New approaches to antigen delivery.

An improved understanding of immunologic events associated with immunization, the identification of promising new antigens, and an increased capacity to generate these antigens through chemical and biotechnology methods have led to many new vaccine opportunities. Inappropriate antigen exposure, however, can result in unwanted outcomes, such as incomplete protection, allergic reactions, autoimmunity, infection, or even tolerization. Thus, proper antigen delivery is critical for achieving the desired outcome. A number of vaccination approaches have now been described with varied degrees of success. The relative success of these approaches can be correlated with antigen delivery to specific presentation cells and stimulation of the immune system at sites where protective immunity is most appropriate. In addition, a greater understanding of mechanisms involving cells and effector molecules in the events of immunity may allow for improved possibilities for initiating, augmenting, and maintaining the response to a delivered antigen. This review provides insights into the various strategies currently being explored to optimize antigen delivery and the immune response to that antigen.