Advances in novel vaccine adjuvants based on TLR4 agonists

Toll-like receptor 4 (TLR4), a type Ⅰ transmembrane protein, has been extensively studied in the Toll-like receptor family at present. TLR4 ligands include lipopolysaccharides (LPS) present in the outer membrane of gram-negative bacteria and monophosphoryl lipid A (MPLA) which is a derivative of LPS. TLR4 agonists, alone, as a major component of compound adjuvants or in combination with other TLRs agonists, have been widely used as adjuvants in various vaccines and demonstrated great potential in vaccine development. This review addressed the discovery, application, features and prospect of novel vaccine adjuvants based on TLR4 agonists, aiming to provide reference for rational use of adjuvants and further development. Key words: Adjuvant; Immunostimulant; TLR4; Vaccine