Induction of anti-glioma natural killer cell response following multiple low-dose intracerebral CpG therapy.
OBJECTIVE
Stimulation of toll-like receptor-9 by CpG oligodeoxynucleotides (CpG-ODN) has been shown to counteract the immunosuppressive microenvironment and to inhibit tumor growth in glioma models. These studies, however, have used high doses of CpG-ODN, which can induce toxicity in a clinical setting. The goal of this study was to evaluate the antitumor efficacy of multiple low-dose intratumoral CpG-ODN in a glioma model.


METHODS
Mice bearing 4-day-old intracranial GL261 gliomas received a single or multiple (two or four) intratumoral injections of CpG-ODN (3 microg) every 4 days. Tumor growth was measured by bioluminescent imaging, brain histology, and animal survival. Flow cytometry and cytotoxicity assays were used to assess anti-glioma immune response.


RESULTS
Two and four intracranial injections of low-dose CpG-ODN, but not a single injection, eradicated gliomas in 70% of mice. Moreover, surviving animals exhibited durable tumor-free remission (> 3 months) and were protected from intracranial rechallenge with GL261 gliomas, showing the capacity for long-term antitumor immunity. Although most inflammatory cells seemed to increase, activated natural killer (NK) cells (i.e., NK(+)CD107a(+)) were more frequent than CD8(+)CD107a(+) in the brains of rechallenged CpG-ODN-treated animals and showed a stronger in vitro cytotoxicity against GL261 target cells. Leukocyte depletion studies confirmed that NK cells played an important role in the initial CpG-ODN antitumor response, but both CD8 and NK cells were equally important in long-term immunity against gliomas.


CONCLUSIONS
These findings suggest that multiple low-dose intratumoral injections of CpG-ODN can eradicate intracranial gliomas possibly through mechanisms involving NK-mediated effector function.
Alizadeh
Darya
D
Division of Neurosurgery, Beckman Research Institute, City of Hope National Medical Center, Duarte, California 91010, USA.
Zhang
Leying
L
Brown
Christine E
CE
Farrukh
Omar
O
Jensen
Michael C
MC
Badie
Behnam
B
D000276:Adjuvants, Immunologic / Q000008:administration & dosage*; D000818:Animals; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D005910:Glioma / Q000188:drug therapy* / Q000276:immunology; D007694:Killer Cells, Natural / Q000276:immunology*; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D009838:Oligodeoxyribonucleotides / Q000008:administration & dosage*; D050378:T-Lymphocytes, Regulatory / Q000187:drug effects; D051217:Toll-Like Receptor 9 / Q000378:metabolism
D000276:Adjuvants, Immunologic; C408982:CPG-oligonucleotide; D009838:Oligodeoxyribonucleotides; D051217:Toll-Like Receptor 9