title: Immunogenicity of a recombinant malaria vaccine candidate, domain I+II of AMA-1 ectodomain, from Indian P. falciparum alleles.
abstract: Among the few vaccine candidates under development, apical membrane antigen (AMA-1) of Plasmodium falciparum is one of the most promising erythrocyte stage malaria vaccine candidates under consideration. The overall structure of AMA-1 appears to be conserved as compared to other surface proteins, but there are numerous amino acid substitutions identified among different P. falciparum isolates. Antisera raised against recombinant AMA-1 or naturally acquired human antibodies were strongly inhibitory only towards homologous parasites. In an attempt to examine the strain specificity of antibodies elicited to AMA-1, we have cloned, expressed and purified two allelic variants of domain I+II of AMA-1 ectodomain from Indian P. falciparum isolates in bacteria. One of these is a new haplotype not reported so far and varies in 18 aa positions from the geographically diverse forms 3D7 and 15 from FVO. Refolded proteins were recognized by a conformation specific monoclonal antibody 4G2.dc1 and hyper immune sera. Immunization of mice and rabbits with the purified proteins using CFA/IFA adjuvant generated high titer polyclonal antibodies. Both the alleles induced high levels of IgG1, IgG2a and IgG2b and a low level of IgG3 in mice. Lymphocyte proliferation assays using splenocytes from immunized mice showed significant proliferative responses and cytokines interleukin-2 (IL-2), IL-4, IL-10 and IFN-gamma presence in the culture supernatants. The anti-AMA-1 rabbit antibodies obtained with both the proteins were active in an in vitro parasite growth invasion/inhibition assay. These results suggest that recombinant AMA-1 domain I+II formulated with CFA/IFA adjuvant elicited cellular and humoral responses and is capable of inducing high titer invasion inhibitory antibodies supporting further development of this vaccine candidate.
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India. pvlalitha@mail.jnu.ac.in
authors.forename: P V
authors.initials: PV
authors.lastname: Lalitha
authors.forename: S
authors.initials: S
authors.lastname: Biswas
authors.forename: C R
authors.initials: CR
authors.lastname: Pillai
authors.forename: R K
authors.initials: RK
authors.lastname: Saxena
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000913:Antibodies, Protozoan / Q000097:blood / Q000276:immunology; D000918:Antibody Specificity; D000953:Antigens, Protozoan / Q000235:genetics / Q000276:immunology*; D049109:Cell Proliferation; D016207:Cytokines / Q000378:metabolism; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D006239:Haplotypes; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007194:India; D008214:Lymphocytes / Q000276:immunology; D017780:Malaria Vaccines / Q000235:genetics / Q000276:immunology*; D016778:Malaria, Falciparum / Q000469:parasitology* / Q000517:prevention & control; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000235:genetics / Q000276:immunology* / Q000302:isolation & purification; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology*; D011817:Rabbits; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013154:Spleen / Q000276:immunology; D014614:Vaccines, Synthetic / Q000235:genetics / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D016207:Cytokines; D016054:DNA, Protozoan; D007074:Immunoglobulin G; D017780:Malaria Vaccines; D008565:Membrane Proteins; D015800:Protozoan Proteins; D014614:Vaccines, Synthetic; C090077:apical membrane antigen I, Plasmodium