IMMUNIZATION OF AOTUS-NANCYMAI WITH RECOMBINANT C-TERMINUS OF PLASMODIUM-FALCIPARUM MEROZOITE SURFACE PROTEIN-1 IN LIPOSOMES AND ALUM ADJUVANT DOES NOT INDUCE PROTECTION AGAINST A CHALLENGE INFECTION

Merozoite surface protein 1 (MSP-1) of Plasmodium falciparum is an ant imalarial vaccine candidate, The highly conserved 19-kDa C-terminal pr ocessing fragment of MSP-1 (MSP-1(19)) is of particular interest since it contains epitopes recognized by monoclonal antibodies which inhibi t the invasion of erythrocytes In vitro. The presence of naturally acq uired anti-MSP-1(19) antibodies in individuals exposed to malaria has been correlated with reduced morbidity, and immunization with an equiv alent recombinant P. yoelii antigen induces substantial protection aga inst this parasite in mice. We have expressed P. falciparum MSP-1(19) in Escherichia coli as a correctly folded protein and immunized Aotus nancymai monkeys by using the protein incorporated into liposomes and adsorbed to alum. After vaccination, the sera from these animals conta ined anti-MSP-1(19) antibodies, some of which competed for binding to MSP-1(19) with monoclonal antibodies that inhibit parasite invasion of eryrthrocytes in vitro, However, after challenge with either a homolo gous or a heterologous strain of parasite, all animals became parasite mic and required treatment. The immunization did not induce protection in this animal model.