Protection of Aotus monkeys by Plasmodium falciparum EBA-175 region II DNAprime-protein boost immunization regimen

Aotus monkeys received 4 doses of Plasmodium falciparum EBA- 175 region II vaccine as plasmid DNA (Dv- Dv) or recombinant protein in adjuvant (Pv- Pv) or as 3 doses of DNA and 1 dose of protein (Dv- Pv). After 3 doses, antibo dy titers were similar to 10(4) in DNA- immunized monkeys and 10(6) in prot ein- immunized monkeys. A fourth dose did not significantly boost antibody responses in the Dv- Dv only or Pv- Pv only groups, but titers were boosted to similar to 10(6) in monkeys in the Dv- Pv group. Four weeks after the l ast immunization, the animals were challenged with 10(4) P. falciparum- par asitized erythrocytes. Peak levels of parasitemia were lower in the 16 monk eys that received region II- containing plasmids or proteins than in the 16 controls (geometric mean: 194,178 and 410,110 parasites/muL, respectively; P = .013, Student's t test). Three of 4 monkeys in the Dv-Pv group did not require treatment. These data demonstrate that immunization with EBA- 175 region II induces a significant antiparasite effect in vivo.