title: Induction of biologically active antibodies in mice, rabbits, and monkeys by Plasmodium falciparum EBA-175 region II DNA vaccine.
abstract: BACKGROUND
  Plasmodium falciparum merozoites bind to and invade human erythrocytes via specific erythrocyte receptors. This establishes the erythrocytic stage of the parasite life cycle that causes clinical disease resulting in 2-3 million deaths per year. We tested the hypothesis that a Plasmodium falciparum ligand, EBA-175 region II (RII), which binds its erythrocyte receptor glycophorin A during invasion, can be used as an immunogen to induce antibodies that block the binding of RII to erythrocytes and thereby inhibit parasite invasion of erythrocytes. Accordingly, we immunized mice, rabbits, and monkeys with DNA plasmids that encoded the 616 amino acid RII.
  
  
  METHODS
  DNA vaccine plasmids that targeted the secretion of recombinant RII protein with and without the universal T-cell helper epitopes P2P30 were used to immunize mice, rabbits, and Aotus monkeys. RII specific antibodies were assessed by IFA, ELISA, blocking of native [35S] labeled EBA-175 binding to human erythrocytes, and growth inhibition assays, all in vitro.
  
  
  RESULTS
  The RII DNA plasmids were highly immunogenic as measured by ELISA and IFA. The anti-RII antibodies blocked the binding of native EBA-175 to erythrocytes, and rosetting of erythrocytes on COS-7 cells expressing RII. Most important, murine and rabbit anti-RII antibodies inhibited the invasion of merozoites into erythrocytes. We immunized nonhuman primates and showed that the RII-DNA plasmids were immunogenic and well tolerated in these monkeys. Monkeys were challenged with parasitized erythrocytes; one of three monkeys that received RII DNA plasmid was protected from fulminant disease. After challenge with live parasites, anti-RII antibody titers were boosted in the immunized monkeys.
  
  
  CONCLUSIONS
  By proving the hypothesis that anti-RII antibodies can block merozoite invasion of erythrocytes, these studies pave the way for the clinical evaluation of EBA-175 as a receptor-blockade vaccine.
authors.affiliation: EntreMed, Inc., Department of Molecular Biology, Rockville, MD 20850, USA. kims@entremed.com
authors.forename: B K
authors.initials: BK
authors.lastname: Sim
authors.forename: D L
authors.initials: DL
authors.lastname: Narum
authors.forename: H
authors.initials: H
authors.lastname: Liang
authors.forename: S R
authors.initials: SR
authors.lastname: Fuhrmann
authors.forename: N
authors.initials: N
authors.lastname: Obaldia
authors.forename: R
authors.initials: R
authors.lastname: Gramzinski
authors.forename: J
authors.initials: J
authors.lastname: Aguiar
authors.forename: J D
authors.initials: JD
authors.lastname: Haynes
authors.forename: J K
authors.initials: JK
authors.lastname: Moch
authors.forename: S L
authors.initials: SL
authors.lastname: Hoffman
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan; D015153:Blotting, Western; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D004912:Erythrocytes / Q000378:metabolism / Q000469:parasitology*; D019084:Fluorescent Antibody Technique, Indirect; D006021:Glycophorins / Q000737:chemistry; D000882:Haplorhini; D006801:Humans; D051379:Mice; D010957:Plasmids / Q000378:metabolism; D010963:Plasmodium falciparum / Q000276:immunology*; D011485:Protein Binding; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism*; D011817:Rabbits; D013997:Time Factors; D019444:Vaccines, DNA
chemical_list: D000953:Antigens, Protozoan; D002352:Carrier Proteins; D006021:Glycophorins; D015800:Protozoan Proteins; D019444:Vaccines, DNA; C065668:erythrocyte-binding antigen 175, Plasmodium