A laboratory assay developed by scientists at FDA could speed the release of pandemic influenza vaccines to the public by shortening the time it takes to test vaccine potency. The FDA scientists developed the new assay in response to the recommendation of a workshop organized by the World Health Organization (WHO) following the 2009 H1N1 influenza pandemic and aninitiative by the US Department of Health and Human Services’ Biomedical Advanced Research and Development Authority (BARDA).
One advantage of the new potency assay is that it does not require the use of antisera for testing influenza vaccines. The current standard potency assay for influenza vaccines uses antibodies against hemagglutinin (HA), a protein on the surface of the virus that is an important component of influenza vaccines. In order to make the antibodies, vaccine viruses aretreated with enzymes to release HA proteins from their surface. If the anti-HA antibodies recognize and bind to the HA, the two molecules form tiny visible rings, demonstrating that the HA is suitable for use in influenza vaccines.Drawbacks to the current assay are that the use of enzymes to release HA from influenza viruses does not reliably produce sufficient amounts of HA and the resulting proteins are difficult to purify before injecting into sheep. The new assay does not use antibodies that attach to HA, instead it is based on thenatural interaction between the influenza virus envelope protein, HA, and the receptor molecule on the surface of target cells lining the human respiratory tract.
The FDA researchers used artificial versions of the HAreceptors known to be targeted by human influenza, and tested whether the HA proteins from influenza vaccines recognized and attached to them. Only those HA proteins that were identical to the viral protein, and thus able to act as a vaccine, were able to fit into the appropriate SA-glycan receptor sites. The scientists used a surface plasmonresonance technique to measure the amount of HA proteins attached to the artificial receptors that were coated on special chips. This allowed them to determine how much HA was in vaccine samples, as well as the stability of those proteins. This assay was also able to measure the amount of HA protein in vaccines that were mixed with adjuvants. Overall, the SPR-based assay measurements of HA content in vaccines agreed closely with those obtained by the standard antibody-based ring-forming assay. This suggests that the newer assay might be reliable enough to replace the slower, standard assay.