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Liposomal Malaria Vaccine in Humans: A Safe and Potent Adjuvant Strategy
Louis F. Fries, Daniel M. Gordon, Roberta L. Richards, James E. Egan, Michael R. Hollingdale, Mitchell Gross, Carol Silverman and Carl R. Alving
Proceedings of the National Academy of Sciences of the United States of America
Vol. 89, No. 1 (Jan. 1, 1992), pp. 358-362
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2358536
Page Count: 5
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This study describes the safety and immunogenicity of a liposome-based vaccine injected into human subjects. Thirty healthy adult male volunteers were immunized with a liposome-encapsulated recombinant protein (R32NS181) containing epitopes from the repeat region of the circumsporozoite protein of Plasmodium falciparum. This antigen had previously been found to be poorly immunogenic in humans when it was adsorbed with Al(OH)3. In the present study, R32NS181 was encapsulated in liposomes containing monophosphoryl lipid A that were subsequently adsorbed to Al(OH)3. Increasing doses of liposomes containing antigen and monophosphoryl lipid A were used, but the liposomes were always adsorbed to the same dose of Al(OH)3. R32-specific serum IgG antibody responses to liposome-encapsulated R32NS181 were much higher than levels attained previously in humans with R32NS181 adsorbed to Al(OH)3. Geometric mean specific IgG levels after three doses ranged from 14 to 33 μ g/ml. Sera from volunteers receiving the two highest doses inhibited P. falciparum sporozoite invasion of cultured hepatoma cells by an average of 92%, a result that was again superior to previously reported vaccines. Moderate but acceptable transient local reactogenicity was noted at high doses of the vaccine formulation, but little or no systemic toxicity was seen despite liposomal monophosphoryl lipid A doses up to 2200 μ g. We conclude that encapsulation of poorly immunogenic circumsporozoite protein repeat peptides in monophosphoryl lipid A-containing liposomes is a successful adjuvant strategy in humans for inducing high levels of specific antibody production.
Proceedings of the National Academy of Sciences of the United States of America © 1992 National Academy of Sciences