Adjuvanticity of stealth liposomes on the immunogenicity of synthetic gp41 epitope of HIV-1

Present study aims to enhance the efficacy of liposomes as an adjuvant by steric protection and strengthen the path of vaccine research. PEG grafted liposomes carrying epitopes on their surface showed enhanced adjuvanticity than liposomes carrying epitopes for elicitation and prolongation of immune response to an antigenic epitope of gp41, a transmembrane protein of HIV-1. The multiples of epitope were incorporated onto the surface of liposomes by conjugating them with phosphatidylethanolamine that was used in the formulation of liposomes at an optimized ratio. Furthermore, the liposomes carrying epitopes on their surface were sterically protected by shielding with methoxy-poly(ethylene glycol), mass 20 kDa. Methoxy-poly(ethylene glycol) was activated to its electrophilic N-succinimide carbonate derivative, methoxy-poly(ethylene glycol)-N-succinimide carbonate, that formed a urethane linkage with the amino group of phosphatidylethanolamine. The epitope was covalently coupled to phosphatidylethanolamine through an amide bond between the –COOH group of the epitope and –NH2 group of phosphatidylethanolamine under the catalysis of 1-ethyl-3-(3-dimethylaminopropy-1)-carbodiimide. PEG grafted epitopes carrying liposomes showed about two times higher immune response and prolonged persistence of antibodies than that of liposomes carrying epitopes without PEG moieties.