Utilising nanoparticles for DNA vaccine delivery

Vaccines have been vital candidate against infectious diseases, and over the past one hundred years have saved millions of lives. The main types of vaccines available to date are subunit, live attenuated, inactivated, conjugate, toxoid and recombinant DNA based vaccines (Tiwle 2014). While effective, each has their own inherent limitations. For example, subunit vaccines cannot induce long term immunity, whereas live, attenuated and inactivated vaccines can have a limited target range (Abhishek et al., 2016). High production costs make recombinant vector based vaccines unavailable to poor economies (Nascimento et al., 2012). Toxoid vaccines need multiple doses with adjuvants and also cause strong local reactions (Baxter 2007). Even though DNA vaccines have the disadvantage of being limited to protein antigens, they offer long term immunity inducing all arms of the immune responses (Khan 2013). Most DNA vaccines are effective in eliciting immune responses without any side effects. The main criterion for a successful DNA vaccine is to have an efficient delivery system which can deliver it safely to the target cells. There are several successful delivery systems available for DNA vaccines; however no standard system is in place. For vaccine trials and effective DNA vaccination, targeting antigen presenting cells would be important. There is an increasing demand for novel DNA vaccine delivery systems, mainly for the non-viral type as they are considered relatively safe. Therefore, in this proof of concept study two novel delivery systems 1) Solid Lipid Nanoparticles (SLNs) and 2) yeast transposon virus like particles (Ty-VLPs) were chosen to study their potential to carry DNA vaccines in vitro to dendritic cells using eGFP plasmid as the reporter plasmid. Positively charged SLNs were synthesised by modified solvent-emulsification method and conjugated with plasmid DNA to form complexes (DNA-SLN complexes). The integrity of these complexes was confirmed by various agarose gel based assays. The SLN/DNA complexes were transfected into DC2.4 cells and analysed by flow cytometry for GFP expression. It was shown that there is a 10-fold increase in the transfection rate using these complexes in DC2.4 cells over plasmid alone and is comparable to that mediated by lipofectamine. On the other hand, Ty-VLPs were purified from the recombinant yeast constructed and plasmid DNA conjugated with them. The transfection efficiency of these complexes were analysed in vitro and was shown to increase compared to plasmid alone. In comparison the SLN system was more efficient for plasmid DNA delivery than Ty-VLPs.