Recombinant bovine/human parainfluenza virus type 3 (B/HPIV3) expressing the respiratory syncytial virus (RSV) G and F proteins can be used to achieve simultaneous mucosal immunization against RSV and HPIV3

Recombinant bovine/human parainfluenza virus type 3 (rB/HPIV3), a recombina nt bovine PIV3 (rBPIV3) in which the F and HN genes were replaced with thei r HPIV3 counterparts, was used to express the major protective antigens of respiratory syncytial virus (RSV) in order to create a bivalent mucosal vac cine against RSV and HPIV3, The attenuation of rB/HPIV3 is provided by the host range restriction of the BPIV3 backbone in primates. RSV G and F open reading frames (ORFs) were placed under the control of PIV3 transcription s ignals and inserted individually into the rB/HPIV3 genome in the promoter-p roximal position preceding the nucleocapsid protein gene. The recombinant P IV3 expressing the RSV G ORF (rB/HPIV3-G1) was not restricted in its replic ation in vitro, whereas the virus expressing the RSV F ORF (rB/HPIV3-F1) wa s eightfold restricted compared to its rB/HPIV3 parent. Both viruses replic ated efficiently in the respiratory tract of hamsters, and each induced RSV serum antibody titers similar to those induced by RSV infection and anti-H PIV3 titers similar to those induced by HPIV3 infection. Immunization of ha msters with rB/HPIV3-G1, rB/HPIV3-F1, or a combination of both viruses resu lted in a high level of resistance to challenge with RSV or HPIV3 28 days l ater. These results describe a vaccine strategy that obviates the technical challenges associated with a live attenuated RSV vaccine, providing, again st the two leading viral agents of pediatric respiratory tract disease, a b ivalent vaccine whose attenuation phenotype is based on the extensive host range sequence differences of BPIV3.