A synthetic lipid A derivative and toll-like receptor 4 (TLR4) agonist, in an oil-in-water emulsion, with potential immunoadjuvant activity. Upon administration, GLA-SE binds to and activates TLR4, thereby stimulating dendritic cells (DCs), monocytes and macrophages. This activation results in the production of proinflammatory cytokines, including interferon alpha, tumor necrosis factor-alpha and the interleukins (IL), IL-1 beta, -6 and -12. This may induce a T helper cell-1 (Th1) immune response and activates a cytotoxic T-lymphocyte (CTL) response against tumor associated antigens (TAAs) upon co-administration of vaccine antigens. TLR4, a member of the TLR family, plays a key role in the activation of innate immunity.