Effect of vaccination with 3 recombinant asexual-stage malaria antigens oninitial growth rates of Plasmodium falciparum in non-immune volunteers

A placebo controlled, randomised, double blind trial was conducted in human volunteers to test a mixture of three recombinant Plasmodium falciparum bl ood stage antigens for its ability to reduce the initial growth rates of pa rasites. The vaccine contained recombinant MSP2 (3D7 allele), a portion of MSP1 (190LCS.T3) and part of the RESA antigen (C terminal 771 amino acids) in the Montanide ISA 720 adjuvant (SEPPIC). Twelve volunteers received two doses of the vaccine, 6 weeks apart. The five participants in the placebo g roup received an equivalent volume of the adjuvant emulsion using the same schedule. Antibody responses were low, as has been reported in earlier stud ies with this combination, while T cell responses were stronger. All the vo lunteers were challenged with approximately 140 ring infected red cells of the 3D7 cloned line, 4 weeks after the second dose. Parasitaemia was determ ined once daily from day 4 using a sensitive and quantitative PCR assay. Al l the volunteers were infected and were treated on day 8, before any develo ped symptoms. There was no significant difference in initial parasite growt h rates between the verum and placebo groups, nor was there any significant correlation between parasite growth rates and any of the measured immunolo gical responses. These results suggest that the formulation tested in this trial did not generate immune responses that were strong enough to reduce p arasite growth in naive volunteers. (C) 2000 Elsevier Science Ltd. All righ ts reserved.