DNA vaccines are also in clinical trials for West Nile virus, Ebola, SARS, and HIV prevention and treatment. Indeed, much of the research done on DNA vaccines in humans has been directed toward developing an HIV vaccine. Nabel says researchers have learned that following a DNA vaccine with a traditional vaccine has a synergistic effect on the immune system’s ability to combat HIV. A phase II clinical trial of such a combined HIV prevention vaccine, sponsored by the vaccine research center, will soon begin recruiting in Africa.
“This is the initial attempt for flu–to find out if we are in the ballpark for protection,” says Nabel. He says that a DNA vaccine alone may be enough to protect the body from flu. If not, the NIH will try a combined approach like those being tested for HIV.
Although Nabel’s is the first DNA vaccine against bird flu to enter clinical trials, San Diego-based Vical is planning to begin clinical testing of a DNA vaccine aimed at another strain of bird flu. Instead of containing genes for a single viral protein, the Vical vaccine has three.
If the bird-flu vaccine is a success, it’s likely that DNA vaccines for seasonal flu would be too. Because flu changes rapidly, a new vaccine must be made annually. Each year, researchers scramble to predict which strain will dominate, then spend six months making the vaccine. And each year, more than 36,000 Americans die of the flu. If researchers could make DNA vaccines, they’d have more time and might be better able to predict which strain they should target, says Margaret Liu, a private consultant and former Merck researcher, who in the mid 1990s was among the first to demonstrate that DNA vaccines can generate a protective immune response in animals.
The holy grail of influenza vaccines, Liu says, is one that would protect against all strains. (See “Universal Flu Vaccines.”) In the interim, DNA vaccines may help researchers meet the biggest challenge: responding rapidly to each year’s new strain, and being prepared to respond quickly to a possible pandemic.