Functional and immunological characterization of Plasmodium vivax RON2 protein

Abstract

Malaria is considered one of the priority areas for research and vaccine development. Plasmodium vivax is the most world-widely distributed and the most prevalent specie in America. Attempts to develop malaria vaccines are primarily focused on Plasmodium falciparum and are directed towards reducing morbidity and mortality. The most advanced clinical trials performed with P. vivax vaccine candidates have only advanced to phase I. Aiming at the development of vaccine against this specie, in the last years we studied multiple aspects of naturally acquired immune response against recombinant proteins representing P. vivax blood stage antigens. Among the most promising malaria vaccine candidates, we found that the Apical Membrane 1 Antigen (AMA1) was highly immunogenic in natural infections (Rodrigues et al. 2005; Morais et al. 2006; Barbedo et al. 2007; Múfalo et al. 2008) and after mouse immunization (Múfalo et al. 2008; Gentil et al. 2010). More recently, using heterologous prime-boost protocols with recombinant protein and/or adenovirus recombinant adenovirus based on AMA1, we established a vaccination schedule in mice (Bouillet et al. 2011), which is currently being tested in Aotus monkeys by Dr. O.Bruna-Romero. These reagents and the respective vaccination schedules were object of a patent application obtained in 2010. In spite of the use of AMA-1 for vaccine development against P. vivax, little is known about the function of this protein, as well as the antibodies induced by natural infection or immunization with recombinant proteins. In the specific case of P. vivax, the absence of efficient and continuous in vitro culture systems has imposed limitations on in vitro testing of potential vaccine candidates. Moreover, there is no experimental model for protection studies because this species does not infect rodents. Based on recent studies with Toxoplasma gondii and P. falciparum showing that AMA1 interacts with RON2 and RON4 proteins during the erythrocyte invasion, our goal is to express and to characterize the protein RON2 of P. vivax to answer the following questions: (i) Is RON2 protein immunogenic? ii) Does P. vivax RON2 interacts with AMA1? iii) Do antibodies against AMA1 and/or RON2 inhibit this interaction? Our hypothesis is that this complex is conserved in P. vivax and we can explore this assay to evaluate the functionality of the antibodies generated by immunization with recombinant P. vivax AMA1 and RON2. (AU)