Mouse care and experimental procedures were performed under pathogen-free conditions in accordance with established institutional guidance and approved protocols from Research Animal Care Committees of the City of Hope. For s.c. tumor challenge, we injected 1 × 10 5 B16, C4 or CT26 tumor cells into 7-8 weeks C57BL/6, C57BL/6.CEA, C3H or Balb/C mice, respectively. After tumors reached average size of ca. 5 mm, mice were injected peritumorally with 0.78 nmol of CpG1668 ODN alone, in combination with Stat3 siRNA or CpG/GpC ODN linked to various double stranded RNA (dsRNA) sequences described above. Tumor growth was monitored every other day. For the analysis of cellular and molecular mechanisms of CpG/GpC-dsRNAs effects, mice were killed after 2-3 weeks of treatment. For experiments on silencing of luciferase activity in vivo, Luc + mice (originally kindly provided by Dr. Christopher H. Contag, Stanford University School of Medicine, CA) were challenged with tumor and treated with 3 daily injections of CpG-Luc siRNA or CpG-scrambled RNA. Lymph nodes as well as tumor specimens were harvested. For B16 lung metastasis model, mice were challenged with 0.5 × 10 5 B16 tumor cells (i.v.) and two d later, after tumors were established, were treated systemically with 0.78 nmol (ca. 1 mg/kg) of CpG1668 ODN or various CpG-dsRNAs. Intravenous injections were repeated every other day for two weeks. Lungs were harvested, fixed and the number of B16 tumor colonies was manually counted. The level of Stat3 silencing was assessed by real-time PCR in DCs isolated from tumor-draining inguinal (for s.c. tumor model) or cervical (for metastasis model) lymph nodes. For immune cell depletion, mice were pretreated with anti-CD8 plus anti-CD4 antibodies (clone 2.43 and GK1.5, respectively, depleting 99% and 98% of CD8 and CD4 cells, respectively) or anti-asialo-GM1 antibodies (Wako, depleting min. 79% of NK cells) before tumor inoculation then injected weekly.