Manipulation of the immune response to malaria antigens using bacterial-derived lipoproteins

Thesis

Malaria is a major cause of illness and death in the world. Much progress has been made in the development of a vaccine against malaria, but there is still no formulation that can induce effective and long-lasting immunity in diverse populations at an affordable cost. Bacterial lipoproteins are potent stimulators of the innate and acquired arms of the immune system. They have been used as vaccines against bacterial diseases, and short lipopeptides have been shown to be potent adjuvants to a diverse range of vaccines against bacterial and viral diseases, and may also be useful in the development of anti-tumour vaccines. Here, the artificial lipidation of selected malaria antigens, MSP1₁₉ of Plasmodium chabaudi chabaudi AS and a multi-epitope string comprising mainly P.falciparum epitopes (SGC), is investigated. Direct lipid modification of the antigens was achieved by fusion of the protein coding sequence to a bacterial lipidation signal sequence that directs the post-translational addition of fatty acids to the protein. Antigens were also expressed as fusion proteins to a naturally occurring lipoprotein of Pseudomonas aeruginosa, L-OprI. The inclusion of L-OprI as an admixed adjuvant boosted the antibody response to MSP1₁₉, and although this response was not protective against a live blood-stage challenge, neither did it lead to increased parasitaemia and mortality. Immunisation of mice with the multi-epitope string SGC as a fusion to the L-OprI lipoprotein induced an antibody response against the SGC component of the molecule while immunisation with protein alone did not. This antibody response was absolutely dependent on covalent linkage of the L-OprI lipoprotein to SGC; the addition of LOprI as an admixed adjuvant did not induce an antibody response to SGC. SGC-specific IFNγ-secretion by whole spleen cells was induced by immunisation with protein, fusion protein or fusion lipoprotein forms of SGC, but there were no significant differences in the numbers of IFNγ-secreting cells between preparations. There are several technical obstacles that must be overcome before artificial lipoproteins can be produced on a large-scale, but efforts to overcome these obstacles would be worthwhile since lipoproteins appear to represent suitable candidates for further investigation as adjuvants to malaria vaccines.

Authors: Mee, E; Edward Mee

• Publication date: 2004
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Immune response; Antigens; Malaria; Lipoproteins; Immunological aspects; Regulation