The Respiratory Syncytial Virus G Protein Enhances the Immune Responses to the RSV F Protein in an Enveloped Virus-like Particle Vaccine Candidate

Abstract

Respiratory syncytial virus (RSV) is a serious human respiratory pathogen, but no RSV vaccine has been licensed. Many of the vaccine candidates are focused on the viral F protein. However, it is the G protein that binds the likely receptor, CX3CR1, in human alveolar lung cells raising the question of the importance of the G protein in vaccine candidates. Using virus-like particle (VLP) vaccine candidates, we have directly compared VLPs containing only the pre-fusion F protein, only the G protein, or both glycoproteins. We report that VLPs containing both glycoproteins bind to anti-F protein specific monoclonal antibodies differently than VLPs containing only the pre-fusion F protein. Using RSV naive cotton rats as an animal model, we have found that VLPs assembled only with the pre-F protein stimulated extremely weak neutralizing antibody (NAb) titers as did VLPs assembled with G protein. However, VLPs assembled with both glycoproteins stimulated quite robust neutralizing antibody titers, titers that were significantly higher than the combined titers induced by pre-F only or G only VLPs. VLPs assembled with both glycoproteins induced improved protection of the animals from RSV challenge compared to pre-F VLPs and induced significantly higher levels of antibodies specific for F protein antigenic sites 0, site III, and AM14 binding site compared with VLPs containing only the pre-F protein. These combined results indicate that assembly of pre-F protein with G protein in VLPs further stabilized the pre-fusion conformation or otherwise altered the conformation of the F protein increasing the induction of protective antibodies. ImportanceRSV causes significant disease in infants, young children, and the elderly. Thus, development of an effective vaccine for these populations is a priority. Most ongoing efforts in RSV vaccine development have focused on the viral fusion (F) protein, however, the importance of inclusion of G in vaccine candidates is unclear. Here, using VLPs assembled with only the F protein or only the G protein or both glycoproteins, we show that VLPs assembled with both glycoproteins are a far superior vaccine, in a cotton rat model, than VLPs containing only F protein or only G protein. The results show that the presence of G protein in the VLPs influences the conformation of the F protein and the immune responses to F protein resulting in significantly higher neutralizing antibody titers and better protection from RSV challenge. These results suggest that inclusion of G protein in a vaccine candidate may improve its effectiveness.