Effects of Sex, Parity, and Sequence Variation on Seroreactivity to Candidate Pregnancy Malaria Vaccine Antigens

Seattle Biomedical Research Institute, Seattle, WA 98109, USA.
The Journal of Infectious Diseases (Impact Factor: 6). 08/2007; 196(1):155-64. DOI: 10.1086/518513
Source: PubMed


Plasmodium falciparum-infected erythrocytes adhere to chondroitin sulfate A (CSA) to sequester in the human placenta, and pregnancy malaria (PM) is associated with the development of disease in and the death of both mother and child. A PM vaccine appears to be feasible, because women become protected as they develop antibodies against placental infected erythrocytes (IEs). Two IE surface molecules, VAR1CSA and VAR2CSA, bind CSA in vitro and are potential vaccine candidates.
We expressed all domains of VAR1CSA and VAR2CSA as mammalian cell surface proteins, using a novel approach that allows rapid purification, immobilization, and quantification of target antigen. For serum samples from East Africa, we measured reactivity to all domains, and we examined the effects of host sex and parity, as well as the effects of parasite antigenic variation.
Serum samples obtained from multigravid women had a higher reactivity to all VAR2CSA domains than did those obtained from primigravid women or from men. Conversely, serum samples obtained from men had consistently higher reactivity to VAR1CSA domains than did those obtained from gravid women. Seroreactivity was strongly influenced by antigenic variation of VAR2CSA Duffy binding-like domains.
Women acquire antibodies to VAR2CSA over successive pregnancies, but they lose reactivity to VAR1CSA. Serum reactivity to VAR2CSA is variant specific, and future studies should examine the degree to which functional antibodies, such as binding-inhibition antibodies, are variant specific.

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    • "We expressed HisAdEx [21] without additional insert in COS-7, and AMA-1 [27] in E. coli using pET28b with subsequent purification and re-folding by the same methods described above for full-length DBL2βPF11_0521 domain. "
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    ABSTRACT: Plasmodium falciparum virulence has been ascribed to its ability to sequester in deep vascular beds, mediated by the variant surface antigen family PfEMP1 binding endothelial receptors like ICAM-1. We previously observed that naturally-acquired antibodies that block a PfEMP1 domain, DBL2β of PF11_0521 allele, from binding to the human ICAM1 receptor, reduce the risk of malaria hospitalization in children. Here, we find that DBL2βPF11_0521 binds ICAM-1 in the low nM range and relate the structure of this domain with its function and immunogenicity. We demonstrate that the interaction with ICAM-1 is not impaired by point mutations in the N-terminal subdomain or in the flexible Loop 4 of DBL2βPF11_0521, although both substructures were previously implicated in binding ICAM-1. These data will help to refine the existing model of DBLβ::ICAM-1 interactions. Antibodies raised against full-length DBL2βPF11_0521, but not truncated forms lacking the N terminal fragment, block its interaction with ICAM-1. Our data suggest that full length domain is optimal for displaying functional epitopes and has a broad surface of interaction with ICAM-1 that is not disrupted by individual amino acid substitutions at putative key residues. This information might be important for the future design of anti-malarial vaccines based on PfEMP1 antigens.
    Full-text · Article · Apr 2013 · PLoS ONE
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    • "Conflicting results have been observed in experiments aimed at determining the recognition of various VAR2CSA domains by antibodies from infected pregnant women, in particular with DBL6ε [16], [17], [18], [23], [24], [25]; each laboratory studied a different DBL domain cloned from different strains [16], [22], [24], [26], [27], [28], [29], [30], [31]. A recent study on a small number of allelic forms of each VAR2CSA DBL [32] showed large differences in IgG recognition between a given domain from various strains; for example, between the DBL6ε domains of 7G8 and FCR3 (5% and 42%, respectively). "
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    ABSTRACT: We studied all consensus sequences within the four least 'variable blocks' (VB) present in the DBL6ε domain of VAR2CSA, the protein involved in the adhesion of infected red blood cells by Plasmodium falciparum that causes the Pregnancy-Associated Malaria (PAM). Characterising consensus sequences with respect to recognition of antibodies and percentage of responders among pregnant women living in areas where P. falciparum is endemic allows the identification of the most antigenic sequences within each VB. When combining these consensus sequences among four serotypes from VB1 or VB5, the most often recognized ones are expected to induce pan-reactive antibodies recognizing VAR2CSA from all plasmodial strains. These sequences are of main interest in the design of an immunogenic molecule. Using a similar approach than for DBL6ε, we studied the five other DBL and the CIDRpam from VAR2CSA, and again identified VB segments with highly conserved consensus sequences. In addition, we identified consensus sequences in other var genes expressed by non-PAM parasites. This finding paves the way for vaccine design against other pathologies caused by P. falciparum.
    Full-text · Article · Jan 2013 · PLoS ONE
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    • "VAR2CSA is an unusually conserved member of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family, which is transcriptionally upregulated in CSA-binding and placental isolates and binds CSA [3-10]. Antibodies to VAR2CSA are developed in a gender specific manner [11,12] and correlate with protection from PAM disease [7] making it the most promising vaccine candidate against placenta malaria, but vaccine development is complicated by protein size (~350 kDa) and polymorphism [13]. "
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    ABSTRACT: VAR2CSA is the main candidate for a vaccine against pregnancy-associated malaria, but vaccine development is complicated by the large size and complex disulfide bonding pattern of the protein. Recent X-ray crystallographic information suggests that domain boundaries of VAR2CSA Duffy binding-like (DBL) domains may be larger than previously predicted and include two additional cysteine residues. This study investigated whether longer constructs would improve VAR2CSA recombinant protein secretion from Pichia pastoris and if domain boundaries were applicable across different VAR2CSA alleles. VAR2CSA sequences were bioinformatically analysed to identify the predicted C11 and C12 cysteine residues at the C-termini of DBL domains and revised N- and C-termimal domain boundaries were predicted in VAR2CSA. Multiple construct boundaries were systematically evaluated for protein secretion in P. pastoris and secreted proteins were tested as immunogens. From a total of 42 different VAR2CSA constructs, 15 proteins (36%) were secreted. Longer construct boundaries, including the predicted C11 and C12 cysteine residues, generally improved expression of poorly or non-secreted domains and permitted expression of all six VAR2CSA DBL domains. However, protein secretion was still highly empiric and affected by subtle differences in domain boundaries and allelic variation between VAR2CSA sequences. Eleven of the secreted proteins were used to immunize rabbits. Antibodies reacted with CSA-binding infected erythrocytes, indicating that P. pastoris recombinant proteins possessed native protein epitopes. These findings strengthen emerging data for a revision of DBL domain boundaries in var-encoded proteins and may facilitate pregnancy malaria vaccine development.
    Full-text · Article · Jul 2009 · Malaria Journal
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