Cytosine-guanine dinucleotides linked through a phosphate backbone have been shown to activate both innate and acquired immune responses. Although CpGs are rarely found in human DNA, they are common in bacterial DNA, and the human immune system recognizes CpGs as an early sign of infection and responds with a powerful immune response. Coley Pharmaceutical Group Inc. believes it can harness this action to treat various diseases, including cancer, allergy and asthma, and infectious diseases, without causing side effects associated with other immunostimulatory agents.

The technology was first identified by Arthur Krieg, professor of medicine at the University of Iowa, who published a paper in Nature, showing that CpGs cause B cells to proliferate and produce certain cytokines. Previously oligonucleotides were not considered to be immunostimulatory. Krieg concluded that there was a possible evolutionary link between vertebrate immune defense mechanisms and the recognition of microbial DNA containing CpGs.