title: Use of immunodampening to overcome diversity in the malarial vaccine candidate apical membrane antigen 1.
abstract: Apical membrane antigen 1 (AMA1) is a leading malarial vaccine candidate; however, its polymorphic nature may limit its success in the field. This study aimed to circumvent AMA1 diversity by dampening the antibody response to the highly polymorphic loop Id, previously identified as a major target of strain-specific, invasion-inhibitory antibodies. To achieve this, five polymorphic residues within this loop were mutated to alanine, glycine, or serine in AMA1 of the 3D7 and FVO Plasmodium falciparum strains. Initially, the corresponding antigens were displayed on the surface of bacteriophage, where the alanine and serine but not glycine mutants folded correctly. The alanine and serine AMA1 mutants were expressed in Escherichia coli, refolded in vitro, and used to immunize rabbits. Serological analyses indicated that immunization with a single mutated form of 3D7 AMA1 was sufficient to increase the cross-reactive antibody response. Targeting the corresponding residues in an FVO backbone did not achieve this outcome. The inclusion of at least one engineered form of AMA1 in a biallelic formulation resulted in an antibody response with broader reactivity against different AMA1 alleles than combining the wild-type forms of 3D7 and FVO AMA1 alleles. For one combination, this extended to an enhanced relative growth inhibition of a heterologous parasite line, although this was at the cost of reduced overall inhibitory activity. These results suggest that targeted mutagenesis of AMA1 is a promising strategy for overcoming antigenic diversity in AMA1 and reducing the number of variants required to induce an antibody response that protects against a broad range of Plasmodium falciparum AMA1 genotypes. However, optimization of the immunization regime and mutation strategy will be required for this potential to be realized.
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Karen S
authors.initials: KS
authors.lastname: Harris
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Adda
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Madhavi
authors.initials: M
authors.lastname: Khore
authors.affiliation: Centre for Biomedical Research, Burnet Institute, Melbourne, Australia.
authors.forename: Damien R
authors.initials: DR
authors.lastname: Drew
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Antonina
authors.initials: A
authors.lastname: Valentini-Gatt
authors.affiliation: Centre for Biomedical Research, Burnet Institute, Melbourne, Australia.
authors.forename: Freya J I
authors.initials: FJ
authors.lastname: Fowkes
authors.affiliation: Centre for Biomedical Research, Burnet Institute, Melbourne, Australia.
authors.forename: James G
authors.initials: JG
authors.lastname: Beeson
authors.affiliation: Department of Structural Vaccinology, Malaria Vaccine Branch, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA.
authors.forename: Sheetij
authors.initials: S
authors.lastname: Dutta
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Robin F
authors.initials: RF
authors.lastname: Anders
authors.affiliation: Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia m.foley@latrobe.edu.au.
authors.forename: Michael
authors.initials: M
authors.lastname: Foley
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D000940:Antigenic Variation / Q000276:immunology; D000953:Antigens, Protozoan / Q000276:immunology*; D014644:Genetic Variation; D008288:Malaria / Q000469:parasitology / Q000517:prevention & control*; D017780:Malaria Vaccines / Q000276:immunology*; D008565:Membrane Proteins / Q000276:immunology*; D008958:Models, Molecular; D016296:Mutagenesis; D009154:Mutation; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000276:immunology*; D011817:Rabbits; D011994:Recombinant Proteins; D013045:Species Specificity
chemical_list: D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D017780:Malaria Vaccines; D008565:Membrane Proteins; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C090077:apical membrane antigen I, Plasmodium