Robust and Long-Lasting Immunity and Protection in Mice Induced by Lipopolyplex-Delivered mRNA Vaccines Expressing the Prefusion Protein of Respiratory Syncytial Virus

Objectives: Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants and children. mRNA vaccines based on the lipopolyplex (LPP) platform have been previously reported, but they remain unapplied in RSV vaccine development. In this study, we developed a novel LPP-delivered mRNA vaccine that expresses the respiratory syncytial virus prefusion protein (RSV pre-F) to evaluate its immunogenicity and protective effect in a mouse model. Methods: We synthesised mRNAs with gene modification for RSV pre-F and prepared mRNA vaccines using the LPP delivery platform, named as RSV pre-F LPP-mRNA. RSV pre-F protein expression in mRNA vaccines was characterized in vitro. Then we evaluated the effects of the immune response and protection of this mRNA vaccine in mice until to 24 weeks post-vaccination. Results: Following the booster immunisation, robust and long-lasting RSV F-specific IgG antibodies were detected in the serum of mice. which exhibited Th1/Th2 balanced IgG response and cross-neutralising antibodies against different subtypes (RSV A2, B18537, and clinical isolate hRSV/C-Tan/BJ 202301), with a clear dose-response relationship observed. RSV F-specific IgG antibodies were maintained in the mice for an extended period, lasting up to 18 weeks post-immunisation. Concurrently, multifunctional RSV F-specific CD8+T cells (IFN–γ, IL-2, TNF- α) were detected in mice. After the RSV A2 challenge, RSV pre-F LPP-mRNA vaccine led to significant reduction of viral replication, while reduced pathological damage was observed in lung tissue. Conclusions: The LPP-delivered mRNA vaccine expressing RSV pre-F induces a robust and long-lasting immune response and protection, indicating good prospects for further development and application.