by We have shown previously that affinity purified antibody required for 50% invasion inhibition was lower for the 3D7 strain parasite, as compared to the FVO strain [27]. the guarded animals were the only ones to have in vitro parasite DW14800 growth inhibitory activity of >70% at 110 serum dilution; immuno-fluorescence titers >8,000; ELISA titers against full-length AMA1 >300,000 and ELISA titer against AMA1 domains1+2 >100,000. A negative correlation between log ELISA titer and day 11 cumulative parasitemia (Spearman rank r?=??0.780, p value?=?0.0001), further confirmed the relationship between antibody titer and protection. High titers of cross-strain inhibitory antibodies against AMA1 are therefore critical to confer solid protection, and the Aotus model can be used to down-select future AMA1 formulations, prior to advanced human trials. Introduction A vaccine based on a recombinant circumsporozoite protein, RTS,S was shown in a recent phase 2 clinical trial in 5C17 month old children to have 53% vaccine efficacy against malaria clinical episodes. [1]. One strategy to build around the success of this vaccine is to combine it with other antigens [2]. Apical Membrane Antigen-1 (AMA1) is usually one DW14800 such promising malaria vaccine candidate [3]. AMA1 is located within the micronemes of merozoites present within blood stage schizonts. At the time of schizont rupture the AMA1 protein gets translocated to the merozoite surface [4], where it plays a vital role in the erythrocyte invasion process [5]. Antibodies against AMA1 are potent inhibitors of merozoite invasion [6]. AMA1 is also present on the surface of sporozoites and AMA1 antibodies inhibit sporozoite invasion into hepatocytes [7]. In the first non human primate vaccine trial reported for AMA1, three rhesus monkeys received 2 doses of an affinity purified native AMA1 protein vaccine adjuvanted with saponin [8]. Following challenge all three control monkeys required radical drug cure due to acute parasitemia. Two of 3 AMA1 immunized monkeys had parasitemia profiles comparable to that of the controls, but one monkey showed a brief delay in patency followed by a self-limiting contamination. Upon re-challenge, all 3 immunized animals showed near sterile protection. In a repeat experiment, 3 monkeys received 3 doses of the AMA1 vaccine. As in the first experiment, only 1 1 out of the 3 monkeys showed a degree of protection. Hence, vaccine efficacy as measured by reduced parasite burden was 33% and as measured by sterile protection was 0%. Notably serum from the protected monkeys had the highest pre-challenge parasite invasion inhibitory activity against merozoites [8]. A subsequent immunization trial used recombinant AMA1 in squirrel monkeys [9]. Five (squirrel) monkeys received 3 doses of a baculovirus-produced recombinant AMA1 protein vaccine adjuvanted with Montanide ISA720. Following challenge with blood stage parasites, all 4 control monkeys required drug treatment for high parasitemia. Four out of the 5 AMA1 vaccinated animals showed suppressed parasitemia profiles compared to the controls. The efficacy of this AMA1 vaccine as measured by reduced parasite burden was 80% and as measured by sterile protection was 0%. Serum from the one non-protected animal had the lowest IFA titer while the two best protected animals had the DW14800 highest titer in the trial. [9]. Another trial used as a challenge parasite in macaque monkeys [10]. Five rhesus monkeys were vaccinated with 3 doses of yeast recombinant AMA1 adjuvanted with SBAS2 (AS02A). These monkeys were then challenged with the heterologous, yet closely related simian malaria parasite rodent malaria parasite also guarded vaccinated mice against lethal challenge with a GPATC3 homologous strain of monkeys were vaccinated with a recombinant FVO strain AMA1 protein adjuvanted with Freund’s complete/incomplete adjuvant [13]. Following challenge with the homologous FVO strain of monkey model, conducted at the Centers for Disease Control (Atlanta GA). Two human-use adjuvants, Montanide ISA720 and AS02A were used in the trial. Since the 3D7 strain of does not invade Aotus RBC’s [17], two heterologous parasite strains, FCH/4 and FVO, were used for the challenge [18], [19], the former strain being much more homologous to 3D7 than the latter strain. Materials and Methods Ethics Statement This study was approved by the CDC Institutional Animal Care and Use Committee. Animals were housed at a CDC primate facility fully accredited by the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC). Aotus monkeys were pair housed, under space recommendations for lab animals set forth by the Care and Use of Laboratory Animals, NIH. Monkeys were.
