Comparative evaluation of two platforms delivering RSV mRNA vaccines expressing modified extracellular domain of G...

Respiratory syncytial virus (RSV) is the leading cause of respiratory infections in infants, young children, and elderly people worldwide. Developing a safe and broadly effective vaccine remains a critical and unmet public health need. This study comparatively evaluated the immunogenicity and protective efficacy of respiratory syncytial virus (RSV) mRNA vaccines expressing a modified G protein extracellular domain (G^ecto), delivered via either lipid nanoparticle (LNP) or lipid-polymer hybrid (LPP) platforms. Both RSV G^ecto-mRNA elicited robust humoral and cellular immunity in mice. Although the humoral immunity in both groups showed a Th2 bias, the advantage of the LNP platform lies in its ability to simultaneously trigger potent humoral and Th1-type cellular immunity. Comparing the two groups, The LNP group elicited a stronger Th1-biased cellular response, manifested by high expression of cytokines such as IL-2 and TNF-α in CD4⁺T cells, and the production of higher neutralizing antibody titers against A/B subtypes of RSV strains than the LPP group,which elicited slightly higher Th2 bias IgG antibody titers. Viral challenge confirmed that both groups provided effective cross-protection against RSV A2 and B9320, significantly reducing lung viral load and histopathology, with comparable protective efficacy.These findings demonstrate that both platforms enabled robust delivery of the RSV G^ecto-mRNA vaccine and generated cross-protective immunity, albeit with divergent response characteristics. These results inform the selection of RSV vaccine delivery platforms aimed at distinct immune correlates of protection.