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US, Japanese Scientists Find Faster Way to Produce Bird Flu Vaccine

Posted on: Tuesday, 1 November 2005, 09:01 CST

US, Japanese scientists find faster way to produce bird flu vaccine

LOS ANGELES, Oct. 31 (Xinhua)-- A novel technique to produce avian influenza vaccine more efficiently could help worldwide governments to tackle the predicted flu pandemic, US and Japanese scientists reported on Monday.

A team of researchers from the University of Wisconsin-Madison and the University of Tokyo found a new way to generate genetically altered and disarmed influenza virus, which are the " seeds" for making flu vaccine in large quantities. Their paper was published in the Oct. 31 online edition of the Proceedings of the National Academies of Science.

Natural viruses manipulate a host cell's reproductive machinery to make new virus particles, which go on to infect other cells and make yet more virus particles. Vaccine makers use monkey kidney cells to make non-virulent viruses that serve as the raw material for vaccines.

The lab-made virus, whose genes are manipulated to disarm its virulence, then can be seeded into chicken eggs to generate the vaccine, which prepare the human immune system to recognize and defeat the wild viruses that spread among humans in an epidemic.

In their paper, the team led by virologists Yoshihiro Kawaoka and Gabriele Neumann, described an improved "reverse genetics" technique that makes it easier to make a seed virus in monkey kidney cells, which churn out millions of copies of the disarmed virus to be used to make vaccines.

Monkey kidney cells are used routinely for generation of seed strains for vaccine production, because they are not known to carry any unknown infectious agents and do not cause tumors.

The new technique improves upon a previous method by significantly reducing the number of plasmid vectors required to ferry viral genes into the monkey kidney cells.

With traditional method, monkey kidney cells must be transfected with 12 plasmids that provide the eight influenza viral RNAs as well as the polymerase and nucleoproteins of the virus. The efficiency is extremely low because monkey kidney cells can not be transfected easily with plasmids.

To overcome this obstacle, the researchers established a reverse genetics system, in which eight polymerase transcription cassettes for viral RNA synthesis are combined on one plasmid.

"By reducing the number of plasmids, we increase the efficiency of virus production," said Kawaoka, a professor at the University of Wisconsin and well-known influenza expert.

"Application of the new system may be especially advantageous in situations of outbreaks of highly pathogenic avian influenza viruses," he noted.

When a new strain of highly virulent influenza emerges to infect humans, vaccine makers must tailor their vaccines to match it because the virus is always genetically different.

This process is a race against time and can take months depending on how quickly new strains are identified, genetically disarmed and subsequently generated in the lab for use to make vaccines in large quantities.

In the event of an outbreak of especially virulent strains of influenza, such as the H5N1 highly pathogenic avian flu virus strain now circulating in Asia and Europe, any efficiency in the manufacture of vaccines will be important.

The new technique promises to ensure ready generation of seed strains for the production of vaccines required to blunt the spread of influenza, according to the researchers.

Source: Xinhua News Agency - CEIS

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