Mechanisms of increased immunogenicity for DNA-based vaccines adsorbed onto cationic microparticles

Investigation into the mechanism of action of vaccine adjuvants provides opportunities to define basic immune principles underlying the induction of strong immune responses and insights useful for the rational development of subunit vaccines. A novel HIV vaccine composed of plasmid DNA-encoding p55 gag formulated with poly-lactide-co-glycolide microparticles (PLG) and cetyl trimethyl ammonium bromide (CTAB) elicits both serum antibody titers and cytotoxic lymphocyte activity in mice at doses two orders of magnitude lower than those required for comparable response to plasmid DNA in saline. Using this model, we demonstrated the increase in potency requires the DNA to be complexed to the PLG–CTAB microparticles. Furthermore, the PLG–CTAB–DNA formulation increased the persistence of DNA at the injection site, recruited mononuclear phagocytes to the site of injection, and activated a population of antigen presenting cells. Intramuscular immunization with the PLG–CTAB–DNA complex induced antigen expression at both the injection site and the draining lymph node. These findings demonstrate that the PLG–CTAB–DNA formulation exhibits multiple mechanisms of immunopotentiation.