NCIt definition : A modified form of lipid A, the biologically active part of Gram-negative bacterial
lipopolysaccharide (LPS) endotoxin, and a Toll-like receptor 4 (TLR4) agonist, with
potential immunostimulatory activity. As a vaccine adjuvant, monophosphoryl lipid
A (MPLA) stimulates both cellular and humoral responses to the vaccine antigen. Compared
to LPS, MPLA exerts a similar immunostimulatory activity but with reduced toxicity.;