8 - Adjuvants

Abstract

An adjuvant is an agent that may stimulate the immune system and increase the response to a vaccine, without having any specific antigenic effect itself. They are predominantly derived from pathogens and often represent pathogen-associated molecular patterns (PAMP) such as LPS, MPL, CpG DNA, bacterial polysaccharide (PS) antigens, bacterial capsular polysaccharide (CPS) conjugates, saponins-QS-21, cytokines, cholera toxin, synthetic oligonucleotides, alum, E. coli heat labile enterotoxin, IL-2, IL-12, GMCSF, lipopeptides, hormones, monophosphoryl lipid A, muramyldipeptide (MDP), T cell-epitope, and vaccine delivery systems such as emulsions, iscoms, liposomes, and microparticles. They activate the cells of the innate immune system. Once activated, the cells of innate immunity drive and focus the acquired immune response. In some studies, delivery systems and immunostimulatory agents have been combined for more effective delivery of the immunostimulatory adjuvant into the antigen-presenting cells (APC). The use of an adjuvant is crucial in rendering the vaccine able to induce an immune response. The use of adjuvant is usually required to induce strong immunological responses to protein antigen. However, serious side effects preclude their use in human vaccines. Currently, the only adjuvant that is licensed for use in human vaccines is an alum. Red blood cells (RBC) can be used as an antigen delivery system for the enhancement of immune targeting for vaccination purposes. Vaccination remains the single most valuable tool in the prevention of infectious disease. Nevertheless, there exists a need to improve the performance of existing vaccines such that fewer boosters are needed or to develop novel vaccines. For the development of effective vaccines for humans, a great need exists for safe and effective adjuvants.