Introduction to DNA Vaccines

DNA vaccines are made up of small plasmids1. Each plasmid has been genetically modified by inserting an identified DNA sequence which codes for an antigenic protein2 of a pathogen. This form of immunisation is termed third generation vaccination, and is a novel technique used to stimulate an effective and holistic immune response in the inoculated patient.

For DNA vaccines to work, they have to be delivered into the patient’s body, just like any other vaccine. There are various delivery methods, with saline intramuscular (IM) injection and gene gun delivery being the most popular. Whilst IM injection requires no special delivery mechanism unlike the gene gun, it uses up a relatively large amount of plasmid DNA, normally100 – 200 micrograms. With the gene gun delivery method, as little as 16 nanograms of plasmid DNA are required – almost a difference by 1000 fold!

DNA vaccines work beautifully in stages to promote an immune response to infection as well as develop immunity:

1. Plasmid DNA (pDNA) enter host’s cell. This is called transfection.
2. It then enters the nucleus of the cell and uses the ‘inner machinery’ to replicate itself just like ordinary genomic DNA.
3. Replication ends with the translation of the DNA sequence embedded in the plasmid to a protein molecule. In this case, it is the specific antigenic protein that we want as our final product.