Immune Responses and Protection Profiles in Mice Induced by Subunit Vaccine Candidates Based on the Extracellular Domain Antigen of Respiratory Syncytial Virus G Protein Combined with Different Adjuvants

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease of infants and older people. There is an urgent need for safe and effective vaccines against RSV infection. In this study, we analyzed the effects of the immune response and protection with the RSV recombinant G protein extracellular domain (G ) combined with various adjuvants as novel subunit vaccines in mice. All groups receiving RSV G combined with adjuvants exhibited robust humoral and cellular immunity compared to those receiving an adjuvant alone or inactivated RSV vaccine. The greatest effect was observed in mice receiving G combined with a CpG ODN + Alum salt adjuvant, resulting in the highest production of neutralizing antibodies against both RSV A and B subtypes, G-specific IgG and IFN-γ production in splenocytes, and interleukin-2 and interferon-γ expression in CD4 T cells. Significant humoral and cellular immune responses were observed in mice immunized with G combined with AddaS03™ or cyclosporin A adjuvants. The vaccine containing the AddaS03™ adjuvant showed significantly high expression of interleukin-4 in CD4 T cells. Cross-protection against a challenge with either RSV A or B subtypes was observed in the G plus adjuvant groups, resulting in a significant decrease in viral load and reduced pathological damage in the mouse lungs. These findings offer valuable insights into the development and application of recombinant RSV G-subunit vaccines with adjuvants.