Virus-like particles containing the extracellular domain of G protein in combination with a CTL peptide of M2 elicit protection against respiratory syncytial virus infection without pulmonary disease.

Abstract

Background and aims: Respiratory syncytial virus (RSV) is a major respiratory pathogen afflicting both infants and the elderly. Although three RSV vaccines have been approved for adults over the age of 60 or pregnant individuals, there are ongoing efforts to develop novel vaccines against RSV infection. This study was designed to develop and evaluate virus-like particles (VLPs) as potential RSV subunit vaccine candidates, with the goal of balancing immunogenicity, protective efficacy, and safety.

Methods: Two types of VLPs were constructed using a recombinant baculovirus (rBV)-insect cell expression system: G_ECD-VLPs (containing the extracellular domain [G_ECD] of RSV G protein) and G_ECD/M2_82-90-VLPs (containing GECD fused with the CTL epitope M2_82-90 of M2 protein). BALB/c mice were vaccinated with these VLPs, and immune responses were assessed via RSV-specific IgG and neutralizing antibody titers, cytokine profiles (IFN-γ, IL-2, TNF-α, IL-10, IL-4, IL-5), and lung T-cell subsets (CD25⁺FoxP3⁺ Treg and Th17 cells). Protective efficacy against RSV infection and immunopathology was further evaluated post-challenge.

Results: Vaccination with both VLPs induced robust RSV-specific IgG and neutralizing antibodies, conferring defense against RSV infection. Compared with the UV-RSV control group, both G_ECD/M2_82-90-VLPs and G_ECD-VLPs groups exhibited significantly increased Th1-type cytokine levels and decreased Th2-type cytokine concentrations (P<0.05, P<0.001). Importantly, compared to G_ECD-VLPs, G_ECD/M2_82-90-VLPs further significantly upregulated the expression of Th1-type cytokines (IFN-γ, IL-2) and regulatory cytokine IL-10, while significantly downregulating Th2-type cytokine IL-4 (all P<0.05). Post-RSV challenge, mice vaccinated with G_ECD/M2_82-90-VLPs exhibited a substantially increased proportion of CD25⁺FoxP3⁺ Treg cells and a decreased percentage of Th17 cells in the lungs. Notably, G_ECD/M2_82-90-VLP vaccination prevented RSV-induced immunopathology.

Discussion: Our findings demonstrate that vaccination with G_ECD/M2_82-90-VLPs elicited a balanced immune response and conferred protection against RSV infection without immunopathology. These data demonstrate that the G_ECD/M2_82-90-VLPs are a potential RSV subunit vaccine candidate.