A proprietary synthetic oligonucleotide-based agonist of toll-like receptor 9 (TLR9), with potential immunostimulating activity. Upon administration, TLR9 agonist IMO-2125 binds to and activates TLR9 expressed by plasmacytoid dendritic cells (pDCs) and B cells. This initiates immune signaling pathways, activates B cells and pDCs, and induces a cytotoxic T-lymphocyte (CTL)-mediated immune response against tumor cells. TLR9 is a member of the TLR family, which plays a fundamental role in pathogen recognition and activation of innate immunity.