CpG Oligodeoxynucleotides (ODN) are small single-stranded DNA molecules containing CpG motifs. Their backbone is partially or completely phosphothioated. ODNs whose CpG motifs are unmethylated are recognized by pattern-recognition-receptors (PRR) like Toll-like Receptor 9 (TLR9) and act as immunostimulants. CpG Oligodeoxynucleotides induce cytokine and interferon production, B-cell and monocyte maturation and the activation of NK-cells and plasmocytoid dendritic cells. CpG Oligodeoxynucleotides are therefore used as adjuvants and in cancer therapy. ODNs containing a TTAGGG-motiv however are TLR9-Antagonists and have immunosuppressive effects.