Allelic variants of full-length VAR2CSA, the placental malaria vaccine candidate, differ in antigenicity and receptor binding affinity

Jonathan P Renn,Matthew V Cowles,Justin Y A Doritchamou,Robert D Morrison,Niraj H Tolia,Almahamoudou Mahamar,Patrick E Duffy,Martin Burkhardt,Rui Ma,Moussa Traore,Bergeline C Nguemwo Tentokam,Bacary S Diarra,Alassane Dicko,Oumar Attaher,Michal Fried

doi:10.1038/s42003-021-02787-7

Abstract

Plasmodium falciparum-infected erythrocytes (IE) sequester in the placenta via surface protein VAR2CSA, which binds chondroitin sulfate A (CSA) expressed on the syncytiotrophoblast surface, causing placental malaria (PM) and severe adverse outcomes in mothers and their offspring. VAR2CSA belongs to the PfEMP1 variant surface antigen family; PfEMP1 proteins mediate IE adhesion and facilitate parasite immunoevasion through antigenic variation. Here we produced deglycosylated (native-like) and glycosylated versions of seven recombinant full-length VAR2CSA ectodomains and compared them for antigenicity and adhesiveness. All VAR2CSA recombinants bound CSA with nanomolar affinity, and plasma from Malian pregnant women demonstrated antigen-specific reactivity that increased with gravidity and trimester. However, allelic and glycosylation variants differed in their affinity to CSA and their serum reactivities. Deglycosylated proteins (native-like) showed higher CSA affinity than glycosylated proteins for all variants except NF54. Further, the gravidity-related increase in serum VAR2CSA reactivity (correlates with acquisition of protective immunity) was absent with the deglycosylated form of atypical M200101 VAR2CSA with an extended C-terminal region. Our findings indicate significant inter-allelic differences in adhesion and seroreactivity that may contribute to the heterogeneity of clinical presentations, which could have implications for vaccine design.

Highlights

Plasmodium falciparum-infected erythrocytes (IE) sequester in the placenta via surface protein VAR2CSA, which binds chondroitin sulfate A (CSA) expressed on the syncytiotrophoblast surface, causing placental malaria (PM) and severe adverse outcomes in mothers and their offspring
Seven different strains of P. falciparum were selected from distinct clusters of VAR2CSA sequences following phylogenetic analysis (Fig. 1a), and the frequency of amino acid mutations was analyzed across VAR2CSA extracellular domains (Fig. 1b)
NF54 and FCR3 were selected as these alleles are currently under clinical evaluation as PM vaccine candidates, and distinct in their dimorphic sequence motif (DSM) in the DBL2X domain of VAR2CSA33

Summary

Introduction

Plasmodium falciparum-infected erythrocytes (IE) sequester in the placenta via surface protein VAR2CSA, which binds chondroitin sulfate A (CSA) expressed on the syncytiotrophoblast surface, causing placental malaria (PM) and severe adverse outcomes in mothers and their offspring. In malaria-endemic areas, the immunity that protects individuals from malaria is thought to be progressively acquired from childhood to adult age[3,4] Despite this pre-existing immunity, women become susceptible to P. falciparum parasitemia during pregnancy leading to PM, especially during first gestation[5]. Placental sequestration results from IE that express the variant surface antigen VAR2CSA on their surface and bind to Chondroitin Sulfate A (CSA) in intervillous spaces and on the syncytiotrophoblast surface[8,9]. Structural studies by cryo-electron microscopy show that the multiple domains of VAR2CSA interact extensively to create an interwoven architecture, and that CSA binds by threading through a major and minor channel of VAR2CSA formed by NTS, DBL1X, DBL2X, ID2α, and DBL4ɛ domains as part of a stable core (extending from NTS to ID3) that is flanked by a flexible DBL5-DBL6 arm[14]

Methods

Results

Conclusion