New Bird Flu Vaccine 100 Percent Effective in Animal Study

PITTSBURGH, Pennsylvania, January 30, 2006 (ENS) - University of Pittsburgh scientists have genetically engineered an avian flu vaccine from components of the deadly H5N1 virus that completely protected mice and chickens from infection. The vaccine can be made quickly and induced a strong immune response in the animals, making it a potentially useful tool for preventing the spread of the virus.

This vaccine contains a live virus, so it activates immune responses better than avian flu vaccines prepared by traditional methods, say the researchers. Because it is grown in cells, it can be produced much more quickly than traditional vaccines, according to the study, published in the February 15 issue of the "Journal of Virology" and made available early online.

“The results of this animal trial are very promising, not only because our vaccine completely protected animals that otherwise would have died, but also because we found that one form of the vaccine stimulates several lines of immunity against H5N1,” said Andrea Gambotto, M.D., assistant professor in the departments of surgery and molecular genetics and biochemistry, University of Pittsburgh School of Medicine, and lead author of the study.

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Dr. Andrea Gambotto is an assistant professor of surgery and co-director of the Vector Core Facility at the University of Pittsburgh Biotechnology Center. (Photo courtesy U. Pittsburgh)
Since the latest outbreak began in December 2003, avian flu has killed more than 80 people in four Southeast Asian countries and killed or led to culling of an estimated 200 million birds across the region and in Turkey and Russia.

Dr. Gambotto and his team constructed the new vaccine by genetically engineering a common cold virus, called adenovirus, to express either all or parts of an avian influenza protein called hemagglutinin (HA) on its surface.

Found on the surface of all influenza viruses, HA allows the virus to attach to the cell that is being infected and so is essential to the virus’ ability to cause illness and death.

Based on the published sequence of the Vietnam and Hong Kong strains of the H5N1 avian influenza virus, members of the University of Pittsburgh Vector Core Facility, led by Wentao Gao, Ph.D., research instructor in the School of Medicine's department of surgery, constructed several adenovirus vectors.

The scientists modified the viruses to serve as vectors, or delivery vehicles, for foreign genes or DNA containing either the full genetic sequence of the HA protein or sequences for only parts, or subunits, of HA.

Collaborating with investigators in the Influenza Branch of the Centers for Disease Control and Prevention, Dr. Gambotto's team tested the ability of their slightly different vaccines to protect mice from infection by wild-type H5N1 by comparing their performance to an adenovirus vector containing no H5N1 genes, or an “empty vector.”

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Technicians check poultry samples for avian flu virus, National Institute for Animal Health, Bangkok, Thailand. (Photo courtesy FAO)
The investigators then observed the exposed mice for any signs of illness, and checked their blood for anti-viral antibodies and other markers of H5N1 immunity.

All of the mice immunized with the empty vector vaccine lost weight beginning about three days after exposure to wild-type H5N1 bird flu virus, and all were dead within six to nine days of exposure.

But most of the mice immunized with the adenovirus containing either the whole or part of the HA protein showed little weight loss and survived the H5N1 infection.

When the investigators looked for evidence of a specific immune response to H5N1, they found similar results.

Co-author Simon Barratt-Boyes, B.V.Sc., Ph.D., associate professor, department of infectious diseases and microbiology, University of Pittsburgh Graduate School of Public Health, said the ability of this particular genetically engineered vaccine to induce both antibody and T cell directed immunity is encouraging.

“This recombinant vaccine can stimulate several lines of defense against the H5N1 virus, giving it greater therapeutic value, said Dr. Barratt-Boyes. "More importantly, it suggests that even if H5N1 mutates, the vaccine is still likely to be effective against it. How effective, we are not sure. We won’t know until that occurs.”

Next, Dr. Gambotto’s group, working with veterinarian David Swayne, Ph.D., at the U.S. Department of Agriculture, tested the new vaccine's effectiveness in chickens, which have almost a 100 percent mortality rate to H5N1 exposure.

The researchers inoculated four groups of chickens either through their noses or with subcutaneous injections under the skin. The chickens were then exposed to doses of whole H5N1 virus 10,000 times greater than the dose given to the mice and much greater than farm chickens get during a natural outbreak.

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Indonesia vaccinated 114 million poultry against avian flu with traditionally made vaccine in 2004. (Photo courtesy FAO)
The chickens that received subcutaneous injection showed no clinical signs of disease. But half of the chickens immunized through the nose died and half survived. The researchers have not yet clarified the reason for these differing results.

Rather than replacing traditional inactivated influenza vaccines, Dr. Gambotto and his colleagues suggest that their adenovirus-based vaccine could be a critically important complement to them.

Because it appears to be so successful in immunizing chickens against H5N1, widespread inoculation of susceptible poultry populations could provide a barrier to the spread of the virus in countries where bird flu has not appeared.

If there were to be a disruption in the traditional vaccine production pipeline, a recombinant vaccine could be an attractive alternative for human immunization as well, they said.

Dr. Gambotto outlined the advantages of this type of vaccine development over traditional approaches. Today, flu vaccines are prepared in fertilized chicken eggs, a process developed more than 50 years ago that requires millions of fertilized eggs that would be in short supply if a pandemic were to occur. The recombinant vaccine approach grows the vaccine in cell cultures, which are unlimited in supply.

Another advantage of the Gambotto approach is its speed.

“It takes a little over a month for us to develop a recombinant vector vaccine compared to a minimum of several months via traditional methods,” Dr. Gambotto explained. “This capacity will be particularly invaluable if the virus begins to mutate rapidly, a phenomenon that often limits the ability of traditional vaccines to contain outbreaks of mutant strains.”

Dr. Gambotto and his group are planning a small clinical trial of the vaccine in humans in the near future.