Towards the Rational Design of a Candidate Vaccine against Pregnancy Associated Malaria : Conserved Sequences of the DBL 6 e Domain of VAR 2 CSA

Background: Placental malaria is a disease linked to the sequestration of Plasmodium falciparum infected red blood cells (IRBC) in the placenta, leading to reduced materno-fetal exchanges and to local inflammation. One of the virulence factors of P. falciparum involved in cytoadherence to chondroitin sulfate A, its placental receptor, is the adhesive protein VAR2CSA. Its localisation on the surface of IRBC makes it accessible to the immune system. VAR2CSA contains six DBL domains. The DBL6e domain is the most variable. High variability constitutes a means for the parasite to evade the host immune response. The DBL6e domain could constitute a very attractive basis for a vaccine candidate but its reported variability necessitates, for antigenic characterisations, identifying and classifying commonalities across isolates. Methodology/Principal Findings: Local alignment analysis of the DBL6e domain had revealed that it is not as variable as previously described. Variability is concentrated in seven regions present on the surface of the DBL6e domain. The main goal of our work is to classify and group variable sequences that will simplify further research to determine dominant epitopes. Firstly, variable sequences were grouped following their average percent pairwise identity (APPI). Groups comprising many variable sequences sharing low variability were found. Secondly, ELISA experiments following the IgG recognition of a recombinant DBL6e domain, and of peptides mimicking its seven variable blocks, allowed to determine an APPI cut-off and to isolate groups represented by a single consensus sequence. Conclusions/Significance: A new sequence approach is used to compare variable regions in sequences that have extensive segmental gene relationship. Using this approach, the VAR2CSA DBL6 domain is composed of 7 variable blocks with limited polymorphism. Each variable block is composed of a limited number of consensus types. Based on peptide based ELISA, variable blocks with 85% or greater sequence identity are expected to be recognized equally well by antibody and can be considered the same consensus type. Therefore, the analysis of the antibody response against the classified small number of sequences should be helpful to determine epitopes. Citation: Badaut C, Bertin G, Rustico T, Fievet N, Massougbodji A, et al. (2010) Towards the Rational Design of a Candidate Vaccine against Pregnancy Associated Malaria: Conserved Sequences of the DBL6e Domain of VAR2CSA. PLoS ONE 5(6): e11276. doi:10.1371/journal.pone. 0011276 Editor: James G. Beeson, Walter and Eliza Hall Institute of Medical Research, Australia Received December 17, 2009; Accepted May 30, 2010; Published June 23, 2010 Copyright: 2010 Badaut et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study received financial support from the Institut de Médecine et d’Epidémiologie Appliquée (grant IMEA-0801), from the European Commission, FP7 program (grant 200889), and from the French National Agency for Research (grant ANR-05-MIME-009-01). C. Badaut was supported by the National Agency of Research (ANR) and by the Institute of Research for Development (IRD). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: cbadaut@gmail.com (CB); Philippe.Deloron@ird.fr (PD)