The protective efficacy of MSP4/5 against lethal Plasmodium chabaudi adami challenge is dependent on the type of DNA vaccine vector and vaccination protocol

The enhancement of immunogenicity of malarial DNA vaccines is important if they are to have practical application in protecting against blood-stage malaria. Here we describe three different DNA vaccine vector types used in conjunction with the blood-stage merozoite surface protein 4/5 (MSP4/5), the murine homologue of Plasmodium falciparum MSP4 and MSP5, in an attempt to enhance survival against lethal Plasmodium chabaudi adami DS blood-stage challenge. MSP4/5 was inserted into VR1020 (secretory), monocyte-chemotactic protein-3 (MCP-3) (chemoattractant), and cytotoxic T-lymphocyte antigen 4 (CTLA4) (lymph node targeting) vectors. Mice were immunized intradermally via gene-gun, IM injection, or boosting with recombinant MSP4/5 protein. Antibody responses after boosting were predominantly of the IgG1 and IgE isotypes, with low avidity antibodies produced in DNA primed groups. Despite antibody responses comparable to recombinant protein immunization, boosting mice primed with antigens encoded by MCP-3 and CTLA4 vectors did not enhance survival compared to vector control groups. Gene-gun vaccination using VR1020/MSP4/5 followed by recombinant MSP4/5 boosting, or gene-gun DNA vaccination alone using MCP-3/MSP4/5, resulted in enhanced survival compared to empty vector control mice. The results suggest that the enhancement of survival against lethal blood-stage malaria challenge after utilizing MSP4/5 DNA vaccination is therefore highly dependent on the route and type of vaccine vector employed.