Liposomes containing lipid A: a potent nontoxic adjuvant for a human malaria sporozoite vaccine.

Liposomes containing lipid A have been developed as adjuvants for inducing humoral immunity to synthetic antigens containing repeat sequence epitopes from the circumsporozoite protein of Plasmodium falciparum. Preclinical studies demonstrated that liposomes containing lipid A and encapsulated antigen could overcome immunosuppression observed with antigen alone. When liposomes containing lipid A were adsorbed with aluminum hydroxide (alum), further stimulation of humoral immunity against encapsulated antigen was observed in animals. In the presence of huge doses of liposomal lipid A pyrogenicity was not observed and adjuvant activity was enhanced. A phase I human clinical trial has been initiated utilizing a vaccine containing a synthetic recombinant antigen and monophosphoryl lipid A in liposomes and nonliposomal alum as a further adjuvant. Preliminary results confirm that the vaccine lacks significant acute toxicity in humans and causes very strong specific humoral immunity against the appropriate epitopes of the target antigen.