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Oral respiratory syncytial virus (RSV) DNA vaccine expressing RSV F protein delivered by attenuated Salmonella typhimurium.

Human respiratory syncytial virus (RSV) is a major viral pathogen of the lower respiratory tract of infants and young children worldwide. No effective prevention measure is available. Attenuated Salmonella strains expressing heterologous antigens can be delivered by the oral route, triggering efficient antigen-specific humoral, cellular, and mucosal immunity. In this study, we orally administered attenuated Salmonella strain SL7207, carrying the plasmid pcDNA3.1/F expressing the RSV F gene, to BALB/c mice and showed significant elevations of serum anti-RSV IgG and bronchoalveolar lavage secretory IgA as compared with the control group carrying empty plasmid (p<0.001). The ratio of IgG1 and IgG2a was 0.96. The experimental group also showed a stronger cytotoxic T cell response (p<0.01 at effector:target ratios of 100:1 and 50:1) and a higher stimulation index value of T cell proliferation (p<0.05) than the respective control group. RSV titers in the lung homogenates of the experimental group on day 3 and day 5 postchallenge were lower than in the control group (p<0.05). Histopathological analysis showed obvious differences in infiltration of inflammatory cells and pulmonary alveolar wall thickness (p<0.01) between the two groups. In summary, our results demonstrate the potential of orally administered SL7207-based DNA vaccines against RSV infection.