Enhancement of immunogenicity and efficacy of a plasmid DNA rabies vaccine by nanoformulation with a fourth-generation amine-terminated poly(ether imine) dendrimer

PURPOSE Delayed onset of, and low magnitude of, protective immune responses are major drawbacks limiting the practical utility of plasmid vaccination against rabies. In this study we evaluated whether nanoformulation with the novel poly(ether imine) (PETIM) dendrimer can enhance the immunogenicity and efficacy of a plasmid-based rabies vaccine. MATERIALS AND METHODS A plasmid vaccine construct (pIRES-Rgp) was prepared by cloning the full-length rabies virus glycoprotein gene into pIRES vector. Drawing upon the results of our previous study, a dendriplex (dendrimer-DNA complex) of pIRES-Rgp was made with PETIM dendrimer (10:1 w/w, PETIM:pIRES-Rgp). In vitro transfection was done on baby hamster kidney (BHK)-21 cells to evaluate expression of glycoprotein gene from pIRES-Rgp and PETIM-pIRES-Rgp. Subsequently, groups of Swiss albino mice were immunized intramuscularly with pIRES-Rgp or PETIM-pIRES-Rgp. A commercially available cell culture rabies vaccine was included for comparison. Rabies virus neutralizing antibody (RVNA) titers in the immune sera were evaluated on days 14, 28, and 90 by rapid fluorescent focus inhibition test. Finally, an intracerebral challenge study using a challenge virus standard strain of rabies virus was done to evaluate the protective efficacy of the formulations. RESULTS Protective levels of RVNA titer (≥0.5 IU/mL) were observed by day 14 in animals immunized with pIRES-Rgp and its dendriplex. Notably, PETIM-pIRES-Rgp produced 4.5-fold higher RVNA titers compared to pIRES-Rgp at this time point. All mice immunized with the PETIM-pIRES-Rgp survived the intracerebral rabies virus challenge, compared with 60% in the group which received pIRES-Rgp. CONCLUSION Our results suggest that nanoformulation with PETIM dendrimer can produce an earlier onset of a high-titered protective antibody response to a plasmid-based rabies vaccine. PETIM dendriplexing appears to be an efficacious nonviral delivery strategy to enhance genetic vaccination.