Generation and analyses of the immunogenic properties of recombinant proteins based on the circumsporozoite antigen of Plasmodium vivax aiming at the development of a universal malaria vaccine

Abstract

P. vivax is the second most prevalent malaria of in the world. Recent data estimates 132-391 million cases annually. In the Americas, P. vivax is the most prevalent species of plasmodium responsible for more than 70% of the cases. The relative inefficiency of the measures of control currently used demands the development of new strategies of prevention such as vaccines, new drugs and new insecticides. Although there is a constant and increasing activity of research, there is not a vaccine capable to prevent infection by the Plasmodium spp. Nevertheless, experimental analyses suggest that the induction of a protective immunity against the pre-erythrocytes forms of malaria can be a tangible objective because: 1) immunizations with diverse radiation-attenuated forms of sporozoites are elicits asymptomatic protection in human hosts; 2) experimental vaccinations in murine models of infection had demonstrated that vaccines based on synthetic and/or recombinant proteins generate powerful protective immunity against a challenge with sporozoites of P. berghei or P. yoelli; 3) vaccinations in children with a recombinant protein based on the P. falciparum CS induced significant degree of protection against the natural exposure to malaria. In last the 12 years, we generated recombinant proteins based of diverse immunodominant antigens of erythrocytes forms of P. vivax. It is our hypothesis that an efficient vaccine formulation against P. vivax malaria will have to contain immunodominant regions of both pre- and erythrocytes forms of the parasite. This strategy aims at increasing the intensity of the immune response and the number of targets in the parasite. It also aims at reducing the impact of the genetic polymorphism and the possibility of selection of antigenic variants. For that purpose, we will need diverse antigens expressed in different forms of the parasite. Based on that, the objective of this project will be the generation of recombinant proteins based in the primary sequence of CS proteins expressed by pre-erythrocytes forms of P. vivax. These proteins will be produced initially in a bacterial expression system, purified and used for experimental immunizations in animal models. We will try to generate three proteins each one containing one of the three repeat imunodominant region and a fourth containing all the three regions in fusion in the same polypeptide. The proteins will be injected in mice in the presence of different adjuvant formulations based in our previous experience of vaccination with recombinant proteins. The comparison of the immune response will be made between animals that had simultaneously received three recombinant proteins representing each form of the antigen, with animals that had only received a protein containing the three regions in fusion. In parallel we will produce the CS protein containing all three repeat imunodominant regions as a fusion protein from a single polypeptide to be expressed by a replication deficient human or simian adenovirus. These recombinant adenoviruses will be used in a protocol of heterogonous prime and boost together with the recombinant proteins. By the end of this project we expect to have from the applied point of view, one or more recombinant proteins that can be used for future clinical immunizations for a vaccine against P. vivax malaria. From the basic point of view, we intend to answer an important question for the development of immunity and vaccines: Is it possible to express three imunodominant epitopes simultaneously in a single protein without causing significant interference. (AU)