DNA vaccine may stem spread

Researchers scrambling to combat a virulent form of bird flu that could mutate into a strain easily spread among humans should consider developing vaccines based on DNA, suggest British biochemical engineers. DNA vaccines, they say, can be produced more rapidly than conventional ones and possibly could save thousands of lives if a global influenza outbreak occurs.

A DNA-based vaccine could be a potent weapon against this emerging threat, particularly if enough conventional vaccine is not available, according to Peter Dunnill and his colleagues at University College London. However, they caution that any DNA vaccine should be used only as needed to slow the spread of the disease because the technique largely is untested in humans.

The avian virus H5N1 has spread among birds throughout Southeast Asia while also being detected in Eastern Europe. (A different, milder strain was found circulating in Canada as well.) The virus has killed over 60 people in Asia since 2003 and forced the slaughter of millions of birds. There have been no confirmed cases of human-to-human transmission, but that could change as the virus continues to mutate.

If that occurs, current production facilities are unlikely to meet global demands for conventional vaccines in time to avert a pandemic, Dunnill warns. Yet, it might be possible to produce a DNA vaccine quickly by adapting the manufacturing processes of selected biopharmaceutical and antibiotic plants in countries such as the U.S., China, and India.

"A DNA vaccine is not a panacea. However, it could be useful if the situation gets out of hand," Dunnill points out. "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."

A DNA vaccine could be produced in as little as two or three weeks, Dunnill surmises. 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 quickly would 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 prevent an influenza pandemic effectively.

Although no commercial influenza DNA vaccine currently is available, they have worked well in animals. However, human trials are still in the early stages, so the safety and efficacy of these vaccines is not fully established in people. These trials, though, could be accelerated, Dunnil1 indicates, particularly if the H5N1 virus eventually causes large numbers of human deaths and outpaces the supply of conventional vaccine.

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