TLR9 agonists as adjuvants for prophylactic and therapeutic vaccines

Distinct immune responses are required for efficient elimination of different pathogens. Programming of the desired type of immune response by safe non-replicating vaccines requires suitable vaccine adjuvants that determine the magnitude and quality of immune responses elicited. Unfortunately, rational vaccine design with a logical choice of adjuvants is hampered by a lack of knowledge about the mechanism(s) of adjuvant activity. Synthetic natural and non-natural oligodeoxynucleotides containing specific motifs centered on a CpG dinucleotide are potent immunostimulatory agents through their binding to toll-like receptor 9 (TLR9). The evolutionary conservation of TLR9 function and the broad therapeutic potential of CpG oligodeoxynucleotides make them of considerable interest for use in human and veterinary medicine. Recent advances in the development and utility of TLR9 agonists in prophylactic or therapeutic vaccines against infectious diseases are focused on.