Diversity Covering AMA1-MSP1 ₁₉ Fusion Proteins as Malaria Vaccines

Abstract

To overcome polymorphism in the malaria vaccine candidate Plasmodium falciparum apical membrane antigen 1 (PfAMA1), fusion protein chimeras comprised of three diversity-covering (DiCo) PfAMA1 molecules (D1, D2, and D3) and two allelic variants of the C-terminal 19-kDa region of merozoite surface protein 1 (MSP119) (variants M1 and M2) were generated. A mixture of fusion proteins (D1M1/D2M2D3) and the D1M1D2M2D3 fusion were compared to a single-unit mixture (D1/D2/D3/M1) in an immunological study in groups of rabbits. Following immunization, titers of antibodies (Abs) against four naturally occurring PfAMA1 alleles were high for all groups, as were growth inhibition assay (GIA) levels against two antigenically distinct laboratory parasite strains. Fusion of AMA1 to MSP119 did not suppress levels of antibodies against the AMA1 component. In addition, the breadth of antibody responses was unaffected. Anti-AMA1 antibodies were largely responsible for parasite growth inhibition, as shown in reversal-of-inhibition experiments by adding competing AMA1 antigen. For all groups, titration of the MSP119 antigen into the GIA led to only a small decrease in parasite inhibition, although titers of antibodies against MSP119 were increased 15-fold for the groups immunized with fusion proteins. GIA with affinity-purified anti-MSP119 antibodies showed that the 50% inhibitory concentrations of the anti-MSP119 antibody preparations were in the same order of magnitude for all animals tested, leading to the conclusion that fusing MSP119 to PfAMA1 leads to a small but significant increase in functional antibody levels. This study shows that combination of multiple vaccine candidates in fusion proteins may lead to improved characteristics of the vaccine.

Invasion-Inhibitory Antibodies Elicited by Immunization with Plasmodium vivax Apical Membrane Antigen-1 Expressed in Pichia pastoris Yeast

“…These laboratories are investing different approaches to overcome the problem imposed by the allelic polymorphism of PfAMA-1 (41)(42)(43). In addition, recent studies using parasites isolated from individuals vaccinated with FMP2.1/ AS02A mapped few amino acid variations as the cause of strainspecific resistance (44).…”

EDiP: the Epitope Dilution Phenomenon. Lessons learnt from a malaria vaccine antigen and its applicability to polymorphic antigens

“…Meningococcal factor H-binding protein appears to be an exception for which an alternative strategy has been used [77]. Previously published data on AMA1 suggest that EDiP requires at least three antigens [28,34,35]. The composition of the variants in the immunization mixture can differ, yet achieve similar results provided, strain-specific epitopes are efficiently diluted (e.g.…”

“…A minimum of three components appear to be required for epitope dilution as two component vaccines did not show broadening beyond the vaccine components [26,34,35]. It was shown that antibody breadth was not significantly improved when three AMA1 DiCo proteins were complemented with four natural alleles (viz.…”

Optimization of a preparative multimodal ion exchange step for purification of a potential malaria vaccine

“…The protein of interest D1M1 is a fusion protein of merozoites surface protein1 MSP1 and apical membrane antigen1 PfAMA1 described by Faber et al [17,18]. D1M1 consists of 619 amino acids with a molecular weight of 71.5 kDa and a pI of 5.2.…”

“…In this work, the chromatographic purification of the malaria vaccine candidate D1M1 [17][18][19][20] was developed and optimized in small scale experiments. The target protein was produced in an integrated production process described by Martens et al [21].…”