Researchers at the U.S. Food and Drug Administration (FDA) have developed a simple, rapid, and sensitive test that identifies individuals who have made antibodies against respiratory syncytial virus (RSV), the most common cause of serious lower respiratory tract infection in infants and young children worldwide. RSV also affects many elderly individuals, especially those with underlying heart or lung disease, accounting for nearly as many hospitalizations as influenza.
The development of the new assay is important because it could be a valuable tool for assessing the efficacy of RSV vaccines during clinical trials since it can help to identify individuals infected with RSV following a winter season. Since many of the current candidate vaccines contain or express only one or a few of the proteins found in the virus, antibody responses to non-vaccine RSV antigens can serve as a marker of exposure and infection in subjects given these vaccines.
An important advantage of the new test, called a Luciferase Immunoprecipitation Systems (LIPS) assay, is that it is less complicated and easier to perform than other assays now available. Moreover, unlike some currently used tests, it readily differentiates immune responses against the two major subtypes of RSV, RSV-GA and RSV-GB.
The LIPS assay detects antibodies against G glycoprotein, (G protein), a molecule that occurs on the surface of the virus. To develop the assay, the FDA scientists genetically engineered RSV G proteins from both subgroups. They tagged each G protein with luciferase, an enzyme that interacts with a protein called luciferin to release light.
The luciferase-tagged G proteins (RSV-GA and RSV-GB) acted as “bait” to antibodies against the G proteins in samples of human serum (the clear fluid of blood without red or white cells), causing them to bind to the tagged proteins. The scientists added special protein beads that bind the antibodies with the luciferase-tagged G proteins to the bottom of a plastic test well. Then they added luciferin and measured the amount of light released when it interacted with luciferase, which enabled them to calculate how strong the antibody response was to the G proteins.
The FDA scientists showed that the LIPS assay could specifically detect anti-RSV-GA and -GB antibodies in mice that had been infected intranasally with RSV-A or -B strains. In addition, the assay detected antibodies against either RSV-A or RSV-B in samples taken from infants who had contracted the disease—depending on which subtype was present. The assay also found that serum from adolescents had antibodies against G proteins from both subtypes, suggesting that adolescents had been exposed to both RSV-A and RSV-B by that time in their lives.
Development of Luciferase Immunoprecipitation Systems (LIPS) Assay to Detect IgG Antibodies against Human Respiratory Syncytial Virus G-Glycoprotein
Vaccines 2019, 7, 16; doi:10.3390/vaccines7010016
Roberta Lynne Crim, Sangeeta Kumari †, Priyanka Jayanti ‡, Susette Audet, Ashwin Kulkarni § and Judy Beeler *
Office of Vaccines Research and Review, CBER, FDA, Silver Spring, MD 20993, USA;
email@example.com (R.L.C.); firstname.lastname@example.org (S.K.); email@example.com (P.J.);
firstname.lastname@example.org (S.A.); email@example.com (A.K.)
* Correspondence: firstname.lastname@example.org; Tel.: +1-240-402-9389
† Present affiliation: ATCC Cell Systems, Gaithersburg, MD 20877, USA.
‡ Present affiliation: Systems Planning and Analysis, Alexandria, VA 22311, USA.
§ Present affiliation: BioHealth Innovations Inc., Rockville, MD 20850, USA.