Expression of the fusion protein of human respiratory syncytial virus from recombinant vaccinia virus vectors and protection of vaccinated mice

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Abstract
Vaccinia virus (VV) recombinants were constructed that contained full-length cDNA copies of the fusion (F) protein gene of human respiratory syncytial (RS) virus. The F protein gene was placed next to the strong early-late VV 7.5-kilodalton promoter and was located within the VV thymidine kinase (tk) gene. Full-length recombinant transcripts that initiated at both the tk and the 7.5-kilodalton promoters accumulated in cells early in infection, and one or more of these transcripts was translated to yield a glycoproten which comigrated with Fo, the fusion protein precursor. This precursor was processed by proteolytic cleavage to produce the two disulfide-liked subunits F1 and F2, which were both glycosylated and of the same electrophoretic mobility as authentic F1 and F2. Immunofluorescence studies demonstrated that the mature F protein was transported to and expressed on the surface of recombinant VV-infected cells. Inoculation of rabbits with a recombinant vector expressing F resulted in the production of antiserum specific for the RS virus F protein. This antiserum neutralized virus infectivity and was capable of preventing fusion in RS virus-infected cells. Mice were vaccinated with recombinants expressing the F protein. At 3 weeks postinoculation, these animals had serum antibody against RS virus F protein. At 5 days after intranasal challenge with RS virus, the lungs of the mice previously vaccinated with recombinants expressing F protein were free of detectable RS virus, whereas the lungs of unvaccinated mice contained 104.2 PFU of virus per g.