The role of CpG in DNA vaccines

One of the most exciting developments in the field of vaccine research in r ecent years has been DNA vaccines, with which immune responses are induced subsequent to the in vivo expression of antigen from directly introduced pl asmid DNA. Strong immune responses have been demonstrated in a number of an imal models against many viral, bacterial and parasitic pathogens, and seve ral human clinical trials have been undertaken. The strong and long-lasting antigen-specific humoral (antibodies) and cell-mediated (T help, other cyt okine functions and cytotoxic T cells) immune responses induced by DNA vacc ines appear to be due to the sustained in vivo expression of antigen, effic ient antigen presentation and the presence of stimulatory CpG motifs. These features are desirable for the development of prophylactic vaccines agains t numerous infectious agents. Furthermore, the strong cellular responses ar e also very desirable for the development of therapeutic DNA vaccines to tr eat chronic viral infections or cancer. Efforts are now focusing on underst anding the mechanisms for the induction of these immune responses, which in turn should aid in the optimization of DNA vaccines. This review will focu s on the role of CpG motifs in DNA vaccines.