Enhancing neutralization of Plasmodium falciparum using a novel monoclonal antibody against the rhoptry-associated membrane antigen

Anne S Knudsen,Melanie R Walker,Maria R Bassi,Lea Barfod,Kasper H Björnsson,Judit P Agullet

doi:10.1038/s41598-022-06921-1

Anne S Knudsen, Melanie R Walker + Show 4 more

Open Access

https://doi.org/10.1038/s41598-022-06921-1

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Journal: Scientific Reports	Publication Date: Feb 23, 2022
Citations: 5	License type: open-access

Affiliation: University of Copenhagen

Abstract

The pathogenesis of malaria is associated with blood-stage infection and there is strong evidence that antibodies specific to parasite blood-stage antigens can control parasitemia. This provides a strong rational for applying blood-stage antigen components in a multivalent vaccine, as the induced antibodies in combination can enhance protection. The Plasmodium falciparum rhoptry-associated membrane antigen (PfRAMA) is a promising vaccine target, due to its fundamental role in merozoite invasion and low level of polymorphism. Polyclonal antibodies against PfRAMA are able to inhibit P. falciparum growth and interact synergistically when combined with antibodies against P. falciparum reticulocyte-binding protein 5 (PfRh5) or cysteine-rich protective antigen (PfCyRPA). In this study, we identified a novel PfRAMA-specific mAb with neutralizing activity, which in combination with PfRh5- or PfCyRPA-specific mAbs potentiated the neutralizing effect. By applying phage display technology, we mapped the protective epitope to be in the C-terminal region of PfRAMA. Our results confirmed previous finding of synergy between PfRAMA-, PfRh5- and PfCyRPA-specific antibodies, thereby paving the way of testing these antigens (or fragments of these antigens) in combination to improve the efficacy of blood-stage malaria vaccines. The results emphasize the importance of directing antibody responses towards protective epitopes, as the majority of anti-PfRAMA mAbs were unable to inhibit merozoite invasion of erythrocytes.

Highlights

The pathogenesis of malaria is associated with blood-stage infection and there is strong evidence that antibodies specific to parasite blood-stage antigens can control parasitemia
Recent data contradict these findings, as Plasmodium falciparum rhoptry-associated membrane antigen (PfRAMA) was shown only to interact with the rhoptry neck proteins PfRON1, PfRON2 and PfRON313,15, indicating that loss of PfRAMA leads to mislocalization or loss of the rhoptry neck proteins, and as a result generates ‘neckless’ rhoptries[13]
To obtain a better understanding of the antiPfRAMA mAbs and their inability to efficiently inhibit P. falciparum growth, we examined their epitopes on PfRAMA

Summary

Introduction

The pathogenesis of malaria is associated with blood-stage infection and there is strong evidence that antibodies specific to parasite blood-stage antigens can control parasitemia. The largest of the apical organelles, the rhoptries, are characterized by a wide bulb region that narrows to a neck towards the apical end of the merozoite Rhoptries contain both protein and lipid components. Multiple rhoptry proteins have been identified, for instance the high-molecular weight (HMW) proteins that form a complex involving PfRhopH1/Clag, PfRhopH2 and PfRhopH3 These proteins are important for erythrocyte invasion and nutrient uptake during P. falciparum blood-stage development[6,7]. Antibodies specific to PfRAMA are able to inhibit in vitro growth of P. falciparum parasites, and a potentiating effect is observed when they are combined with antibodies specific to PfRh5 or P fCyRPA17 Another attractive feature of PfRAMA is its low antigenic diversity[20], which in combination with its important role in merozoite invasion and rhoptry biogenesis, makes it a strong blood-stage vaccine c andidate[13]

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Conclusion