<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A proprietary vaccine adjuvant consisting of an oil-in-water emulsion of saponin QS21 and monophosphoryl lipid A with potential immunostimulating activity. Mono-phosphoryl lipid A is a detoxified derivative of lipid A, a component of lipopolysaccharide (LPS) found in most gram-negative bacteria. QS21 is a purified saponin fraction extracted from the South American tree Quillaja saponaria Molina. When co-administered with peptide vaccines, the adjuvant vaccine may elicit strong humoral and cellular immune responses.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>