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 naïve 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.

Evidence for a functional interaction between the respiratory syncytial virus fusion and attachment proteins in the envelope of infectious virus particles

“…The interaction between the F and G proteins has also been demonstrated in RSV virus-like particles (VLPs) [44], suggesting that that the formation of a protein complex is an intrinsic biological property of these proteins and is not dependant on virus infection. Furthermore, the VLPs containing both the F and G proteins exhibit enhanced neutralising antibody titres in animals compared with VLPs that only contain the F protein, suggesting that the G protein may stabilise the F protein in its pre-fusion form [45]. In the context of the infectious virus, we can hypothesise that in the virus envelope the interaction with the G protein may lead to stabilization of the F protein in its pre-fusion form.…”