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 Ecoli 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 vitroneutralization 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.

Author summary

A vaccine against RSV that provides protection without potential for disease enhancement is required. The G attachment protein represents an important candidate for inclusion in an effective RSV vaccine. However, the contribution of different antigenic sites to protection against RSV is not completely understood. We evaluated the protective efficacy of recombinant unglycosylated RSV-G protein vaccine produced in Ecoli (REG) vs. CCD-deletion (REG ΔCCD). We also investigated immunogenicity and protective efficacy of all antigenic sites identified in post-primary infection infant sera using GFPDL that includes N- and C-terminal G subdomains, and linear peptides. The REG ΔCCD, N- and C-terminal subdomains and peptides generated antibody titers in rabbits and mice. Vaccinated mice challenged intranasally with RSV demonstrated significant reduction of viral replication in the nasal cavity and lungs. Our study highlights the safety and immunogenicity of recombinant G protein as economical protective vaccine against RSV disease.