Scientists at the U.S. Food and Drug Administration (FDA) have developed an assay that assesses the ability of antibodies to neutralize Ebola virus, using a technique that does not require the use of Ebola virus itself and can be automated for rapid testing of large numbers of samples.
The new FDA assay is important because the effectiveness of most licensed viral vaccines is based on their ability to trigger production of neutralizing antibodies. Therefore, methods for assessing neutralization activity of antibodies will likely be an important component for evaluating the effectiveness of Ebola virus vaccines and identifying correlates of protection (measurable signs of immunity).
The assay is based on a widely used technique called micro-neutralization, which measures the ability of antibodies to prevent viruses from infecting animal cells and reproducing themselves. The greater the neutralization of a virus by antibodies, the fewer the number of viruses are able to infect cells and the less the viruses can replicate themselves by making copies of viral genetic material.
A key attribute of the assay is built upon the use of a genetically modified, non-disease-causing virus called vesicular stomatitis virus (VSV). The modified VSV carries part of the genome from Ebola virus and can substitute for Ebola virus in certain assays—an approach previously used at FDA.
The use of genetically engineered VSV eliminates the need for additional precautions, like a BSL-4 laboratory, because the modified virus is incapable of causing Ebola disease. These laboratories are designed for working with pathogens that pose a high risk of life-threatening disease through aerosol transmission and for which there is no vaccine or treatment. The FDA assay is appropriate for BSL-2 laboratories, which are widely available and do not require the more elaborate containment requirements of BSL-4. The need for BSL-4 laboratories for scientists to work with Ebola virus has complicated the worldwide effort to study the virus and develop and assess the effectiveness of Ebola virus vaccines.
The FDA scientists genetically modified different versions of VSV, so each one carried on its surface one of four variations of a molecule called an envelope glycoprotein (GP) found on different strains of the Ebola virus. Then they used a technique called quantitative polymerase chain reaction to measure the amount of genetic material produced by the hybrid VSV after it had been exposed to commercially available antibodies to Ebola virus. Automating the process should offer an important time advantage to public health scientists during investigations of an outbreak. The assay can determine within 6 to 16 hours if antibodies are effective against the Ebola virus.
The scientists showed that the assay was able to assess whether specific antibodies targeting each GP neutralized the different hybrid VSV variants, preventing the virus from infecting the cells and multiplying. Moreover, the results of the Ebola antibody assays agreed with those obtained by other, more complex assays, now used for such testing. This suggests that the assay will be useful in evaluating the ability of antibodies, triggered either by vaccines or natural infection, to neutralize specific varieties of the virus. Moreover, it might be possible to adapt the assay to assess neutralizing antibodies against other viral pathogens.
Development of a micro-neutralization assay for ebolaviruses using a replication-competent vesicular stomatitis hybrid virus and a quantitative PCR readout
Vaccine 17 April 2017
Stella S. Lee, Kathryn Phy, Keith Peden ⇑, Li Sheng-Fowler
Laboratory of DNA Viruses, Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, MD 20993, United States
⇑ Corresponding author at: Building 52/72, Room 1220, CBER, FDA, 10903 New Hampshire Avenue, Silver Spring, MD 20993, United States.
E-mail address: email@example.com (K. Peden).