Comparison of Immune Responses to Different Versions of VLP Associated Stabilized RSV Pre-Fusion F Protein

Abstract

Efforts to develop a vaccine for respiratory syncytial virus (RSV) have primarily focused on the RSV fusion protein. The pre-fusion conformation of this protein induces the most potent neutralizing antibodies and is the focus of recent efforts in vaccine development. Following the first identification of mutations in the RSV F protein (DS-Cav1 mutant protein) that stabilized the pre-fusion conformation, other mutant stabilized pre-fusion F proteins have been described. To determine if there are differences in alternate versions of stabilized pre-fusion F proteins, we explored the use, as vaccine candidates, of virus-like particles (VLPs) containing five different pre-fusion F proteins, including the DS-Cav1 protein. The expression of these five pre-F proteins, their assembly into VLPs, their pre-fusion conformation stability in VLPs, their reactivity with anti-F monoclonal antibodies, and their induction of immune responses after the immunization of mice, were characterized, comparing VLPs containing the DS-Cav1 pre-F protein with VLPs containing four alternative pre-fusion F proteins. The concentrations of anti-F IgG induced by each VLP that blocked the binding of prototype monoclonal antibodies using two different soluble pre-fusion F proteins as targets were measured. Our results indicate that both the conformation and immunogenicity of alternative VLP associated stabilized pre-fusion RSV F proteins are different from those of DS-Cav1 VLPs.

Progress in the development of virus-like particle vaccines against respiratory viruses

“…For presentation of pre-fusion F protein on the surfaces of VLPs, the pre-fusion stabilizing DS-Cav1 pre-fusion F with or without foldon domain was fused to the TM of NDV F protein [99]. A recent study reported that NDV VLPs containing pre-fusion F stabilized single chain F with deletions of the peptide 27 sequence and cleavage sites and point mutations could induce higher RSV neutralizing antibodies in cotton rats, compared to NDV VLP with DS-Cav1 F [100].…”

“…RSV pre-fusion stabilizing mutations (DS-Cav1) with a foldon stabilizer retained pre-F site Ø epitopes and site II neutralizing epitopes in soluble proteins [136]. It is likely that additional mutations together with DS-Cav1 or alternative mutations in RSV F will be required for further stabilization of pre-fusion F protein antigens on VLP platforms [99,100]. RSV F nanoparticle formulations of recombinant F proteins produced in the insect cell expression system are under advanced clinical trials of maternal vaccination to protect infants although the vaccine phase III clinical trial in the elderly was not successful [132,133,137].…”

Comparisons of Antibody Populations in Different Pre-Fusion F VLP-Immunized Cotton Rat Dams and Their Offspring

“…A very important question for vaccine development is whether the different mutation-stabilized pre-fusion F proteins are indeed the same in terms of structure, antibodies induced, and protection from RSV challenge afforded by their use as immunogens. We have recently addressed these questions by comparing the reactivity to monoclonal antibodies and the immunological properties of virus-like particles (VLPs) assembled with different versions of mutation-stabilized pre-fusion F proteins [18,30]. We have reported that five different pre-fusion F proteins, in VLPs, bind differently to representative pre-fusion specific monoclonal antibodies (mAb) [18].…”

“…We have recently addressed these questions by comparing the reactivity to monoclonal antibodies and the immunological properties of virus-like particles (VLPs) assembled with different versions of mutation-stabilized pre-fusion F proteins [18,30]. We have reported that five different pre-fusion F proteins, in VLPs, bind differently to representative pre-fusion specific monoclonal antibodies (mAb) [18]. Compared to VLPs assembled with DS-Cav1 F protein, two of these alternative mutation-stabilized pre-fusion F protein VLPs induced, in mice, neutralization titers 3 to 4-fold higher than DS-Cav1 F VLPs [18].…”

“…We have reported that five different pre-fusion F proteins, in VLPs, bind differently to representative pre-fusion specific monoclonal antibodies (mAb) [18]. Compared to VLPs assembled with DS-Cav1 F protein, two of these alternative mutation-stabilized pre-fusion F protein VLPs induced, in mice, neutralization titers 3 to 4-fold higher than DS-Cav1 F VLPs [18]. Furthermore, we showed that the specificities of the population of antibodies induced in mice by the five different VLP-associated pre-fusion F proteins were different as defined by differences in the serum inhibition of binding of representative monoclonal antibodies to the soluble forms of the pre-fusion F protein [18].…”