Immunogenicity and efficacy of recombinant RSV-F vaccine in a mouse model.

RSV vaccine development has constraints due to safety issues encountered by formalin-inactivated FI-RSV vaccines. A desirable vaccine should induce Th(1) responses and a strong mucosal immunity to provide complete protection from RSV infection. In the present paper, we developed and evaluated a mucosal vaccine against RSV in a mouse model. The antigenic regions corresponding to residues 412-524 of RSV-F protein were amplified by RT-PCR and cloned into a vector containing the ctxA(2)B gene of the cholera toxin. The recombinant protein was expressed in E. coli and properties of the recombinant protein were analyzed by SDS-PAGE, Western blot and G(M1)-ELISA. The purified recombinant protein (rRF-412) was used to immunize BALB/c mice intranasally. The results from our studies show that the rRF-412 immunogen induced mucosal (IgA) and systemic antibody (IgG, IgG1, IgG2a, and IgG2b) responses which neutralized RSV. The IgG1/IgG2a ratios indicated a Th(1)-biased antibody response. The Th(1) (TNF-alpha, IL-12p70, IFN-gamma, IL-2) and Th(2) (IL-10, IL-4 and IL-5) cytokine profiles were analyzed after stimulation of spleen cells from mice immunized with purified RF-412 protein. Similar to the antibody response, we observed that the rRF-412 immunogen induced a mixed Th(1)/Th(2) cytokine immune response with a Th(1)-bias response. Serum antibodies were capable of neutralizing RSV and mice immunized with rRF-412 were significantly protected from live RSV challenge. Our data provides evidence that the rRF-412 immunogen may be a potential mucosal vaccine candidate against RSV.

Respiratory syncytial virus recombinant F protein (residues 255-278) induces a helper T cell type 1 immune response in mice.

We have developed and evaluated an immunodominant respiratory syncytial virus (RSV) F antigen in a mouse model. The antigenic region corresponding to amino acids 255-278 of the RSV F protein was cloned into a vector containing the ctxA(2)B gene of cholera toxin (CT). The recombinant protein was expressed in Escherichia coli and analyzed on sodium dodecyl sulfate-polyacrylamide gels. The purified protein was evaluated by immunoblot and ganglioside GM(1) enzyme-linked immunosorbent assay to confirm the expression of the RSV F protein and to correct association of the recombinant protein to form a holotoxin-like chimera, respectively. We hypothesized that genetic fusion of modified CT-based adjuvant with RSV F immunodominant epitopes (rRF-255) would induce protective humoral and cellular immune responses in mice. Intranasal immunization of mice with rRF-255 overall induced higher concentrations of anti-RSV F-specific antibodies in both serum and saliva as compared with mice immunized intranasally with RSV or phosphate-buffered saline (PBS). Antibody isotype analysis (IgA, IgG1, IgG2a, and IgG2b) was also performed. The predominant IgG2a antibody isotype response in combination with cytokine analysis of helper T cell type 1 (interferon-gamma, interleukin [IL]-2, IL-12 p70, and tumor necrosis factor-alpha) and helper T cell type 2 (IL-4 and IL-10) responses revealed that rRF-255 antigen induces a prominent helper T cell type 1 immune response in mice. The rRF-255 antigen also induced serum neutralizing antibodies in immunized mice. Analysis of RSV load in lungs showed that rRF-255 immunization provided significant protection compared with PBS control animals.