Construction, Expression, and Evaluation of the Naturally Acquired Humoral Immune Response against Plasmodium vivax RMC-1, a Multistage Chimeric Protein

Characterization of T and B cell epitopes in PvCyRPA by studying the naturally acquired immune response in Brazilian Amazon communities

Plasmodium vivax, a challenging species to eliminate, causes millions of malaria cases globally annually. Developing an effective vaccine is crucial in the fight against vivax malaria, but considering the limited number of studies focusing on the identification and development of P. vivax-specific vaccine candidates, exploring new antigens is an urgent need. The merozoite protein CyRPA is essential for P. falciparum growth and erythrocyte invasion and corresponds to a promising candidate antigen. In P. vivax, a single study with multiple vaccine candidates indicates PvCyRPA with strong association with protection, outperforming classic malaria vaccine candidates. However, little is known about the specific naturally acquired response in the Americas, as well as the antigen epitope mapping. For this reason, we aimed to investigate the cellular and humoral immune response elicited against PvCyRPA in Brazilian endemic areas to identify the existence of immunodominant regions and the potential of this protein as a single or even a multi-stage specific malaria vaccine candidate for P. vivax. The results demonstrated that PvCyRPA is naturally immunogenic in Brazilian Amazon individuals previously exposed to malaria, which presented anti-PvCyRPA cytophilic antibodies. Moreover, our data show that the protein also possesses important immunogenic regions with an overlap of B and T cell epitopes. These data reinforce the possibility of including PvCyRPA in vaccine formulations for P. vivax.

Immunogenicity of PvCyRPA, PvCelTOS and Pvs25 chimeric recombinant protein of Plasmodium vivax in murine model

In the Americas, P. vivax is the predominant causative species of malaria, a debilitating and economically significant disease. Due to the complexity of the malaria parasite life cycle, a vaccine formulation with multiple antigens expressed in various parasite stages may represent an effective approach. Based on this, we previously designed and constructed a chimeric recombinant protein, PvRMC-1, composed by PvCyRPA, PvCelTOS, and Pvs25 epitopes. This chimeric protein was strongly recognized by naturally acquired antibodies from exposed population in the Brazilian Amazon. However, there was no investigation about the induced immune response of PvRMC-1. Therefore, in this work, we evaluated the immunogenicity of this chimeric antigen formulated in three distinct adjuvants: Stimune, AddaVax or Aluminum hydroxide (Al(OH)3) in BALB/c mice. Our results suggested that the chimeric protein PvRMC-1 were capable to generate humoral and cellular responses across all three formulations. Antibodies recognized full-length PvRMC-1 and linear B-cell epitopes from PvCyRPA, PvCelTOS, and Pvs25 individually. Moreover, mice's splenocytes were activated, producing IFN-γ in response to PvCelTOS and PvCyRPA peptide epitopes, affirming T-cell epitopes in the antigen. While aluminum hydroxide showed notable cellular response, Stimune and Addavax induced a more comprehensive immune response, encompassing both cellular and humoral components. Thus, our findings indicate that PvRMC-1 would be a promising multistage vaccine candidate that could advance to further preclinical studies.

Molecular Research on Plasmodium Infection and Immunity

The WHO's global strategy for malaria targets a reduction of at least 90% of both incidence and mortality rates for 2030 [...].