A newly developed vaccine has successfully protected mice against the deadly 1918 Spanish flu virus, U.S. scientists reported on Tuesday.
The scientists also created a technique for identifying antibodies that neutralize this virus, a tool that could help contain future pandemic flu strains, according to a report in the latest online advance edition of the Proceedings of the National Academy of Sciences.
The findings are important to understanding and preventing the recurrence of the H1N1 influenza virus that caused the 1918 pandemic, and to protecting against future flu virus strains in the future, including the H5N1 avian flu virus, the researchers said.
The 1918-1919 pandemic, the most deadly flu outbreak in modern history, killed 30 million or more people worldwide. Scientists are afraid that a new flu virus strain would cause a similar disaster.
"A key to containing pandemic flu viruses is to understand their vulnerabilities and determine whether they can evade immune recognition," said Gary Nabel, director of the Vaccine Research Center at U.S. National Institute of Allergy and Infectious Diseases who led the study.
"What we learn about the H1N1 virus that caused the 1918 pandemic is pertinent to other pandemic viruses and to the development of effective and universal vaccines."
Using the genetic sequence information for the 1918 flu virus, the researchers created plasmids, small strands of DNA designed to express specific characteristics, carrying genes for the virus' hemagglutinin (HA) protein, the surface protein found in all flu viruses that allows the virus to stick to a cell and cause infection.
They created two types of plasmids: one to reflect the HA found in the original 1918 flu virus; the other an altered HA protein designed to weaken the virus.
Mice were then injected with a DNA vaccine containing both types of plasmids to determine whether they would generate immune responses to the 1918 virus.
The researchers found significant responses both in terms of production of T-cells, the white blood cells critical in the immune system's battle against invading viruses, as well as the production of neutralizing antibodies.
All of the 10 immunized mice survived when they were exposed to reconstructed 1918 virus 14 days later, and eight of the 10 mice that received antibodies from the immunized mice also survived the challenge, the researchers reported.
To evaluate the vaccine's antibody-inducing capabilities while minimizing exposure of lab personnel to the deadly virus, the researchers also created artificial viruses, or pseudoviruses, featuring the HA of the 1918 flu virus but stripped of the ability to cause infection.
The pseudoviruses were then incubated with antibody-containing blood samples from the mice immunized with the DNA vaccine and those that were not. The researchers found that the antibodies from the immunized mice neutralized the pseudoviruses while the blood samples from the mice that were not immunized had no effect.
This method was also effective in identifying neutralizing antibodies to the H5N1 avian flu virus and could be used to screen for monoclonal antibodies that may be used as an antiviral treatment, according to Nabel.