Induction of Multifunctional Broadly Reactive T Cell Responses by a Plasmodium vivax Circumsporozoite Protein Recombinant Chimera

Abstract

dPlasmodium vivax is the most widespread species of Plasmodium, causing up to 50% of the malaria cases occurring outside subSaharan Africa. An effective vaccine is essential for successful control and potential eradication. A well-characterized vaccine candidate is the circumsporozoite protein (CSP). Preclinical and clinical trials have shown that both antibodies and cellular immune responses have been correlated with protection induced by immunization with CSP. On the basis of our reported approach of developing chimeric Plasmodium yoelii proteins to enhance protective efficacy, we designed PvRMC-CSP, a recombinant chimeric protein based on the P. vivax CSP (PvCSP). In this engineered protein, regions of the PvCSP predicted to contain human T cell epitopes were genetically fused to an immunodominant B cell epitope derived from the N-terminal region I and to repeat sequences representing the two types of PvCSP repeats. The chimeric protein was expressed in soluble form with high yield. As the immune response to PvCSP has been reported to be genetically restricted in the murine model, we tested the immunogenicity of PvRMC-CSP in groups of six inbred strains of mice. PvRMC-CSP was able to induce robust antibody responses in all the mouse strains tested. Synthetic peptides representing the allelic forms of the P. vivax CSP were also recognized to a similar extent regardless of the mouse strain. Furthermore, the immunization regimen induced high frequencies of multifunctional CD4؉ and CD8 ؉ PvRMC-CSP-specific T cells. The depth and breadth of the immune responses elicited suggest that immunization with PvRMC-CSP can circumvent the genetic restriction of the immune response to P. vivax CSP. Interestingly, PvRMC-CSP was also recognized by naturally acquired antibodies from individuals living in areas where malaria is endemic. These features make PvRMC-CSP a promising vaccine candidate for further development. P lasmodium vivax is the most widespread species of Plasmodium, causing up to 50% of the malaria cases occurring outside sub-Saharan Africa, with an estimated 2.48 billion people living in areas with risk of malaria transmission (1-4). Unlike Plasmodium falciparum, P. vivax is able to persist in a latent stage called hypnozoite within infected parenchymal liver cells. Activation of hypnozoites weeks or months after the primary infection leads to new blood stage infections, causing relapses and opportunities for further transmission (5).A vaccine targeting the P. vivax preerythrocytic stages preventing the entry of sporozoites into hepatocytes or inhibiting the liver stage development could block the production of hypnozoites. The most-characterized antigen and one of the few vaccine candidates for P. vivax tested in clinical trials is the circumsporozoite protein (CSP). CSP is an attractive target, since anti-CSP antibodies derived from naturally infected patients or from volunteers exposed to irradiated sporozoites have the ability to inhibit the infection of hepatic cells by sporozoites in vitro (6). Unlike P. ...

A chimeric protein-based malaria vaccine candidate induces robust T cell responses against Plasmodium vivax MSP119

“…1A,B ). We have previously validated the relevance of using this topology for the design of chimeric proteins to improve the immunogenicity of P. yoelii and P. vivax antigens in murine models 9 24 25 26 27 . The promiscuous T cell epitopes (i.e.…”

“…In contrast, PvRMC-MSP1 recognition was present in patients that did not have active malaria, which could be an effect of our vaccine design strategy as we use well-defined T and B cell epitopes to avoid the inclusion of regions of low immunogenic potential. We have previously demonstrated that our constructs are better recognized by naturally infected individuals when compared to native proteins and can circumvent the HLA restriction associated to these antigens 27 35 . These characteristics make our proteins not only desirable for vaccination but also useful for seroepidemiological studies.…”

“…Here, we report the design and characterization of a Recombinant Modular Chimera (RMC) based on PvMSP1 in which defined cognate promiscuous T cell epitopes were genetically linked through GPGPG spacers to enhance the immunogenicity of PvMSP1 19 . We have previously used this approach in proof of concept studies using synthetic peptides or recombinant proteins 26 27 35 . CD data support the rationale for using this protein topology.…”

“…There were no associations between the PvRMC-MSP1 responses with the HLA alleles present in the population studied. We have shown that our chimeric proteins can circumvent genetic restriction to the recognition of pre-erythrocytic and erythrocytic P. vivax antigens 27 35 . It is important to test this protein in non-human primates from different genetic backgrounds to confirm the induction of non-genetically restricted immune responses, a highly desirable characteristic for a P. vivax malaria vaccine.…”

“…The characteristics of the study participants have been previously described 27 35 . Briefly, 253 individuals from the malaria endemic region of Rondonia, Brazil were included in this survey.…”