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New Bird Flu Vaccine Nears Human Tests

DNA-Based Vaccine Could Be Ready Fast if Flu Pandemic Hits
By
WebMD Health News
Reviewed by Louise Chang, MD

Jan. 30, 2006 -- A new bird flu vaccine promises broad protection against bird flu -- even if the virus mutates.

In animal tests, the genetically engineered vaccine protects chickens and mice against the deadly H5N1 bird flu virus, the strain that has killed people in Asia and Europe.

Human safety tests are poised to start in just a few months, says University of Pittsburgh researcher Andrea Gambotto, MD.

"We are ready to go," Gambotto tells WebMD. "We are ready to start production of vaccine for human trials. In a couple of days, we expect to hear from the federal government about funding for clinical production. Four to six months after that, we can begin human trials."

Vaccines and Virus Mutations

It's not your dad's flu vaccine. Normal flu vaccines -- including the bird flu vaccine now in limited production -- are made from inactivated flu virus grown in hens' eggs. It's a tried-and-true technology that's been around for decades.

But inactivated flu vaccines work only against the exact virus strain they are made from. If a flu virus mutates even slightly -- what experts call genetic "drift" -- the vaccine won't work. That's why the seasonal flu vaccine has to be changed every year or so.

Also, it takes longer to grow vaccine viruses in eggs than it does to grow them with more modern cell-culture techniques. And in the case of bird flu, to which humans have no pre-existing immunity, vaccine protection may take at least two shots given weeks apart.

How the New Approach Works

Gambotto's team uses a different approach. Instead of making a vaccine from pieces of killed virus, the researchers use a common cold virus -- adenovirus -- genetically engineered to carry bird flu DNA. When given by nose spray or injection, these vaccine viruses infect human cells. They go through a single round of replication, during which they "express" pieces of bird flu virus.

These pieces of bird flu virus do two things. One is to stimulate production of antiflu antibodies. These antibodies quickly form a first line of defense against flu infection and disease.

The second thing they do -- something the current inactivated vaccine does not do -- is stimulate antiflu T-cell immunity. This long-lasting form of immunity offers a second line of defense. And it may offer protection against drift variants of the virus used in the vaccine.

"In humans, the H5N1 bird flu takes about two weeks to kill, so there is time for T cells to come out and give protection," Gambotto says.

Will It Work?

Adenoviruses induce very powerful immune responses, says flu expert John Treanor, MD, director of the vaccine and treatment evaluation unit at the University of Rochester in New York.

"Applying this to an H5 bird flu vaccine makes a lot of sense," Treanor tells WebMD. "Gambotto's team shows it can be quite protective in the mouse model. ... That is interesting because this could be a pathway toward a more broad-based vaccine that could protect against all viruses in the H5 subtype."

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