Immunostimulatory CpG oligonucleotides (ODN) activate cells that express TLR 9 and have been shown to improve the host’s response to tumor antigens. Unfortunately, the immunosuppressive microenvironment that surrounds many cancers inhibits Ag-specific cellular responses and thus interferes with CpG-mediated immunotherapy. Myeloid-derived suppressor cells (MDSC) represent an important constituent of this immunosuppressive milieu. Large numbers of MDSC are present in and near tumor sites where they inhibit the activity of antigen-specific T and NK cells. Current studies indicate that the delivery of CpG ODN directly into the tumor bed reduces the immunosuppressive activity of monocytic (CD11b+, Ly6G−, Ly6Chigh) MDSC. Monocytic MDSC express TLR9 and respond to CpG stimulation by i) losing their ability to suppress T cell function, ii) producing Th1 cytokines and iii) differentiating into macrophages with tumoricidal capability. These findings provide insight into a novel mechanism by which CpG ODN contribute to tumor regression, and support intra-tumoral injection as the optimal route for their delivery.

The characteristic features of bronchial asthma reflect the orchestrated activity of Th2 cells. Oligodeoxynucleotides containing CpG motifs (CpG) have recently been highlighted as an immunomodulator that biases toward a Th1-dominant phenotype. We have previously reported that intratracheal coadministration of CpG and allergen inhibited airway eosinophilia and hyperresponsiveness in a synergistic manner. To substantiate the synergism between CpG and Ag, we introduced a covalently linked conjugate between CpG and Ag and examined the efficacy on airway eosinophilia and Th2 cytokine production. We found that the conjugated form of CpG plus Ag was 100-fold more efficient in regulating airway eosinophilia than the unconjugated mixture. The inhibitory effects lasted for at least 2 mo. The inhibition of airway eosinophilia by the conjugate was Ag specific and associated with an improvement of the airway hyperresponsiveness and the unresponsiveness of the Ag-specific Th2 cells in the regional lymph nodes. The CpG-Ag conjugate was 100-fold more effective than the unconjugated mixture for inducing in vitro Th1 differentiation in an IL-12-dependent manner. Our data show that CpG conjugated to Ag can work as a novel Ag-specific immunomodulator and imply that inhalation of allergen-CpG conjugate could be a desensitization therapy for patients with bronchial asthma.

CpG Oligonucleotides (ODN) are immunomodulatory synthetic oligonucleotides designed to specifically agonize Toll-like receptor 9. Here, we review recent progress in understanding the mechanism of action of CpG ODN and provide an overview of human clinical trial results using CpG ODN to improve the vaccines for cancer, allergy and infectious disease.

Endotoxic shock is a life-threatening condition caused by exposure to bacterial LPS. LPS triggers the release of acute phase, proinflammatory, and Th1 cytokines that facilitate the development of endotoxic shock. Synthetic oligodeoxynucleotides (ODN) expressing suppressive TTAGGG motifs effectively down-regulate the production of proinflammatory and Th1 cytokines elicited by a variety of immune stimuli. The current results demonstrate that suppressive ODN protect mice from LPS-induced endotoxic shock. Underlying this protective effect is the ability of suppressive ODN to bind to and prevent the phosphorylation of STAT1 and STAT4, thereby blocking the signaling cascade mediated by LPS-induced IFN-β and IL-12. These findings suggest that suppressive ODN might be of use in the treatment of endotoxic shock.