Influence of live respiratory syncytial virus priming on the immune response generated by a recombinant vaccine candidate, BBG2Na.

Respiratory syncytial virus is one of the major respiratory pathogens for infants and immunocompromized children. With the exception of young children, all the population has encountered RSV and is seropositive. Recent reports have demonstrated however that the virus also affects the elderly and represents a major cause of illness associated with an excess of morbidity and mortality. We have generated a recombinant RSV vaccine, BBG2Na, which is highly protective in rodents against RSV infection. The aim of this study was to evaluate the ability of the vaccine to increase anti-RSV protection in RSV-primed mice and to characterize the induced immune responses. Immunization with BBG2Na increased the anti-RSV-A serum antibody titers of RSV-primed mice with induction of both IgG1 and IgG2a antibodies attesting for a mixed Th response. Moreover, the level of the induced anti-G2Na antibodies was greater in seropositive mice. Finally, sera from RSV-primed mice displayed a higher protective efficacy after transfer into naive mice following subsequent immunization with BBG2Na than sera of mice immunized with RSV-A only. Our results demonstrate that BBG2Na is immunogenic and increases the protective efficacy of serum antibodies in RSV-primed mice; they support the possibility of performing clinical trials in the seropositive human population.