A new method of making flu vaccines is faster, more efficient, and more robust than the one that has been in use for the last 50 years. It has the potential to scale up rapidly, to deal with new strains of influenza such as this year's H1N1, and to help stem a pandemic tide. However, a U.S. Food and Drug Administration advisory panel voted in late November not to approve the technology, which involves growing key vaccine ingredients inside caterpillar cells instead of in chicken eggs, as is currently done. The FDA says that the company behind the new approach, Protein Sciences, based in Meriden, CT, needs to test it further before the method can be approved for use in the United States.
Growing immunity: These images show insect cells growing without virus genes (top) and with virus genes (bottom). Scientists say the approach can produce 100,000 doses of vaccine per week, and can be adapted for different viruses, including H1N1 (swine flu).Jose Romero, chief of pediatric disease at Arkansas Children's Hospital and a member of the 11-person FDA panel, says that, while the company has more to do in order to prove safety, the cell-based technology shows considerable promise.
"This type of technology is going to move traditional influenza vaccinology into the 21st century," says Romero. "We recognize that there may come a day when a strain does arrive that cannot be supported by growth in traditional egg-based technology, and this and other cell-based technologies can breach that problem and provide us with another avenue for developing vaccines."
Today's egg-based vaccine technology is slow and unwieldy, requiring at least six months' of production time and millions of eggs to supply enough doses for a regular flu season. If a new virus appears unexpectedly, the antiquated system wouldn't be able to gear up fast enough to produce a new vaccine, many experts agree. What's more, if the virus itself were derived from birds, it might reduce the supply of eggs, hampering the country's main means of vaccine production.
For the past decade, Protein Sciences, along with a number of other companies, has been looking to cell-based vaccines as a more efficient and robust alternative. Instead of growing viruses in chicken eggs, researchers inject virus strains into insect cells. Both the virus and the cells then grow and multiply quickly in bioreactors. Scientists break the cell walls and harvest a key protein, called hemagglutinin, produced by the virus. This protein, found on the influenza virus's outer surface, is responsible for binding to cells in the body, causing a viral infection. Scientists purify and inactivate the harvested protein so that it can stimulate an immune response without causing an infection. The protein is the main ingredient in a vaccine. Protein Sciences' technology is a slight variation on the conventional cell-based approach. Instead of growing live viruses, the company replicates viral DNA within cells. The genes for hemagglutinin are extracted from a dead flu virus and injected into baculovirus--a virus that infects a caterpillar called the armyworm. The baculovirus is then injected into ovary cells isolated from the armyworm. In a bioreactor, the virus eats away at cells, replicating DNA and producing hemagglutinin.
"Because the starting material is a DNA sequence, it eliminates a lot of steps you have to go through, because the flu virus itself is not part of this production process," says John Treanor, a medical advisor to the company and professor of microbiology and immunology at the University of Rochester Medical Center in New York. "You also don't have concerns of workers getting infected, versus using a growing virus."
Treanor headed four clinical trials to test the vaccine for effectiveness against seasonal flu. The trials compared the effects of the company's vaccine against a conventional one in 3,231 people aged 18 and older.
The company presented its results to the FDA advisory board. While the new vaccine was found to protect against seasonal flu symptoms in those 18 to 49, it was not possible to draw significant conclusions for older participants. Several older subjects suffered from facial swelling after receiving the vaccine, and one developed a temporary paralysis on one side of the face. This might have been a preexisting condition, but researchers couldn't be sure if the condition was independent of the vaccine. "When you have one case, it's hard to know," says Treanor.
The FDA panel recommended that the company expand the patient group to determine whether the vaccine is safe in a larger, older population.
Other companies seeking FDA approval for similar cell-based vaccines include Novartis, which opened a vaccine manufacturing plant in North Carolina this week and plans to produce vaccines from dog kidney cells.
FluGen, a vaccine company based in Madison, WI, has also entered the race. It is growing flu virus in manipulated hamster ovary cells--a cell line that has already been approved by the FDA for producing drugs to treat rheumatoid arthritis. FluGen is a little behind its bigger competitors, but CEO Paul Radspinner says he will take a lesson from Protein Sciences' experience when it comes time to seek FDA approval. "Maybe it's a learning point," says Radspinner. "We'll be very careful with where we go with clinical trials where there's a database of patients coming through, and [make sure] that preexisting conditions are being noted."
By Jennifer Chu
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