-4 blockade yields long-term survival and a protective antigen-specific memory response in a murine glioma model.
abstract: BACKGROUND
  Glioblastoma (GBM) is the most common malignant brain tumor in adults and is associated with a poor prognosis. Cytotoxic T lymphocyte antigen -4 (CTLA-4) blocking antibodies have demonstrated an ability to generate robust antitumor immune responses against a variety of solid tumors. 4-1BB (CD137) is expressed by activated T lymphocytes and served as a co-stimulatory signal, which promotes cytotoxic function. Here, we evaluate a combination immunotherapy regimen involving 4-1BB activation, CTLA-4 blockade, and focal radiation therapy in an immune-competent intracranial GBM model.
  
  
  METHODS
  GL261-luciferace cells were stereotactically implanted in the striatum of C57BL/6 mice. Mice were treated with a triple therapy regimen consisted of 4-1BB agonist antibodies, CTLA-4 blocking antibodies, and focal radiation therapy using a small animal radiation research platform and mice were followed for survival. Numbers of brain-infiltrating lymphocytes were analyzed by FACS analysis. CD4 or CD8 depleting antibodies were administered to determine the relative contribution of T helper and cytotoxic T cells in this regimen. To evaluate the ability of this immunotherapy to generate an antigen-specific memory response, long-term survivors were re-challenged with GL261 glioma en B16 melanoma flank tumors.
  
  
  RESULTS
  Mice treated with triple therapy had increased survival compared to mice treated with focal radiation therapy and immunotherapy with 4-1BB activation and CTLA-4 blockade. Animals treated with triple therapy exhibited at least 50% long-term tumor free survival. Treatment with triple therapy resulted in a higher density of CD4+ and CD8+ tumor infiltrating lymphocytes. Mechanistically, depletion of CD4+ T cells abrogated the antitumor efficacy of triple therapy, while depletion of CD8+ T cells had no effect on the treatment response.
  
  
  CONCLUSIONS
  Combination therapy with 4-1BB activation and CTLA-4 blockade in the setting of focal radiation therapy improves survival in an orthotopic mouse model of glioma by a CD4+ T cell dependent mechanism and generates antigen-specific memory.
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Zineb
authors.initials: Z
authors.lastname: Belcaid
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Jillian A
authors.initials: JA
authors.lastname: Phallen
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Jing
authors.initials: J
authors.lastname: Zeng
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Alfred P
authors.initials: AP
authors.lastname: See
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Mathios
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Chelsea
authors.initials: C
authors.lastname: Gottschalk
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Sarah
authors.initials: S
authors.lastname: Nicholas
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Meghan
authors.initials: M
authors.lastname: Kellett
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Jacob
authors.initials: J
authors.lastname: Ruzevick
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Christopher
authors.initials: C
authors.lastname: Jackson
authors.affiliation: Department of Oncology and Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Emilia
authors.initials: E
authors.lastname: Albesiano
authors.affiliation: Department of Oncology and Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Durham
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Xiaobu
authors.initials: X
authors.lastname: Ye
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Phuoc T
authors.initials: PT
authors.lastname: Tran
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Betty
authors.initials: B
authors.lastname: Tyler
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: John W
authors.initials: JW
authors.lastname: Wong
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America; Departments of Oncology, Ophthalmology, and Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Henry
authors.initials: H
authors.lastname: Brem
authors.affiliation: Department of Oncology and Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Drew M
authors.initials: DM
authors.lastname: Pardoll
authors.affiliation: Department of Oncology and Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Charles G
authors.initials: CG
authors.lastname: Drake
authors.affiliation: Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Lim
mesh_terms: D000818:Animals; D000906:Antibodies / Q000627:therapeutic use; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D060908:CTLA-4 Antigen / Q000037:antagonists & inhibitors*; D045744:Cell Line, Tumor; D005260:Female; D005910:Glioma / Q000188:drug therapy* / Q000276:immunology / Q000532:radiotherapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D053261:Tumor Necrosis Factor Receptor Superfamily, Member 9 / Q000819:agonists*
chemical_list: D000906:Antibodies; D060908:CTLA-4 Antigen; D053261:Tumor Necrosis Factor Receptor Superfamily, Member 9