Effects of QS-21 on Innate and Adaptive Immune Responses

Immunological adjuvants typically fall within two classifications: (a) “vehicle” adjuvants that transport antigen from injection sites to lymphoid tissues (generally particulate adjuvants such as emulsions, liposomes, or mineral salts) and (b) “immunomodulators” that act on antigen-presenting cells (APCs) or other cells to induce a cytokine response that influences the immune response to a co-adminstered antigen (). Most immunomodulators are derived from bacterial sources (). These include lipopolysaccharides and derivatives such as lipid A or unmethylated deoxyribonucleic acid (DNA) or oligonucleotide sequences, such as CpG enriched sequences from bacteria. However, natural products from other sources can also act as immunomodulators. One such product is the plant saponin QS-21.