Antigenicity of a Bacterially Expressed Triple Chimeric Antigen of Plasmodium falciparum AARP, MSP-3(11) and MSP-1(19): PfAMSP-Fu(35)

Development of fusion chimeras as potential vaccine candidates is considered as an attractive strategy to generate effective immune responses to more than one antigen using a single construct. Here, we described the design, production, purification and antigenicity of a fusion chimera (PfAMSP-Fu(35)), comprised of immunologically relevant regions of three vaccine target malaria antigens, PfAARP, PfMSP-3 and PfMSP-1. The recombinant PfAMSP-Fu(35) is expressed as a soluble protein and purified to homogeneity with ease at a yield of ~ 7 mg L(-1). Conformational integrity of the C-terminal fragment of PfMSP-1, PfMSP-1(19) was retained in the fusion chimera as shown by ELISA with conformation sensitive monoclonal antibodies. High titre antibodies were raised to the fusion protein and to all the three individual components in mice and rabbits upon immunization with fusion chimera in two different adjuvant formulations. The sera against PfAMSP-Fu(35) recognized native parasite proteins corresponding to the three components of the fusion chimera. As shown by invasion inhibition assay and antibody mediated cellular inhibition assay, antibodies purified from the PfAMSP-Fu(35) immunized serum successfully and efficiently inhibited parasite invasion in P. falciparum 3D7 in vitro both directly and in monocyte dependent manner. However, the invasion inhibitory activity of anti-AMSP-Fu(35) antibody is not significantly enhanced as expected as compared to a previously described two component fusion chimera, MSP-Fu(24). Therefore, it may not be of much merit to consider AMSP-Fu(35) as a vaccine candidate for preclinical development.