TLR5-dependent immunogenicity of a recombinant fusion protein containing an immunodominant epitope of malarial circumsporozoite protein and the FliC flagellin of Salmonella Typhimurium

Recently, we described the improved immunogenicity of new malaria vaccine candidates based on the expression of fusion proteins containing immunodominant epitopes of merozoites and Salmonella enterica serovar Typhimurium flagellin (FliC) protein as an innate immune agonist. Here, we tested whether a similar strategy, based on an immunodominant B-cell epitope from malaria sporozoites, could also generate immunogenic fusion polypeptides. A recombinant His6-tagged FliC protein containing the C-terminal repeat regions of the VK210 variant of Plasmodium vivax circumsporozoite (CS) protein was constructed. This recombinant protein was successfully expressed in Escherichia coli as soluble protein and was purified by affinity to Ni-agarose beads followed by ion exchange chromatography. A monoclonal antibody specific for the CS protein of P. vivax sporozoites (VK210) was able to recognise the purified protein. C57BL/6 mice subcutaneously immunised with the recombinant fusion protein in the absence of any conventional adjuvant developed protein-specific systemic antibody responses. However, in mice genetically deficient in expression of TLR5, this immune response was extremely low. These results extend our previous observations concerning the immunogenicity of these recombinant fusion proteins and provide evidence that the main mechanism responsible for this immune activation involves interactions with TLR5, which has not previously been demonstrated for any recombinant FliC fusion protein.

Breakthroughs towards a malaria vaccine

Since the 1960s, the scientist Ruth Nussenzweig, C.V. Starr Professor atNew York University School of Medicine, has been working to developan antimalarial vaccine. In her testimony, she traces some of the stagesthrough which her research has passed. At the beginning of herstudies, most scientists held that it would be impossible to developsuch a vaccine. However, a different opinion had been expressed in apaper on avian malaria written some forty years earlier by a Britishresearcher and his collaborators from India. The immunizationprinciple developed by this group was irradiation of sporozoites inorder to deactivate the parasite that causes malaria. Ruth Nussenzweigrevived and expanded upon this line of research, which nowunderpins her efforts to devise an antimalarial vaccine for human use