Basic StudiesAntitumor Activity Mediated by CpG: The Route of Administration is CriticalLou, Yanyan*; Liu, Chengwen*; Lizée, Gregory*; Peng, Weiyi*; Xu, Chunyu*; Ye, Yang*; Rabinovich, Brian A.†; Hailemichael, Yared*; Gelbard, Alexander*; Zhou, Dapeng*; Overwijk, Willem W.*; Hwu, Patrick*Author Information *Departments of Melanoma Medical Oncology †Experimental Diagnostic Imaging, The Center for Cancer Immunology Research, The University of Texas M.D. Anderson Cancer Center, Houston, TX This study is in part supported by the grants from NCI, R01 CA123182, P01 CA128913, and R01 CA116206. All authors have declared there are no financial conflicts of interest with regards to this study. Reprints: Patrick Hwu, Department of Melanoma Medical Oncology, Unit 430, The Center for Cancer Immunology Research, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030 (e-mail: email@example.com). Received August 4, 2010 Accepted December 13, 2010 Journal of Immunotherapy: April 2011 - Volume 34 - Issue 3 - p 279-288 doi: 10.1097/CJI.0b013e31820d2a05 Buy Metrics Abstract Unmethylated CpG oligodeoxynucleotides (CpG) are synthetic toll-like receptor 9 agonists that activate innate immune cells and which have been tested as an immune therapy in a number of cancer clinical trials. Although some antitumor immune responses have been reported, so far the majority of studies have failed to show significant clinical responses to CpG. Here we showed that the route of administration is critical to the antitumor activity of CpG. Although intravenous (i.v.) injection of CpG was capable of inducing the activation and expansion of tumor antigen-specific T cells, most of these activated T cells failed to migrate to tumor sites. By contrast, intratumoral (i.t.) injection of CpG led to extensive tumor infiltration of antigen-specific T cells and subsequent tumor suppression. We further showed that very high levels of inflammatory chemokines [regulated upon activation, normal T-cell expressed, and secreted (RANTES), interferon-inducible protein-10 (IP-10), monocyte chemoattractant protein-1, monocyte chemotactic protein (MCP5), macrophage inflammatory proteins (MIP1α, and MIP1β)] were induced in the tumor microenvironment after i.t. CpG injection, compared with administration by the i.v. route. It is interesting to note that, in vivo depletion of plasmacytoid dendritic cells greatly reduced the levels of chemokines induced; also, T-cell accumulation and antitumor effect were impaired. We also showed that i.t. but not i.v. CpG injection induced a broad antigen-specific T-cell response against tumor-derived antigens. Collectively, our data provides evidence that the route of CpG administration is a critical factor in mediating antitumor activity. By inducing localized inflammatory signals at tumor sites, i.t. CpG effectively promotes the migration, activation and function of immune cells, ultimately leading to improved tumor control. © 2011 Lippincott Williams & Wilkins, Inc.