Respiratory syncytial virus (RSV) is the major respiratory pathogen of infants and children. Although much is known about the molecular biology of the virus and the epidemiology of RSV-related disease is well studied, RSV-induced immune response and pathogenesis are poorly understood.and a safe and effective vaccine has not yet been developed. RSV is an enveloped virus containing ten genes in a single stranded, negative-sense RNA genome. The fusion (F) and attachment (G) glycoproteins are present in the viral envelope and are target antigens for development of potential vaccines. Vesicular stomatitis virus (VSV) is an attractive viral vector system for expression of RSV antigens. Recent recovery of VSV from cDNA has enabled development of VSV-based vectors for foreign gene expression. Membrane proteins expressed from such recombinants are usually incorporated at high levels into viral particles. Such viruses are excellent candidates for live or inactivated vaccines:- The RSV-F and G have been cloned from RSV genomic RNA. These genes have been inserted individually into the VSV plasmid vector and recombinant virus produced. The expression of these RSV antigens was confirmed with immunofluorescence and the staining pattern was similar to that of wild-type RSV infected cells. RSV-G was processed and is incorporated into virions. Expression of RSV-F in recombinant virus infected cells drastically changed the phenotype of viral-induced cytopathic effects to cell fusion and large syncytium formation. Characterization of VSV-RSV viral particles is underway. Ultraviolet light irradiated and replication defective VSV-RSV recombinant clones only capable-of a single abortive infectious cycle will be developed to establish a potential RSV vaccine. Elicitation of the immune response in the mouse will be studied. RSV F and G specific and neutralizing antibodies will be measured in immunized animals. Pulmonary viral replication of RSV will be assayed in mice immunized with VSV-RSV recombinants and challenged with wild type RSV. A TH1 or TH2 immune response to RSV in immunized animals will be determined by semiquantitative PCR of cytokine mRNAs in pulmonary tissue. Lung histopathology in immunized RSV challenged mice will be examined. The studies proposed represent essential first steps in the development of a novel strategy for prevention of RSV disease.