Bovine parainfluenza virus type 3 (PIV3) expressing the respiratory syncytial virus (RSV) attachment and fusion proteins protects hamsters from challenge with human PIV3 and RSV

MedImmune Vaccines Inc., 297 North Bernardo Avenue, Mountain View, CA 94043, USA Correspondence Aurelia Haller hallera{at}medimmune.com Parainfluenza virus type 3 (PIV3) and respiratory syncytial virus (RSV) are the main causes of ubiquitous acute respiratory diseases of infancy and early childhood, causing 20–25 % of pneumonia and 45–50 % of bronchiolitis in hospitalized children. The primary goal of this study was to create an effective and safe RSV vaccine based on utilizing attenuated bovine PIV3 (bPIV3) as a virus vector backbone. bPIV3 had been evaluated in human clinical trials and was shown to be attenuated and immunogenic in children as young as 2 months of age. The ability of bPIV3 to function as a virus vaccine vector was explored further by introducing the RSV attachment (G) and fusion (F) genes into the bPIV3 RNA genome. The resulting virus, bPIV3/RSV(I), contained an insert of 2900 nt, comprising two translationally competent transcription units. Despite this increase in genetic material, the virus replicated to high titres in Vero cells. This recombinant virus expressed the RSV G and F proteins sufficiently to evoke a protective immune response in hamsters upon challenge with RSV or human PIV3 and to elicit RSV neutralizing and PIV3 haemagglutinin inhibition serum antibodies. In effect, a bivalent vaccine was produced that could protect vaccinees from RSV as well as PIV3. Such a vaccine would vastly reduce the respiratory disease burden, the associated hospitalization costs and, most importantly, decrease morbidity and mortality of infants, immunocompromised individuals and the elderly. Present address: VaxGen Inc., Brisbane, CA 94005, USA.