Improving ability of RSV microneutralization assay to detect G-specific and cross-reactive neutralizing antibodies through immortalized cell line selection

Antibodies face the challenge against human respiratory syncytial virus

In the December 22 issue of Cell, Bartsch et al. describe functional profiling of the antibody response to respiratory syncytial virus in human adults vaccinated with an experimental adenovirus-based prefusion-stabilized HRSV-F vaccine and subsequently intranasally challenged with HRSV. The authors identified various antibody effector functions as humoral correlates of protection.

RSV neutralization assays - Use in immune response assessment

Respiratory syncytial virus (RSV) is a leading cause of respiratory illness among children and infants worldwide, yet no licensed vaccine exists to reduce the risk of disease. At least 16 RSV vaccine candidates are currently in clinical development and many are designed to induce robust virus neutralizing immune responses. RSV neutralizing antibody (nAb)-mediated interventions such as intravenous immunoglobulin (IVIG) and palivizumab provide passive protection against serious lower respiratory tract disease due to RSV, validating nAbs as a correlate of protection. To identify correlates of protection for vaccine candidates that have demonstrated their protective efficacy, an investigator can use assays designed to measure nAb responses. However, there is no standard method of measurement; individual laboratories have developed their own methods to measure the ability of nAbs to reduce the infectivity of a defined virus dose in a variety of cell lines, leading to establishment of the broad variety of RSV neutralization assay formats currently in use. Standardizing the RSV neutralization assay is an essential step toward better assessment of nAb responses to vaccine candidates. Use of a common reference standard by all makes comparing the immunogenicity of different vaccine candidates feasible. In the context of vaccine development, the WHO 1^st International Standard for Antiserum to RSV (RSV IS) has been shown to be suitable for harmonizing results across laboratories and assay formats used to measure nAb titers to RSV/A and RSV/B in human sera. This review describes the broad variety of RSV virus neutralization assay formats currently in use and the importance of the RSV IS for harmonization of results across formats and across laboratories. It also outlines good practices for key assay components and data analysis to promote the quality and consistency of measuring RSV nAb titers in serum specimens.

Evaluation of the respiratory syncytial virus G-directed neutralizing antibody response in the human airway epithelial cell model

Human respiratory syncytial virus (RSV) is a major cause of serious respiratory tract infections in infants and the elderly. Recently it was shown that the RSV G glycoprotein mediates attachment to cells using CX3CR1 as a receptor, and that G-specific neutralizing antibodies can be detected using human airway epithelial (HAE) cell cultures. To investigate the contributions of G-specific antibodies to RSV neutralization, we performed HAE neutralization assays on sera from RSV G-immunized mice or RSV-infected infants. We confirmed that G-specific neutralization using serum from mice or humans could only be detected on HAE cultures. We also found that RSV G-specific antibodies in infants were either subgroup specific or cross-neutralizing. Altogether, our results suggest that G is an important target for generating neutralizing antibodies and would be beneficial to include in an RSV vaccine. Further, inclusion of G antigens from both RSV subgroups may enhance the vaccine cross protection potency.