Research Article: Protective antigenic sites in respiratory syncytial virus G attachment protein outside the central conserved and cysteine noose domains

Date Published: August 24, 2018

Publisher: Public Library of Science

Author(s): Jeehyun Lee, Laura Klenow, Elizabeth M. Coyle, Hana Golding, Surender Khurana, Ralph A. Tripp.

http://doi.org/10.1371/journal.ppat.1007262

Abstract

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract disease in infants. Previously, we elucidated the antibody repertoire following primary RSV infection in infants. Whole genome-fragment phage display libraries (GFPDL) expressing linear and conformational epitopes from RSV bound 100-fold more phages within attachment protein (G) following primary RSV infection. The G-reactive epitopes spanned the N- and C-termini of G ectodomain, in addition to the central conserved domain (CCD). In the current study, we examined the contribution of antigenic regions of G outside of the CCD to RSV-specific immunity. We evaluated the immunogenicity, neutralization and protective efficacy of all RSV-G antigenic sites identified following primary RSV infection using recombinant E. coli expressed G ectodomain (REG), CCD-deleted G ectodomain (REG ΔCCD), N- and C-terminal G subdomains, and antigenic site peptides. The REG ΔCCD, N- and C-terminal subdomains and peptides generated antibody titers in rabbits and mice that bound fully glycosylated Recombinant Mammalian expressed G ectodomain (RMG) and intact RSV virion particles but minimal in vitro neutralization titers compared with the intact G ectodomain. Vaccinated mice were challenged intranasally with RSV-A2 Line 19F. Viral replication in nasal cavity and lungs was significantly reduced in vaccinated animals compared to unimmunized controls. Control of viral loads post-RSV challenge correlated with serum antibody binding to the virus particles. In addition, very low Th2/Th1 cytokine ratios were found in the lungs of REG ΔCCD vaccinated mice after challenge. These data demonstrate the presence of multiple protective sites in RSV G protein outside of the CCD that could contribute to the development of a bacterially produced unglycosylated G protein as safe and protective vaccine against RSV disease.

Partial Text

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract disease among infants and children globally [1] [2] [3]. Hospitalizations for respiratory tract disease among young children, especially in less than one year old, is most often attributed to RSV infection[4] [5]. Furthermore, despite the development of immunity following RSV infection during childhood, individuals remain susceptible to RSV upper respiratory tract reinfection life-long[6, 7] [8].

The contribution of immune response against the RSV attachment protein G to either protection or potential enhanced disease have been well documented [8]. The G protein undergoes constant diversification in circulating RSV strains, and may contribute to the ability of the virus to reinfect throughout life [9–11]. Several monoclonal antibodies targeting the G protein were demonstrated to have protective activity against severe disease in animal models as well as anti-inflammatory effects [19, 26–29]. These MAbs bound to either linear or conformational epitopes overlapping and surrounding the CCD/cysteine noose CX3CR1 binding regions. Furthermore, levels of anti-G antibodies, in addition to antibodies against pre-F, were associated inversely with disease severity in RSV-infected infants and young children (<2yr) [14]. Therefore, dissecting the immune response to the G protein is important for better understanding of RSV viral immunity and the design of RSV G based vaccines [30].   Source: http://doi.org/10.1371/journal.ppat.1007262