Immunogenicity of a recombinant protein containing the Plasmodium vivax vaccine candidate MSP119 and two human CD4+ T-cell epitopes administered to non-human primates (Callithrix jacchus jacchus)

One of the most promising vaccine candidates against the erythrocytic forms of malaria is the 19 kDa C-terminal region of the merozoite surface protein 1 (MSP119). As part of our studies aimed at the development of a Plasmodium vivax malaria vaccine, we characterized the immunogenic properties of a new bacterial recombinant protein containing the P. vivax MSP119 and two helper T-cell epitopes, the synthetic universal pan allelic DR epitope (PADRE) and a new internal MSP1 P. vivax epitope (DYDVVYLKPLAGMYK). We found that the recognition of His6MSP119-DYDVVYLKPLAGMYK-PADRE was as good as the recognition of His6MSP119 indicating that the presence of the T-cell epitopes PADRE and DYDVVYLKPLAGMYK did not modify the MSP119 epitopes recognized by human IgG. The recombinant protein His6MSP119-DYDVVYLKPLAGMYK-PADRE proved to be highly immunogenic in marmosets (Callithrix jacchus jacchus) when administered in incomplete Freund's adjuvant. However, when administered in other adjuvant formulations such as Quil A, CpG ODN 2006 or MPL/TDM, antibody titers to MSP119 were significantly lower. Among these three adjuvants, Quil A proved to be the most efficient one generating antibody titers significantly higher than the others. These results indicated that under the circumstances evaluated, adjuvants were key for the immunogenicity of the recombinant protein His6MSP119-DYDVVYLKPLAGMYK-PADRE.