Invasion-Inhibitory Antibodies Elicited by Immunization with Plasmodium vivax Apical Membrane Antigen-1 Expressed in Pichia pastoris Yeast

<jats:title>ABSTRACT</jats:title><jats:p>In a recent vaccine trial performed with African children, immunization with a recombinant protein based on<jats:named-content content-type="genus-species">Plasmodium falciparum</jats:named-content>apical membrane antigen 1 (AMA-1) conferred a significant degree of strain-specific resistance against malaria. To contribute to the efforts of generating a vaccine against<jats:named-content content-type="genus-species">Plasmodium vivax</jats:named-content>malaria, we expressed the ectodomain of<jats:named-content content-type="genus-species">P. vivax</jats:named-content>AMA-1 (PvAMA-1) as a secreted soluble protein in the methylotrophic yeast<jats:named-content content-type="genus-species">Pichia pastoris</jats:named-content>. Recognized by a high percentage of sera from individuals infected by<jats:named-content content-type="genus-species">P. vivax</jats:named-content>, this recombinant protein was found to have maintained its antigenicity. The immunogenicity of this protein was evaluated in mice using immunization protocols that included homologous and heterologous prime-boost strategies with plasmid DNA and recombinant protein. We used the following formulations containing different adjuvants: aluminum salts (Alum),<jats:named-content content-type="genus-species">Bordetella pertussis</jats:named-content>monophosphoryl lipid A (MPLA), flagellin FliC from<jats:named-content content-type="genus-species">Salmonella enterica</jats:named-content>serovar Typhimurium, saponin Quil A, or incomplete Freund's adjuvant (IFA). The formulations containing the adjuvants Quil A or IFA elicited the highest IgG antibody titers. Significant antibody titers were also obtained using a formulation developed for human use containing MPLA or Alum plus MPLA. Recombinant PvAMA-1 produced under “conditions of good laboratory practice” provided a good yield, high purity, low endotoxin levels, and no microbial contaminants and reproduced the experimental immunizations. Most relevant for vaccine development was the fact that immunization with PvAMA-1 elicited invasion-inhibitory antibodies against different Asian isolates of<jats:named-content content-type="genus-species">P. vivax</jats:named-content>. Our results show that AMA-1 expressed in<jats:named-content content-type="genus-species">P. pastoris</jats:named-content>is a promising antigen for use in future preclinical and clinical studies.</jats:p>