Cytokines and chemokines are expressed at different levels in small and large murine colon-26 tumors following intratumoral injections of CpG ODN.

Direct tumor injections of (CpG ODN) into murine colon tumor 26 (CT-26) tumors can induce a potent antitumor response. Tumor size at the beginning of treatment determines the final therapeutic outcome, with smaller tumors responding favorably to CpG ODN therapy whereas large tumors do not. CpG ODN injections in small tumors resulted in tumor necrosis and extensive inflammatory cell infiltration, with average survival that is significantly higher (48.1 +/- 34 days) when compared to control ODN-treated mice (16.1 +/- 3.5 days). Cytokines and chemokines are expressed at different levels in small and large CT-26 tumors following intratumoral injections of CpG ODN. We observed that granulocyte-macrophage colony-stimulating factor and interleukin (IL) 6 are the major cytokines that were overexpressed in CpG ODN-treated small tumors but not in large tumors. Similarly, several chemokines (CXCL1, CCL2, and CCL3) were also significantly higher in CpG ODN-treated small tumors compared to control ODN-treated tumors.