A DNA vaccine targeting West Nile virus in equines was launched in December by the Fort Dodge Animal Health division of Wyeth. That vaccine was reportedly the first DNA vaccine for any species to be registered with a government regulatory body. It was also one of the many milestones and advancements in DNA vaccine development and manufacturing methods outlined by speakers at the recent International Society of DNA Vaccines conference in Las Vegas, organized by BioConferences International.
Wyeth’s development program proved that DNA vaccines can be as efficacious as traditional vaccines. “This was proof of concept for DNA vaccines as a class,” explained Hsien-Jue Chu, DVM, Ph.D., executive vp, animal health research and development. This is the fourth vaccine for West Nile virus to reach the market since Wyeth’s West Nile Innovator, launched in 2001, and two subsequent recombinant-based vaccines.
In the early part of this decade, experimental DNA vaccines seemed effective in rodents, where “it was easy to induce an immune response. It was difficult to make it work in large animals, however,” Dr. Chu recounted. Success came when an immune-modulator was added to the plasmid DNA, which probably allowed the intramuscularly-injected DNA to target the cells more effectively. Now, the DNA-based West Nile vaccine confers at least one year immunity—the same duration of immunity that is demonstrated by traditional vaccines, he said.
The lessons learned from the West Nile DNA vaccine program are being applied to rabies and other vaccines, he said, and work is under way to see whether it is possible to lengthen the conferred immunity. Programs at other companies, Dr. Chu said, involve DNA vaccines to treat melanoma in dogs and to target a particular pathogen in fish that affects salmon farms.
Even before Wyeth launched its equine DNA vaccine targeting West Nile virus, companies were working to create the technologies needed to produce and scale-up aspects of DNA vaccine development.