Virus-like Particle Vaccine Expressing the Respiratory Syncytial Virus Pre-Fusion and G Proteins Confers Protection against RSV Challenge Infection

Abstract

Respiratory syncytial virus (RSV) causes severe lower respiratory tract disease in children and the elderly. However, there are no effective antiviral drugs or licensed vaccines available for RSV infection. Here, RSV virus-like particle (VLP) vaccines expressing Pre-F, G, or Pre-F and G proteins on the surface of influenza virus matrix protein 1 (M1) were produced using the baculovirus expression system, and their protective efficacy was evaluated in mice. The morphology and successful assembly of VLPs were confirmed by transmission electron microscope (TEM) and Western blot. High levels of serum IgG antibody response were detected in VLP-immunized mice, and significantly higher levels of IgG2a and IgG2b were found in the Pre-F+G VLP immunization group compared to the unimmunized control. Serum-neutralizing activity was higher in the VLP immunization groups compared to the naïve group, with Pre-F+G VLPs demonstrating superior neutralizing activity to the single antigen-expressing VLP groups. Pulmonary IgA and IgG responses were generally comparable across the immunization groups, with VLPs expressing the Pre-F antigen eliciting higher IFN-γ in spleens. The frequencies of eosinophils and IL-4-producing CD4+ T cell populations were substantially lower in the lungs of VLP-immunized mice, with the PreF+G vaccine inducing a significant increase in CD4+ and CD8+ T cells. VLP immunization significantly decreased the viral titer and inflammation in the lungs of mice, with Pre-F+G VLPs conferring the best protection. In conclusion, our present study suggests that the Pre-F+G VLPs could be a potential vaccine candidate against RSV infection.

Intranasal Vaccination with a Respiratory-Syncytial-Virus-Based Virus-like Particle Displaying the G Protein Conserved Region Induces Severe Weight Loss and Pathology upon Challenge with Wildtype Respiratory Syncytial Virus

“…Although we previously showed that N is not required for VLP assembly [ 18 ], we opted to include N because humans mount a significant humoral and cellular response to N, and N is increasingly recognized as a virulence factor [ 21 , 22 , 23 , 24 , 25 , 27 , 29 , 65 ]. Whereas several studies show that G and F antigens are ultimately better when combined in one vaccine [ 15 , 87 ], this study served to test our approach and GCR antigen design and its ability to raise protective Abs. In contrast to most other subunit approaches, we applied our VLPs IN because the initial site of infection is a factor in the induction of tissue-resident memory cells and because of the mounting evidence for the importance of local mucosal immunity in reducing RSV infection and disease severity in animals and humans [ 29 , 68 , 69 , 70 , 71 ].…”

“…It was previously shown that G protein is not necessary for enhanced disease to occur [ 88 ], and G does not always induce enhanced disease [ 15 , 16 , 17 , 85 ]. In our case, VLP-GCR induced very low levels of anti-G Abs, and challenge of vaccinated animals with wt RSV displayed weight losses that exceeded the post-challenge weight losses observed in mock-vaccinated mice.…”

“…VLPs, in general, can induce relevant immune responses and can cross-present to induce both Th1 and Th2 responses [ 7 , 8 , 9 , 10 ]. In the case of RSV, recent reports show that VLPs can induce protective anti-RSV immunity without VED, in some cases without adjuvant [ 11 , 12 , 13 , 14 , 15 ]. The latter is true also for other non-live vaccine approaches [ 16 , 17 ].…”

Virus-Like Particles Assembled Using Respiratory Syncytial Virus Matrix Protein Elicit Protective Immunity in Mice

“…VLPs were characterized via transmission electron microscopy and Western blot following the methods previously described. 11 Briefly, VLPs stained with 2% uranyl acetate were observed using the Bio-High voltage EM system (JEM-1400 Plus at 120kV and JEM-1000BEF at 1000kV, JEOL Ltd., Tokyo, Japan) and checked for proper assembly. For Western blot analysis, VLPs were separated using 10% sodium dodecyl sulfate polyacrylamide gels.…”

“…Initially, VLP assembly using entirely authentic RSV protein components was disregarded due to inefficient virion particle assembly resulting in low yields. 8 This led to the formation of heterologous VLPs using the protein components derived from the Newcastle disease virus, influenza virus, and others, [9][10][11] as the process of RSV VLP assembly was poorly understood at the time. Later studies did reveal that the RSV F, M, N, and P proteins are the minimum requirements for proper particle assembly, with phenylalanine residue in the F protein cytoplasmic tail and the M protein being integral for virion assembly.…”