CpG ODNs are synthetic oligonucleotides that contain unmethylated CpG dinucleotides in particular sequence contexts (CpG motifs)1 . These CpG motifs are present at a 20-fold greater frequency in bacterial DNA compared to mammalian DNA. CpG ODNs are recognized by Toll-like receptor 9 (TLR9) leading to strong immunostimulatory effects2 . Three classes of stimulatory CpG ODNs have been identified, classes A, B and C, which differ in their immunostimulatory activities3-4. Class A CpG ODNs are characterized by a phosphodiester central CpG-containing palindromic motif and a phosphorothioate 3’ poly-G string. They induce high IFN-a production from plasmacytoid dendritic cells (pDC) but are weak stimulators of TLR9-dependent NF-kB signaling. Class B CpG ODNs contain a full phosphorothioate backbone with one or more CpG dinucleotides. They strongly activate B cells but stimulate weakly IFN-a secretion. Class C CpG ODNs combine features of both classes A and B. They contain a complete phosphorothioate backbone and a CpGcontaining palindromic motif. Class C CpG ODNs induce strong IFN-a production from pDC and B cell stimulation. ODN 2395 is a Class C CpG ODN with a preference for human and murine TLR9.