Figure 2

Principles of different carriers for DNA vaccine delivery to host cells. (1) Bacterial-mediated delivery. (a) Bacteria, such as L. monocytogenes, E. coli, and S. flexneri, carrying a recombinant plasmid invade host cells, escape from the vacuole system, then die in the cytosol and release the plasmid [102]. (b) Bacteria, such as Salmonella, first invade the host cells, remain in the vacuole, then die due to metabolic attenuation and release the recombinant plasmid into the cytosol [102]. (2) Polycations are able to compress the molecular size of plasmids into compact structures by converting the negative charges to positive. The high surface cationic charge of an encapsulated plasmid mediates both size condensation and buffering capacity that diminish the requirement for the addition of endosomolytic agents. Buffering leads to osmotic swelling, membrane lysis and subsequent plasmid release [103].