RSV fusion (F) protein DNA vaccine provides partial protection against viral infection.

The present study was conducted to investigate the feasibility and efficacy of a RSV F DNA vaccine incorporated with a mucosal adjuvant. Two DNA vaccine vectors (DRF-412 and DRF-412-P) were developed containing residues 412-524 of the RSV F gene. These antigenic regions were cloned into the phCMV1 DNA vaccine vector. One of the DNA vaccine vectors, DRF-412, contained the ctxA(2)B region of the cholera toxin gene as a mucosal adjuvant. The in vitro expressions of these DNA vectors were confirmed in Cos-7 cells by indirect immunofluorescence and Western blot analyses. In vivo expression of the cloned gene was further confirmed in mouse muscle tissue by immunohistological analysis. The active transcription of the RSV F gene in mouse muscle cells was confirmed by RT-PCR. The purified DRF-412 and DRF-412-P DNA vectors were used to immunize mice by intramuscular injections. Our results indicated that DRF-412 and DRF-412-P vaccine vectors were as effective as live RSV in inducing neutralization antibody, systemic Ab (IgG, IgG1, IgG2a, and IgG2b) responses, and mucosal antibody responses (Ig A). The Th1 (TNF-alpha, IL-12p70, IFN-gamma, IL-2) and Th2 (IL-10, IL-6) cytokine profiles were analyzed after stimulation of spleen cells from mice immunized with purified RF-412 protein. We observed that mice inoculated with vector DRF-412 induced a higher mixed Th1/Th2 cytokine immune response than DRF-412-P. Reverse transcriptase and quantitative real-time PCR (qRT-PCR) revealed that mice immunized with the DRF-412 vector contained less viral RNA in lung tissue and the lung immunohistology study confirmed that mice immunized with DRF-412 had better protection than those immunized with the DRF-412-P vector. These results indicate that the RSV DRF-412 vaccine vector, which contains the cholera toxin subunit ctxA2B as a mucosal adjuvant may provide a better DNA vaccination strategy against RSV.