Immunization of experimental monkeys against Plasmodium falciparum: use of synthetic adjuvants.

The replacement of Freund's adjuvant by a possible safe adjuvant for effective immunization of owl monkeys (Aotus trivirgatus griseimembra) against a human malaria parasite, Plasmodium falciparum, has been investigated. Experiments involved the use of two synthetic adjuvants: MDP (N-acetylmuramyl-L-alanyl-D-isoglutamine) and stearoyl-MDP (6-O-stearoyl-N-acetylmuramyl-L-alanyl-D-isoglutamine). In both cases, P. falciparum merozoites obtained through short-term in vitro cultivation were used as antigen. MPD was used as adjuvant in 5 owl monkeys; 2 control monkeys died and of the 3 experimental monkeys only 1 survived. In contrast, in another experiment where stearoyl-MDP was used as adjuvant, there was 100% protection of 4 immunized monkeys against a challenge with the homologous strain of P. falciparum. The results of the second experiment are encouraging for the development of an effective and safe vaccine for human malaria.