Recombinant vaccinia viruses carrying the N gene of human respiratory syncytial virus: studies of gene expression in cell culture and immune response in mice.

The construction and characterization of vaccinia virus recombinants carrying the nucleocapsid (N) protein gene of human respiratory syncytial (RS) virus are described. Recombinant viruses were constructed that contained the N gene oriented either positively or negatively with respect to the 7.5-kilodalton vaccinia virus promoter. In addition, a positively oriented recombinant was constructed that lacked an out-of-frame AUG codon in the 5'-terminal noncoding region. In HEp-2 cells, both positive-orientation recombinants induced the synthesis of a protein which comigrated with N protein and was precipitated by antisera to RS virus. Sera from mice immunized with these recombinants specifically precipitated the RS virus N protein. Analysis of mRNA and protein expressed from the recombinant N genes showed that deletion of the upstream AUG codon markedly improved the efficiency of protein synthesis. Mice were vaccinated with the high-expressing recombinant and subsequently challenged with live RS virus. The results of these experiments demonstrated that the immune response to N protein afforded a significant degree of protection against RS virus disease.