Comparative immunization study using RNA and DNA constructs encoding a part of the Plasmodium falciparum antigen Pf332

Development of nucleic acid-based vaccines against parasitic diseases shows great promise, although certain concerns about safety aspects of conventional DNA vaccines have been raised. This study presents a comparison of antibody responses induced in mice by DNA and RNA-based immunization with vectors encoding a part of the P. falciparum antigen Pf332. Two types of plasmids were used, one conventional DNA plasmid containing a cytomegalovirus promoter and one suicidal DNA plasmid encoding the Semliki Forest virus (SFV) replicase. RNA, encoding the SFV replicase and the relevant antigen, was delivered either as naked RNA or packaged in SFV suicide particles. In general, the antibody responses induced by the DNA plasmids were low and peaking after three injections, the conventional plasmid giving the highest responses. Also the RNA delivered in SFV particles consistently induced antibody responses, although comparatively low. Analyses of the ratio of immunoglobulin (Ig)G1/IgG2a subclasses in the responses indicated that all plasmids resulted in a bias for a Th2-type of response, while the SFV-particles elicited a Th1 type of response. Importantly, all these immunogens induced an immunological memory, which could be efficiently activated by a booster injection with the corresponding protein, with unchanged patterns of IgG subclasses.