Background: Human respiratory syncytial virus (HRSV) imposes a significant disease burden on infants and the elderly. Intranasal immunization using attenuated live vaccines and certain vector vaccines against HRSV has completed phase II clinical trials with good safety and efficacy.Recombinant protein vaccines for mucosal immunization require potent mucosal adjuvants. Type I interferon (IFN), as a natural mucosal adjuvant, significantly enhances antigen-presenting cell processing and antigen presentation, promoting the production of T and B cells. Methods: This study utilized human α2b interferon (IFN-human) and mouse α2 interferon (IFN-mouse) as nasal mucosal adjuvants in combination with fusion protein (F). Intranasal immunization was performed on BALB/c mice to evaluate the immunogenicity of the formulation in vivo. Results: Compared to the F protein immunization group, mice in the F + IFN-Human and F + IFN-Mouse experimental groups exhibited significantly increased neutralizing antibody titers and augmented secretion of IFN-γ and IL-4 by lymphocytes, and both of them could induce the production of high-titer specific IgA antibodies in mice (p < 0.001).The F + IFN-Human immunization induced the highest IgG and IgG1 antibody titers in mice; however, the F + IFN-Mouse immunization group elicited the highest neutralizing antibody titers (598), lowest viral loads in the lungs (Ct value of 31), and fastest weight recovery in mice. Moreover, mice in the F + IFN-Mouse immunization group displayed the mildest lung pathological damage (Total score of pathological injury was 2). Conclusions: In conclusion, IFN-Mouse, as a mucosal adjuvant for HRSV recombinant protein vaccines, demonstrated superior protective effects in mice compared to IFN-Human adjuvants.

Human respiratory syncytial virus (HRSV) poses a significant disease burden on global health. To date, two vaccines that primarily induce humoral immunity to prevent HRSV infection have been approved, whereas vaccines that primarily induce T-cell immunity have not yet been well-represented. To address this gap, 25 predicted T-cell epitope peptides derived from the HRSV fusion protein with high human leukocyte antigen (HLA) binding potential were synthesized, and their ability to be recognized by PBMC from previously infected HRSV cases was assessed using an ELISpot assay. Finally, nine T-cell epitope peptides were selected, each of which was recognized by at least 20% of different donors’ PBMC as potential vaccine candidates to prevent HRSV infection. The protective efficacy of F-9PV, a combination of nine peptides along with CpG-ODN and aluminum phosphate (Al) adjuvants, was validated in both HLA-humanized mice (DR1-TCR transgenic mice, Tg mice) and wild-type (WT) mice. The results show that F-9PV significantly enhanced protection against viral challenge as evidenced by reductions in viral load and pathological lesions in mice lungs. In addition, F-9PV elicits robust Th1-biased response, thereby mitigating the potential safety risk of Th2-induced respiratory disease during HRSV infection. Compared to WT mice, the F-9PV mice exhibited superior protection and immunogenicity in Tg mice, underscoring the specificity for human HLA. Overall, our results demonstrate that T-cell epitope peptides provide protection against HRSV infection in animal models even in the absence of neutralizing antibodies, indicating the feasibility of developing an HRSV T-cell epitope peptide-based vaccine.

The authors would like to make the following corrections to this published paper