DNA vaccine for avian influenza?
"A DNA vaccine is not a panacea, however it could be useful if the situation gets out of hand," Dunnill says. "But if we're going to try it, we need to move. You can't expect to walk into a production facility, hand over the instructions, and expect them to make it on the spot. It's going to take some weeks, and we really don't know how much time we have."It's an interesting idea. For DNA vaccination, genes (or portions of genes) from the organism you want to vaccinate against are put into a plasmid (a circular loop of DNA). The plasmid also contains a promoter--a gene which will control expression of this gene--that is able to function in human cells. The plasmid is then injected, just like a regular vaccine is. However, to be functional, it has to be taken up into the human cells, and the pathogen genes on the plasmid have to be transcribed (made into mRNA) and translated into protein. Depending on what types of cells take up the plasmid, this can lead to both antibody and cell-mediated immune responses, which is something few regular vaccines can do (they depend mostly on the antibody-mediated response). The downfall with these vaccines is that they remain largely untested, but their potential to be used in an influenza outbreak might be the kick in the pants funding agencies need to provide money for scientists to work harder on these, and for regulatory agencies to provide an accelerated approval process.
A DNA vaccine could be produced in as little as two or three weeks, Dunnill says. To do it, scientists would create a "loop" of DNA that contains the construction plans for a protein on the outer surface of the H5N1 virus. When that DNA is injected into cells, it would quickly reproduce the protein and trigger immunization in much the same way as a conventional vaccine.
In contrast, producing conventional vaccines from viruses incubated in fertilized eggs can take up to six months, which is too long to effectively prevent an influenza pandemic, Dunnill says.