The immunogenicity and efficacy of a hybrid recombinant protein derived from the N-terminal end of the
glutamate-rich protein (GLURP) and the C-terminal portion of the merozoite surface protein 3 (MSP3) of Plasmodium falciparum was evaluated in Saimiri sciureus monkeys. The GLURP/MSP3 hybrid protein, expressed in
Lactococcus lactis, was administered in association with alum, Montanide ISA720, or complete or incomplete Freund
adjuvant (CFA/IFA) in groups of five animals each. The three formulations were shown to be immunogenic, but the
one with alum was shown to be weak compared to the other two, particularly CFA/IFA, which provided very high
antibody titers (enzyme-linked immunosorbent assay titers of >3,000,000 and immunofluorescence antibody test
titers of 6,400). After a challenge infection with P. falciparum FUP strain, all five monkeys from the GLURP/MSP3-
alum group showed a rapid increase in parasitemia, reaching 10% and were treated early. The two monkeys with
the highest antibody titers in group GLURP/MSP3-Montanide ISA720 had a delay in the course of parasitemia and
were treated late due to a low hematocrit. In the GLURP/MSP3-CFA/IFA group, parasitemia remained below this
threshold in four of the five animals and, after it reached a peak, parasitemia started to decrease and monkeys were
treated late. When all animals were grouped according to the outcome, a statistically significant association between
high antibody titers and partial protection was observed. The challenge infection boosted the antibody titers, and
the importance of this event for vaccine efficacy in areas where this parasite is endemic is discussed. In conclusion,
these data suggest that GLURP and MSP3 can induce protection against malaria infection if antibodies are induced
at properly high titers.
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